FINNISH METEOROLOGICAL INSTITUTE CONTRIBUTIONS
No. 15
SIZE DISTRIBUTION MEASUREMENTS AND CHEMICAL ANALYSIS OF AEROSOL COMPONENTS
Tuomo A. Pakkanen
DISSERTATION
To be presented, with the permission of the Faculty of Science of the University of Helsinki for public criticism in main Auditorium of the Department of Chemistry on June 19, 1995, at 12 o'clock noon.
Finnish Meteorological Institute Helsinki 1995 ISBN 951-697-433-3 ISSN 0782-6117
Yliopistopaino Helsinki 1995 Published by Series title, number and report code of publication Finnish Meteorological Institute Contributions No. 15, FMI-CONT-15 P.O. Box 503 FIN-00101 HELSINKI Date Finland June 1995 Name of project
Tuomo Pakkanen Comissioned by
Title
Size distribution measurements and chemical analysis of aerosol components
Abstract The principal aims of this work were to improve the existing methods for size distribution measurements and to draw conclusions about atmospheric and in-stack aerosol chemistry and physics by utilizing size distributions of various aerosol components measured. A sample dissolution with dilute nitric acid in an ultrasonic bath and subseguent graphite furnace atomic absorption spectrometric analysis was found to result in low blank values and good recoveries for several elements in atmospheric fine particle size fractions below 2 pm of equivalent aerodynamic particle diameter (BAD). Furthermore, it turned out that a substantial amount of analytes associated with insoluble material could be recovered since suspensions were formed. The size distribution measurements of in-stack combustion aerosols indicated two modal size distributions for most components measured. The existence of the fine particle mode suggests that a substantial fraction of such elements with two modal size distributions may vaporize and nucleate during the combustion process. In southern Norway, size distributions of atmospheric aerosol components usually exhibited one or two fine particle modes and one or two coarse particle modes. Atmospheric relative humidity values higher than 80% resulted in significant increase of the mass median diameters of the droplet mode. Important local and/or regional sources of As, Br, I, K, Mn, Pb, Sb, Si and Zn were found to exist in southern Norway. The existence of these sources was reflected in the corresponding size distributions determined, and was utilized in the development of a source identification method based on size distribution data. On the Finnish south coast, atmospheric coarse particle nitrate was found to be formed mostly through an atmospheric reaction of nitric acid with existing coarse particle sea salt but reactions and/or adsorption of nitric acid with soil derived particles also occured. Chloride was depleted when acidic species reacted with atmospheric sea salt particles. The chloride loss was found to decrease with increasing particle size suggesting that surface reaction mechanisms were important. Overall, the results obtained in this work describe the present methods used in all steps of accurate size distribution measurements of aerosol components and demonstrate the usefulness and possibilities of size distribution measurements in various scientific studies.
Publishing unit Finnish Meterorological Institute,Air Quality Department Classification (UDC) Key words 504.064.2, 541.182.2/.3 aerosol, atmosphere, in-stack, impactor, Berner impactor, 543.2 dissolution, analysis, spectroscopy, GFAAS, ETAAS, particle, particle size, size distribution, element, air pollution 551.510.42 ISSN and series title ISSN 0782-6117 Finnish Meteorological Institute Contributions Language ISBN English 951-697-433-3 Sold by Pages Price 157 Note Julkaisija Julkaisun saija, numeroja raporttikoodi llmatieteen laitos Contribution No 15, FMI-CONT-15 Vuorikatu 24 PL 503 Julkaisuaika 00101 HELSINKI Kesakuu 1995 Teklja(t) Projektin nimi
Tuomo Pakkanen Toimeksiantaja
i Nlmlke
Aerosolikomponenttien kokojakaumamittauksetja kemiallinen analyysi
i i TllvIstelmS Taman tyon tarkoituksena oli kehittaa aerosolien kokojakaumamittauksissa kaytettavia menetelmia i seka kayttaa ilmakehasta ja savupiipuista mitattuja aerosolikomponenttien kokojakaumia aerosolien i kemiallistenja fysikaalisten ominaisuuksien tutkimiseen. Laimeaan typpihappoon liuotetuista, halkaisijaltaan alle 2 pm Mukkasista pystyttiin analysoimaan useita metalleja grafiittiuuniatomiabsorptiomenetelmalla. Liuotusmenetelmaa kaytettaessa nollanay- tearvot olivat pienia ja liukenemattomat hiukkaset muodostivat suspension, mika mahdollisti pienten j pitoisuuksien seka liukenemattoman materiaalin analysoinnin. i Savupiipuista keratyissa naytteissa olivat useat aerosolikomponentit jakautuneet kahteen moodiin. Pienempien hiukkasten (halkaisijaltaan noin 0.05 - 0.2 pm) moodin ilmeneminen voidaan selittaa siten, etta komponentti ensin hoyrystyy palamisprosessissa ja sitten nukleoituu. Etela-Norjassa oli ilmakehan aerosolikomponenteilla tavallisesti yksi tai kaksi moodia pienissa (halkaisija < 2 pm) hiukkasissa ja yksi tai kaksi moodia suurissa (halkaisija > 2 pm) hiukkasissa. Ilmakehan suhteellisen kosteuden ollessa yli 80% kasvoi pisaramoodin hiukkaskoko. Etela-Noijassa havaittiin olevan paikallisia ja/tai alueellisia eri alkuaineiden paastdlahteita. Nama paastdlahteet i vaikuttivat mitattuihin kokojakaumiin, mita kaytettiin hyvaksi kehitettaessa uutta kokojakamniin perustuvaa paastolahteiden paikallistamismenetelmaa. Suomen etelarannikolla muodostui nitraattia ilmakehan suuriin hiukkasiin paaasiassa typpihapon reagoidessa suurten merisuolahiukkasten kanssa, seka pienemmassa maarin typpihapon ja suurten maaperahiukkasten vuorovaikutuksesta. Kloridi vaheni merisuolahiukkasista kun happamat aineet reagoivat merisuolan kanssa. Kloridin vaheneminen oli pienempaa suuremmilla hiukkasilla, mika viittaa pintareaktiomekanismeihin. Tassa tyossa kuvataan aerosolikomponenttien kokojakaumamittauksien eri vaiheissa kaytettavia menetelmia seka esitellaan kokojakaumamittauksien kayttomahdollisuuksia erilaisissa tutkimuksissa.
Julkalsljayksikko llmatieteen laitos, Ilmanlaatuosasto t Luokitus (DDK) Asiasanat 504.062.2, 541.182.2/.3 aerosolit, ilmakeha, paastot, naytteenotto, impak- i 543.2 torit, liuotus, analyysimenetelmat, spektroskopia, 551.510.42 hiukkaskoko, alkuaineet, ilmanlaatu ISSN Ja avalnnlmlke ISSN 0782-6117 Finnish Meteorological Institute Contributions Kiel! ISBN i Suomi 951-697-433-3 Myynti Sivumaard Hinta llmatieteen laitos, Kirjasto 157 PL 503 Lisatietoja 00101 Helsinki
'Y. ACKNOWLEDGEMENTS The work described in this thesis was carried out at the Finnish Meteorological Institute and at the University of Ghent, Belgium. The directors of these institutes are acknowledged for providing the research environment needed in this work. The encouragement and comments of Prof. Lauri Halonen are acknowledged. I thank Prof. Maija-Liisa Riekkola and Doc. Erkki Hasanen for their constructive and valuable comments about the manuscript.
I am deeply indebted to Dr. Risto Hillamo for his continuing co-operation, ideas and encouragement and to Dr. Esko Kauppinen and Dr. Willy Maenhaut for their extensive co operation concerning aerosol sampling and analysis and preparation of the manuscripts. I thank Mr. Petri Keronen, Dr. Geert Ducastel and Dr. Jozef Pacyna for their co-operation and help in performing the PIXE analysis and inversions of the size distribution data. I thank also Doc. Yqo Viisanen, Dr. Philippe Comille, Dr. Geert Hebbrecht and Mr. Veli-Matti Kerminen for their useful comments and help and Mr. Arto Jappinen, Mr. Jan Cafmeyer, Mr. Kari Markkanen, Mr. Juha Hatakka, Mr. Jukka Kiiski and Mrs. Helena Saari for their assistance during this work. The members of the aerosol research group and the laboratory group at the Finnish Meteorological Institute are acknowledged for their help and support. Special thanks are given to Doc. Sylvain Joffre for his guidance and help in getting financial support for this work. The Academy of Finland, the Maj and Tor Nessling Foundation and the Nordic Council of Ministers are acknowledged for their financial help. Finally, I thank my wife Eija for her understanding and support during this work.
May 1995
Tuomo Pakkanen NOMENCLATURE
The following abbreviations are used in the text most frequently.
Abbreviation Meaning
BLPI Berner low-pressure impactor BAD equivalent aerodynamic particle diameter FAAS flame atomic absorption spectrometry GFAAS graphite furnace atomic absorption spectrometry IC ion chromatography ICP-AES inductively coupled plasma atomic emission spectrometry ICP-MS inductively coupled plasma - mass spectrometry INAA instrumental neutron activation analysis Milli-Q water distilled, deionized water MOUDI micro-orifice uniform deposit impactor NIST National Institute of Standards and Technology PIXE particle induced X-ray emission RSD-method relative size distributions method SDI small deposit area low-pressure impactor SFU stacked filter unit (=two stage filter sampler) SRM standard reference material STPF-method stabilized temperature platform furnace method XRF X-ray fluorescence CONTENTS
LIST OF PUBLICATIONS 6
1. INTRODUCTION 7
2. GENERAL BACKGROUND 9
3. A REVIEW FOR SIZE DISTRIBUTION MEASUREMENTS 14 3.1. Background 14 3.2. Features of some experimental details of the papers reviewed 15 3.3. Applications of size distribution measurements 15
4. CONTAMINATION CONTROL 16 4.1. Choosing collection substrate materials 16 4.2. Preparation and storage of polycarbonate substrates 17 4.3. Reagents and cleaning the equipment 17 4.4. Washing and storage of Berner low-pressure impactors 18 4.5. Loading the impactor and sampling 19 4.6. Unloading the impactor and sample storage 19 4.7. Blank values of sample preparation methods 19
5. EXPERIMENTAL 21
5.1. Sampling instruments 21
5.2. Materials 21 5.2.1. Collection substrates and chemicals 21 5.2.2. Sample containers 21
5.3. Sample preparation 22 5.3.1. Dissolution of atmospheric BLPI samples for GFAAS and 22 ICP-MS analysis 5.3.2. Dissolution of in-stack combustion samples for 23 metal analysis
5.4. Analytical techniques 24 5.4.1. GFAAS analysis of atmospheric and in-stack BLPI samples 24
6. RESULTS AND DISCUSSION 26
6.1. GFAAS analysis of atmospheric BLPI samples 26 6.1.1. Blank values and limits of determination 26 6.1.2. Recoveries from NIST SRM 1648 26 6.1.3. Recoveries from BLPI samples 27 6.1.4. Analysis of insoluble particles by GFAAS 27 6.1.5. GFAAS analysis of atmospheric filter samples 27
6.2. GFAAS analysis of in-stack combustion aerosol samples 28 6.3. Sources and size distributions of atmospheric aerosol components 28 6.3.1. Sources and size distributions of atmospheric aerosol 28 constituents in southern Norway 6.3.2. Size distributions of major atmospheric inorganic ions 29 in Helsinki
6.4. Use of size distribution measurements in characterizing formation of 29 atmospheric coarse particle nitrate aerosol
6.5. PIXE analysis of MOUDI impactor samples 30
6.6. Recommendations for size distribution measurements of selected 30 aerosol components
7. CONCLUSIONS 32
REFERENCES 36
TABLES 1 - 9
FIGURES 1 - 7
PUBLICATIONS I - VH 6 LIST OF PUBLICATIONS
This thesis consists of the following publications:
I Pakkanen T.A., Hillamo R.E. and Maenhaut W. (1993) Simple nitric acid dissolution method for electrothermal atomic absorption spectrometric analysis of atmospheric aerosol samples collected by a Berner-type low-pressure impactor. Journal of Analytical Atomic Spectroscopy 8, p. 79 - 84.
It Kauppinen E.I. and Pakkanen T.A. (1990) Mass and element size distributions of aerosols emitted by a hospital refuse incinerator. Atmospheric Environment 24A, p. 423 - 429. m Kauppinen E.I. and Pakkanen T.A. (1990) Coal combustion aerosols: a field study. Environmental Science & Technology 24, p 1811 - 1818.
IV Maenhaut W., Ducastel G., Hillamo R.E., Pakkanen T. and Pacyna J. (1993) Atmospheric aerosol studies in southern Norway using size-fractionating sampling devices and nuclear analytical techniques. Journal of Radioanalytical and Nuclear Chemistry, Articles, 167, p 271 - 281.
V Pakkanen T.A., Hillamo R.E., Keronen P., Maenhaut W., Ducastel G. and Pacyna J. (1995) Sources and physico-chemical characteristics of the atmospheric aerosol in southern Norway. Atmospheric Environment (submitted).
VI Maenhaut W., Ducastel G., Hillamo R.E. and Pakkanen T.A. (1993) Evaluation of the applicability of the MOUDI impactor for aerosol collections with subsequent multielemental analysis by PIXE. Nuclear Instruments and Methods in Physics Research B75, p. 249 - 256.
VII Pakkanen T.A. (1995) Study of formation of coarse particle nitrate aerosol. Atmospheric Environment (submitted). 7
1. INTRODUCTION
Particle size is an important factor in our understanding of sources, sinks and transformation processes of atmospheric aerosols and of particle interaction with atmospheric radiation (Charlson, 1987; Heintzenberg, 1989; Kerminen et al., 1994). Heintzenberg (1989) further stressed that for a complete understanding of the atmospheric aerosol, chemically resolved aerosol size distributions and the state of particle mixture, external or internal, need to be determined on a global scale.
In the atmosphere, fine particles control number and surface distribution of the condensed matter present in the aerosol. In many densely populated regions fine particles can also dominate the aerosol mass. However, in his review Heintzenberg (1989) pointed out that most of the fine particle data available in the literature suffer from the lack of a well-defined upper particle size limit at about 2 pm of equivalent aerodynamic particle diameter (BAD). During sampling process the particle sizes can be controlled by using various types of impactor including an Andersen cascade impactor (Lee, 1972), a Berner low-pressure impactor (BLPI)(Berner and Ltirzer, 1980), a micro-orifice uniform deposit impactor (MOUDI)(Marple et al., 1991) and a small deposit area low-pressure impactor (SDI)(Hillamo, 1994). Compared to the two-stage sequential filter sampling (Cahill et al., 1977; Heidam, 1981) impactors have better sampling characteristics and some provide a method for collection of up to 12 particle size fractions (Hillamo 1994). Thus, impactors can be used for detailed size distribution measurements. Another, totally different method for size distribution measurements is to collect an aerosol sample and inspect the size and composition of individual particles (Bruynseels and Van Grieken, 1985).
Millford and Davidson (1985; 1987) review a large number of size distribution measurements where different impactor types and analysis methods have been used. Choosing the analysis technique best suited for size distribution measurements of aerosol components depends on the components to be analysed since the limits of detection will vary from analyte to analyte for any given analytical method. Indeed, choice of the sampling instrument must take into account the characteristics of the analytical method or vice versa since the analyzing power of some techniques such as particle induced X-ray emission (PIXE) or X-ray fluorescence (XRF) are dependent on the shape of the sample deposit. 8 In 1985, when this work was started, the main objectives were to develop representative aerosol sampling by impactors and the achievement of accurate analysis methods for the samples collected. Different reagents and materials were tested in order to make the procedural blank values as low as possible. Later on, other important features of size distribution measurements like, for instance aerosol chemistry and physics in the atmosphere and in-stack conditions, and measurement of atmospheric gases were also included. In these studies, several different scientific disciplines were incorporateded the most important being aerosol physics, analytical chemistry, air chemistry, and meteorology.
In this thesis a large number of carefully measured size distributions of numerous aerosol components is presented (publications n, HI, IV, V, VII). The atmospheric (publications I, IV, V, VI, VII) and in-stack (publications II, HI) aerosol samples were collected using a BLPI (publications I, n, EH, IV, V, VII) or MOUDI (publication VI) impactor. The analysis methods GFAAS (publications I, U, HI), INAA (publications I, IV, V), PIXE (publications n, m, TV, V, VI), ICP-MS (publication V) and IC (publications V, VII) were utilized. Dissolution methods for Berner impactor samples with blank values low enough to enable accurate size distribution measurements of aerosol components with the GFAAS method were developed (publications I, n, HI). The dissolution methods were applied to in-stack combustion aerosols (publications II and HI) and to atmospheric aerosols (publications I, V). Due to the low concentrations of aerosol components in individual impactor stages, extensive contamination control was followed during washing, handling and storing of the sampling instruments, collection substrates and samples (publications I, II, HI, IV, V, VI and VII). This thesis is based on the publications I - VII which are included as appendices.
Summary of the aims of this thesis: -measurement of accurate size distributions of aerosol components -development of suitable analysis methods for impactor samples -minimizing the blank contribution for impactor measurements by testing different washing procedures, reagents, materials and sample dissolution methods -to apply size distribution measurements for studies of atmospheric and in-stack chemistry and physics -to make recommendations for suitable analysis methods for selected aerosol components 9
2. GENERAL BACKGROUND
Aerosols Aerosols are suspensions of liquid and/or solid particles in a gaseous medium. The particle size range in an aerosol can vary from the nanometer level up to about hundred micrometers of BAD. Several different fields of research including clean manufacturing technologies, industrial hygiene, cloud physics and chemistry, air pollution and pollution control are important aspects of aerosol science.
Aerosols consist of particles of different size and chemical composition and are often divided into two main categories: natural and man-made or anthropogenic aerosols. In addition, aerosol particles can be called either primary or secondary, depending on whether they are emitted into or formed in the atmosphere. The atmospheric aerosol exhibits normally two or three main modes for the particle mass (Seinfeld, 1986; Wall et al., 1988; John et al., 1990): one or two fine modes in the size range of about 0.1 - 1.0 pm of BAD, and a coarse particle mode at about 2-10 pm of BAD. John et al. (1990) name the smaller and larger fine particle modes the condensation and the droplet modes, respectively. Normally, the atmospheric coarse particle mode consists predominantly of natural marine and crustal rock aerosols, whereas fine particles are largely of anthropogenic origin. A major part of atmospheric fine particles are secondary and formed through various gas to particle conversion processes (Heintzenberg, 1989). Sulphur dioxide (S02) emissions especially are a threat to natural ecosystems because in the atmosphere S02 is transformed to particulate sulphate which is the major component of acid rain. Estimations of the amounts of aerosol components emitted from various source types can be found in the reviews of Nriagu (1989) and Pacyna (1989).
Aerosol particles, once emitted into or formed in the atmosphere, are easily transported by moving air masses. Nowadays anthropogenic pollutants can be observed all over the world. Measurements made at remote locations such as the South Pole and Arctic regions (Whitlow et al., 1992), as well as those made in the air over oceans far from continents (Fitzgerald, 1991), clearly indicate that anthropogenic pollutants are responsible of a major part of the toxic compounds found there. Ice samples taken from ice cores in Greenland and in the Antarctic (Whitlow et al., 1992) give information on the history of pollutant concentrations back for thousands of years. These pollutant history studies indicate that concentrations of numerous toxic aerosol components have substantially increased during this century.
I.:.. 10 Therefore, the control of anthropogenic emissions and atmospheric pollutant concentrations is essential.
Particle residence times in the atmosphere depend strongly on their size (Jaenicke, 1978). The residence times for fine particles are normally between a few days and a couple of weeks, while large particles deposit usually much faster. The processes by which atmospheric aerosol particles are transported to various surfaces on the Earth include dry and wet deposition, and deposition by fog (Heintzenberg, 1989; Galloway, 1982).
Impactors A simple way of sampling is use of total aerosol filters that collect particles on one single filter. A more sophisticated application is the so called stacked filter unit (Cahill et al., 1977; Heidam, 1981), which collects the aerosol in two size fractions, a fine (BAD < 2.5pm) and a coarse fraction (BAD > 2.5 pm). Various inertial impactors like BLPI (Berner and Liirzer, 1980), MOUDI (Marple et al., 1991) and SDI (Hillamo, 1994), can divide the sampled aerosol in several size fractions (typically 7 - 12) in the size range of about 0.03 - 20 pm BAD. Impactors are easy to operate and comparatively inexpensive. Particle size calibration methods for Berner-type low-pressure impactors can be found in Wang and John (1988), and in Hillamo and Kauppinen (1991). To avoid coarse particle bounce off in the impactor, the coarse particle collection substrates are usually greased (Hillamo and Kauppinen, 1991). Accurately measured impactor samples can be used in evaluation of number -, volume -, and mass size distributions of various aerosol components.
Contamination problems Avoiding contamination is essential in all the work involving the measurement of low concentrations (Ross, 1984). Extreme care should be taken in all stages of the handling and storing of the sampling instruments, collection substrates, and collected samples. The analyte concentrations in the samples collected usually depend on the collection time and can often be estimated before sampling. The precautions and contamination control for sampling can be planned according to these estimated concentrations. Short sampling times may require careful washing of the sampling equipment. Substrates made of special material and precautions to exclude interfering gases and aerosols may also be needed. Clean bench or clean room conditions are recommended for all measurements but are essential when short sampling times are used (Ross, 1984). Contamination problems are discussed in more detail 11 in Chapter 4.
Analysis of aerosols The reviews of Milford and Davidson (1985 and 1987) and Sneddon (1983) indicate that the analysis methods commonly utilized in measuring the concentrations and size distributions of various components in aerosol samples are ion chromatography (IC), graphite furnace atomic absorption spectroscopy (GFAAS), flame atomic absorption spectroscopy (FAAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), inductively coupled plasma mass spectroscopy (ICP-MS), X-ray fluorescence spectroscopy (XRF), particle induced X-ray emission spectroscopy (PDCE) and instrumental neutron activation analysis (INAA). Straightforward comparison of the limits of detection or limits of determination obtained using the different analysis methods is difficult (Maenhaut, 1989). The limits of detection of the various analytical techniques can depend on parameters such as the total amount of sample available, the amount of sample needed for the analysis of each component, the measurement time, irradiation time (in INAA analysis), the sample volume after dissolution for techniques requiring liquid sample introduction and whether the technique is multielemental or not. Even details like the collection substrate material and the shape of the sample deposit on the substrate may cause problems to certain analysis methods. Other important considerations when choosing the analysis method are the cost of analysis, the time needed for measurement of various components and the choice between the use of destructive or non-destructive methods. Thus, the choice of proper analysis methods for aerosol samples depends on numerous aspects and is usually a compromise after a careful consideration of these parameters and the goals of the research project. The most common analysis methods for aerosols are discussed in Chapter 3.
Dissolution of aerosol samples Some analysis methods like, for instance IC, GFAAS, FAAS, ICP-AES and ICP-MS usually need dissolution, extraction or decomposition of the sample prior to analysis. In the Berner impactor the aerosol is collected on 7 - 11 stages (particle size ranges) and therefore the aerosol mass on a given individual stage will be low. Due to the low aerosol mass per stage, accurate measurements using this type of instrument require low blank values for analysis. Different methods including distillation and chelation can be used to minimize the blanks. If the samples have to be dissolved, the choice of dissolution method is critical when considering the resulting blank values of the components to be measured. Another important 12 feature of various dissolution methods is the extent of solubility of the sample. Solubilization studies have been performed for bulk (total) aerosol samples and for non-size segregated reference materials: Nadkami (1984), Lamothe et al. (1986), Broekaert et al. (1982) and Wang et al. (1989) used mixtures of strong acids at elevated temperatures and pressures. Comparisons of different dissolution methods have also been conducted using digestion on a hot-plate (Yamashige et al, 1989; Infante and Acosta, 1988) and high pressure digestion in a closed teflon bomb (Wang et al., 1989). However, the results and conclusions from these studies on bulk samples may not necessarily apply to aerosol samples that are collected with a cascade impactor, where the particles are separated into several size fractions. The fine particle fractions (BAD < 2pm) of such samples contain much less crustal rock material than bulk aerosol samples. Consequently, various elements may be present in forms that are more easily solubilized.
GFAAS analysis of aerosol samples collected using impactors In the beg inning of the 1980:s Slavin et al. (1981) presented their Stabilized Temperature Platform Furnace method (STPF-method) for GFAAS analysis. Usually this method produces the most reliable GFAAS analysis results because interferences during analysis are minimized. However, BLPI samples are normally very lightly loaded, from a few micrograms to a few hundred micrograms, and severe interferences are rare during such analysis. In Pakkanen (1988) it is shown that for fine particle impactor samples the atomization of several analytes can be performed off the wall of a pyrolytic graphite coated graphite tube. The use of off-the- wall methods has some advantages over STPF methods. When a sample is atomized off the wall, a greater sample volume can be used for analysis and lower concentrations can be detected. If STPF methods are employed, a chemical modifier is often required and the analysis take a longer time because additional autosampler steps are needed. Moreover, the use of modifiers can result in higher blank values.
There are some studies showing that GFAAS analysis of solid samples is possible (Rettberg and Holcombe, 1986; Wennrich and Dittrich, 1987). However, such analyses are often limited to a few special types of samples only. Karwowska and Jackson (1986) have studied GFAAS analysis of solid samples ground to a powder and suspended in liquid media. Analyses of such slurry (suspension) samples are promising. 13
Size distribution measurements of aerosol components Particle mass number and surface area size distributions measured by impactors give basic information on different aerosol populations. Additional details of size distributions can be obtained using inversion codes (Wolfenbarger and Seinfeld, 1990 and 1991). Several researchers have shown that measuring size distributions is useful for numerous important scientific applications including aerosol deposition (Ottley and Harrison, 1992; Hillamo et al., 1993a), air chemistry studies (Wall et al., 1988), and identification of aerosol sources (Wall et al., 1988). Size distributions of aerosol components are altered by different chemical reactions and physical processes such as nucleation, condensation, coagulation, evaporation, and cloud processing. Size distributions of atmospheric aerosol components often vary together with the meteorological parameters relative humidity, temperature, wind speed and direction, radiation, and rain (Tang, 1978; Heintzenberg, 1989). If the analyte concentrations are low, sampling periods of up to 72 hours are needed for subsequent analysis, as has been demonstrated for samples collected in the Antarctic region (Radlein and Heumann, 1992). Unfortunately, use of long sampling times gives no information regarding whether or not, and to what extent, size distributions did change during the sampling period. A review of recent size distribution measurements is presented in Chapter 3.
Instead of sampling different particle size fractions separately, inspection of individual particles can be applied for size distribution measurements. Particle sizes can be determined using microscopes. The usual methods in individual particle analysis are various X-ray based scanning electron microscopy (SEM) techniques. In their studies of individual atmospheric aerosol particles various research groups have identified numerous different particle types according to particle composition and size (Bruynseels and Van Grieken, 1985; Bruynseels et al., 1988; Xhoffer et al., 1991; Mamane and Gottlieb, 1992; Mouri et al., 1993; Wu and Okada, 1994; De Bock et al., 1994). In these studies up to 25000 individual particles were inspected (Xhoffer et al., 1991). In spite of its usefulness, this method is not discussed further in this thesis because it is beyond the scope of this work.
2 21405 14
3. A REVIEW FOR SIZE DISTRIBUTION MEASUREMENTS
3.1. Background
Milford and Davidson (1985 and 1987) have reviewed size distribution measurements of atmospheric aerosol components. These reviews cover measurements from all over the world and reported in the literature from the early studies up until about 1985. Milford and Davidson (1985 and 1987) presented average size distributions and the corresponding standard deviations for more than 40 components: Al, As, Ba, Br, Ca, Cd, Ce, Cl, Co, Cr, Cs, Cu, Eu, Fe, Ga, Hf, Hg, I, In, K, Mg, Mn, Na, Ni, NO/, Pb, SO/", Sb, Sc, Se, Si, Sm, Sr, Ta, Th, Tl, U, V, W, Zn, NO/ and SO/". The individual size distributions of many elements were found to be relatively consistent, despite the different sampling locations, time periods and experimental methods used. However, most of those measurements performed before 1985 have only a few size fractions below 1 (im BAD and, consequently, the size distributions of aerosol components remain inaccurate for those particle sizes below 1 pm. For example, Milford and Davidson reported that combustion elements, that often exist predominantly in fine particles, have usually one fine particle mode. However, inspection of recent measurements indicate that collection of a larger number of fine particle size fractions can reveal more than one fine particle mode (Wall et al., 1988; John et al., 1990).
In this chapter a selection of important size distribution measurements published after about 1985 are reviewed according to the analysis method(s) used. For the sake of completeness, also the publications I - VH of this thesis are added to the tables presented in this chapter. Some of the experimental details in these measurements are presented: sampling site, impactor type, range and number of sampled size fractions, collection substrate material, type of back up filter (if used) and the components for which size distributions are presented. In most publications, the number of components analyzed is higher than the number of components for which size distributions are presented. The tables la - lg present size distribution measurements where the analysis was performed using the INAA, FIXE, XRF, GFAAS or FAAS, ICP-AES or ICP-MS, IC and other methods, respectively. In addition, size distribution measurements for organic carbon, inorganic carbon and specified organic compounds are presented in Table lh. Table 2 shows the compilation of data presented concerning blank values, limits of detection and limits of determination. Note that for some of the references reviewed the information about experimental details was incomplete which resulted in some 15 gaps in the Tables la - 2. Table 3 presents some scientific applications of the publications reviewed and, finally, Table 9 in Section 6.6 gives recommendations for analysis methods suitable for the determination of size distribution of some selected aerosol components.
3.2. Features of some experimental details of the papers reviewed
The vast majority of the measurements reviewed in the Tables la - 2 were made in North America, Europe or in Japan and only a few measurements are presented from other parts of the world. Some in-stack measurements and laboratory studies are included in the review. The impactor types used in these measurements are numerous and cover different aerosol size fractions from about 0.01 pm to 100 pm BAD.
The choice of the substrate and filter materials used was variable with the following being the most popular: teflon, polycarbonate, polyethylene, cellulose, Mylar, quartz, aluminum foil and fiber glass. The substrate and filter materials should be chosen carefully with respect to the sampling time, analysis methods envisaged and the components to be analyzed.
In the papers reviewed, size distributions are presented for the following 56 inorganic components: Ag, Al, As, Au, Ba, Br, C, Ca, Cd, Ce, Cl, Co, Cr, Cs, Cu, Be, Ga, Hf, I, In, Ir, K, La, Mg, Mn, Mo, Na, Nd, Ni, Pb, Rb, S, Sb, Sc, Se, Si, Sm, Sn, Sr, Ta, Ti, V, W, Y, Yb, Zn, Zr, Cl', NO/, SO/', NH4+, Na+, K+, Mg2*, Ca2* and total sample mass. References dealing with size distribution measurements of organic species are presented in Table lh but the various components are not listed here.
3.3. Applications of size distribution measurements
In Table 3 a selection of the publications, reviewed in the Tables la - 2, are divided into three main categories according to applications of the size distribution data: 1) deposition of atmospheric aerosols, 2) aerosol sources and transport and 3) atmospheric and in-stack chemistry and physics. Category 3, atmospheric and in-stack chemistry and physics, includes publications where the size distributions are discussed in terms of atmospheric acidity, volatility of aerosol components, cloud processes, aerosol - soil fractionation, air - to - sea transfer, air trajectories, meteorological conditions, visibility, health effects etc. For closer examination of these topics attention is drawn to the publications listed in Table 3. 16
4. CONTAMINATION CONTROL
Since aerosol samples collected by impactors are classified in up to 12 fractions by particle size, the mass concentration in each individual size fraction is usually low, the total mass per substrate (stage) typically being less than about 400 pg. The total sampled aerosol mass in the particle size fraction of about 0.03 - 0.1 pm BAD can be less than 5 pg, when normal sampling conditions of 20 - 30 1/min flowrate and 24 - 48 h sampling times are employed. The use of long sampling times should be avoided for the determination of accurate size distributions since the distribution of various aerosol constituents may change with time due to changes in sampling conditions. Consequently, in order to be able to use short sampling times, low blank values for the components measured are of paramount importance. Before using new batches of collection substrates, test tubes, reagents etc. the blank contributions should be evaluated because of possible variations between batches. The contamination control should be planned and implemented carefully in order to obtain the lowest possible limits of detection for the analysis methods used. This chapter presents basic characteristics of contamination control and some details of the contamination control procedures described by Pakkanen (1988). When short sampling times are used and/or analyte concentrations are low it is essential to follow the presented or corresponding procedures carefully.
4.1. Choosing collection substrate materials
The material from which the collection substrates are manufactured should be chosen depending on the analysis methods used and components to be analysed. For example, Mylar film and polycarbonate film have been tested as collection substrate material for subsequent GFAAS analysis (Pakkanen 1988): blank values were measured for digestions with concentrated nitric acid (suprapur), concentrated hydrogen peroxide (suprapur) and concentrated hydrochloric acid (suprapur) in borosilicate beakers. Table 4 presents a comparison of blank values for reagents only, Mylar film and polycarbonate film. Values of Table 4 indicate that compared to polycarbonate film, Mylar film gives high blank values for Ca, Mg, Pb and Zn when the samples are digested using the procedure described above. 17 4.2. Preparation and storage of polycarbonate collection substrates
Polycarbonate film of size 25 x 20 cm is commercially available (Nuclepore Corp.). The highest purity film (aerosol quality) is the best suited for impactor sampling. Eight substrates with outer diameter of 7 cm can be obtained from each film. The films are usually packed in plastic packages of 25 or 50 films. If possible the packages should not be opened during preparation of substrates. Instead, the substrates should be pressed through the unopened package using a carefully cleaned (water and isopropanol), sharp punch. The substrates and separating papers are then immediately removed from the punch with clean forceps and placed in a washed (water and isopropanol) air tight storage box. The storage box should be kept closed (air tight) to avoid contamination from aerosol and gases (e.g. NH3 and HN03) when not in use. It may be useful to prepare only the required number of "fresh" substrates so that storage times are as short as possible and the risk of contamination is minimized.
To avoid coarse particle bounce off during sampling the coarse particle collection substrates should be greased. Hillamo and Kauppinen (1991) describe an accurate greasing method where the amount of grease can be well controlled. Another possibility is to use a small brush for greasing. However, the brushing method often leads to unnecessary high amount of the grease and rolling up of the substrates during unloading the impactor which makes handling of the substrate difficult.
4.3. Reagents and cleaning the equipment
All liquids and reagents should be of the highest possible purity. If lower purity reagents have to be used the blank value should be tested for all components to be determined. The importance of this issue is demonstrated in Pakkanen (1988) where blank values were compared from nitric acid digestions using pro analysi grade nitric acid or suprapur nitric acid: use of the suprapur nitric acid resulted in 1.5, 5, 2, 15, and 3 times lower blank values for Cu, Mn, Mg, Na and K, respectively. Laboratory air, forceps, some parts of the impactor, testtubes, pipette tips, GFAAS sample cups, scissors, tip of the autosampler of the GFAAS instrument and graphite tubes come into contact with the collection substrates or dissolved samples and therefore represent possible sources of contamination. Clean room or clean bench conditions are recommended to minimize contamination occuring via laboratory air (Ross, 1984). The forceps and the scissors should be wiped frequently with clean tissue wipe 18
(preferably a type that does not release small paper pieces) wetted first with distilled and deionized water and then with a second piece wetted with isopropanol. While using a wetted wipe it is important to note which part of the paper is touched by hand or gloves: only clean, untouched part of the wipe should be used for wiping. Moreover, several layers of tissue paper should be used to prevent leaching of contaminants from finger tips during wiping. The test tubes and pipette tips can be rinsed with 2 molar nitric acid and with distilled, deionized water. The GFAAS sample cups can be rinsed with Milli-Q water. In many GFAAS instruments the autosampler tip is rinsed automatically with dilute nitric acid. Graphite tubes can be cleaned by heating up the tubes before use according to the manufacturers* instructions.
The inorganic anions and cations usually analyzed with ion chromatography are water soluble Cl", NO/, SO/", Na+, NH4+, K+, Mg2* and Ca2+. In this case using strong acids (e.g. HC1, HN03 and H2S04) for washing is risky because removing the acid anion by rinsing with water may be incomplete and too high anion concentrations are obtained. It is recommended that only Milli-Q water is used for rinsing the equipment used in IC analysis.
4.4. Washing and storage of Berner low-pressure impactors
The cleanliness of the impactor is especially critical for those impactor parts that come to contact with collection substrates. On the other hand, the jet holes of impactor stages should be clean to ensure that the calibration for particle size is unchanged. The inner parts of the impactor can be washed in an ultrasonic bath with Milli-Q water and then with isopropanol. Immediately after the isopropanol treatment, the parts are dried with purified (aerosol filter) pressurized air. In particular, the jet orifices are blown clean. After drying, the impactor is immediately assembled and sealed to make it air tight. Washing of the impactor is laborious and time consuming and consideration should be used in planning the washing schedule for impactors. Washing the impactor is usually needed only after every fifth or tenth collection. Instead of washing, the impactor can be cleaned after each sampling by using clean paper wetted with isopropanol to wipe those impactor parts that come to contact with the collection substrates. 19
4.5. Loading the impactor and sampling
If possible, the impactor should be loaded in a clean room or on a clean bench where precautions to exclude aerosol and interfering gases (HN03, S02, HC1, NH3) have been made. H3P04-impregnated filters can be used to remove NH3 and NaOH- or Na^CO^impregnated filters to remove acidic gases from the air stream. The washed and sealed impactor is opened and the collection substrates are quickly installed using clean forceps. Before loading, the substrates can be treated with a radioactive a-source to minimize the electrostatic charges on the substrates (this is particularly important for polycarbonate substrates). If not removed, the electrostatic forces can make handling of the polycarbonate substrates almost impossible. The impactor o-rings should be greased with special vacuum oil to ensure that inside the impactor there are no leaks. After all substrates are loaded, the impactor is immediately closed, sealed air tight and stored. The impactor should remain sealed until just before sampling and then after sampling the impactor should be immediately resealed.
4.6. Unloading the impactor and sample storage
During the unloading process of the impactor and storage of the samples there is oncemore a contamination risk. Therefore, the impactor should be unloaded in a clean room or on a clean bench equipped with proper precautions against contamination by aerosols and interfering gases. If necessary, the sample substrates are again treated with an a-source to dissipate electrostatic forces. The dry samples can be stored in a refrigerator or in a cold room at temperature below 5°C. Cutting off narrow strips of the substrate outer and inner edges is a good precaution to minimize contamination from the impactor.
4.7. Blank values of sample preparation methods
To achieve maximum benefits from the analysis methods used, the procedural blank values should be below the limits of detection of the methods. However, for certain elements, it can be difficult to find collection substrate materials, reagents and sample vials clean enough to reach such optimal conditions. In choosing materials for sample preparation and analysis, issues like blank contribution and cost of material, expected analyte concentrations in the sample, necessity of sample dissolution etc. should be considered. In some cases cheap lower purity products may be clean enough but should be tested before use. An important point 20 affecting the blank values is the solvent chosen. The purity of the solvent may vary from time to time due to contamination and use of different batches. Therefore, before dissolution of the samples it is important to establish that the solvent is clean and free of contamination. The same batch of solvent should be used for sample dissolution and for preparation of standards. Sometimes problems may arise with the analysis which can lead to prolongation of the measurements. Therefore, for each set of samples and the corresponding standards sufficient solvent should be prepared to cater for such a situation. Blank values from some dissolution procedures and materials are presented by Pakkanen (1988). 21
5. EXPERIMENTAL
An overview of the size distribution sampling methods, collection substrate materials, analysis methods and sample preparation procedures used in this thesis is presented in Table 5. A detailed discussion of the various experimental subjects is presented in the Sections 5.1. - 5.4.
5.1. Sampling instruments
As indicated in Table 5, two different impactor types were used for aerosol sampling in the publications I - VII: BLPI (Berner and Liirzer, 1980) and MOUDI (Marple et al., 1991). All instruments were calibrated before use as described in Hillamo and Kauppinen (1991). The 50% cut-off points of the impactors used depend on atmospheric pressure and temperature and on sampling flow rate and are presented separately in the seven publications. Publications n and m deal with in-stack sampling and the other publications with atmospheric sampling.
5.2. Materials
5.2.1. Collection substrates and chemicals
Table 5 presents the collection substrate materials used for impactor sampling in the various publications I to VU. In publications II and HI some BLPI samples were collected on aluminum foil but these samples were only measured gravimetrically. The blank contributions from polycarbonate and mylar substrates in GFAAS analysis are compared in Table 4.
Throughout this work suprapur reagents (suprapur 65% HN03 - Merck; suprapur 37% HC1 - Merkc; suprapur 30% H2Oz - Merck) and double distilled or distilled and deionised water (Milli-Q) were used for sample dissolution procedures.
5.2.2. Sample containers
Dry impactor samples were stored in washed airtight plastic boxes and/or in petri dishes and/or in stainless steel containers specially designed for storage of BLPI samples. Sometimes, for periods up to about one week, BLPIs were sealed with parafilm or stailess steel stoppers and samples were left inside the BLPI. 22
5.3. Sample preparation
The analysis techniques INAA, PIXE and XRF do not usually require dissolution of the sample. In these analysis methods the dry samples are quickly prepared for analysis in a clean room or on a clean bench. Some other analysis methods like, for instance IC, GFAAS and ICP-MS usually require sample dissolution. In publication I a simple dissolution method for metal analysis from fine particle BLPI samples is presented. This procedure is explained in brief in the Section 5.3.1. For the BLPI samples refered to in this thesis, fine particles originate from stages 1 through 7, ie for particles of BAD smaller than 2 pm. Regardless of the analysis method used it is important to follow proper contamination control procedures during sample preparation and analysis (see Chapter 3). An overview of the sample preparation methods used in the publications I - VII of this thesis is presented in Table 5.
5.3.1. Dissolution of atmospheric BLPI samples for GFAAS and ICP-MS analysis
The following dissolution method is presented in detail in Pakkanen (1988) and in publication I and therefore only an overview is given here. This method is not recommended for nitrate analysis or any IC analysis because nitric acid is used as solvent and because H+ ions may lead to the deterioration of IC-columns. However, a similar procedure can be used for the IC determination of water soluble anions and cations when samples are dissolved in distilled, deionized water only.
The impactor samples are cut into pieces with clean scissors in a clean room or on a clean bench with precautions against contamination by aerosol and possible interfering gases. The pieces are placed in acid washed test tubes or plastic bottles, 5 ml of 0.2 molar nitric acid (Suprapur) is added and the sample containers are immediately closed with a stopper. It is estimated that in this procedure the lowest possible sample volume to ensure efficient dissolution and enough sample for GFAAS analysis of the 13 elements Al, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V and Zn is 2 - 3 ml. Use of a sample volume greater than 5 ml lowers the analyte concentrations and may thus increase the measurement error on the samples with the lowest concentrations. On the other hand, a sample volume of 10 - 20 ml enables use of FAAS as the analysis method for Na, K, Mg and Ca. The sample containers should preferably be transparent so that the aerosol deposits (spots) on the impaction film can be visually inspected. To ensure good contact of the deposits with the solution the containers 23
are shaken by hand and placed in an ultrasonic bath at 50 °C for 20 min. Subsequently, the containers are again hand-shaken and inspected to check whether or not the aerosol spots are removed from the surface of the impaction substrates. This dissolution procedure (shaking by hand + ultrasonic bath) is repeated until there are no visible spots left on the substrates. Usually, the procedure has to be carried out two or three times. The nitric acid is left in
contact with the impaction film and with any remaining insoluble particulate residue until the GFAAS analysis is performed. In this work, the analyses were usually started about 24 h after the dissolution. For certain impaction stages (particle size fractions) the spots sometimes may remain slightly visible after the repeated dissolution treatment, possibly because of staining due to soot. The dissolution method was tested with impactor samples analyzed by GFAAS and INAA and with National Institute of Standards and Technology (NIST) standard reference material (SRM) 1648 Urban Particulate Matter (see Sections 6.1.2. and 6.1.3.).
In connection with publications IV and V a limited test (not published) of the above dissolution method for filter samples was performed by analyzing fine particle polycarbonate filter samples by ICP-MS, PIXE and INAA. Results from this experiment are discussed in Section 6.1.5.
5.3.2. Dissolution of in-stack combustion samples for metal analysis
To dissolve the coal combustion aerosol samples (publication HI), about 1/4 of the substrate was placed in a borosilicate beaker washed by boiling with several aliquots (4-5 ml) of concentrated nitric acid (suprapur) in the beakers and rinsing with distilled, deionized water after each treatment. Two ml of concentrated nitric acid (suprapur), 0.5 ml of concentrated hydrogen peroxide (suprapur) and 2 ml of concentrated hydrochloric acid (suprapur) was added and the sample was digested on an electric hot plate until the liquid was evaporated. The dry sample was then dissolved in 10 ml of distilled, deionized water and placed in an ultrasonic bath for 30 min. The refuse incinerator samples (publication II) were dissolved in a similar fashion to the coal combustion samples but hydrochloric acid was not used. The GFAAS analysis was performed according to the principles presented in Section 5.4.1. Some samples were also analyzed by PIXE. A comparison of the GFAAS and PIXE results is given in Kauppinen (1987). Blank values of the sample preparation method for coal combustion samples are presented in Table 4. 24
In principle the sample dissolution method in dilute nitric in an ultrasonic bath should also be valid for fine particle combustion samples. However, up to now no tests have been performed to verify if the fine particle combustion aerosols can be analysed from dilute nitric acid solutions prepared as described in section 5.3.1.
5.4. Analytical techniques
The various analysis methods used in this thesis are listed in Table 5. More details about the GFAAS method are presented in Section 5.4.1. The PIXE and INAA methods are not discussed since the analysis procedures used are explained elsewhere (Schutyser et al., 1978; Maenhaut et al., 1981; Maenhaut and Raemdonck, 1984). Also, the ICP-MS and IC analysis described in publications V and VII were performed routinely and are discussed further only in the corresponding publications. In publications I and V parallel analysis were performed using different analysis methods.
5.4.1. GFAAS analysis of atmospheric and in-stack BLPI samples
In this section GFAAS: analysis of BLPI samples in publications I, II and HI is discussed. Many details indicated below may also be useful when other impactor types and/or analytical methods are employed. All GFAAS analyses discussed in this work were performed at the Finnish Meteorological Institute, Helsinki. The spectrometer was a Perkin-Elmer Model 3030 equipped with an HGA-600 graphite furnace and an AS-60 autosampler. A deuterium lamp was utilized for background correction. The graphite tubes and platforms were coated with pyrolytic graphite. To be able to dilute samples several times by a factor of 2, the sample injection volume used in the analysis was 96 pi (5 - 99 possible), except for Zn, for which it was 40 pi. Each sample was analyzed only once and quantification was effected via a calibration graph that was established from three standard solutions and a zero standard, as described by Barnett (1984). Because the total sample volume was only 5 or 10 ml, Na, K, Mg and Ca, normally determined by flame atomic absorption spectroscopy (FAAS), had to be measured by GFAAS. Quantification was based on the peak area of the absorption line, which made it possible to use lower atomization temperatures and flatter absorption signals. This made the detection limits poorer in some cases but allowed determination of higher concentrations. Thus a whole set of impactor samples could be analyzed with a single calibration graph simply by using the dilution possibilities of the autosampler only. 25
In the beginning of the eighties Slavin et al. (1981) presented their Stabilized Temperature Platform Furnace method (STPF-method). Usually this method produces the most reliable
GFAAS analysis results because interferences arising during analysis are minimized. However, BLPI samples are normally lightly loaded, from a few micrograms to a few hundred micrograms, and severe interferences are rare during such analysis. In publication I the atomization of the analyte was performed off the wall of a pyrolytically coated graphite tube. However, Zn was atomized from a platform as is usually the case in the STPF methods. Several BLPI samples were analyzed by both off-the-wall and STPF methods and excellent agreement was generally observed. Also, the reference material NIST SRM 1648 was analyzed by both techniques and again the results were found to agree well, although the STPF method yielded slightly higher values, i.e., by 5, 3, 9, and 9% for Cd, Pb, Mn and Fe, respectively. The observed differences probably resulted from the fact that the nitric acid was in contact with the sample one week longer in the case of samples analyzed by the STPF method.
The use of off-the-wall methods has some advantages over STPF methods. When a sample is atomized off the wall, a greater sample volume can be used for analysis and lower analyte concentrations can usually be detected. If STPF methods are employed, a chemical modifier is often required and the analyses last longer because additional autosampler steps are needed. However, when a BLPI sample is heavily loaded, it is recommended that the analysis of those stages with the highest loadings are checked by FAAS or an STPF method, at least for those elements (e.g. Na, K, Cd, Mn and Pb) that are sensitive to interferences in GFAAS. The exact analytical conditions used for various elements in this work are presented in publication I.
i.-. 26
6. RESULTS AND DISCUSSION
In this chapter the results obtained from the publications I - VII are summarized. Furthermore, the combined data set reviewed in Chapter 3 is used as a basis for recommendations about analysis methods suitable for analysis of some selected aerosol components.
6.1. GFAAS analysis of atmospheric BLPI samples
6.1.1. Blank values and limits of determination
Table 6 (from publication I) presents blank values for polycarbonate substrates and limits of determination obtained using the GFAAS method described in Section 5.4.1. and the dissolution method which utilizes dilute nitric acid in an ultrasonic bath (Section 5.3.1.). The samples were dissolved in 5 ml of 0.2 molar nitric acid. Table 6 shows that the blank values of Al, Cd, Cu, Mn, Ni, Pb and V are at, or below, the limits of determination of the method. Ca, Fe, K, Mg, Na and Zn also exhibit reasonably low blank levels. The polycarbonate film gives rise to substantial blank values for Cr, but is otherwise a suitable material for aerosol collection with subsequent GFAAS analysis for the above elements. In addition, polycarbonate Film was found to have low blank values for most analytes for the PIXE and INAA methods (publications IV and V, Maenhaut et al., 1993) and for the IC method (publication VII). However, polycarbonate film or the collected material on polycarbonate seem to adsorb gaseous ammonia and therefore, care should be taken to avoid contamination during storage and analysis (Pakkanen et al., 1994).
6.1.2. Recoveries from NIST SRM 1648
The dissolution method presented in section 5.3.1. was tested using NIST SRM 1648 samples which represent total aerosol samples (publication I). A large fraction of the NIST material remained undissolved, however some elements showed reasonably good recoveries. Use of normal dissolution times of 1-2 days resulted in recoveries of about 80% or more for Cd, Cu, Mg, Pb and Zn. Extended dissolution times of one or two weeks did not markedly enhance recoveries of most elements. 27
6.1.3. Recoveries from BLPI samples
Al, Cu, Mg, Mn, Na and V were analyzed by GFAAS and INAA methods from atmospheric BLPI samples (publication I). The GFAAS recoveries were determined by comparing GFAAS and INAA results, the latter serving as reference. The results obtained from one BLPI sample are presented in Table 7. The results indicate that the recoveries for Cu, Mn, Na and V from the fine particle impactor stages (7-1) of the BLPI samples were clearly better than those obtained from the NIST reference material. A crustal element aluminum behaves differently and the results are discussed in section 6.1.4. Overall, the dissolution method presented in section 5.3.1. produces recoveries higher than 85% for Cd, Cu, Mg, Mn, Na, Pb, V and Zn in fine particle impaction stages.
6.1.4. Analysis of insoluble particles by GFAAS
By comparison of results for filtered and unfiltered samples it was shown that about 75% of the recovered aluminum from unfiltered NIST SRM 1648 samples (representing total aerosol) was insoluble material and that the total recovery was about 40% (publication I). Similar experiments were performed with atmospheric BLPI samples the results of which are presented in Figure 1 (publication I). It can be seen that there is a trend for the distribution ratio of Al in unfiltered and filtered samples to increase with increasing particle size. This can be explained by the limited solubility of the soil dust particles and the reduced ability of the coarser particles to go into suspension.
6.1.5. GFAAS analysis of atmospheric filter samples
This thesis mainly deals with cascade impactor samples. However, a limited comparison test for applicability of the dissolution method (Section 5.3.1.) for fine particle filter samples was performed by analysing the samples by ICP-MS, PIXE and INAA. The recoveries from filter samples were compared in connection with publications IV and V but were not published earlier. Table 9 indicates that the agreement between results from dissolved samples (ICP-MS) and those of the corresponding solid samples (PIXE and INAA) was within about 10% for the elements Ca, Na, Pb, S, V and Zn. However, the ratios for Al varied from 0.04 to 1.71 indicating that some measurement problems were encountered for this element. Nevertheless, the results of Table 8 indicate that dissolution in dilute nitric acid (5.3.1.) can give good 28 recoveries for several elements in fine particles collected on polycarbonate filters. The dissolution method may be valid for atmospheric fine particles collected on some other filter types too.
6.2. GFAAS analysis of in-stack combustion aerosol samples
The in-stack refuse incinerator experiment (publication II) revealed that mass size distributions of Na, K, Zn, Cd, Pb, and S were bimodal, but Mg, Al, Cl, Ti and Fe were only found in coarse mode particles. The corresponding elemental geometric mean aerodynamic diameters varied between 0.1 and 0.2 pm for the fine mode and between 6 and 10 pm for the coarse mode. The existence of the fine mode peak in the size distributions of Na, K, Zn, Cd, Pb and S indicates that these elements are at least partially vapourized during the refuse incineration process.
The in-stack coal combustion samples were collected after an electrostatic precipitator and analyzed by GFAAS and PIXE methods (publication ]H). Mass and all the elements determined (Na, Mg, Al, Si, S, K, Ca, Ti, Fe, V, Mn, Ni, Cu, Zn, Sr, Cd and Pb) were found to have bimodal size distributions. The size distributions are presented in Figure 2 (Si, S, Ti and Sr were analyzed by PIXE). About 5% of particle-bound Na, Mg, Al, Si, Ti, Fe, Mn and Zn were found in the fine particle mode. S, Ca, V, Cu, Sr, Cd and Pb were enriched in the fine-mode particles, the fraction in the fine mode varying from 9% for Pb to 80% for S. The geometric mean diameters for the coal combustion samples were about 0.05 pm and 2 pm for the fine and coarse modes, respectively.
6.3. Sources and size distributions of atmospheric aerosol components
6.3.1. Sources and size-distributions of atmospheric aerosol constituents in southern Norway
Publication IV describes use of BLPI impactors in southern Norway to measure elemental and mass size distributions from atmospheric aerosol. The performance of the impactors was verified by making parallel measurements with stacked filter units (SFU, Cahill et al., 1977; Heidam, 1981). The avarage ratio of elemental concentrations from the BLPI and SFU measurements varied between 1.20 and 0.77 for most elements studied. Average atmospheric 29 size distributions for aerosol mass and the 25 elements Na, Mg, Al, Si, S, Cl, K, Ca, Sc, Ti, V, Mn, Fe, Cu, Zn, As, Br, Mo, Sb, I, Cs, La, Sm, W and Pb are presented in Figure 3 (publication IV).
Southern Norway is strongly affected by long-range transport of pollutants from Western and Central Europe and from Russia (Amundsen et al., 1992; Comille et al., 1990; publication V). Because of the deleterious effects of these pollutants on the Norwegian ecosystems, it is important to assess their sources and to understand their transformation and removal processes. In spring 1988, Pakkanen et al. (publication V) used various size-fractionating sampling methods to collect atmospheric aerosols at Birkenes and Nordmoen, in southern Norway. At Birkenes, BLPI impactors were used to measure mass and elemental size distributions (see also publication IV). Conventional methods together with a new method based on the size distributions measured, the Relative Size Distributions method or RSD- method, were used to identify existing pollutant sources important for the Birkenes site. The RSD-method was able to reveal most of the pollutant sources found using the conventional methods. Details of the RSD-method can be found in publication V. Figure 4 presents some atmospheric size distributions of selected elements from one BLPI sample and Figure 5 presents the corresponding RSD - curves.
6.3.2. Size distributions of major atmospheric inorganic ions in Helsinki
Figure 6 (from publication VII) presents atmospheric size distributions of Na+, Ca2+, Cl" and N03" ions from six BLPI samples collected during the Nordic HN03/N03" and NH3/NH4+ gas/particle intercomparison in Helsinki, 11. - 22. May, 1992 (Pakkanen et al. 1994). The corresponding size distributions of the important atmospheric ions S042* and NH4+ are shown in Pakkanen et al. (1994) but are not presented here. The main features of these size distributions are similar to those presented by Wall et al. (1988) for atmospheric ions in California.
6.4. Use of size distribution measurements in characterising formation of atmospheric coarse particle nitrate aerosol
The size distribution data collected during the Nordic HN03/N03* and NH3/NH4+ gas/particle intercomparison in Helsinki, 11. - 22. May, 1992 (Pakkanen et al. 1994) were inspected in
3 21405 30 order to study the formation of atmospheric coarse particle nitrate aerosol at the sampling site (publication VII). The size distributions of Na+, Ca2+, Cl" and N03" ions, presented in Figure
6 , together with various ion balances between the ions measured, indicated that coarse particle nitrate was mostly formed in atmospheric surface reactions between gaseous nitric acid and sea salt aerosol. This reaction resulted in evaporation of chloride from sea salt as hydrochloric acid. The chloride evaporation was almost complete for the sea salt particles of about 1-2 |im BAD suggesting that all sea derived chlorides of this particle size may have reacted with atmospheric acidic species. The study further indicated the possibility of an atmospheric reaction between gaseous hydrochloric acid and coarse soil particles. The data from one BLPI sample showed a coarse particle nitrate concentration higher than could be explained by the reaction of nitric acid and sea salt alone. In this case it was obvious that nitric acid also reacted with coarse soil particles. Figure 7 shows that in all six measurements the nitrate fraction associated with soil particles increased with increasing particle size which results from the fact that the relative abundancies of soil particles compared to those of sea salt particles also increased with increasing particle size.
6.5. PIXE analysis of MOUDI impactor samples
A MOUDI impactor (Marple et al., 1991) was used by Maenhaut et al. (publication VI) in Helsinki, Finland, to determine element size distributions in the atmosphere. Whilst analyzing the samples by PIXE it turned out that several of the deposits were inhomogeneous at the millimeter level. However, it was shown that concentration data can be obtained by PIXE provided that the analyzed area is carefully selected and appropriate correction factors for the nonuniformity are employed. In publication VI Maenhaut et al. compared also the suitability of the three different impactor types MOUDI, BLPI and PIXE international Battelle type impactor for PIXE analysis. The impactor types, being highly different for flow rate and/or shape of the deposits, were shown to produce rather similar limits of detection for the various elements with the MOUDI impactor exhibiting the lowest or best values.
6.6. Recommendations for size distribution measurements of selected aerosol components
Analyticalmethods The recommendations presented here are principally based on the references reviewed in the Tables la - 2 which also include the publications I - VH of this work. It is considered that 31
a component, whose size distributions are frequently analyzed by a certain analysis method, can be successfully analyzed by this particular analysis method. Thus, as one can see in Table 9, the aerosol components for which several suitable analysis methods exist, are listed against the techniques in question. Whether or not a size distribution of a certain component can be
determined at the sampling site may depend on numerous issues like, for instance type of sampling instrument (number of stages, size range collected, sampling flow rate), sampling time, analyte concentration during sampling, wind speed and wind direction, shape of aerosol deposition, etc. Thus, the recommendations in Table 9 are a rough estimate about the components that can be analyzed by each method in the following conditions: 24 - 48 h sampling time at a rural site, sampling flow rate of about 20 - 30 litres per minute, 8-10 size fractions, average atmospheric analyte concentrations and low blank values. Size distributions of the most common atmospheric aerosol components, including SO/", NH4+, Na, Fe and many others, can be measured in considerably shorter time period, of course.
Materials As discussed in Chapter 4, all materials used for size distribution measurements should preferably be the highest possible purity to ensure low procedural blank values for the analytes. Polycarbonate film was used as collection substrate material in all the seven publications of this thesis. Polycarbonate blanks and samples collected on polycarbonate material were analyzed by INAA (publications I, IV, V), PIXE (publications n, m, IV, V, VI), GFAAS (publications I, n, HI), ICP-MS (publication V) and IC methods (publications V, VH) and the blank values of most analytes were found to be low. Consequently, polycarbonate is one possible choice as collection substrate material if the above analysis methods are utilized.
Useful measuments Measurement of some specific aerosol components can be useful for further data verification, identifying of aerosol sources and for interpretation of data. It is recommended that the quality of analysis is checked by analyzing a few samples by two different analytical methods. Another way of checking the accuracy of the analysis is the use of appropriate reference materials.
Some aerosol components can be used to identify aerosol sources. For example Na has been widely used as a reference component for sea derived aerosol (Wall et al., 1988; publication 32
VH). Al, Si, Fe, Ca and Ti are the usual indicators for crustal rock material (publications V, VII) and Ni and V can often be attributed to emissions from oil burning and oil refineries. More information about identification of aerosol sources can be obtained from Nriagu (1989) and Pacyna (1989) who have studied a large variety of both natural and anthropogenic aerosol sources.
7. CONCLUSIONS
The size distribution measurements of aerosol components described in this thesis allowed several conclusions concerning analysis of aerosols, sources and transport of atmospheric aerosols, and physical and chemical phenomena occuring for atmospheric and in-stack aerosols to be drawn.
The choice of the various collection substrates and back-up filter materials used in size distribution measurements, as well as other materials and reagents, are critical parameters for minimizing the analyte blank contributions and careful testing of all materials and reagents used should be performed. Moreover, different sample pretreatment procedures and different analysis methods may result in widely different blank values for a certain collection substrate material. In addition to low blank values, the prerequisite for being able to determine detailed size distributions is that five or more size fractions per one log-unit in particle diameter is collected.
A sample dissolution method that utilizes dilute nitric acid and an ultrasonic bath treatment was developed and found to produce low blank values and recoveries greater than 85% for Cd, Cu, Mg, Mn, Na, Pb, V and Zn from atmospheric fine particle size fractions analyzed by GFAAS. Even a large part of the insoluble material in fine and coarse particle fractions could be recovered by this technique since suspensions were formed. The limited solubility and the reduced ability to form suspension resulted in the fact that aluminum was less effectively recovered when the particle size increased. However, this phenomenon was not so pronounced for Cu, Mg, Mn, Na and V.
The studies concerning in-stack coal combustion aerosols showed that components such as total particulate mass, Al, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, Pb, S, Si, Sr, Ti, V and Zn, can 33 have bimodal size distributions when samples are collected after an electrostatic precipitator: the mass mean diameters (MMD) of fine and coarse modes were about 0.05 and 2 pm, respectively. On the other hand, in-stack hospital refuse incinerator samples collected after a cyclone only exhibited the coarse mode for Al, Ca, Cl, Fe, Mg and Ti whereas in case of total mass, Cd, K, Na, Pb, S and Zn the mass size distributions were bimodal. The mass fractions found in fine and coarse modes can be very different for different components.
Size distribution measurements carried out in Birkenes, southern Norway, usually showed one or two fine particle modes and one or two coarse modes for the components measured. Ambient relative humidities higher than about 80% increased the MMD values of the droplet mode from about 0.4 - 0.6 pm to roughly 0.8 - 1.0 pm. The size distributions measured were helpful in determining local and/or regional sources of As, Br, I, K, Mn, Pb, Sb, Si and Zn in southern Norway. To efficiently utilize size distributions in source identification, the relative size distributions method (RSD method) was developed. Interelemental ratios in emissions measured in the British Isles and in air masses originating from the British Isles and measured in southern Norway or southern Sweden were found to be similar for several pollution elements. The long term concentration levels of several pollution elements have been fairly stable in southern Scandinavia during the eighties. Compared to the background levels, however, the episodic pollutant concentrations can be 20-50 times higher in air masses coming from the British isles or from the central or eastern Europe.
Size distribution studies carried out in Helsinki, Finland, indicated that atmospheric coarse particle nitrate was formed in the atmosphere when nitric acid reacted with and/or adsorbed on coarse sea salt and soil particles. The fraction of nitrate associated with soil particles was found to increase with increasing particle size, which is reasonable since compared to sea derived particles, the abundance of soil particles was greater at larger particle sizes. Nitrate associated with sea salt particles dominated except in one case. The study also indicated that chloride loss from sea-salt particles decreased with increasing particle size suggesting that surface reaction mechanisms are involved. The chloride loss can be complete for particles smaller than about 2 pm of BAD which shows that, in addition to NaCl, other sea derived chlorides such as KC1, MgCl2 and CaCl2 may react with acidic species in the atmosphere. Moreover, the size distribution data obtained in this Helsinki study give some evidence for the possible atmospheric reaction of hydrochloric acid with coarse soil particles. 34
Recommendations for suitable analysis methods for measurement of size distributions of selected aerosol components were given. These include the six common methods INAA, PIXE, XRF, GFAAS or FAAS, ICP-MS or ICP-AES and IC and are based on the review presented. Thus, the following analysis methods have been used in measuring size distributions of the components indicated: INAA Al, As, Br, Cl, Cs, I, K, La, Mg, Mn, Mo, Na, Sb, Sc, Se, Sm, V, W PIXE Al, Br, Ca, Cl, Cu, Fe, K, Mn, Ni, Pb, S, Si, Ti, Zn XRF Br, Cu, Fe, K, S, Si, Pb GFAAS, FAAS Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V, Zn ICP-MS, ICP-AES Ag, Al, As, Cd, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Sb, Ti, V, Zn IC Cl\ NO,', S042", NH/, Na+, K+, Mg2*, Ca2*
It is noted that use of new high performance ICP-MS instruments can possibly, because of their extremely low limits of detection, produce size distributions of such aerosol components that exist at very low concentrations.
Until now most of the atmospheric size distribution measurements have been carried out in North America, Europe or Japan, and have been conducted mainly in the atmospheric boundary layer. Measurements from other parts of the world are needed for better understanding of the global atmospheric environment and from the upper troposphere to obtain more information on the long-range transport. Also, studies involving in-stack and plume size distribution measurements of aerosol components have not yet been widely performed. Such measurements can give valuable information on the chemistry and physics of exhaust aerosols prodeced by various industrial processes. These measurements can also be utilized in assessing source contributions at various receptor sites. Continuous size distribution curves, obtained using data inversion, can reveal additional details of the size distributions measured. Use of data inversion methods is strongly recommended, even though only a few such measurements have been published until now. Size distribution measurements of components in large and giant aerosol particles are important when estimating particle deposition velocities and in fine particles because of their harmful health effects and because of their importance in many chemical and physical processes. However, accurate size distribution measurements of aerosols below 0.1 gm BAD and above 15 gm EAD are scarce. These measurements obviously suffer from difficulties in sampling and/or from the existence of analytes at very low concentrations. 35
Conditions in the atmospheric and in industrial processes can change over a time scale of some minutes. These changes may result in differences in the size distributions of aerosol components over a short time period. Long sampling times may result in size distributions that are composites of initially highly different size distributions. Compared to these time averaged size distribution curves, those measured during exact and constant conditions are more informative. More work is needed to obtain measurements to a level that will enable determination of short term size distributions measured during constant conditions. To reach this goal, impactors with higher sampling flow rates, materials with lower procedural analyte blank values and analysis methods with lower limits of detection are needed. Furthermore, to be able to fully utilize size distribution measurements which allow a deeper insight to several chemical and physical phenomena, better data interpretation methods should be developed. REFERENCES
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Yamashige T., Yamamoto M. and Sunahara H. (1989) Comparison of decomposition methods for the analysis of atmospheric particulates by atomic absorption spectrometry. Analyst 114, 1071-1077. Yoshizumi K. and Hoshi A. (1985) Size distributions of ammonium nitrate and sodium nitrate in atmospheric aerosols. Environ. Sci. Technol. 19, 258-261. Yoshizumi K. and Asakuno K. (1986) Characterization of atmospheric aerosols in Chichi of the Ogasawara (Bonin) Islands. Atmos. Environ. 20, 151-155. Zhang X. and McMurry P.H. (1992) Ecaporative losses of fine particulate nitrates during sampling. Atmos. Environ. 26A, 3305-3312. Zhang X., Arimoto R., An Z., Chen T., Zhang G., Zhu G. and Wang X. (1993) Atmospheric trace elements over source regions for Chinese dust: concentrations, sources and atmospheric deposition on the loess plateau. Atmos. Environ. 27A, 2051-2067. Table la. Size distributions analyzed using INAA-method. impactor type, size range in pm and number of impaction back-up sampling size distributions reference impaction stages substrate filter site presented for Barrie, 1988 Andersen, 10 - 0.43 (-) polyethylene cellulose Canada Al, As, Ba, Br, Ca, Cl, Cu, In, Mn, Na, Se, Ti, V Barrie et al. 1994 Berner, 21 - 0.04 (5) polyethylene none Canada Br, Cl, I, Na, V Dodd et al., 1991 MOI, 2.5 - 0.08 (5) teflon teflon USA Al, As, Ca, Ce, Cl, Fe, Ga, Hf, I, In, K, La, Mn, Mo, Na, Sb, Sc, Se, Sm, Ta, Ti, V Dulac et al., 1989 Sierra, >7.2 - 0.49 (5) cellulose cellulose Mediterranean Al, Na German! et al., 1994 Mark HI, 35 - 0.33 (7) teflon glass fiber * Al, Ag, Br, Ca, Cd, Cl, Co, Cs, K, Mn, Na, Zn Kowalczyk et al., 1982 SA, 15 - 0.5 (6) polycarbonate polycarbonate Washington DC Al, Mn Maenhaut et al., 1993 Berner, 5.4 - 0.011 (10) polycarbonate none * Al, As, Ba, Br, Ca, Cl, Co, Cr, Eu, Fe, Ga, I, K, Mg, Mn, Mo, La, Na, Ni, Sb, Sc, Se, Sm, Sr, Th, Ti, V, W, Zn, (mass) Okamoto and Kobayashi, Andersen, - (7) teflon yes Japan Cl 1991 polyethylene yes Japan Ondov et al., 1990 MOI >4.9 - 0.092 (6 or 8 ) teflon teflon Maryland, USA Al, As, Au, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Cu, Fe, Ga, Hf, I, In, Ir, K, La, Mg, Mn, Mo, Na, Nd, S, Sb, Sc, Se, Sm, Ta, Ti, V, W, Yb, Zn Tsukada et al., 1991 Andersen, >7 - 0.43 (7) yes fluoropore Japan 129J, 127j Yoshizumi and Asakuno, 1986 Andersen, 30 - 0.08 (9) teflon none Japan Al, Cl, Na, V, (mass) publication IV Berner, 16 - 0.03 (10) polycarbonate none Norway Al, As, Br, Cl, Cs, I, K, La, Mg, Mn, Mo, Na, Sb, Sc, Sm, V, W, (mass) publication V Berner, 16 - 0.03 (10) polycarbonate none Norway Al, As, Br, Cl, Cs, I, K, La, Mg, Mn, Mo, Na, Sb, Sc, Sm, V, W, (mass) yes: information on type not supplied -: information not found * : in-stack mass is measured gravimetrically Table lb. Size distributions analyzed using PIXE-method. impactor type, size range in pm and number of impaction back-up sampling size distributions reference impaction stages substrate filter site presented for Artaxo and Hansson, 1995 Battelle, >4 - 0.25 (5) plastic polycarbonate Amazon Basin Al, Br, Ca, Cl, Cr, Cu, Fe, K, Mn, Ni, P, Pb, Rb, S, Si, Sr, Ti, V, Zn, Zr Eltayeb et al., 1993 FIXE, >10.3 - 0.15 (7) polycarbonate polycarbonate in laboratory Al, Ca, Fe, K, Mn, Si, Ti, [Rb,Sr,Y,Zr] (mass) resuspended soil Ferek et al., 1983 Battelle, >1.6 - 0.4 (3) mylar nuclepore USA (aircraft) Ca, Cl, Fe, S, Si Heintzenb and Covert, 1987 yes, 0.50 - 0.01 (9) yes none Spitzbergen Fe, Ni, Pb, S, Zn (mass) Hietel and Tschiersch, 1988 Berner, 16 - 0.06 (9) yes none - Br, Fe, Pb, S, Zn Hillamo et al., 1993a FIXE, >11 - 0.135 (7) polycarbonate polycarbonate Greenland Al, Br, Ca, Cl, Fe, K, Mg, Mn, Na, Ni, Pb, S, Si, Ti, Zn Lannefors et al., 1983 Battelle, >8 - 0.25 (6) yes nuclepore Sweden Ca, Cl, Cu, Fe, K, Mn, Ni, Pb, S, Ti, V, Zn Martinsson et al., 1992 Battelle, >4 - 0.25 (5) yes nuclepore Italy Mn, S, Zn Reid et al., 1994 DRUM, 15 - 0.07 (8 ) mylar none California Ca, Cl, Fe, Si Zhang et al., 1993 FIXE, >16 - 0.25 (7) mylar film yes China Al, As, Ca, Fe, K, S, Si, Ti, Zn publication IV Berner, 16 - 0.03 (10) polycarbonate none Norway Ca, Cu, Fe, K, Mn, Pb, S, Si, Ti, Zn (mass) publication V Berner, 16 - 0.03 (10) polycarbonate none Norway Ca, Cu, Fe, K, Mn, Pb, S, Si, Ti, Zn (mass) publication n Berner, 17 - 0.024 (10) polycarbonate none * Al, Cl, Fe, S, Ti (mass) publication m Berner, >16 - 0.03 (11) polycarbonate none * S, Si, Sr, Ti (mass) [ ]: some elements may have been analyzed using other analysis methods yes: information on type not supplied -: information not found * : in-stack mass is measured gravimetrically 6 Table lc. Size distributions analyzed using XRF-method. impactor type, size range in pm and number of impaction back-up sampling size distributions reference impaction stages substrate filter site presented for Eltayeb et al., 1993 PIXE, >10.3 - 0.15 (7) polycarbonate polycarbonate * [Rb, Sr, Y, Zr], (mass) Dodd et al., 1991 MOI, 2.5 - 0.08 (5) teflon teflon Maryland USA Br, Pb, S Hasan and Dzubay, 1987 MOI, 3 - 0.088 (4) teflon teflon Denver Br, K, Pb, S, (mass) Haster et al., 1992 PIXE, 22 - 0.06 (9) quartz none Ireland Co, Pb, Se, V North Sea Fe, Pb Lyons et al., 1993 Bering, >4 - 0.05 (8 ) teflon none Los Angeles Cu, Fe, Mn, Ni, Pb, Zn Marple et al., 1991 MOUDI, 18 - 0.056 (8 ) yes yes Grand Canyon Al, Ca, S, Si, (mass) [ ]: some elements may have been analyzed using other analysis methods yes: information on type not supplied -: information not found * : in laboratory resuspended soil mass is measured gravimetrically Table Id. Size distributions analyzed using GFAAS- and/or FAAS-methods. impactor type, size range in pm and number of impaction back-up sampling size distributions reference impaction stages substrate filter site presented for Baeyens and Dedeurwaerder, Sierra, >9.3 - 0.67 (5) cellulose cellulose North Sea Al, Cd, Cu, Fe, Mn, Na, Pb, Zn 1991a Dasch and Cadle, 1990 In-Tox, >8.2 - 0.17 (7) glass coverslips teflon Michigan Na, Ca Dulac et al., 1989 Sierra, >7.2 - 0.49 (5) cellulose cellulose Mediterranean Al, Cd, Na, Pb German! et al., 1994 Mark m, 35 - 0.33 (7) teflon glass fiber * Pb Master et al., 1992 Sierra, 7.2 - 0.5 (6) cellulose none North Sea [Pb, V] Holsen and Noll, 1992 Anderson, 10 - 0.43 (8 ) Mylar yes Chicago Ca, Pb, (mass) Noll, >36.5 - 6.5 (4) Mylar Chicago Ca, Pb, (mass) Holsen et al, 1993 Anderson, >10 - 0.43 (9) Mylar yes USA Ca, Pb, (mass) Noll, >36.5 - 6.5 (4) Mylar USA Ca, Pb, (mass) Ortiz et al., 1993 Berner, >10.2 - 0.14 (7) Al foil none Chile Ca, Fe, Mg, Mn, Pb, Zn Andersen, >2.84 - 0.41 (5) Al disks yes Chile Cu, Fe, Mg, Mn, Pb, Zn Ottley and Harrison, 1992 May ultimate, >20 - 0.5 (6) cellulose teflon North Sea Na* Ottley and Harrison, 1993 May ultimate, >20 - 0.5 (6) cellulose teflon North Sea Al, Cd, Cu, Fe, Na, Pb, Zn Van Daalen, 1991 Sierra, >7.2 - 0.50 (5) Whatman 230 cellulose South Holland [As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Se, Sn, V, Zn] publication II Berner, 17 - 0.024 (10) polycarbonate none * Ca, Cd, K, Mg, Na, Pb, Zn, (mass) Mylar none * Ca, Cd, K, Mg, Na, Pb, Zn, (mass) Al film none * (mass) publication HI Berner, >16 - 0.03 (11) polycarbonate none * Al, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V, Zn, (mass) Al film none * (mass) [ ]: some elements may have been analyzed using other analysis methods mass is analysed gravimetrically yes: information on type not supplied * : in-stack Table le. Size distributions analyzed using ICP-AES and/or ICP-MS methods. impactor type, size range in pm and number of impaction back-up sampling size distributions reference impaction stages substrate filter site presented for Master et al., 1992 Sierra, 7.2 - 0.5 (6) cellulose filters none North Sea [Pb,V] Hillamo et al., 1988 Berner, >16 - 0.03 (10) polycarbonate none Norway As, Pb, V Infante and Acosta, 1991 Andersen, >7 - 1.1 (4) fiber glass fiber glass Puerto Rico Al, Cd, Cu, Fe, Mn, Ni, Pb, V, Zn Van Daalen, 1991 Sierra, >7.2 - 0.5 (5) Whatman 230 cellulose South Holland [As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Se, Sn, V, Zn] [ ]: some elements may have been analysed using other analysis methods Table If. Size distributions analyzed using IC-method. impactor type, size range in pm and number of impaction back-up sampling size distributions reference impaction stages substrate filter site presented for Barrie et al., 1994 Berner, 21 - 0.04 (5) polyethylene none Canada NO/, SO/', NH4+, Mn Dasch and Cadle, 1990 In-Tox, >8.2 - 0.17 (7) glass coverslips teflon Michigan Cl", NO,', SO/' Gabler and Heumann, 1993 Sierra, 10 - 0.49 (5) cellulose cellulose Germany Cl", NO,', SO/' Hillamo et al., 1992 Berner, 16 - 0.03 (10) polycarbonate none Norway Cl', NO,", SO/', NH/, Na+, Ca2t (mass) Hillamo et al., 1993b Berner, 16 - 0.03 (10) polycarbonate none Finland Cl', NO,", SO/', NH/, Na+, K+, Mg2*, Ca2+ Ottley and Harrison, 1992 May "ultimate", >20 - 0.5 (6) cellulose teflon North Sea Cl', NO/, SO/', NH/ Pakkanen et al. 1994 Berner, 16 - 0.03 (10) polycarbonate none Helsinki NO,', SO/', NH/ Pierson et al., 1989 Andersen, 9 - 0.4 (8 ) cellulose quartz fiber Pennsylvania SO/', NH/ Sloane et al., 1991 MOUDI, >3.16 - 0.03 (8 ) teflon teflon Denver, USA NO,", SO/" (mass) Wall et al., 1988 Berner, 16 - 0.06 (9) Tedlar none California CV, NO/, SO/', NH/, Na+ publication YU Berner, 16-1 (4) polycarbonate none Helsinki Cl', NO/, Na+, Ca2t mass is measured gravimetrically Table lg. Size distribution measurements using various analysis methods. impactor type, size range reference in p.m and number of impaction back-up sampling size distribution (analysis methods) impaction stages substrate filter site presented for Gabler and Heumann, 1993 Sierra, 10 - 0.49 (5) cellulose cellulose Germany and I (IDMS) Weddell Sea Harrison and Pio, 1983 Andersen, >7 - 0.08 (6) quartz filters none England C1-, NO/, SO,:', NH4+, Na+ (various) Injuk et al., 1992 Berner, 16 - 0.06 (9) Al foil none North Sea Cd, Cu, Pb, Zn (ASV) Lin et al., 1994 Andersen, 10 - 0.43 (6) mylar yes Chicago mass (gravimetric) Noll, >36.5 - 6.5 (4) mylar none Chicago mass Van Daalen, 1991 Sierra, >7.2 - 0.50 (5) cellulose cellulose South Holland [As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Se, Sn, V, Zn] (polarography) Yoshizumi and Hoshi, 1985 Andersen, 30 - 0.08 (9) quartz none Tokyo NH4NO3, NaN03, total NO, (various) teflon none Tokyo NH4N03, NaN03, total NOa Yoshizumi and Asakuno, 1986 Andersen, 30 - 0.08 (9) teflon none Japan N03", S042", NH4+, mass (various) [ ]: some elements probably analyzed using other methods yes: information on type not supplied ASV: anodic stripping voltammetry IDMS: isotope dilution mass spectrometry Table lh. Size distribution measurements for carbon and organic species using various analysis methods. impactor type and range (|lm) impaction back-up sampling reference and number of impaction stages substrate filter site Heintzenberg and Covert, 1987 - yes - Spitzbergen Kaupp el al., 1994 Berner, >12.2 - 0.15 (5) Al foil glass fiber Germany Ludwig and Klemm, 1988 AERAS, >12.2 - 0.15 (5) teflon Whatman GM-A - Nunes and Pio, 1993 Sierra, - (5) glass fibre - - Okamoto and Kobayashi, 1991 Andersen, - (7) yes - Japan Sloane et al., 1991 MOUDI, >3.16 - 0.03 (8 ) Al foil yes Denver Tang et al, 1994 multi-channel diffusion yes - Los Angeles denuder, 2.5 - 0.4 (3) yes: information on type not supplied - : information not found Table 2. Limits of detection and/or limits of determination (LOD) and blank values for various collection substrates and analysis methods. impactor type, size range in nm and nymber of impaction analysis values reference impaction stages substrate method information presented for Baeyens and Dedeurwaerder, Sierra, >9.3 - 0.67 (5) cellulose GFAAS, FAAS blanks Al, Cd, Cu, Fe, Mn, Na, Pb, Zn 1991a Ferek et al., 1983 Battelle, >1.6 - 0.4 (3) Mylar PIXE LOD Al, Ca, Cl, Fe, K, Pb, S, Si, Ti Master et al., 1992 PIXE, 22 - 0.06 (9) quartz XRF LOD As, Ba, Ca, Co, Cr, Cu, Fe, K, Mn, Ni, Pb, Se, Sr, Ti, V, Zn Sierra, 7.2 - 0.5 (6) cellulose ICP-AES LOD Ba, Ca, Cr, Cu, Fe, K, Mn, Ni, Pb, Sr, Ti, V, Zn Sierra, 7.2 - 0.5 (6) cellulose GFAAS LOD As, Co, Cr, Cu, Ni, Pb, Se, V, Zn Infante and Acosta, 1991 Andersen, >7 - 1.1 (4) fiber glass ICP blanks Al, Ca, Cu, Fe, Mg, Mn, Ni, Pb, V, Zn Maenhaut et al., 1993 Berner, 5.4 - 0.011 (10) polycarbonate INAA blanks Al, As, Ba, Br, Ca, Cl, Co, Cr, Eu, Fe, Ga, I, K, La, Mg, Mn, Mo, Na, Ni, Sb, Sc, Se, Sm, Sr, Th, Ti, V, W, Zn Ondov et al., 1990 MOI, >4.9 - 0.092 (6 or 8) teflon INAA blanks 46 elements teflon+ApL INAA blanks 46 elements Ortiz et al., 1993 Berner, >10.2 - 0.14 (7) Al foil GFAAS LOD Cd, Cu, Ni Ottley and Harrison, 1993 May ultimate, >20 - 0.5 (6) Whatman 541 GFAAS, FAAS LOD Al, Cd, Cu, Fe, Na, Pb, Zn Wall et al., 1988 Berner 16 - 0.06 (9) Tedlar IC blanks Cl’, NO,', SO/, Na+, K+, Mg2*, Ca2* publication I Berner, 16 - 0.03 (10) polycarbonate GFAAS LOD, blanks Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V, Zn polycarbonate+ApL GFAAS blanks Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na; Ni, Pb, V, Zn publication II Berner, 16 - 0.03 (10) Mylar+ApL GFAAS blanks Ca, Cd, K, Mg, Na, Pb, Zn Berner, 16 - 0.03 (10) polycarbonate+ApL GFAAS blanks Ca, Cd, K, Na, Pb, Zn Berner, 16 - 0.03 (10) polycarbonate+ApL PIXE blanks Al, Cl, Fe, S, Ti ApL: Apiezon L vacuum grease Table 3. Scientific applications of size distribution measurements. 1) Deposition of atmospheric aerosols. Dulac et al., 1989; Hillamo et al., 1993a; Holsen et al., 1993; Injuk et al., 1992; Lin et al., 1994; Ottley and Harrison, 1992; Ottley and Harrison, 1993; Zhang et al., 1993; 2) Sources and transport of atmospheric aerosols. Artaxo and Hansson, 1995; Baeyens and Dedeurwaerder, 1991a; Baeyens and Dedeurwaerder, 1991b; Dodd et al., 1991; Eltayeb et al., 1993; Harrison and Pio, 1983; Infante and Acosta, 1991; Injuk et al., 1992; Jaffrezo et al., 1993; Kowalczyk et al., 1982; Lannefors et al., 1983; Lyons et al., 1993; Martinsson et al., 1992; Okamoto and Kobayashi, 1991; Ottley and Harrison, 1992; Ottley and Harrison, 1993; Pierson et al., 1989; Reid et al., 1994; Wall et al., 1988; Zhang et al., 1993; publications II, HI, V, VH 3) Atmospheric and in-stack chemistry and physics. Baeyens and Dedeurwaerder, 1991b; Barrie et al., 1994; Dasch and Cadle, 1990; Dodd et al., 1991; Eltayeb et al., 1993; German! et al, 1994; Harrison and Pio, 1983; Infante and Acosta, 1991; Injuk et al, 1992; Jaffrezo et al., 1993; Maenhaut et al., 1993; Martinsson et al, 1992; Okamoto and Kobayashi, 1991; Ortiz et al., 1993; Ottley and Harrison, 1992; Pierson et al., 1989; Sloane et al., 1991; Tang et al., 1994; Wall et al., 1988; Yoshizumi and Hoshi, 1985; publications II, HI, V, VH Table 4. Comparison of reagent blank values using Mylar film and polycarbonate film (|ig/l). The samples were digested to dryness in borosilicate beakers with 2 ml of concentrated nitric acid (suprapur), 0.5 ml of concentrated hydrogen peroxide (suprapur) and 2 ml of concentrated hydrochloric acid (suprapur) and dissolved in 10 ml of 0.2 molar nitric acid. Data is from Pakkanen (1988). A1 Ca Cd Cr Cu Fe K Mg Mn Na Ni Pb V Zn R 4 10 0.06 0.3 0.4 8 5 5 0.2 15 <3 0.3 <1 3 M - 2000 0.08 - 0.5 - - 25 0.2 - <3 22.0 - 80 p 4 10 0.08 10 0.5 8 5 5 0.2 15 <3 0.4 <1 4 R: blank values for reagents only M: blank values for Mylar film + reagents P: blank values for polycarbonate film + reagents not measured Table 5. Impactor type and the corresponding collection substrate materials, analysis methods and sample preparation procedures used in the publications I - VII. sampling substrate analysis sample dissolution publication instrument materials methods procedure I BLPI pc GFAAS dissolution in 5 ml of 0.2 molar HN03 in an ultrasonic bath at 50°C INAA # n BLPI pc, mylar, A1 GFAAS wet ashing in 2 ml 65% HN03, 2 ml 37% HC1 and 0.5 ml 30% H202 and subsequent dissolution in 10 ml of double distilled water PIXE # m BLPI pc, mylar, A1 GFAAS wet ashing in 2 ml 65% HN03 and 0.5 ml 30% H202 and subsequent dissolution in 10 ml of double distilled water PIXE # rv BLPI pc INAA, PIXE # PCI pc INAA, PIXE # V BLPI pc INAA, PIXE # ICP-MS* dissolution in ,5 ml of 0.2 molar HNG3 in an ultrasonic bath at 50°C IC* dissolution in distilled and deionised water VI MOUDI pc PIXE # vn BLPI pc IC dissolution in 5 ml of distilled and deionised water BLPI: Berner low-pressure impactor MOUDI: micro-orifice uniform deposit impactor PCI: PIXE international Battelle type impactor INAA: instrumental neutron activation analysis GFAAS: graphite furnace atomic absorption spectroscopy IC: ion chromatography PIXE: proton induced X-ray emission ICP-MS: inductively coupled plasma - mass spectrometry pc: polycarbonate film (Nuclepore Corp.) *: some samples only #: INAA and PIXE analysis did not involve any sample dissolution or specific sample handling procedures Table 6 . Detection limits and blank values (jJ.g/1) for dissolution in test tubes with 5 ml of 0.2 molar nitric acid. The blank values and associated standard deviations are based on 5 samples (from publication I). Detection Blank 1 Blank 2 Element limit* (PC+HNO3)# (PC+ApL+HNCy# A1 1.0 1 ±0.5 1.5 ± 1 Ca 0.30 1 ±0.5 3.5 ± 1.5 Cd 0.020 0.01 ± 0.01 0.02 ± 0.01 Cr 0.25 10 ±4 10 ±4 Cu 0.40 0.1 ± 0.1 0.2 ± 0.1 Fe 0.30 1.5 ± 1 2.5 ± 1 K 0.070 1 ±0.5 1 ±0.5 Mg 0.020 0.5 ± 0.2 0.8 ± 0.4 Mn 0.20 0.1 ±0.05 0.1 ± 0.05 Na 0.030 . 1 ± 0.5 1.5 ±1 Ni 1.0 <0.5 <0.5 Pb 0.60 <0.3 <0.3 V 1.0 <0.5 <0.5 Zn 0.020 0.5 ± 0.2 0.7 ± 0.4 *: Quantitative detection limit of GFAAS (injection volume 96 |il). The values were determined by diluting a standard solution to the point where the precision of ten replicate analyses from one sample was no longer in the limits of ± 10%. #: PC = polycarbonate film (15 cm2); ApL = Apiezon L vacuum grease (0.1-0.3 mg). Table 7. Recoveries (%) for the BLPI samples, as derived from comparing the GFAAS results with the INAA data. The GFAAS samples were dissolved in dilute nitric acid. Stage 10 stands for the coarsest particles (BAD about 8-16 pm) and stage 1 for the finest (0.03-0.06 pm). Stages 1-7 represent fine particles (BAD 0.03-2 pm). Table is from publication 1. stage No. A1 Cu Mg Mn Na V 10 28 118 80 78 91 105 9 35 91 114 78 87 94 8 47 90 107 89 136 101 7 51 89 - 84 168" 101 6 39 - - 84 102 102 5 45 - - 99 112 97 4 - - - 99 260' 109 3 86 108 94 2 : - : 1 average 1-7 45 90 107 101 -: concentration close to the detection limit(s) of GFAAS or INAA. *: data not retained when calculating the averages. Table 8. Average ratios of ICP-MS results to PIXE and/or 1NAA results for concentrations of some elements in atmospheric fine particles on polycarbonate filters. element ratio type of ratio S (18) 0.92 ICP-MS/PIXE Na (21) 0.95 ICP-MS/INAA A1 (12) 0.50* ICP-MS/INAA Ca (10) 1.12 ICP-MS/PIXE V (18) 1.07 ICP-MS/INAA Mn (7) 0.50 ICP-MS/(PIXE and INAA) Zn (19) 1.05 ICP-MS/PIXE As (19) 1.29 ICP-MS/INAA Pb (17) 0.96 ICP-MS/PIXE (n): number of comparisons *: ratios were variable and the average is probably too high Table 9. Some analysis methods and aerosol components for which size distributions can be usually* measured using the analysis method indicated. Analysis method Components for which atmospheric size distributions can usually be obtained INAA Al, As, Br, Cl, Cs, I, K, La, Mg, Mn, Mo, Na, Sb, Sc, Se, Sm, V, W PIXE Al, Br, Ca, Cl, Cu, Fe, K, Mn, Ni, Pb, S, Si, Ti, Zn XRF Br, Cu, Fe, K, S, Si, Pb GFAAS Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V, Zn ICP-MS Ag, Al, As, Cd, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Sb, Ti, V, Zn IC C1-, NO3-, SO/-, NH4+, Na+, K+, Mg2*, Ca2* *: measurements made in the following conditions: rural site, 24-48 h sampling with flow rate of 20-30 liters per minute, 8-10 size fractions 3.5 3 r2 1.5 1 0.1 1 10 100 Particle diameter, pm Figure 1. Ratio of unfiltered to filtered Al according to particle size (from BLPI sample, closed squares) and for a total aerosol sample (NIST SRM 1648 Urban Particulate, open squares). The average particle size is estimated for the NIST sample. J ■’ Particle Stokes Diameter, urn 10.00 ■ 3000 • 20.00 Z 5X0 • Particle Stokes Diameter, jim Figure 2. Element size distributions from two in-stack coal combustion samples. Si, S, Ti and Sr were analyzed by FIXE, other elements by GFAAS. 0062 016 0.52 19 7.6 0062 016 0.52 19 7.6 0062 016 0 52 1 9 7 6 0062 0090 033 095 3.6 0032i 0090i i 033i i OSSi r r36n r 0032 0090 033 OSS 36 Cl x2S MS x 20 NO x 5.6 Mg xI3 Co x 085 Br x 036 1 23456769 10 1 23456789 10 1 23456789 10 STAGE NUMBER Figure 3. Average atmospheric size distributions from southern Norway (publication V). ( 5 21405 4a 4b 5000 90 LPf-9 LPI-9 ao 4000 70 60 3000 50 40 2000 30 20 1000 10 0 0 Particle Diameter, jum Particle Diameter, jam Figure 4. Atmospheric size distributions of selected elements for BLPI sample 9 (from publication V). The sample was collected in southern Norway. V/SX1495 ■ Mn/Sxl280 • Zn/Sx142 ■ As/Sx2140 ■ Sb/Sx2750 ■ 1/5x1960 - Pb/Sxl23 • Br/Sx830 -x- K/Sx59 -x- • Cu/Sx3740 Particle diameter, pm Figure 5. Selected atmospheric RSD-curves (S is the reference element) for BLPI sample 9 (from publication V). The sample was collected in southern Norway. Am/AlogDp, nm ol/m3 Am/AlogDp , nmol 25 Figure BLPI-4 BLPI-f 6 , Atmospheric size distributions of some inorganic BLPI-2 BLPI-5 ions in Helsinki (from publication VII), BLPI-3 BLPI-6 . i t tt . reVk- i (5 0.6 BLPl-3 BLPl-4 BLPl-5 BLPl-6 BLPI-stage Fig. 7. The fraction of nitrate associated with soil particles. Figure Is from publication VII. Finnish Meteorological Institute Contributions 1. J off re, Sylvain M., 1988. Parameterization and assessment of processes affecting the long-range transport of airborne pollutants over the sea. 49 p. 2. Solantie, Reijo, 1990. The climate of Finland in relation to its hydrology, ecology and culture. 130 p. 3. Joffre, Sylvain M. and Lindfors, Virpi, 1990. Observations of airborne pollutants over the Baltic Sea and assessment of their transport, chemistry and deposition. 41 p. 4. Lindfors, Virpi, Joffre, Sylvain M. and Damski, Juhani, 1991. Determination of the wet and dry deposition of sulphur and nitrogen compounds over the Baltic Sea using actual meteorological data. 111 p. 5. Pulkkinen, Tuija, 1992. Magnetic field modelling during dynamic magne- tospheric processes. 150 p. 6. Ldnnberg, Peter, 1992. Optimization of statistical interpolation. 157 p. 7. Viljanen, Ari, 1992. Geomagnetic induction in a one- or two-dimensional earth due to horizontal ionospheric currents. 136 p. 8. Taalas, Petteri, 1992. On the behaviour of tropospheric and stratospheric ozone in Northern Europe and in Antarctica 1987-90. 88 p. 9. Hongisto, Marke, 1992. A simulation model for the transport, transformation and deposition of oxidized nitrogen compounds in Finland — 1985 and 1988 simulation results. 114 p. 10. Taalas, Petteri, 1993. Factors affecting the behaviour of tropospheric and stratospheric ozone in the European Arctic and Antarctica. 138 s. 11. Malkki, Anssi, 1993. Studies on linear and non-linear ion waves in the auroral acceleration region. 109 p. 12. Heino, Raino, 1994. Climate in Finland during the period of meteorological observations. 209 p. 13. Janhunen, Pekka, 1994. Numerical simulations of E-region irregularities and ionosphere-magnetosphere coupling. 122 p. 14. Hillamo, Risto E., 1994. Development of inertial impactor size spectroscopy for atmospheric aerosols. 148 p. 15. Pakkanen, Tuomo A., 1995. Size distribution measurements and chemical analysis of aerosol components. 157 p. JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, FEBRUARY 1993, VOL 8 79 Simple Nitric Acid Dissolution Method for Electrothermal Atomic Absorption Spectrometric Analysis of Atmospheric Aerosol Samples Collected by a Berner-type Low-pressure Impactor Tuomo A. Pakkanen and RIsto E. Hillamo Finnish Meteorological Institute, Air Quality Department, Sahaajankatu 22 £, SF-00810 Helsinki, Finland Willy Maenhaut University of Ghent, Institute of Nuclear Sciences, Proeftuinstraat 86, B-9000 Ghent, Belgium The aim of this study was to develop a simple dissolution method for atmospheric aerosol samples collected using a Berner Impactor. Particular care was taken to ensure that the procedural blank contributions were as low as possible for the elements investigated. The impactor samples were treated for two or three 20 min periods with 0.2 mol M nitric acid in polystyrene test-tubes in an ultrasonic bath at 50 °C. Electrothermal atomic absorption spectrometry (ETAAS) with a graphite furnace was used to determine 14 elements: Al, Ca, Cd, Or, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V and Zn. With the exception of Zn, for which a platform was used, all analytes were atomized off the wall of the graphite tube. The blank values for Al, Cd, Cu, Mn, Ni, Pb and V were found to be at or below the detection limits of the method. The blank values for Ca, Fe, K, Mg, Na and Zn varied between 0.5 and 3 fig I-' but Cr showed an unsuitably high blank of 8 fig M. The dissolution method was tested on the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1648 Urban Particulate and the recoveries were found to be 80-93% for Pb, Zn, Cd and Cu. The least recoverable elements In this matrix were Al, Cr, Fe, K and Na, with recoveries between 20 and 44%. A prolonged dissolution time had only a minor effect on the recoveries. Additional tests involved the analysis of ambient aerosol samples, collected with a cascade impactor, by both ETAAS and instrumental neutron activation analysis (INAA), with the latter technique providing the reference values. Six elements (Al, Cu, Mg, Mn, Na and V) were measured by both techniques. Compared with the NIST material, the fine particle (equivalent aerodynamic cut-off diameter<2 pm) impactor samples clearly showed better recoveries for Cu (91%), Mn (90%), Na (102%) and V (96%). Similar or even better recoveries are also expected for fine particle Cd, Zn and Pb, which were not measured in our INAA procedure but exhibited the highest recoveries for the NIST material. For Al, on the other hand, the results from the impactor samples were similar to those for the NIST material and there was a trend that the recoveries were decreasing with increasing particle size, because of incomplete dissolution of the soil dust particles and a lower ability of the coarser particles to form a suspension. Moreover, coarse particle Al was recovered mostly as particulate material. It Is assumed that our dissolution method is valid for measuring fine particle Cd, Cu, Mg, Mn, Na, Pb, V and Zn In ambient aerosol samples collected on polycarbonate film by various types of impactors. Keywords: Atmospheric aerosols; dissolution; nitric acid; electrothermal atomic absorption spectrometry; cascade impactor Mass size distributions for atmospheric trace elements are associated with insoluble particles in those fine-size frac generally determined by collecting atmospheric aerosol tions may be accurately determined if the fine particles can samples with cascade impactors and subsequently analysing form a suspension in the solvent medium. the impaction foils by a sensitive analytical technique. As The aim of this work was to establish a suitable discussed by Maenhaut, 1 several techniques, including dissolution method for atmospheric aerosol samples col neutron activation analysis, X-ray techniques, optical lected with a Berner-type low-pressure impactor, so that atomic spectrometric techniques, and mass spectrometry, several elements could be accurately measured by electroth may be used for analysing aerosol samples. When one ermal atomic absorption spectrometry (ETAAS) using a resorts to atomic absorption spectrometry (AAS) or to graphite furnace. Also, as typically only very small amounts techniques that utilize an inductively coupled plasma (ICP) of the analyte elements are collected in the finest particle for sample excitation, the aerosol samples generally have to stages of the Berner impactor, the dissolution method had be subjected to an extraction, dissolution or decomposition to be set up so that the blank values of the dissolution procedure prior to the analysis. Solubilization studies have procedure were minimal. been performed for bulk (total) aerosol samples and for non-size segregated reference materials. Nadkami,2 La- mothe et al.,3 Broekaert el al.* and Wang et al? used Experimental mixtures of strong acids at elevated temperatures and Aerosol Sampling and Sample Handling pressures. Comparisons of various dissolution methods have been carried out using digestion on a hot-plate 6,7 and Aerosol samples were collected at two different locations, high-pressure digestion in a closed Teflon bomb. 5 However, v/z. in Helsinki in June 1987 and in Utsjoki, Finnish the results or conclusions from these studies on bulk Lappland, in February 1988,* and thus represent urban samples may not necessarily apply to aerosol samples that summer air and Arctic winter air, respectively. During the are collected with a cascade impactor, where the particles Utsjoki sampling the whole country was covered by snow. are separated into several size fractions. The fine particle To give some idea of the amounts of metals in the fractions [equivalent aerodynamic cut-off diameter atmosphere, concentrations in different particle sizes (EAD)<2/im) of such samples contain much less crustal (Table 1) of the Helsinki sample are 0.3-130 ng m-3 for Al rock material than bulk aerosol samples and various and 0.08-3.4 ng m-3 for V. The concentration in the liquid elements may be present in forms that are much more easily depends on the sampled air volume and the number of solubilized. Further, even elements that are predominantly spots analysed and varied between 1 and 17 and between 1 80 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, FEBRUARY 1993, VOL. 8 by INAA and the results for Al, Cu, Mg, Mn, Na and V were Table 1 50% cut-off diameters (EAD) (/an) for the various compared with those obtained by ETAAS. impaction stages of Berner impactor samples collected at Helsinki and Utsjoki Dissolution Method for AAS Stage No. Helsinki Utsjoki For the Berner impactor samples, one sixth to one half Pre-stage 15.7 14.0 section of each impaction film was used for the dissolution 10 7.5 6.7 9 3.7 3.3 experiment and subsequent AAS analysis. Each section was 8 1.92 1.72 placed in an acid-washed 10 ml polystyrene test-tube, 5 ml 7 0.93 0.84 of 0.2 mol l-1 nitric acid (Suprapur) were added and the 6 0.51 0.46 tube was immediately closed off with a stopper. The test- 5 0.34 0.30 tubes were transparent so that the aerosol deposits (spots) 4 0.176 0.162 on the impaction film could be visually inspected. To 3 0.108 0.103 ensure good contact of the deposits with the solution the 2 0.062 0.064 tubes were shaken by hand, then placed in an ultrasonic 1 0.031 0.034 bath at 50 °C for 20 min. Subsequently, the tubes were again hand-shaken and a visual examination determined whether the aerosol spots were removed from the surface of and 175 /rg l-1 for V and Al, respectively, for the Helsinki the impaction substrates. This dissolution procedure (shak sample. ing by hand-1-ultrasonic bath) was repeated until there were The sampling device was a Berner-type low-pressure no visible spots left on the substrates. Usually, the proce impactor 9 with one pre-stage and ten regular impaction dure had to be carried out two or three times. The nitric stages. The stage jet orifices of the Berner impactor used in acid was left in contact with the impaction film and with this study were found 10 to be of the same size, which makes any remaining insoluble particulate residue until the the aerosol collection symmetrical and on each substrate all ETAAS analysis was done. To establish how much a pro the impaction deposits (spots) should have the same longed dissolution time enhanced the recoveries, this time concentration of a certain element. Air was drawn through period was varied from Id to a few weeks. For certain the device at a flow rate of about 251 min"" 1 and the total air impaction stages (particle size fractions), the spots some volume was 142.4 and 68.8 m3 for the Helsinki and the times remained slightly visible after the repeated dissolution Utsjoki samples, respectively. The 50% EADs for the treatment, possibly because of staining due to soot carbon. various stages at the experimental sampling conditions were No attempt was made to determine whether volatilization calculated as described by Hillamo and Kauppinen 10 and losses occurred during the dissolution procedure. are presented in Table 1. In addition to the Berner impactor samples, the National The collection substrates in the impaction stages con Institute of Standards and Technology (NIST) standard sisted of poreless Nuclepore polycarbonate films of 10 /an reference material (SRM) 1648 Urban Particulate Matter thickness. For the pre-stage and the coarse particle stages was subjected to the dissolution treatment. These experi 10-7 these films were coated with Apiezon L vacuum ments were carried out with subsamples of about 100 mg of grease10 to give adhesive properties to the substrates and to NIST material. minimize particle bounce-off. As indicated below, this In order to examine whether some elements such as Al coating did not contribute significantly to the blank levels of were in suspension rather than truly in solution after the the analyte elements. Before use, the impactor was washed dissolution procedure, the final liquid was filtered for some with distilled, de-ionized water obtained with a Milli-Q impactor samples and in two experiments with the NIST system (Millipore) and propan-2-ol (Merck, analytical- SRM. In this filtration, use was made of Millipore Millex- reagent grade). All the accessories needed for handling the HV4 filters (pore size 0.45 /tm). However, the filtration had substrates and the samples were washed with 0.2 mol 1~* the effect that the blank values for Al became higher and nitric acid (Suprapur) and/or Milli-Q-purified water and/or unstable, and this increased the uncertainty in the results of propan-2-oi. Whenever possible, the impactors were loaded this examination. and unloaded on a clean bench, otherwise the handling of the samples was performed in the field or in a normal ETAAS Analysis laboratory. Contamination from the laboratory air is expected to be minimal, however, as the analysis of blank The ETAAS analyses were performed at the Finnish impaction substrates that were handled in the same way as Meteorological Institute, Helsinki, within 1 month after the the real samples resulted in low blank values, as will be sampling. The spectrometer was a Perkin-Elmer Model indicated below. Nevertheless, the use of a clean bench ora 3030 equipped with an HGA-600 graphite furnace and an clean room is strongly recommended." The samples were AS-60 autosampler. For background correction a deuterium stored in tightly closed plastic boxes in a dark storage room. lamp was utilized. The graphite tubes and platforms were The ETAAS analyses were performed within 1 month after coated with pyrolytic graphite. To be able to dilute samples the collection but the instrumental neutron activation several times by a factor of 2, the sample injection volume analysis (INAA) was carried out in September 1989. (5-99 /A are possible) used in the analysis was 96 /d, except for Zn, for which it was 40/d. The experimental conditions used for the various elements are given in Table 2. Each Instrumental Neutron Activation Analysis sample was analysed only once and quantification was One quarter sections of the impaction films of the various effected via a calibration line that was established from stages of the Berner impactor samples and of blank three standard solutions and a zero standard, as described impaction films were subjected to INAA. The INAA by Barnett." Because the total sample volume was only involved a 5 min irradiation of each quarter section at a flux 5 ml, Na, K, Mg and Ca, normally determined by flame of about 3xl0 12ncm -2s-1 in the Thetis reactor of the AAS, also had to be measured by ETAAS. Quantification University of Ghent, and two y-spectrometric measure was based on the peak area of the absorption line, which ments with a high-resolution Ge detector. Full details of the made it possible to use lower atomization temperatures and INAA procedure were given by Maenhaut and Zoller 12 and flatter absorption signals. This made the detection limits Schutyser et alP The short-lived isotopes were determined poorer but allowed the determination of higher concentra- JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, FEBRUARY 1993, VOL. 8 81 Table 2 Analytical conditions for ETAAS. Most of these methods are sensitive to interferences and are valid only if the total mass of the sample is low Aluminium Cadmium Calcium* Wavelength: 309.3 nm Wavelength: 228.8 nm Wavelength: 422.7 nm Slit: 0.7 nm Slit: 0.7 nm Slit: 0.7 nm Tube: Pyrolytic graphite coated Tube: Pyrolytic graphite coated Tube: Pyrolytic graphite coated Temperature programme— Temperature programme— Temperature programme— TimeZs Time/s TimeZs Furnace Furnace Furnace tempcrature/ eC Ramp Hold tcmpcrature/ ’C Ramp Hold lemperatureTC Ramp Hold 90 2 2 90 2 2 90 2 2 140 2 30 140 2 30 140 2 30 1100 6 15 250 6 15 900 6 15 2500 1 5 1800 1 5 2400 1 6 2650 1 5 2650 1 5 2650 1 5 Chromium Copper Iron Wavelength: 357.9 nm Wavelength: 324.8 nm Wavelength: 248.3 nm Slit: 0.7 nm Slit: 0.7 nm Slit: 0.2 nm Tube: Pyrolytic graphite coated Tube: Pyrolytic graphite coated Tube: Pyrolytic graphite coated Temperature programme— Temperature programme— Temperature programme— Time/s TimeZs TimeZs Furnace Furnace Furnace temperatureZ°C Ramp Hold temperatureTC Ramp Hold temperaturefC Ramp Hold 90 2 2 90 2 2 90 2 2 140 2 30 140 2 30 140 2 30 900 6 15 800 6 15 1000 6 15 2100 0 3 2100 0 3 2300 5 2650 1 5 2650 1 5 2650 1 5 Potassium Magnesium Manganese Wavelength: 766.5 nm Wavelength: 285.2 nm Wavelength: 279.5 nm Slit: 0.7 nm Slit: 0.7 nm Slit: 0.2 nm Tube: Pyrolytic graphite coated Tube: Pyrolytic graphite coated Tube: Pyrolytic graphite coated Temperature programme— Temperature programme— Temperature programme— Time/s TimeZs TimeZs Furnace Furnace Furnace tcmpcraturc/°C Ramp Hold temperature/°C Ramp Hold teraperatureZ°C Ramp Hold 90 2 2 90 2 2 90 2 2 140 2 30 140 2 30 140 2 30 800 6 15 800 6 15 900 6 15 2400 I 1.5f 2200 1 3 1900 0 2 2650 1 5 2650 1 5 2650 1 5 Sodium Nickel Lead Wavelength: 589.0 nm Wavelength: 232.0 nm Wavelength: 283.3 nm Slit: 0.7 nm Slit: 0.2 nm Slit: 0.7 nm Tube: Pyrolytic graphite coated Tube: Pyrolytic graphite coated Tube: Pyrolytic graphite coated Temperature programme— Temperature programme— Temperature programme— Time/s TimeZs TimeZs Furnace Furnace Furnace temperatureZ°C Ramp Hold temperaturcTC Ramp Hold temperaturefC Ramp Hold 90 2 2 90 2 2 90 2 2 140 2 30 140 2 30 140 2 30 800 6 15 900 6 15 450 6 15 2300 1 2 50 15 2200 4 2650 1 5 2400 0 4 2650 1 5 2650 1 5 Vanadium Zinc Wavelength: 318.4 nm Wavelength: 213.9 nm Slit: 0.7 nm Slit: 0.7 nm Tube: Pyrolytic graphite coated Tube: Pyrolytic graphite coated, with platform Chemical modifier 6 p% Mg(NO,)2 Temperature programme— Temperature programme— TimeZs TimeZs Furnace Furnace temperatureZ°C Ramp Hold temperatureZeC Ramp Hold 90 2 2 90 2 2 140 2 30 140 2 30 1200 6 15 700 6 15 50 1 15 1700 0 3 2600 0 6 2650 I 5 2650 I 5 •Graphite tubes give a signal at the wavelength of calcium and before analysis the tubes should be heated 10-20 times at 2650 °C. fAtomization time should be kept short because the signal from the clean graphite tube increases with time. 82 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, FEBRUARY 1993, VOL. 8 lions. Thus a whole set of impactor samples could be acid was always 5 ml. The blank levels of various elements analysed with a single calibration graph by using the (in n% M) for.both ungreased and greased films are given in dilution possibilities of the autosampler only. Table 3. A comparison was also made with the quantitative Usually, the best results for ETAAS analysis are ob detection limits (DLs) of the ETAAS procedure. These DLs tained using stabilized temperature platform furnace were determined by diluting a standard solution to the (STPF) conditions, 15 which minimize interferences during point where the repeatability of ten replicate ETAAS analysis. However, Berner impactor samples are normally analyses (injection volume 96 /d) from one sample was no very lightly loaded, the total mass per substrate typically longer within the limits of ± 10%. being below 400 jrg, and severe interferences are rare during The blank values of Al, Cd, Cu, Mn, Ni, Pb and V are at such analyses (for the NIST material this argument is not or below the quantitative DLs of tire technique, and Ca, Fe, valid). In this work the atomization of the analyte was K, Mg, Na and Zn have reasonably low blanks in the range performed off the wall of a pyrolytic graphite coated 0.5-3 /rg 1_1. Further, the blank values for the greased graphite tube and only Zn was atomized using the STPF polycarbonate film are very similar to those for method. Several Berner impactor aerosol samples were the ungreased film and only Ca seems to be liberated from analysed by both methods and excellent agreement was the grease. Also, in previous work it was found that the generally observed. Also, the reference material NIST SRM Apiezon L vacuum grease released only negligible amounts 1648 was analysed by both techniques, and again the results of the various elements. 16 The polycarbonate film gives rise were found to agree well, although the STPF method to substantial blank values for Cr, but is otherwise a yielded slightly higher values, i.e., by 5,3,9 and 9% for Cd, suitable material for aerosol collection with subsequent Pb, Mn and Fe, respectively. The differences may result ETAAS analysis. Despite these low blank values, it was from the fact that the nitric acid was in contact with the observed that the analyte amounts on the two last impac sample 1 week longer in the STPF method. tion stages (Nos. 2 and 1) of our Berner impactor samples The use of off-the-wall methods has some advantages were very close to the blank values. It is therefore strongly over STPF methods. When a sample is atomized off the recommended that the blank values be examined before wall, a greater sample volume can be used for analysis and any actual aerosol sampling and/or ETAAS analyses are lower concentrations can be detected. If STPF methods are carried out when different batches of Nuclepore polycarbo employed, a chemical modifier is often required and the nate film, test-tubes or nitric acid are used. analyses last longer because additional autosampler steps are needed. However, when a Berner impactor sample is Examination of Aluminium Concentration in Solution abnormally heavily loaded, it is recommended that the analysis of those stages with highest loadings be checked by The low recoveries of Al, Cr and Fe (Table 5) indicate that flame AAS or an STPF method, at least for those elements aluminosilicates and crustal rock particles are definitely not {e.g., Na, K, Cd, Mn and Pb) that are sensitive to completely dissolved by the dissolution procedure pre interferences in ETAAS. sented here. In order to examine how far the Al measured by ETAAS is truly in solution rather than in suspension, quarter sections of the various impaction films from one Results and Discussion impactor sample (collected during summer at Helsinki) were subjected to the dissolution procedure and subsequent Blank Values and Detection Limits filtration. The same was also done with various subsamples Several unexposed (blank) polycarbonate impaction films of NIST SRM 1648 Urban Particulate Matter. The results were subjected to the dissolution procedure described of these experiments are presented in Table 4. With the above. In these experiments half of a film was placed in the impactor sample, about half of the recovered coarse particle polystyrene test-tube and the volume of 0.2 mol l-1 nitric Al is in suspended particulate form, and there is a tendency for that fraction to increase with increasing particle Al. The result for stage 6 is an exception, possibly because Table 3 Detection limits and blank values (pg 1~* 1). The blank values and associated standard deviations are based on 5 samples (dissolution experiments) Table 4 Detection Blank 1 Blank 2 Berner impactor sample and for NIST SRM 1648 Urban Particu- Element limit* (PC+HNO,)t (PC+ApL+HNO,)f late Matter Al 1.0 1 ±0.5 1.5 ±1 Impactor stage Ratio unfiltered to filtered Al Ca 0.30 1 ±0.5 3.5 ±1.5 Cd 0.020 0.01 ±0.01 0.02 ±0.01 10 2.4 Cr 0.25 10±4 10±4 9 1.8 Cu 0.40 0.1 ±0.1 0.2 ±0.1 8 1.7 Fe 0.30 1.5 ±1 2.5 ±1 7 1.7 K 0.070 1 ±0.5 1 ±0.5 6 3.0 Mg 0.020 0.5 ±0.2 0.8 ±0.4 5 1.3 Mn 0.20 0.1 ±0.05 0.1 ±0.05 4 __ • Na 0.030 1 ±0.5 1.5 ± 1 3 __ • Ni 1.0 <0.5 <0.5 2 __ • Pb 0.60 <0.3 <0.3 1 __ » V 1.0 <0.5 <0.5 NIST SRM 1648f Zn 0.020 0.5 ±0.2 0.7 ±0.4 A 3.2 * Quantitative detection limit of ETAAS (injection volume B 2.5 96/d). The values were determined by diluting a standard solution (injection volume 96/d) to the point where the consistency of ten The Al concentration was close to the blank value. replicate analyses from one sample was no longer in the limits of tTwo slightly different dissolution-ETAAS schemes were used: ±10%. (A) test-tube in ultrasonic bath at 50 °C for 20 min, ETAAS after 1 tPOpolycarbonate film (15 cm1); ApL=Apiezon L vacuum d; (B) test-tube in ultrasonic bath at 50 °C for 60 min, ETAAS after grease (0.1-0.3 mg). 9 d. In each scheme two different subsamples were examined. JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, FEBRUARY 1993, VOL. 8 83 of an analytical error due to the variable A1 blank value in Table 6 Recoveries (%) for the Helsinki aerosol samples, as the filtration procedure. For NIST SRM 1648, A1 is mostly derived from comparing the ETAAS results with the INAA data recovered in particulate form. (dissolution of the ETAAS samples in 0.01 mol 1~‘ nitric acid) Stage No. Al Cu Mg Mn Na V Recoveries for NIST SRM 1648 10 28 118 80 78 91 105 Table 5 gives the recoveries for various elements as 9 35 91 114 78 87 94 obtained by applying the dissolution procedure without 8 47 90 107 89 136 101 filtration to NIST SRM 1648 (about 100 mg samples) and 7 51 89 84 (168)f 101 analysis by ETAAS. Because the mass of the NIST samples 6 39 84 102 102 is high compared with that of impactor samples, a larger 5 45 99 112 97 __ « sample volume of 10 ml was used. Two slightly different 4 99 (260)f 109 3 __ * 86 108 94 dissolution-ETAAS schemes (A and B) were used, the 2 _ « __ • __ • __ * difference being that the ultrasonic bath treatment lasted 60 I __ * __ • __ * __ • min in scheme B compared with only 20 min in scheme A, and there was a 9 d period between the dissolution step and Average 7-1 45 90 107 101 the ETAAS in scheme B compared with only 1 d in scheme The concentration was close to the detection limit(s) of ETAAS A. This arrangement was made to see how much a or INAA. prolonged dissolution time enhances the recoveries. In each fData in parentheses were not retained when calculating the scheme, two different subsamples were examined. The data averages. for Ni and V are based on only one subsample, however. The results in Table 5 are similar to those that were Table 7 Recoveries (%) for the Utsjoki aerosol samples, as derived obtained by Infante and Acosta7 with a mixture of HC1 and from comparing the ETAAS results with the INAA data (dissolu HNOj. It was observed that a large fraction of the reference tion of the ETAAS samples in 0.2 mol l-1 nitric acid) material did not go into solution in our procedure and that most of the insoluble material sedimented to the bottom of Stage No.* Al Cu Mn Na V the test-tubes in 5-10 min after shaking. Despite the large 10 -t -t 46 —t —t fraction of insoluble material, reasonable recoveries were 9 43 55 91 80 —t obtained for some elements, e.g., for Cd (85%), Cu (80%), 8 45 70 (211* 102 68 Mg (77%), Pb (99%) and Zn (86%). A prolonged ultrasonic 7 57 79 (162* 107 93 bath treatment and longer standing time (scheme B) 6 61 97 88 (161* 96 enhanced the solubilization for Al, K, Mn, Na and Ni but 5 67 100 (150* 101 88 had no effect on the recovery of the important pollutant 4 44 -t 91 83 83 elements Cd, Cu, Pb, V and Zn. Average 7-4 57 92 -5 97 90 •Films from stages 3-1 were not analysed by INAA. Recoveries for the Berner Cascade Impactor Samples tThe concentration was close to the detection limit(s) of ETAAS or INAA. For the Berner cascade impactor samples the recoveries fData in parentheses were not retained when calculating the were determined by comparing the ETAAS and INAA averages. results, the latter serving as reference. Exceptionally, the {Contamination (or other) problems. Helsinki aerosol samples used in this comparison were dissolved in more dilute nitric acid, i.e., 0.01 mol l-1 (pH and the ETAAS analyses were performed after 2 weeks. For 2). However, if the acid strength is less than 0.1 mol l-1 the the Utsjoki aerosol samples, 0.2 mol I-1 (pH 0.7) nitric acid risk of ion adsorption on the walls of the sample container and a 60 min ultrasonic bath treatment was used, and the (test-tube and/or ETAAS cup) is increased.' 7-" The ultra ETAAS measurements were carried out after 2d. The sonic bath treatment for the Helsinki samples lasted 30 min recoveries for the Helsinki samples are presented in Table 6 and those for the Utsjoki samples in Table 7. Table 5 Recoveries (%) of elements after applying the dissolution The recoveries for Cu, Mn, Na and V from the fine procedure to NIST SRM 1648 Urban Particulate Matter. Two particle impactor stages (7-1) of the Berner impactor slightiy different dissolution-ETAAS schemes (A and B) were used samples are clearly better than those obtained from the (see footnote of Table 3 for details). Data are averages for each NIST reference material, although there appear to be some based on two sub-samples (except for Ni and V dissolution contamination or other problems with Mn and Na. Simi experiments). Agreement between the two sub-samples was usually larly, better recoveries from the fine particles can be within ±5% and in only two instances, Mg(A) and Cr(B) was expected for most of the other elements that were measured agreement worse than ± 10% in the NIST material, but not determined by INAA in the impactor samples. However, for a crustal element such as Element A B Al, the NIST material and impactor samples yield similar Al 38 48 recoveries, although there is a trend for the recovery to Cd 85 84 decrease with increasing particle size. This can be explained Cr 20 20 by the limited solubility of the soil dust particles in the Cu 80 82 Fe 42 45 aerosol and the reduced ability of the coarser particles to go K 34 45 into suspension. For the Utsjoki samples, all five elements Mg 77 80 listed in Table 7 seem to have worse recoveries with Mn 66 75 increasing particle size, but it should be mentioned that the Na 44 54 analytical errors for the large particle stages were greater Ni 40 72 here because of the low winter concentrations. Aluminium, Pb 99 93 on the other hand, is more completely dissolved from the V 61 63 Utsjoki samples than from the Helsinki samples. This may Zn 86 86 be a consequence of the fact that some snow was collected on the coarse particle stage impaction films. Possibly the 84 JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY, FEBRUARY 1993, YOU 8 snow had scavenged some fine particles., However, a more the reduced ability to form a suspension for the coarser likely explanation is that the higher A1 recoveries for the mineral particles. For Cu, Mg, Mn, Na and V this Utsjoki samples are the result of the stronger nitric acid phenomenon is not so pronounced. Furthermore, coarse used. Also, differences in particle origin and nature may particle Al was mainly recovered in suspended form. influence the solubilities and the ability to form a suspen A drawback of the proposed dissolution method is that sion. The different particulate mass-to-solution volume mineral soil dust particles are incompletely solubilized. ratios of the impactor samples and the NIST samples may have some influence when the solubilities of these different The authors thank Arto Jappinen for his assistance with the samples are compared. However, we believe that this is not collection of the Utsjoki samples. T. A. P. and a problem as it could be seen that a large part of the NIST R. E. H. thank the Maj and Tor Nessling Foundation and sample was insoluble. In any event, if lower masses of the the Academy of Finland for funding this work. W. M. NIST sample were used it should have resulted in similar or acknowledges support from the Belgian Nationaal Fonds higher recoveries in Table 5. More work is needed to verify voor Wetenschappelijk Onderzoek, the Interuniversitair the recoveries of Ca, Cr, Fe, K and Ni from impactor Instituut voor Kemwetenschappen and the Impulse Pro samples. gramme ‘Global Change, ’ supported by the Belgian State- Prime Minister ’s Service-Science Policy Office. Conclusions From experiments with NIST SRM 1648 Urban Particulate References Matter it can be concluded that a simple 20 min treatment with 0.2 mol l-1 nitric acid in an ultrasonic bath is able to 1 Maenhaut, W„ Control and Fate of Atmospheric Trace Metals, yield high recoveries for several metals from a total aerosol ed. Pacyna, J. M„ and Ottar, B., NATO ASI Scries, Kluwer, (non-size segregated) sample. The recoveries were higher Dordrecht, 1989, pp. 259-301. 2 Nadkami, R. A., Anal. Chem., 1984,56, 2233. than 80% for Cd, Cu, Pb and Zn. For most metals a 3 Lamothe, P. J., Fries, T. L, and Consul, J. J., Anal. Chem., prolonged dissolution time did not enhance the recovery 1986,58, 1881. except for Al, K, Mn and Ni, recoveries of which became 4 Broekaert, J. A. C., Wopenka, B., and Puxbaum, H., Anal. slightly higher, and probably the same is true for impactor Chem., 1982,54,2174. samples also. 5 Wang, C.-F., Miau, T. T., Pemg, J.Y.,Yeh, S.J., Chiang, P. C„ By comparing the ETAAS with the INAA results the Tsai, H. T., and Yang, M.H., Analyst, 1989,114, 1067. elemental recoveries of Al, Cu, Mg, Mn, Na and V from the 6 Yamashige, T., Yamamoto, M., and Sunahara, H., Analyst, impactor samples could be calculated. These recoveries 1989,114, 1071. were compared with the corresponding recoveries from the 7 Infante, R. N., and Acosta, I. L, At. Spectrosc., 1988,9, 191. 8 Jappinen, A., Pakkanen, T., Keronen, P., Kulmala, M„ NIST samples; values for Cu, Mg, Mn, Na and V were Hillamo, R., and Viisanen, Y., J. AerosolSci., 1988,19, 1243. clearly better from the impactor samples, especially for the 9 Berner, A, Lurzer, C. H„ Pohl, L, Preining, O., and Wagner, fine particles. For the fine particle Berner impactor samples P., Sci. Total Environ., 1979, 13, 245. it can be concluded that the recoveries are higher than 85% 10 Hillamo, R. E., and Kauppinen, E. I., Aerosol Sci. Technol., for Cd, Cu, Mg, Mn, Na, Pb, V and Zn, even though there 1991,14, 33. seemed to be some contamination or other problems with 11 Ross, H. B., Methodology for the Collection and Analysis of Mn and Na. Trace Metals in Atmospheric Precipitation, Report CM-67, Dissolution with 0.2 mol l-1 nitric acid in an ultrasonic Department of Meteorology, University of Stockholm, 1984. bath at 50 °C may provide a routine method in the analysis 12 Maenhaut, W., and Zoller, W. H„ J. Radioanal. Chem., 1977, 37,637. of fine particle Berner impactor samples for Cd, Cu, Mg, 13 Schutyser, P., Maenhaut, W., and Dams, R., Anal. Chim. Acta, Pb, V and Zn and probably also for Mn and Na. However, 1978,100, 75. in Table 2, only the ETAAS methods for Cu, V and Zn are 14 Barnett, W. B., Spectrochim. Acta, Part B, 1984,39, 829. suitable for routine analysis. The methods for the other 15 Slavin, W., Manning, D. L, and Camrick, G. R.,At. Spectrosc., elements in Table 2, even though fast and practical, are 1981,2, 137. easily affected by various interferences. In this work the 16 Pakkanen, T. A, and Hillamo, R.E..J. Aerosol Sci., 1988,19, NIST SRMs and the Berner impactor aerosol samples were 1303. analysed both by STPF methods and off-the-wall of the 17 Sekerka, I., and Lechner, l., Influence of Container Material on graphite tube, and very similar results were obtained. the Loss of Silver, Mercuric and Cupric Ions From Water However, if the impactor samples are abnormally heavily Solutions, Technical Bulletin 69, Inland Waters Directorate, Water Quality Branch, Ottawa, Canada, 1972. loaded, it may be necessary to check the correctness of the 18 Haraldsson, C., and Magniisson, B„ paper presented at Heavy off-the-wall results for a few heavily loaded stages by flame Metals in the Environment Conference, Heidelberg, 1983. or STPF methods. From the experiments with the Berner impactor samples, it appeared that there is a tendency for Al to be less Paper 2/02290G effectively solubilized and recovered with increasing parti Received May 5, 1992 cle size. This can be explained by the limited solubility and Accepted August 20, 1992 Atmospheric Environment VoL 24A, No.2, pp. 423-429,1990. 0004-6981/90 $3.00+0.00 Printed in Great Britain. © 1990 Pergamon Press pic MASS AND TRACE ELEMENT SIZE DISTRIBUTIONS OF AEROSOLS EMITTED BY A HOSPITAL REFUSE INCINERATOR Esko I. Kauppinen * Technical Research Centre of Finland, Laboratory of Heating and Ventilating, Lampomiehenkuja 3, SF-02150 Espoo, Finland and Tuomo A. Pakkanen Finnish Meteorological Institute, Air Quality Laboratory, Sahaajankatu 22 E, SF-00810 Helsinki, Finland (First received 17 June 1988 and in final form 10 May 1989) Abstract —Mass and elemental size distributions of hospital refuse incineration aerosols were measured in the aerodynamic particle size range 0.02-17 pm with an in-stack compressible flow, low pressure impactor. Oil was used as a supplementary fuel in the refuse combustion process and flue gases were cleaned with a cyclone. Mass size distributions were bimodaL The geometric aerodynamic mean diameter of the fine mode varied between 0.1 and 0.2 pm and the corresponding coarse mode mean between 6 and 10 pm. Mg, Al, Cl, Ti and Fe were found only in coarse mode particles. Elemental size distributions of Na, K, Zn, Cd, Pb and S were bimodal. Over 90% of the particle phase of S, 20-80% of Zn, 62-77% of Cd and 7-74% of Pb, respectively, were found in the fine mode particles. This existence of the fine mode peak in the size distributions of Na, K, Zn, Cd, Pb and S indicates that at least part of these elements vaporizes during the refuse incineration process. Key word index: Aerosols, hospital refuse incineration, size distributions, heavy metals, low pressure impactors. 1. INTRODUCTION As hospital waste is usually burned in smaller units than municipal waste, emission regulations can be Incineration of municipal waste and municipal sewage more lax, which further enhances the possibility of sludge is an important emission source of many toxic high emission factors for hospital waste incineration. trace elements found in ambient aerosols (Greenberg The knowledge of refuse incineration aerosol size et al., 1978a,b, 1981; Law and Gordon, 1979; Bennett distributions is of fundamental importance in order to and Knapp, 1982; Gerstle and Albrinck, 1982; Na- design efficient emission control equipment and to tusch, 1982; Pacyna, 1984). Pacyna (1984) has esti model incineration aerosol dispersion and behaviour mated that in Europe, 3.0, 1.7, 0.7 and 7.0% of the in the atmosphere. Further, the behaviourof different emissions of Cd, Cu, Pb and Zn, respectively, originate elements during an incineration process can be studied from refuse incineration. Based on enrichment factors, if the distribution of elements with particle size is Greenberg et al. (1978a,b) have found that in urban known. For example, detailed size distribution meas environments near incinerators, incineration can be urements, both in the laboratory and field com the major source of Cd and Zn. The potential environ bustors, have been essential to study particle forma mental impact of refuse incineration aerosols is further tion mechanisms and behaviour of elements during enhanced by their high water solubility and small pulverized coal combustion process (e.g. Flagan and particle size distributions of trace metals (Natusch, Friedlander, 1978; Taylor and Flagan, 1982; Damle et 1982). al., 1982). However,the existing size distribution data Incineration of hospital waste is a special case as of municipal waste and wastewater sludge inciner this material usually contains plastics like polyethyl ation aerosols, as measured with conventional inertial ene, polypropylene and polyvinyl chloride up to 20% impactors, is limited to particles larger than about by weight, which is approximately four times the 0.5 pm in diameter (Greenberg et aL, 1978a,b, 1981; amount found in municipal solid waste (Allen et al, Bennett and Knapp, 1982). No detailed size distribu 1986). Resulting HC1 emissions can therefore be high. tion measurements have been reported in the sub- micron size range of about 0.03-03 pm, which is usually the most penetrating size range for electro ’To whom correspondence should be addressed. static precipitators and baghouses used to clean flue 423 424 Esko I. Kauppinen and Tuomo A. Pakkanen gases (McCain et al, 1976; McElroy et al, 1982; STACK Shendrikar et al, 1983). In this study, differential size distributions of mass and 12 elements (Na, Mg, K, Ca, Zn, Cd, Pb, Fe, Al, Ti, S, Cl) of hospital refuse incineration aerosols were measured in the aerodynamic size range of about 0.02-17 pm. Light oil was used as a supplementary fuel. Flue gases were cleaned by a cyclone. Aerosol particles were size classified in situ using an in-stack low pressure impactor. Composition (element mass BAROMETRIC fraction) size distributions of Na, K, Zn, Cd and Pb were determined from measured differential size dis tributions. Possible particle formation mechanisms Fig. 1. A schematic diagram of the in-stack low pressure impactor sampling system. The behaviour of the impactor is and behaviour of elements during incineration process controlled by regulating the impactor downstream absolute is discussed on the basis of measured aerosol size gas pressure to give the overall impactor outlet-to-inlet distribution data. pressure ratio the value (0.083) used in impactor calibration. Sampling is started when the impactor downstream gas temperature is equal to the flue gas temperature. 2. PROCESS DESCRIPTION Hospital waste was burned in a Hogfors-incinerator Substrate weight stability during sampling was evaluated by collecting impactor samples through two high efficiency equipped with two light oil burners. Plastic sacks and 47 mm quartz fiber filters (Munktell MK 360, manufactured paper boxes containing unassorted hospital waste, i.e. by Stora Kopparberg, Grycksbo, Sweden). Filters collected plastics, glassware, paper, drugs, solvents and waste aerosol particles, allowing only the gaseous part of the from operations done in the hospital, were loaded aerosol to enter BLPI stages. manually into the furnace through the opening on the 3.2. Analytical techniques top of the furnace. Waste feed rate varied between 100 Gravimetric analysis of impactor samples was carried out and 200 kgh-1. The corresponding oil-firing rate was by weighing the substrates carefully before and after sam 50-80 kgh-1, giving the total heating power of the pling with the Mettler Me 3030 microbalance. incinerator of about 1 MW. Flue gas temperatures The metal content of impactor samples was determined with the graphite furnace atomic absorption spectrometer measured at the exhaust point of the furnace were in (GFAAS). One quarter of the substrate was wet-ashed in the the range 800-1200 °C. Combustion gases were solution containing 2 ml 65% HN03 and 0.5 ml 30% H202. cleaned with a cyclone followed by a blower, which fed Then 10 ml H20 was added and the sample was kept in flue gases via a horizontal duct to the main stack of the ultrasonic bath for 30 min. The resulting solution was ana heating system of the hospital. lyzed for its metal content with GFAAS. One impactor sample set (test 4) was analyzed with PIXE- method (Particle Induced X-ray Analyses) by Element Ana lysis Corporation at Tallahassee, Florida, U.S.A. Detailed J. EXPERIMENTAL description of the PIXE-method is given elsewhere (Element Analysis Corporation, 1986). 3.1. Sampling methods Size-classified aerosol samples were collected isokinetic- 3.3. Data reduction ally in-stack from the horizontal duct after the cyclone with Combustion aerosol size distributions were determined the 11-stage, multijet, compressible flow BLPI (HAUKE from analyses results by assuming the collection efficiency of 25/0.015) low pressure impactor, design of which is described each impactor stage to be a step function at the cut-point by Berner and Lurzer (1980) and by Berner (1984). The particle size, i.e. no cross sensitivity corrections were made. calibration of BLPI low pressure stages is described in detail Aerosol gas composition was assumed to be that of dry air. by Hillamo and Kauppinen (1990). This assumption is estimated to introduce cut diameter Thin aluminum, Mylar and polycarbonate (poreless Nuc- uncertainties smaller than those associated with the use of lepore) films were used as impaction substrates. They were laboratory calibration data to calculate the cut points at greased with a thin, homogeneous layer (14-100 pgcm -2) of elevated temperatures. BLPI flow rate at sampling condi Apiezon L- or Apiezon H-vacuum grease using the method tions was determined from the mass flow rate measured at described by Hillamo and Kauppinen (1990). Before sam corresponding temperatures in laboratory conditions (Kaup pling, the greased substrates were baked in the oven for 24 h pinen, 1987). The cut diameters of the incompressible flow at 150 °C. stages 7-11 were calculated using Marple ’s theory (Rader The sampling system is shown schematically in Fig. 1. and Marple.,1985). The cut diameters of high-velocity, com Before sampling BLPI was allowed to heat up in the duct pressible flow stages 1-6 were determined by using ^/Stks0- with the inlet facing downstream. When BLPI outlet tem values from laboratory calibration (Hillamo and Kauppinen, perature reached the inlet temperature, it was rotated to face 1988), calculating the jet core velocity from the pressure drop upstream and sampling was started by opening the regulat across the stage and evaluating the Cunningham slip correc ing valve and adjusting the downstream pressure to the value tion factor at the upstream stagnation pressure of the impac of 83 mbar. As the process gas pressure was about 1 atm, this tor stage (Biswas and Flagan, 1984). As the particle density of sampling method ensured that the BLPI stage operating 1 gem-3 was used, the resulting cut points are aerodynamic absolute gas pressures were the same as those used in the diameters at BLPI stage upstream stagnation pressures. experimental calibration, i.e. fixing the sample flow rate and Aerodynamic cut diameters, calculated using the gas tem individual stage pressure ratios. perature T—150 °C, are given in Table 1. Tabic 1. Low pressure impactor aerodynamic cut diameters DSO tc at in-stack sampling conditions, gravimetric and elemental analyses results (pg, except Cd: ng) of the impactor samples and corresponding background (blank) values. The substrate materials were Apiezon-H-vacuum grease on aluminum film (test 1), Apiczori L-vacuum grease on Mylar film (tests 2 and 5) and Apiczon L-vacuum grease on polycarbonate film (test 4), respectively Stage 1 2 3 4 5 6 7 8 9 10 11 blank ^SO.ie 0.024 0.046 0.069 0.14 0.32 0.53 1.1 2.2 4.1 8.7 17 (pm) Test 1 m 24 219 775 899 450 463 688 1443 2239 1169 - 100 2 m 128 243 629 302 133 163 278 478 736 1913 - 60 Na 0 9.5 70.5 25.5 0 0 6.5 26.5 14.5 15.5 - 1.8 Mg 0 0 0 0 0 0 0.2 2.1 3.2 4.6 - 0.3 ass M K 0.7 5.5 25.6 9.3 0 0 1.8 2.1 4.7 4.3 - 0.3 Ca 2 6 7 5 2 0 3 10 13 16 - 21 Zn 4.8 15.4 52.4 21.6 3.0 1.4 2.8 6.1 8.1 7.6 - 0.9 d n a Cd 0.12 0.90 0.04 0.13 0.16 0.12 - 0.001 0.28 0.29 0.04 0.08 e c tra Pb 0.60 1.5 3.7 2.1 0.48 0.54 1.8 4.0 5.2 4.3 - 0.13 4 Na 9.4 16.2 10.0 1.9 0 0.3 2.8 7.7 6.4 3.2 _ 0.15 ent elem K 2.6 4.3 5.1 0.2 0 0 0.6 2.0 1.5 0.8 - 0.05 Ca 0 0.2 0.2 0.5 0.3 0.3 1.3 1.7 2.4 1.9 - 0.1 - Zn 0.48 0.85 0.48 0.09 0.02 0.14 0.73 2.31 2.72 1.08 0.04 size Cd 0.105 0.187 0.131 0.034 0.023 0.017 0.042 0.105 0.117 0.047 - 0.0008 diti i s n tio u istrib d Pb 3.22 5.26 3.22 0.78 0.34 0.40 1.23 3.73 4.38 1.62 - 0.005 Fe* 0 0 0 0 0 0.063 0.405 0.468 0.589 0.888 - 0.005 Al* 0 0 0 0 0 0 0.237 0.803 2.06 1.02 - 0.039 Ti* 0 0 0 0 0 0.026 0.276 0.589 1.09 1.32 - 0.006 S‘ 6.08 16.5 10.4 1.34 0.152 0.108 0.607 0.919 1.84 0 - 0.035 Cl* 0.037 0.223 0.091 0.043 0 0.324 2.56 4.69 8.62 2.28 0.007 5 m 123 238 727 1003 315 323 542 1165 2318 2013 - 60 Na 0 19.5 28.5 45.5 3.5 32.5 29.5 47.5 102 58.5 - 1.8 Mg 0 1.1 0.2 0.2 0.2 1.5 2.8 5.7 19.8 16.8 - 0.3 K 0 1.7 11.1 17.6 0.6 1.9 11.0 15.7 26.3 15.1 - 0.3 Ca 0 0 0 0 0 4 11 30 35 33 - 21 Zn 9.6 28.9 70.3 117 30.8 50.6 65.1 81.4 125 84.6 - 0.9 Cd 0.20 0.44 1.23 1.79 0.24 0.18 0.21 0.48 0.72 0.48 - 0.001 Pb 7.6 28 146 221 48 30 17 39 64 46 - 0.13 Blank mass (m): The maximum weight change (pg) of the corresponding substrate during substrate stability test. GFAAS : The amount of the element found (pg, except Cd: ng), when 1/4 of the substrate is analyzed with GFAAS. PIXE : The result of the blank substrate PIXE-analysis (pg cm-2). •Analyzed with PIXE. & 426 Esko I. Kauppinen and Tuomo A. Pakkanen 4. RESULTS AND DISCUSSION Table 2. Total mass and elemental concentrations and dis tribution between line and coarse modes of the hospital 4.1. Sample analysis refuse incineration aerosols Results of gravimetric, GFAAS and PIXE analyses Total concentration Distribution between modes are given in Table 1, which shows the mass and (pgNm' 3) fine (%) coarse (%) element content of BLPI samples, corresponding background (blank) values and BLPI aerodynamic Mass 39,600-91,000 30-32 68-70 cut diameters at in-stack sampling conditions. The Na 460-750 35-65 35-65 Mg 80-230 0-32 68-100 blank value of the gravimetric analysis is the maxi Al 33 0 100 mum weight change of the corresponding substrate S 300 91 9 during sampling, determined by substrate stability Cl 150 4 96 tests. GFAAS background is the amount of element K 140-480 33-76 24-67 found, when 1/4 substrate is analyzed, including the Ca 70-540 4-34 66-96 Ti 26 0 100 elements dissolving from the substrate, containers and Fe 19 0 100 liquids. PIXE background (pgcm-2) is the result of Zn 71-3160 23-80 20-77 the blank substrate PIXE analysis. The background Cd 6.4-28.4 62-77 23-38 resulting from substrates is usually small when com Pb 190-3070 7-74 26-63 pared to the amount of element found in the sample. GFAAS-background of Ca of test 2 is an exception, the background value being comparable to that of the variations of both concentrations and particle size sample. distributions are caused by non-constant combustion conditions, i.e. the feed rate and composition of the 4.2. Size distributions hospital refuse burned varied during sampling. Differential mass size distributions of hospital re The bimodal structure of hospital refuse inciner fuse incineration aerosols are shown in Fig. 2. Mass ation aerosol mass distributions is similar to that distributions are clearly bimodal, having a fine particle measured for pulverized coal combustion aerosols. mode at about 0.1-0.2 pm and a coarse particle mode However, the fine mode of refuse incineration aerosols at about 6-10 pm. The geometric standard deviation is more pronounced, 30-35% of the particle mass is of the fine mode varies between 1.6 and 1.9. found in the fine mode. Corresponding fine mode mass Elemental size distributions of Na, Mg, Al, S, Cl, K, fraction of coal combustion aerosols is typically Ca, Ti, Fe, Zn, Cd and Pb are given in Fig. 3. Total 0.2-2.2% and 5-20% as measured before and after the particle mass and elemental concentrations and frac flue gas cleaning systems, like electrostatic precipit tionation between fine and coarse particles is given in ators and baghouses, respectively (Damle et al., 1982; Table 2. Differential size distributions of Na, K, Zn, McElroy et al., 1982; Markowski and Filby, 1985). Cd and Pb are bimodal. Most of the particle-phase S, Bimodal structure of Na, K, Zn, Cd and Pb size about 90%, is found in the fine mode particles. Mg, Al, distributions suggests that at least a part of these Cl, Ca, Ti and Fe size distributions exhibit only coarse elements vaporizes during incineration process. The mode. The apparent fine mode peak in the Ca size existence of Cl only in the coarse mode particles distribution of test 2 is probably an artifact caused by indicates that vaporized Cl is in the gas phase at the the large Ca background of the substrate. Large sampling point. Composition size distributions of Na, K, Zn, Cd and Pb are shown in Fig. 4. The error bars shown with Mass Size Distributions data points are calculated from the gravimetric and GFAAS analyses errors. Na, K and Zn content of particles increases with decreasing particle size in the x test t size range 1-10 pm. Below 1 pm, Na, K and Zn - ° TEST2 composition size distributions are fairly flat. Particle 6 TESTS Cd content increases with decreasing particle size in the size range 0.2-10 pm. Below 0.2 pm particle Cd content is relatively constant. Pb composition size distribution shows variable behaviour.The flatness of Na, K, Zn and Cd composition size distributions in the sub-pm size range suggests that homogeneous nucleation of vaporized compounds of these metals is a possible fine particle formation mechanism (Flagan Stage-pressure Aerodynamic Diameter, fim and Friedlander, 1978). The amount of C in the impactor samples was not Fig. 2 Differential mass size distributions of hospital refuse incineration aerosols. Oil was used as a sup measured. Impactor sample spots were deep black in plementary fuel during incineration process. 1 Nm3 color, suggesting the presence of both soot in fine = 1 m3 dry gas 1 atm and 0°C. particles and char or coke in coarse particles. The sum i Mass and trace element size distributions 427 Stage-pressure Aerodynamic Diameter, pm Fig. 3. Differential elemental size distributions of hospital refuse incineration aerosols. Na, Mg, K, Ca, Zn, Cd and Pb were analyzed with GFAAS-method. Fe, Al, Ti, S and Cl were analyzed with PIXE-method. Circles, squares and triangles correspond to tests 2, 4 and 5, respectively. of Na, K, Zn and Pb is 20-40% of the gravimetric impactor during sampling due to vapor condensation mass in the fine mode particle size range. This also or evaporation. If many particles are bouncing, large suggests the presence of the soot in the fine particles, deposits are usually seen above the collection plate on because the difference between gravimetric mass and the lower surface of the jet plate (Lundgren and sum of Na, K, Zn and Pb cannot be explained totally Balfour, 1980). Corresponding deposits were very with the oxides or sulfates of Na, K, Zn and Pb. small in this study, indicating insignificant bounce. As Because V and Ni were not analyzed and compara particles were probably metal oxides and soot or char, ble size distribution data for the combustion of pure they were not very bouncy (Hinds et al., 1985). Because oil or hospital waste have not been published, the the low pressure impactor was the only method used impact of oil combustion on the measured size dis to measure particle size distributions in this study, the tributions cannot be determined. However, because absolute amount of bounce could not be determined. light fuel oil Pb, Cd and Zn concentrations are low, Particle size changes during sampling due to vapor high metal concentrations in the fine mode aerosols condensation or evaporation can be estimated, if the result from the combustion of hospital waste. properties and concentrations of vapors are known The main sources of errors associated with the (Biswas, 1985). Unfortunately, properties and concen combustion aerosol size distribution measurement trations of vapors were not known in this study. using compressible flow low pressure impactors are Because sampling temperatures were clearly above the the particle bounce and particle size changes inside the dew point of water, which is the most probable 6 21405 428 Esko I. Kauppinen and Tuomo A. Pakkanen & i 30.0 1.0 - 20.0 wI 0.5 - 10.0 10"2 10-1 1 10 102 10‘2 10-1 1 10 102 Stage-pressure Aerodynamic Diameter, p m Fig. 4. Composition size distributions (mass fraction as the function of particle size) of Na, K, Zn, Cd and Pb. Circles and triangles correspond to tests 2 and 5, respectively. condensing component of the combustion aerosols, metric mean aerodynamic diameter of the fine mode particle size changes during sampling are not expected mass size distributions varied between 0.1 and 0.2 pm. to be significant Corresponding geometric standard deviations varied Because the properties of refuse and types of in between 1.6 and 1.9. The coarse mode peaked between cineration systems can be different in other hospitals, 6 and 10 pm. incineration aerosol size distribution data presented in Elemental size distributions of Mg, Al, Cl, Ca, Ti this study are not necessarily inherent to hospital and Fe were unimodal, exhibiting only coarse modes. refuse incineration aerosols in general. However, the Na, K, Zn, Cd, Pb and S had bimodal size distribu significant amount of particle mass and particle- tions. Over 90% of the particle-phase S was found in bound heavy metals like Zn, Cd and Pb found in the the fine mode particles. Fine particles were enriched fine mode particles at about 0.1-0.2 pm aerodynamic with heavy metals. 23-80% of particle-bound Zn, diameter must be taken into account, when flue gas 62-77% of Cd and 7-74% of Pb, respectively, were cleaning methods, behaviour and dispersion in the found in the fine mode particles. atmosphere and adverse environmental effects of hos pital refuse incineration aerosols are considered. Be Acknowledgements—The authors gratefully acknowledge the cause heavy metal concentrations are high, flue gas assistance of Mr R. Hillamo, Mr K. Larjava and Mr P. cleaning is needed. Efficient particulate trace metal Rouhiainen during the collection and analysis of the low pressure impactor samples. This paper was written while one emission reduction requires the use of control devices of the authors, E. I. Kauppinen, was at the University of having high collection efficiencies down to about Florida, Gainesville, Florida, U.S.A. Discussions with Prof. 0.01 pm, i.e. the use of devices like electrostatic pre D. A. Lundgren and Mr R. W. Vanderpool are greatly cipitators or fabric filters. Inertial separators and acknowledged. This work was supported by the Academy of scrubbers will not meet this requirement. Finland and Maj and Tor Nessling Foundation. REFERENCES 5. CONCLUSIONS Allen R. J., Brenniman G. R. and Darling C. (1986) Inciner Mass size distributions of hospital refuse inciner ation of hospital waste. JAPCA 36, 829-831. ation (oil as a supplementary fuel) aerosols were found Bennett R. L. and Knapp K. T. (1982) Characterization of to be bimodal. When samples were collected down particulate emissions from municipal wastewater sludge incinerators. Envir. Sci. Technol. 16, 831-836. stream the mechanical particle separator (cyclone) at Berner A. (1984) Design principles of the AERAS low press the flue gas temperatures of about 150°C, the geo ure impactor. In Aerosols. Science, Technology, and In Mass and trace element size distributions 429 dustrial Applications of Airborne Particles (edited by Liu bounce in a cascade impactor: a field study. Am. Ind. Hyg. B. Y. H., Pui D. Y. H. and Fissan H. J.), pp. 139-142. Ass. J. 46, 517-523. Elsevier, New York. Kauppinen E. I. (1987) Measurement of combustion aerosol Berner A. and Lurzer C. (1980) Mass size distributions of size distributions with compressible flow inertial impac traffic aerosols at Vienna. J. phys. Chem. 84, 2079-2083. tors. Licentiatum Thesis (in Finnish), University of Biswas P, (1985) Impactors for aerosol measurements: devel Helsinki, Department of Physics, Helsinki, Finland. opments and sampling biases. PhD Thesis, California Law S. L. and Gordon G. E. (1979) Sources of metals in Institute of Technology, Pasadena, California, U.S.A. municipal incinerator emissions. Envir. Sci. Technol. 13, Biswas P. and Flagan R. G (1984) High-velocity inertial 432-438. impactors. Emir. Sci. Technol. 18, 611-616. Lundgren D. A. and Balfour W. D. (1980) Use and limitations Damle A. S., Ensor D. S. and Ranade M. B. (1982) Coal of in-stack impactors. USEPA Report EPA-600/2-80-048. combustion aerosol formation mechanisms: a review. Aer Markowski, G. R. and Filby R. (1985) Trace element concen osol Sci. Technol. 1, 119-133. tration as a function of particle size in fly ash from a Element Analysis Corporation (1986) Quality Assurance/ pulverized coal utility boiler. Envir. Sci. Technol. 19, Quality Control Document Element Analysis Corpor 796-804. ation, Tallahassee, Florida, U.S.A. McCain J. D., Gooch J. P. and Smith W. B. (1976) Results of Flagan R. C. and Friedlander S. K. 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Technol. 12, 1329-1332. of the trace elements from anthropogenic sources in Eu Greenberg R. R., Zoller W. H. and Gordon G. E. (1978b) rope. Atmospheric Environment 18,41-50. Composition and size distributions of particles released in Rader D. J. and Marple V. A. (1985) Effect of ultra-Stokesian refuse incineration. Envir. Sci. Technol. 12, 566-573. drag and particle interception on impaction character Greenberg, R. R., Zoller W. H. and Gordon G. E. (1981) istics. Aerosol Sci. Technol. 4, 141-156. Atmospheric emissions of elements on particles emitted Shendrikar A. D, Ensor D. S, Cowen S. J., Woffinden G. J. from the Parkway sewage-sludge incinerator. Envir. Sci. and McElroy M. W. (1983) Size-dependent penetration of Technol. 15, 65-70. trace elements through a utility baghouse. Atmospheric Hillamo R. E. and Kauppinen E. I. (1990) On the per Environment 17, 1411-1421. formance of the Berner low pressure impactor. Aerosol Sci. Taylor D. D. and Flagan R. G (1982) The influence of Technol. (submitted). combustor operation on fine particles from coal com Hinds W. C., Liu W.-G and Froines J. R. (1985) Particle bustion. Aerosol Sci. Technol. 1,103-117. Environ. Scl. Technol. 1990, 24, 1811-1818 Coal Combustion Aerosols: A Field Study Esko I. Kaupplnen* Technical Research Centre of Finland, Laboratory of Heating and Ventilating, Lampomiehenkuja 3, SF-02150 Espoo, Finland Tuomo A. Pakkanen Finnish Meteorological Institute, Air Quality Laboratory, Sahaajankatu 22 E, SF-00810 Helsinki, Finland Table I. Properties of Bituminous Coal from Poland (Dry ■ Mass and elemental size distributions of aerosols e- Basis) mitted in the particle size range 0.01-11 pm (Stokes di ameter) from a boiler firing pulverized, bituminous coal moisture, % 10.6 from Poland were measured by using in situ particle size ash content, % 15.5 classification with an in-stack compressible flow low- volatile matter, % 26.5 pressure impactor. Samples were collected after the nonvolatile matter, % 47.4 electrostatic precipitator. Mass and elemental size dis sulfur, % 0.86 tributions of Na, Mg, Al, Si, S, K, Ca, Ti, Fe, V, Mn, Cu, heating value, MJ/kg 24.5 Zn, Sr, Cd, and Pb were bimodal. Geometric mass mean diameters of the fine and coarse modes were about 0.05 with in-stack low-pressure impactors and with electrical and 2 pm, respectively. Corresponding geometric standard mobility analyzers (EAA) from diluted combustion gases deviations were 1.4 and 1.8. About 5% of the particle mass have been reported (4,11). However, accurate composition and particle-bound Na, Mg, Al, Si, Ti, Fe, Mn, and Zn were and size distribution data are needed when the various found in the fine-particle mode. S, Ca, V, Cu, Sr, Cd, and modes of ash behavior and the enrichment of fine-mode Pb were enriched in the fine-mode particles; i.e., ~80% particles with toxic, volatile species are to be determined of the particle-phase S, 17% of Ca, 23% of V, 22% of Cu, (7). 11% of Sr, 34% of Cd, and 9% of Pb were in the sub Combustion aerosol characteristics have been shown to micron fine-mode particles. 1 depend on the properties of mineral matter in the parent coal Coal properties can vary widely, depending strongly on the origin of the coal. Because most of the combustion 1. Introduction aerosol composition data has been measured for combus Coal combustion is an important source of particulate tion of U.S. coals, accurate measurements of combustion emissions to the atmosphere. As the result of many field aerosol properties and emissions from the combustion of and laboratory studies (1-6), coal combustion aerosol size coals having different origins are needed. distributions have been found to be bimodal. The fine- This paper describes studies to characterize the prop particle mode around 0.1 pm, which is believed to be erties of the particles emitted from the combustion of formed via nucleation of vaporized ash components and pulverized, bituminous coal originating from Poland. growth via coagulation and heterogeneous condensation, Combustion aerosol characteristics were measured after has received considerable attention. The submicron par the flue gas cleaning system (electrostatic precipitator), ticles have been found to be enriched with many toxic trace because the main emphasis of this study was to accurately elements (4-17). Submicron particles also have a higher measure the stack emissions of particle mass and various probability to penetrate through common flue gas cleaning matrix and trace elements of the coal ash as a function of equipments, like electrostatic precipitators and baghouses, particle size. Particles were size classified in situ with a than the bulk of coarse fly ash particles formed in the calibrated, in-stack low-pressure impactor. Because combustion process (4,10,12). Once emitted in the at greased substrate weight loss by evaporation during sam mosphere, fine particles have long residence times and a pling has been reported to be the main difficulty associated high probability of penetrating into the alveolar regions with submicron combustion aerosol mass size distribution of lungs when inhaled. The potential environmental im measurements using high-velocity inertial impactors (11, pact of nucleation-condensation-generated fine-mode 16), the stability of substrates used during in-stack sam particles may further be enhanced by their relatively high pling was carefully evaluated by sampling filtered flue gas water solubility and surface concentration of toxic elements with the low-pressure impactor. Composition (element (13). mass fraction) size distributions were determined from In laboratory-scale combustion experiments of various measured differential size distributions. Possible particle pulverized U.S. coals, the composition of the fine mode has formation mechanisms and behavior of elements during been found to vary considerably, depending mainly on the the combustion process are discussed on the basis of properties of mineral matter in the parent coal and on measured aerosol size distribution data. combustion conditions (9,14,15). Available fine-mode composition size distribution data, i.e., element mass 2. Process Description fraction of the aerosol particles as the function of particle High bituminous coal imported from Poland was burned size, measured at field combustion systems is more limited in a pulverized coal boiler equipped with 16 burners on in volume and accuracy, because particle size has mainly four levels at the corners of the furnace. The average been measured with low-pressure impactors lacking de properties of the Polish coal (dry basis) are given in Table tailed laboratory calibration (4,10,11). As neutron ac I. Coal consumption was 17.2 kg/s. The boiler was op tivation analysis has mainly been used to analyze the erated at fuel-lean combustion conditions, i.e., flue gas 02 low-pressure impactor samples, submicron size distribution concentration of ~4.5%. Flue gases were cleaned with an data for the highly toxic trace elements like Pb and Cd electrostatic precipitator (ESP), which had eight electri have not been reported. Discrepancies up to a factor of cally independent sections. The ESP was designed to 2 between fine-mode mean sizes measured simultaneously achieve 99.7% overall collection efficiency for the inlet 0013-936X/90/0924-1811S02.50/0 © 1990 American Chemical Society Environ. Scl. Technol.. Vol. 24, No. 12, 1990 1811 Table II. Summary of the Coal Combustion Aerosol Low-Pressure Impactor Sample Characteristics, Including Types of Substrates, Sampling Times, Impactor Inlet and Outlet Temperatures, and Analysis Methods substrate m « tt,b Tta,‘ 7'ou0d analysis sample film grease' "fig min °C °C SST* & GFAAS* PIXE* SSBLPI 2 M1" APL 220-1310 15 116 116 SSBLPI 4 Al* APL 180-480 5 114 112 SSBLPI 6 N' APL 400-840 21 116 110 SSBLPI8 Al* 10 119 115 SSBLPI 10 N' APL 100-785 5 117 117 SSBLPI 14 see Table III 30 123 120 °The amount of the grease on the film. 6Sampling time. c Gas temperature at the impactor inlet dGas temperature at the impactor outlet 'Substrate stability test * Gravimetric analysis. * Graphite furnace atomic absorption spectroscopy. * Particle-induced X-ray emission analysis. 1 Mylar film. ' Apiezon L vacuum grease. * Aluminum film. ^Polycarbonate (poreless Nuclepore) film. mass concentration of 14 g/Nm3 (1 Nm3 = 1 m3 of dry gas at 1 atm and 0 °C). STACK 3. Experimental Section 3.1 Sampling Methods. Size-classified coal combustion aerosol samples were collected in-stack from the duct after the ESP before the main blower with an 11-stage, multijet, compressible-flow low-pressure impactor (BLPI, Hauke 25/0.015) (17,18). The average gas velocity in the duct was measured with a Pitot tube. The diameter of the impactor sampling nozzle was chosen to equalize the gas velocity at the nozzle tip and that measured by the Pitot tube. The calibration of BLPI low-pressure stages is de scribed in detail elsewhere (19). Thin aluminum (Al), Mylar (M), and polycarbonate (poreless Nuclepore, NP) films were used as impaction Figure 1. Schematic diagram of the In-stack low-pressure Impactor substrates. In order to prevent particle bounce, films were sampling system. The behavior of the Impactor Is controlled by reg greased with a thin, homogeneous layer of Apiezon L ulating the impactor downstream absolute gas pressure to give the overall impactor outlet-to-inlet pressure ratio the value (0.083) used (APL) vacuum grease. Films were greased by generating in impactor calibration. grease aerosols and impacting grease particles on the ro tating films with a radial slit impactor (19). Before sam pling, the greased substrates were baked in the oven 22 charge on the weighing results. h at 125 °C, in order to increase substrate weight stability Na, Mg, Al, K, Ca, V, Mn, Fe, Ni, Cu, Zn, Cd, and Pb during in-stack sampling. contents of impactor samples were determined with the The sampling system is shown schematically in Figure graphite furnace atomic absorption spectrometer 1. Before sampling BLPI was allowed to heat-up in the (GFAAS). Before analysis, */ 4 of the substrate was wet- duct with the inlet facing downstream. When the BLPI ashed in a solution containing 2 mL of 65% HN03,2 mL outlet temperature reached the inlet temperature, the im of 37% HCl, and 0.5 mL of 30% H202. Following the pactor was rotated to face upstream and sampling started evaporation of liquid by heating, 10 mL of deionized H20 by opening the regulating valve and adjusting the down was added and the sample was kept in an ultrasonic bath stream pressure to 83 mbar. As the process gas pressure for 30 min. The resulting solution was analyzed for its was ~1 atm, this sampling method assured the BLPI stage metal content with GFAAS. operating absolute gas pressures to be the same as those Impactor samples were analyzed by PIXE (particle-in used in the experimental calibration, i.e., fixing the sample duced X-ray analyses) by Element Analysis Corp. at flow rate and individual stage pressure ratios. Tallahassee, FL. A detailed description of the PIXE Substrate weight stability during sampling was evaluated method, including sample radiation, measurement of the by collecting one impactor sample (SSBLPI14; see Table X-ray spectra, and the method to calculate the concen II) through two high-efficiency 47-mm quartz fiber filters trations of elements in the sample from the measured (Munktell MK 360, manufactured by Stora Kopparberg, spectrum, is given elsewhere (20). Mg, Al, Si, S, K, Ca, Grycksbo, Sweden). Filters collected aerosol particles, Ti, V, Mn, Fe, Ni, Cu, Zn, Sr, and Pb were detected by allowing only the gaseous part of the aerosol to enter BLPI PIXE. As the surface mass concentration of the particles stages. on the impactor substrate vary depending on the location Pulverized coal, furnace bottom ash, and ESP-collected relative to jets, the quantitative elemental analysis of the fly ash samples were collected regularly during the sam Berner-type low-pressure impactor samples is difficult with pling period. surface-sensitive methods like PIXE. Mg, Al, K, Ca, V, 32. Analytical Techniques. Gravimetric analysis of Mn, Fe, Ni, Cu, Zn, and Pb concentrations were measured impactor samples was carried out by weighing the sub with both GFAAS and PIXE. A detailed comparison of strates carefully before and after sampling on a Mettler the PIXE and GFAAS results is given elsewhere (21). Pixe Me 3030 microbalance in a clean, almost constant humidity results were lower than those of GFAAS. Typically the laboratory room. Before gravimetric analysis the sub ratio of PIXE/GFAAS increased with increasing mass of strates were exposed to an ion stream generated by an the element in the sample and decreasing energy of the a-active source, in order to reduce the effects of electrical X-ray peak used to determine the PIXE result. In ad- 1812 Environ. Sci. Techno!., Vol. 24, No. 12, 1990 ( Table III. Results of the Substrate Stability Tests® Table IV. Concentrations of Matrix Elements and Trace Elements in Coal, Furnace Bottom Ash, and Fly Ash substrate substr mass Collected by the Electrostatic Precipitator 1 stage film6 APL® concn, fig change, fig furnace 1 N -18 coal bottom ash fly ash 6 N -21 2 N 400 -31 matrix elements, % 3 N 100 +1 Na 0.07 0.98 0.20 7 N 400 +i Mg 0.19 1.7 0.95 Al 8 N 100 -5 1.8 8.4 8.5 Si 11 N 880 +4 2.8 24 27 4 Al 440 +6 S 0.49 0.24 0.09 9 Al 450 +8 Cl 0.12 0.64 nd 6 5 M 250 +37 K 0.23 1.5 1.5 10 M 360 +33 Ca 0.54 2.9 2.8 Ti 0.10 0.40 0.40 0 In which the weight change of the substrate is measured when Fe 0.66 5.4 5.8 filtered flue gas is sampled with the impactor. Before sampling the trace elements, ppm substrates were baked in the oven 22 h at 125 eC. Pure poly V 41 110 131 carbonate (N) films were not baked. fcN, polycarbonate (poreless Cr 31 121 128 Nuclepore) film; Al, aluminum film; M, Mylar film. *Apiezon L Mn 132 809 767 vacuum grease. Co' 6.5 7.8 15 Ni 21 87 94 dition, the PIXE/GFAAS ratio was found to be the Cu 36 87 97 function of the impactor sample deposit spot geometry. Zn 33 71 122 Therefore the PIXE results for Si, S, Ti, and Sr were Ga 1.4 11 12 adjusted by using the GFAAS/PIXE ratio of the neigh As' 2.4 0.8 2.5 Se' 1.0 <0.5 0.7 boring elements, i.e. Br 12 20 nd 6 mSi — Mm %)™Si,PlXE Sr 93 524 450 Zr 38 153 150 mS ~ fctitjd "*■ ^K)mS,PIXE Cd' 0.4 <0.4 0.6 Mg' 0.1 <0.1 0.1 ^Ti = H(8c. ^v)mTiJ'IXE Pb 19 21 38 “Co, As, Se, Cd, and Hg were analyzed with GFAAS, other ele mSr = Zn + Rpb) mSr,PIXE (1) ments with PIXE. Given concentration is the mean value of three samples. 6nd, not detected. 'Analyzed with GFAAS. Here [ = 'n iiGPAAs/mi,PDCE * = Al, K, Ca, V, Zn, Pb (2) Particles were assumed to be spherical. On the basis of nij is the amount of element/ in the sample (j = Si, S, Ti, analyses results, particle density was calculated to be p. and Sr). m, Gp AAS and m,;pi XE are the GFAAS and PIXE = 2.45 g/cm3. results of element t, respectively. Because the masses of particles collected on the adjacent impactor stages vary 4. Results and Discussion up to a factor of 15, the semiquantitative nature of these 4.1 Substrate Stability. The results of the substrate analysis results for Si, S, Ti, and Sr does not necessarily stability test are given in Table III, which shows mass have a large effect on the form of their size distributions changes of various substrates on BLPI stages, when the calculated from PIXE data. impactor sample is taken through two high-efficiency A summary of the characteristics of the collected im quartz fiber filters. Weight changes of APL + NP sub pactor samples, including substrates, sampling times, im strates were found to be small, usually less than 6 pg. The pactor inlet and outlet temperatures, substrate stability weight change of APL + NP substrate on BLPI stage 2, tests, and sample analysis, is given in Table H. PIXE was -31 pg, was an exception, being probably the result of a the main analysis method for coal, furnace bottom ash, and gravimetric analysis error. APL + Al substrates were also ESP-collected fly ash samples. Co, As, Se, Cd, and Hg quite stable, showing weight changes less than 10 pg. APL contents of these samples were measured with GFAAS. + M substrates gained weight, probably through the re 3.3. Data Reduction. Combustion aerosol size dis actions between combustion aerosol gaseous components tributions were determined from analyses results by as and Mylar film. Ungreased polycarbonate films lost suming the collection efficiency of each impactor stage to weight, ~20 pg, if they were not baked in the oven before be a step function at the cut-point particle size; i.e., no sampling. Gravimetric analysis errors due to substrate cross-sensitivity corrections were made. Particle bounce unstability were estimated to be 5 pg for APL + NP and impactor inlet and wall losses were assumed to be substrates (10 pg for stages 1 and 2), 10 pg for APL + Al negligible. Aerosol gas composition was assumed to be that substrates, and 40 pg for APL M substrates. of dry air. BLPI flow rate at sampling conditions was 4.2. Elemental Composition of Coal, Furnace Bot determined from the mass flow rate measured at corre tom Ash, and Fly Ash. Matrix and trace-element con sponding temperatures in laboratory conditions (21). centrations of coal, furnace bottom ash, and fly ash col The cut diameters of incompressible-flow BLPI stages lected by the ESP are given in Table IV. Co, As, Se, Cd, 7-11 were calculated by using Marple impactor theory (22). and Hg were analyzed with GFAAS, all other elements The cut diameters of compressible-flow stages 1-6 were with PIXE. The result given for each element is the mean calculated by using the Stky,1/2 values determined at the value of the analysis of three samples. Co, Zn, As, Se, Cd, laboratory calibration (19), calculating the jet core velocity and Pb concentrations of ESP fly ash were found to be from the" stage downstream to upstream stagnation pres higher than those of the furnace bottom ash. sure ratio and evaluating the Cunningham slip correction 4.3 Size Distributions. Differential mass size distri factor at the stage upstream stagnation pressure (23,24). butions of coal combustion aerosols are shown in Figure Environ. Sci. Techno!., Vol. 24, No. 12. 1990 1813 ##% Mass Size Distributions Table V. Total Mass and Elemental Concentrations and Distribution between Fine and Coarse Modes of Coal Combustion Aerosols® ra SSBLPI2 •O SSBLPI4 total concn, 1 finemode* coarse mode' •o SSBLPI6 : * SSBLPI8 jig/Nm3 fig/Nm3 % jig/Nm3 % < 20 mass 24270 1460 6 22810 94 matrix elements Na 140 7 5 133 95 Mg 427 17 4 410 96 E 5 : Al 1444 43 3 1401 97 Si 1927 96 5 1830 95 s 191 151 79 40 21 K 240 12 5 228 95 Particle Stokes Diameter, gm Ca 1021 174 17 847 83 Figure 2. Differential mass size distributions of coal combustion Ti 146 6 5 138 95 aerosols. Sample SSBLPI8 was collected by using ungreased Al Fe 1078 43 4 1035 96 substrates. Other samples were collected from substrates greased trace elements with Apiezon L vacuum grease. V 21.4 4.9 23 16.5 77 Mn 35.4 1.1 3 34.3 97 2 as the function of particle Stokes diameter. The size Ni 6.23 0.44 7 5.80 93 distributions of Na, Mg, Al, K, Ca, V, Mn, Fe, Ni, Cu, Zn, Cu 10.2 2.2 22 8.0 78 Cd, and Pb were determined by using GFAAS analysis Zn 21.3 1.3 6 20.0 94 results, and those of Si, S, Ti and Sr from adjusted PIXE Sr 14.2 1.6 11 12.6 89 Cd 0.40 0.13 34 0.27 66 results, as discussed above. Mass distributions are clearly Pb 8.32 0.75 9 7.57 91 bimodal. The geometric mass mean diameter of the fine-particle mode is ~0.05 pm. The coarse-particle mode “Mass concentrations are the mean values of five impactor peaks at ~2 pm. The geometric standard deviations of samples. Element concentrations are the mean values of samples SSBLPI6 and SSBLPI10. *1 Nm3 - 1 m3 dry gas at 1 atm and 0 the fine and coarse modes are about 1.4 and 1.8, respec °C. tively. Elemental size distributions of the matrix elements Na, Mg, Al, Si, S, K, Ti, Ca, and Fe are given in Figure 3a. aerosols can be expected due to particle size dependent Elemental size distributions of the trace elements V, Mn, collection efficiency and rapping reentrainment. However, Ni, Cu, Zn, Sr, Cd, and Pb are shown in Figure 3b. Total because the fine-mode size distribution is very narrow, a particle mass and elemental concentrations and fraction very sharply size-dependent ESP penetration curve is ation between fine and coarse particles are given in Table needed to change the fine-mode mean size by the factor V. Size distributions of all elements analyzed (except Ni) of 2 as the aerosol penetrates through the ESP. Further, are bimodal, having fine and coarse modes at about the as the ESP penetration has been reported to increase with same particle sizes as mass size distributions. The amount increasing particle diameter in the range 0.05-0.2 pm (12, of Ni in the impactor sample corresponding to the fine 27), this indicates that the fine-mode mean size of the coal mode peak is about equal to the background of the greased combustion aerosol in this study would increase during polycarbonate substrate. However, fractionation of par ESP penetration, thus increasing the discrepancy between ticle-bound elements between fine- and coarse-mode the results of this study and those measured in field studies particles varies. Matrix elements Na, Mg, Al, Si, K, Ti, with the EAA before the ESP (4,11,25-27). Particles and Fe and trace elements Mn and Zn follow the trend of reentrained from the ESP will affect the size distribution the total particle mass; i.e., ~5% of these elements are measured after the ESP in addition to the particles pen found in the fine-mode particles. S, Ca, V, Cu, Sr, Cd, and etrating the ESP. According to experimental studies, Pb are enriched in the fine-particle mode. rapping emissions contribute mostly to particles larger The distinct bimodality of measured size distributions than 3 pm (27,28). Below 3 pm the rapping emissions have supports the theoretical model proposed by Flagan and been reported to contribute less than 30% to the aerosol Friedlander (7) for particle formation during pulverized concentration. Therefore, the rapping reentrained particles coal combustion. The fine-mode mean particle size, ~0.05 are not believed to have a major effect on the size distri pm, agrees well with the data measured in laboratory butions measured in this study. combustion experiments (5,6,9,14, IS) and with the field Because the chemical compounds of analyzed elements data measured with in-stack low-pressure impactors (11). were not determined, the compound of sulfur (sulfuric acid On the contradictory, the fine-mode peak sizes measured and/or sulfates) cannot be determined. The ratio S/Ca in field studies before and after the ESP with EAA from for the fine-mode samples varied between 0.6 and 1.0, diluted flue gases (4,11,25-27) are considerably larger than suggesting the presence of CaSO<. the results of this study. Dynamical processes changing Main sources of errors associated with the size distri the particle size distributions during the dilution process bution measurement using compressible-flow low-pressure are a possible explanation for the observed discrepancy. impactors are particle bounce and particle size changes However, when comparing coal combustion aerosol size inside the impactor during sampling due to vapor con distribution data, the extreme complexity of the com densation or evaporation. The amount of particle bounce bustion process and difficulties associated with the particle is found to be the function of the jet velocity, the particle size distribution measurement must be remembered. Stokes number, the properties of the collection surface, Combustion aerosol properties depend strongly on the and the hardness of particle material (29-31). If many furnace design and operation and on the properties of the particles are bouncing, large deposits can be seen above parent coal and the mineral matter in the coal. When size the collection plate on the lower surface of the jet plate distributions are measured after the electrostatic precip (31). Corresponding deposits were barely visible in this itator, further changes to the properties of the combustion study, indicating insignificant bounce. Because the low- 1814 Environ. Sci. Techno!., Vol. 24, No. 12, 1990 I a Particle Stokes Diameter, |i.m b 40jOO • I a 5SX} to-3 10* 2 10-1 itr3 lo-2 10*1 i Particle Stokes Diameter, (im « Figure 3. (a) Elemental size distributions of matrix elements Na, Mg, Al, Si, S, K, TI, Ca, and Fe. Si, S, and Ti were analyzed by PIXE, other elements by GFAAS, Circles and squares correspond to samples SSBLPI 6 and SSBLPI 10, respectively, (b) Elemental size distributions of trace elements V, Mn, Ni, Cu, Zn, Sr, Cd and Pb. Sr was analyzed by PIXE, other elements by GFAAS. Circles and squares correspond to samples SSBLPI 6 and SSBLPI 10, respectively. Environ. Scl. Technol., Vol. 24, No. 12, 1990 1815 pressure impactor was the only method used to measure Mg particle size distributions in this study, the absolute amount of bounce cannot be determined. Particle size changes during sampling due to vapor condensation or evaporation can be estimated, if the properties and con centrations of vapors are known (32). Unfortunately, properties and concentrations of condensing vapors were ijfeli not exactly known in this study. Because sampling tem Hr* Hr* i to 10* if* to -1 i 10 to* if* itr1 i 10 io* peratures were near the dew point of water and sulfuric * acid, some condensation may have occurred inside the impactor during sampling. One impactor sample, SSBLPI 8, was collected by using ungreased aluminum substrates. The resulting size distribution (see Figure 2) is, however, very similar to those measured with greased substrates. This suggests that particles were not very bouncy, probably a°S88 °S=s because of being covered with a layer of condensed liquid. Condensation due to the aerodynamic cooling of the com ti io-3 nr 1 i io io* iff* if' io io* so* if* i io io% pressible flow jet would occur only at the low-pressure c, r TI 10 Fe stages 1-6; i.e., the coarse-mode particles above 0.3 pm would not be covered with liquid layer because of con ti " densation inside the impactor. This suggests that con o « TI oo 6 "o''tea-:-- densation had occurred before the aerosol entered the 8°° oV o ‘ impactor. L " SWt 4.4. Behavior of Elements during the Combustion ...... ?8ae-o~ Oj Process. Composition size distributions (element mass io* io* i io io% if* if: i io io% if* if: i io 10% fractions of particles as the function of particle size) of matrix and trace elements are shown in Figure 4, parts a Particle Stokes Diameter, |im and b, respectively. The error bars shown with data points are calculated from the equation " ecoo V 3000 m- N1 A (m,/mG) = Ami/mi + A mG/mG (3) I T »» where A(m;/mG) is the relative error of the composition it size distribution data point, m; the mass of the element 1 if £ in the sample, and mG the gravimetric mass. Am; and 1 . Am0 are the errors of the GFAAS and gravimetric analysis. Gravimetric analysis error was estimated to be the max if* if: i io io* if* if: i io imum weight change of the substrate as determined by the substrate stability test GFAAS analysis error was calcu lated from the equation g 2000 Am,- = 0.1m, + blank,- (4) k where blank; is the amount of element £ in the blank substrate. Because the analysis results of Si, S, Ti, and --•■-Vo" Sr are semiquantitative in nature, no error estimation is 1 L.— made for these elements. The dashed line shown in Figure if* if: i io io% if* if: i io io* if* if* i io 10% 4 is the corresponding concentration of the element in fly ash collected with the ESP, as given in Table IV. The apparent depletion of Al, Si, K, and Fe with respect to the fly ash collected with the ESP results from uncertainties associated with PIXE analysis results of fly ash Al, Si, K, and Fe content and particle Si content The main coarse-particle formation mechanism during the combustion process is the carryover of the incom- bustable mineral component of the coal, ash (3, 7). Fine if* if: i io io% if% if* i io io* particles are mainly formed by nucleation of vaporized fly Particle Stokes Diameter, [Am ash components near the surface of the burning coal particle and subsequent growth of nuclei via coagulation Figure 4. (a) Composition size distributions (mass fraction as the and heterogeneous condensation of vapors of more volatile function of particle size) of matrix elements. Circles and squares fly ash components at lower gas temperatures (33-37). The correspond to samples SSBLPI 6 and SSBLPI 10, respectively. Dashed line shows the concentration In the ESP fly ash, as analyzed vaporization of refractory elements is believed to be the by PIXE. (b) Composition size distributions of trace elements. Circles result of the reduction of their oxides in the locally re and squares correspond to samples SSBLPI 6 and SSBLPI 10, re ducing atmosphere surrounding the burning coal particle. spectively. Dashed line Is the concentration In the ESP fly ash, as When reduced vapors diffuse away from the parent coal analyzed by PIXE (except Cd, which was analyzed by GFAAS). particle, they encounter a greater oxygen potential and reoxidize. Resulting saturation ratios can be so high that suiting composition size distribution depends on the pre nucleation can occur. When fine particles are formed via vailing gas-to-particle conversion mechanisms (4). If nucleation and subsequent self-coagulation, their number particles are formed by a single component vapor nu and mass size distributions are very narrow. If an element cleation and grow only by coagulating with themselves, vaporizes completely during combustion, the form of re- resulting composition size distributions are flat, inde 1816 Environ. Scl. Techno!., Vol. 24, No. 12, 1990 pendent of particle size. Heterogeneous condensation of of laboratory studies. The mode of occurrence of the el vapors on existing particles results from composition size ements in the parent coal (i.e., organically bound or as distributions, which vary as Dp" 1 (free molecular regime) sociated with Si-rich grains), coal particle diameter, and or as Dp" 2 (continuum regime). When condensation nuclei the combustion temperature are important factors when coagulate with coarse-mode particles, composition size determining the vaporization rate of elements during distribution of coarse particles varies also as Dp '2 (7). If combustion (34-36). During the combustion of coals with an element vaporizes only partially during the combustion high Si content at high temperatures, low vaporization process, heterogeneous condensation of vapor on the coarse rates of Na have been observed due to the low reactivity particles will cause the composition size distribution of Na associated with the silica-rich melt (35). The im particle size dependence to differ from Dp 2". Usually ho portant factor determining the fraction of vapor condensed mogeneous nucleation, heterogeneous condensation, and on the fine- and coarse-mode fly ash particles is the cooling growth by coagulation are competitive processes. This will rate before the measurement of the fractional size distri further affect the form of resulting aerosol composition size bution. When the cooling rate decreases, the importance distributions. of the Kelvin effect increases (due to lower saturation Composition size distributions of the matrix elements ratios), resulting in a lower fraction of the vaporized ele Na, Mg, Al, Si, K, Ti, and Fe and the trace element Mn ment to condense on the fine-particle mode (35). The ratio are fairly flat This indicates that a small fraction of these of cooling rates reported by Neville and Sarofim (35) for elements may vaporize and nucleate during the combustion their laboratory experiments to those estimated for field- process. Particle S, Ca, V, Cu, Sr, and Cd concentrations scale combustors (7) varies between 4 and 14. If the va increase almost inversely proportional to particle diameter porizing-nucleating elements are distributed nonuniformly below 1 pm. Above 1 pm, composition size distributions in the coal particles, fine-mode particles with nonuniform of these elements are almost independent of particle size. composition may be formed; e.g., some particles may be Heterogeneous condensation of S, Ca, V, Cu, Sr, and Cd enriched with Ca and some with Si (37). The Ca-rich vapors is the most probable reason for observed particle particles can neutralize the sulfuric acid coatings that in size dependence of their composition size distributions. crease ESP collection efficiency and therefore selectively Above X pm the nonvaporized part of the fly ash dominates escape (39). As the detailed distribution of elements in the composition size distribution (35). The depletion of the coal particles, coal particle size distributions, and Na, Mg, Al, Si, K, Ti, Fe, and Mn below 1 pm may result combustion temperatures were not measured and the from the condensation of large quantities of Ca and S. aerosol was sampled after the ESP, definitive conclusions Due to difficulties in measuring the submicron mass size regarding the behavior of Na and Ca cannot be made. distributions of coal combustion aerosols, available com Clearly, more detailed field studies, including aerosol position size distribution data measured from real-scale number, mass, and elemental size distribution measure combustion units is mostly limited to particles larger than ments over the entire size range of about 5 nm-50 pm ~0.3 pm. Zn, Cd, and Pb composition size distribution before the gas cleaning devices, and detailed analyses of data of Davison et al. (38) in the aerodynamic size range coal and combustion conditions are needed in order to fully of 0.65-11 pm agree qualitatively well with the results of clarify the differences between the results of this study and this study. those from laboratory studies regarding the behavior of ash components during pulverized coal combustion. Neville and Sarofim (35, 36) have reported elemental fractional size distribution data for the laboratory-scale 5. Conclusions combustion of Montana lignite coal, measured with the electrostatic classification method in the size range Mass and Na, Mg, Al, Si, S, K, Ca, Ti, Fe, V, Mn, Cu, 0.01-0.04 pm and with the inertial impactor above 0.3 pm. Zn, Sr, Cd, and Pb size distributions of aerosols emitted Their results agree well for Fe and Mg with the results of from a boiler firing pulverized, bituminous coal from Po this study. However, Ca, Na, Al, and Zn behave clearly land were measured to be bimodal. When samples were differently. In this study, particle Ca concentration in collected immediately after the electrostatic precipitator, creased with decreasing particle size, whereas particle Na, geometric mass mean diameters of fine and coarse modes Al, and Zn concentrations were fairly constant in the were about 0.05 and 2 pm, respectively. Corresponding submicron size range, indicating relatively low volatilization geometric standard deviations were 1.4 and 1.8. About 5% of Na, contradictory to the results of Neville and Sarofim of particle mass and particle-bound Na, Mg, Al, Si, Ti, Fe, (35, 36). The fractional size distributions of Pb and Zn Mn, and Zn were found in the fine-particle mode. S, Ca, found in this study, showing apparent discontinuity at V, Cu, Sr, Cd, and Pb were enriched in the fine-mode ~0.4 pm, resemble the results of Neville and Sarofim (35) particles; i.e., ~80% of the particle-phase S, 17% of Ca, for Na, indicating condensation of these vapors shortly 23% of V, 22% of Cu, 11% of Sr, 34% of Cd, and 9% of after the combustion of char. Pb were in the submicron fine-mode particles. Taylor and Flagan (9) have reported fractional size Acknowledgments distribution data of Al, Ca, Si, Fe, S, and Zn for the com bustion of subbituminous coal at a laboratory furnace We gratefully acknowledge the assistance of Mr. R. under near-stochiometric and fuel lean combustion con Hillamo, Mr. K. Larjava, and Mr. P. Rouhiainen during ditions. They have used a low-pressure impactor method the collection and analysis of the low-pressure impactor similar to the one used for this study. Their results for samples and the help of Mr. J. Virtanen during the con Al, Si, and S from fuel-lean combustion experiments are struction of the sampling system. This paper was written similar to those of this study, whereas Ca, Fe, and Zn show while E.I.K. was at the University of Florida, Gainesville, variable behavior. The results of Taylor and Flagan (9) FL. Discussions with Prof. D. A. Lundgren and Mr. R. W. from near-stochiometric combustion experiments are sim Vanderpool are acknowledged. Comments of Dr. J. Joki- ilar to those of this study for Al, Si, Fe, and S, but Ca shows niemi during the preparation of the revised version are variable behavior. acknowledged. There are many possible reasons for the differences of Registry No. Na, 7440-23-5; Mg, 7439-95-4; Al, 7429-90-5; Si, Na and Ca behavior found in this study and the results 7440-21-3; S. 7704-34-9; K, 7440-09-7; Cm, 7440-70-2; Ti, 7440-32-6; Environ. Sd. Technol.. Vol. 24, No. 12. 1990 1817 Fe, 7439-89-6; V, 7440-62-2; Mn, 7439-96-6; Ni, 7440-02-0; Cu, (21) Kauppinen, E. Licentiatum Thesis (in Finnish), University 7440-50-8; Zn, 7440-66-6; Sr, 7440-24-6; Cd, 7440-43-9; Pb, of Helsinki, Helsinki, Finland, 1987. 7439- 92-1; Cr, 7440-47-3; Co, 7440-48-4; Ga, 7440-55-3; As, (22) Rader, D. J.; Marple, V. A. Aerosol Sci. Technol. 1985, 4, 7440- 38-2; Se, 7782-49-2; Br, 7726-95-6; Zr, 7440-67-7; Hg, 7439- 141. 97-6. (23) Kauppinen, E.; Hillamo, R; Ruuskanen, J.; Hakkarainen, T. ; Rouhiainen, P. J. Aerosol Sci. 1986, 17,506. Literature Cited (24) Biswas, P.; Flagan, R C. Environ. Sci. Technol. 1984,78, (1) Raask, E.; Wilkins, D. M. J. Inst. Fuel 1965,38, 255. 611. (2) Gumz, W.; Kirsch, H.; Mackowsky, M.-T. Schlackenkunde; (25) Markowski, G. R; Ensor, D. S.; Hooper, R G.; Carr, R C. Springer-Verlag: Berlin, 1958. Environ. Sci. Technol. 1980, 14,1400. (3) Sarofim, A. F.; Howard, J. B.; Padia, A. S. Combust. Sci. (26) Candelaria, R B.; Palermo, G. E. Atmos. Environ. 1982, 16, 2287. Technol. 1977, 16,187. (4) McElroy, M. W.; Carr, R. C.; Ensor, D. S.; Markowski, G. (27) Ensor, D. S.; Markowski, G.; Woffinden, G.; Legg, R; R Science 1982, 215, 13. Cowan, S.; Murphy, M.; Shendrikar, A. D.; Pearson, R; (5) Taylor, D. D.; Flagan, R C. Aerosol Sci. Technol. 1982, 1, Scheck, R Evaluation of Electrostatic Precipitator Per 103. formance at San Juan Unit No. 1. EPRI Report CS-3252; Carr, R C.; McElroy, M. W., EPRI Project Managers; (6) Quann, R. J.; Neville, M.; Janghorbani, M.; Mims, C. A.; Sarofim, A. F. Environ. Sci. Technol. 1982, 16, 776. Electric Power Research Institute: Palo Alto, CA, 1983. (7) Flagan, R. C.; Friedlander, S. K. In Recent Developments (28) Van Bush, P. Environ. Sci. Technol. 1984, 18, 699. in Aerosol Science; Shaw, D. T., Ed.; Wiley: New York, (29) Turner, J. R.; Hering, S. W. J. Aerosol Sci. 1987,78,215. 1978; pp 25-59. (30) Hinds, W. C.; Liu, W.-C.; Froines, J. R Am. Ind. Hyg. Assoc. (8) Ondov, J. M.; Ragaini, R C.; Biermann, A. H. Environ. Sci. J. 1985, 46, 517. Technol. 1979, 73, 946. (31) Lundgren, D. A.; Balfour, W. D. Use and Limitations of (9) Taylor, D. D.; Flagan, R. C. In Atmospheric Aerosols: In-S tack Impactors; Report EPA-600/2-80-048; USEPA, Source/Air Quality Relationships; Macias, E. S., Hopke, U. S. Government Printing Office: Washington, DC, 1989. P., Eds.; Wiley: New York, 1981; pp 25-59. (32) Biswas, P. Ph D. Dissertation, California Institute of (10) Shendrikar, A. D.; Ensor, D. S.; Cowen, S. J.; Woffinden, Technology, 1985. G. J.; McElroy, M. W. Atmos. Environ. 1982, 17, 1411. (33) Senior, C. L.; Flagan, R C. Aerosol Sci. Technol. 1982, 1, (11) Markowski, G. R.; Filby, R. Environ. Sci. Technol. 1985, 371. 79, 796. (34) Quann, R J.; Sarofim, A. F. 19th Symposium (Interna (12) McCain, J. D.; Gooch, J. P.; Smith, W. B. J.—Air Pollut. tional) on Combustion; The Combustion Institute: Control Assoc. 1976,25,117. Pittsburgh, PA, 1982; pp 1429-1440. (35) Neville, M.; Sarofim, A. F. Fuel 1985, 64, 384. (13) Amdur, M. O.; Sarofim, A. F.; Neville, M.; Quann, R. J.; (36) Neville, M.; Sarofim, A. F. 19th Symposium (International) McCarthy, J. F.; Elliot, J. F.; Lam, H. F.; Rogers, A. E.; on Combustion; The Combustion Institute: Pittsburgh, PA, Conner, M. W. Environ. Sci. Technol. 1986, 20,138. (14) Flagan, R C.; Taylor, D. D. 18th Symposium (Interna 1982; pp. 1441-1449. tional) on Combustion; The Combustion Institute: (37) Helble, J.; Neville, M.; Sarofim, A. F. 21th Symposium (International) on Combustion; The Combustion Institute: Pittsburgh, PA, 1981; pp 1227-1237. (15) Neville, M.; McCarthy, J. F.; Sarofim, A. F. Atmos. Environ. Pittsburgh, PA, 1986; pp 411-417. (38) Davison, R L.; Natusch, D. F. S.; Wallace, J. R; Evans, 1983, 77, 2599. C. A. Environ. Sci. Technol. 1974,8,1107. (16) Damle, A. S.; Ensor, D. S.; Ranade, M. B. Aerosol Sci. Technol. 1982, 7, 119. (39) Sarofim, A. F. Massachusetts Institute of Technology, (17) Berner, A.; Lurzer, C. J. Phys. Chem. 1980, 84, 2079. Cambridge, MA, personal communication, 1990. (18) Berner, A. In Aerosols. Science, Technology, and Industrial Applications of Airborne Particles; Liu, B. Y. H., Pui, D. Received for review December 1, 1988. Revised manuscript Y. H., Fissan, H. J., Eds.; Elsevier: New York, 1984; pp received November 6,1989. Accepted June 28,1990. This work 139-142. was supported by the Academy of Finland and Maj and Tor (19) Hillamo, R; Kauppinen, E. Aerosol Sci. Technol., in press. Nessling Foundation. Part of the results of this study was (20) Quality Assurance/Quality Control Document. Element presented at the Annual Meeting of the American Association Analysis Corp.: Tallahassee, FL, 1986. for Aerosol Research, Seattle, WA, September 14-19,1987. 1818 Environ. Sci. Technol., Vol. 24, No. 12, 1990 Journal ofRadioanalytical andNuclearChemistry, Articles, Vol. 167, No. 2 (1993) 271-281 ATMOSPHERIC AEROSOL STUDIES IN SOUTHERN NORWAY USING SIZE-FRACTONATING SAMPLING DEVICES AND NUCLEAR ANALYTICAL TECHNIQUES W. MAENHAUT,* G. DUCASTEL,* R. E. HILLAMO,” T. A. PAKKANEN,” J. M. PACYNA*** 'Institute for Nuclear Sciences, Proeftuinstraat 86, B-9000 Ghent (Belgium) "Finnish Meteorological Institute, Saluiajankatu 22 E, SF-00810Helsinki (Finland) ‘"Norwegian Institute for Air Research, P.O. Box 64, N-2001 Lillestrdm (Norway) (Received September22,1992) Atmospheric aerosol samples were collected during spring sampling campaigns in 1988 and 1989 at Birkenes and Nordmoen in southern Norway. The aerosol collectors used included stacked filter units (SFUs), a low volume sampler (referred to as ILVS), which consists of a filter preceded by three impaction stages, and an 11-stage Berner low-pressure impactor (LP1). All samples were analyzed for up to about 40 elements by INAA and PIXE. The resuls obtained from parallel samplings were intercompared in terms of ratios ILVS/SFU and LPI/SFU, whereby these ratios were calculated separately for the coarse and fine size fractions. For the ILVS/SFU parallel samplings, excellent agreement was observed between the results for the fine fraction, with the overall mean average ratio (based on 21 samples and 22 elements) being 0.99 ±0.10. For the coarse fraction, the overall mean ILVS/SFU ratio (based on 21 elements) was 0.75 ± 0.13. This low result is explained by different upper-particle-size cut-offs of the two samplers. For the parallel samplings with LPI and SFU, the agreement was poorer, but still reasonable. The atmospheric concentrations observed at the two sites in the two campaigns and also the LPI size distributions for the various elements are discussed briefly. Introduction Southern Norway is a receptor site for atmospheric pollutants from various source regions, including Western and Central Europe and the former Soviet Union .1-3 Be cause of the deleterious effects of these pollutants on the Norwegian ecosystems, it is important to assess their sources and to understand their processes of transformation and removal. Very useful information concerning these issues can be obtained by size-fractionated aerosol samplings at southern Norwegian background stations coup led with multielement analysis by nuclear and nuclear-related analytical techniques. In this paper, multielement data obtained from intensive sampling campaigns carried out at two different sites in spring 1988 and 1989 are presented. Several types of size-fractionated samplers were operated in parallel at each location, and a de tailed comparison of the results from these parallel samples is given. Furthermore, the atmospheric concentrations observed at the two sites in the two campaigns are briefly discussed. A short discussion is also given of the detailed size distributions for the various elements, as derived from measurements with a low-pressure cascade impactor. On the basis of these size distribution data the major source processes for the various elements are identified. Elsevier Sequoia S. A., Lausanne Akadjmiai Kiadd, Budapest w. MAENHAUTet al.: ATMOSPHERIC AEROSOL STUDIES Experimental Sampling The samplings were carried out at two locations in southern Norway, i.e., at Birkenes (58° 23' N, 8° 15’ E) and Nordmoen (60° 16' N, 11° 06’ E). At both sites, the Norwegian Institute for Air Research (NILU) had installed background sampling stations for routine measurement of selected ions and metals in air and precipita tion .4 As far as the aerosol collections are concerned, the NILU samplings are limited to total filter samplings. Our samplers were operated at the NILU background sta tions during two intensive sampling campaigns in spring 1988 and spring 1989. The 1988 campaign took place from April 11 until May 4, and the 1989 campaign from April 27 until May 13. Various size-fractionating aerosol samplers were used in these campaigns, i.e., stacked filter units (SFUs), a low-volume sampler with pre-impaction stages (referred to as ILVS) and two types of cascade impactors. The SFUs5’6 consisted of two se quential 47-mm-diameter filter holders, in which Nuclepore polycarbonate filters of 8-pm pore size (Apiezon-coated) and of 0.2-pm pore size were placed. At the flow rate used (typically 5-10 1/min), the SFU separates the particulate material into two size fractions of > 2 pm and <2 pm equivalent aerodynamic diameter (EAD).7 The ILVS sampler was designed by HILLAMO.8 It is operated at a flow rate of 15 1/min, and consists of a 47 mm diameter filter holder, which is preceded by three impaction stages with cut diameters for 50% collection efficiency of 10, 6 and 2 pm EAD. Stage 1 in this ILVS has a single orifice, but stages 2 and 3 contain 12 and 24 jets, respec tively. As collection surfaces in the impaction stages, polycarbonate film (poreless Nuclepore) was used. The films were coated with Apiezon L vacuum grease, and had an annular shape for stages 2 and 3. In the filter stage, a 47-mm-diameter 0.4 pm pore-size Nuclepore filter was used. The two types of cascade impactors used were a small 11/min, 8-stage PIXE International Battelle type cascade impactor (PCI),9’10 and an 11-stage Berner low-pressure impactor (LPI),11’12 operating at 25 1/min. Here, only the results from the LPI will be presented. This LPI contains 11 impaction stages (numbered 11 through 1) with cut diameters that are 16, 8, 4, 2, 1, 0.5, 0.25, 0.125, 0.060, 0.030 and 0.015 pm EAD according to the manufacturer. However, from experimental determinations and calculations, HILLAMO and KAUPPINEN13 de duced that the cut points for the 11 LPI stages are instead 16, 7.6, 3.8,1.9, 0.95, 0.52, 0.33, 0.16, 0.090, 0.062 and 0.032 pm EAD. In the present work, the latter values were adopted. The impaction surfaces for the LPI consisted of polycarbonate film (poreless Nuclepore). For stages 11 through 7, the film was coated with Apiezon L vacuum grease. Daily samples were collected with the SFUs and the ILVS; but the samples with the PCI and LPI were taken on a 2-2-3 day schedule. In many of the samplings, the filters or collection surfaces were weighed both before and after sampling, so that suspended particle mass concentrations could be derived. An overview of which samplers were used at each of the two sites in each of the two campaigns is pre sented in Table 1. The table also indicates the number of samples collected with each device. For certain SFU samplings there were operating problems during collection, which rendered the sample worthless. During the 1988 campaign, this was the case 272 W. MAENHAUT et al.: ATMOSPHERIC AEROSOL STUDIES Table 1 Overview of the sampling devices used at Birkenes and Nordmoen during spring 1988 and spring 1989 sampling campaigns.* The number of samples collected with each device is given in parentheses, and followed by the number of samples analyzed, if different from that collected** Site 1988 campaign 1989 campaign Birkenes SFU (22/21) SFU (15/13) PCI (9) PCI (6) LPI (9/8) Nordmoen SFU (23/21) SFU (14/13) ILVS (23) pa (5) LPI (5) 'SFU denotes slacked filter unit, ILVS is a low volume sampler consisting of filter holder preceded by three impaction stages, PCI stands for 8 -stage PIXE International cascade impactor and LPI for 11-stage Berner low-pressure impactor. **The difference between the two numbers is due to the fact that there were operational problems during some samplings or that some samples were not analyzed (see text). for SFU sample No. 13 from Birkenes, and for SFU samples Nos. 15 and 20 from Nordmoen. In the 1989 campaign, SFU samples 13 and 15 from Birkenes were invalidated by those problems. Analysis The various samples (and blanks of each collection material used) were analyzed by both instrumental neutron activation analysis (INAA) and particle-induced X-ray emission analysis (PIXE). For PIXE one-quarter of each filter (or film) was.used, whereas the fraction analyzed by INAA varied from one-quarter up to three-quarters. The INAA and PIXE analyses were carried out at Ghent with procedures similar to those that have been described before .14"18 For each sample the INAA and PIXE results were combined into one data set. Because of element-dependent differences in precision and detection limits of the two techniques, the PIXE data were selected for some elements, the INAA values for others, and the average of the PIXE and INAA values was used for still other elements. Birkenes LPI sample No. 1 of the 1988 campaign was not analyzed, nor was Nordmoen SFU sample No. 3 from the 1989 campaign. Also, the stage-11 impaction film was excluded from the analysis for all LPI samples, and the stage-1 impaction film for all ILVS samples. Results and discussion Intercomparison of the results from parallel samples An SFU and an ILVS were operated in parallel at Nordmoen in the 1988 cam paign, whereas an SFU and an LPI were operated in parallel at Birkenes in 1988 and at Nordmoen in 1989. The results obtained for the parallel samplings were intercom- 273 W. MAENHAUT etal.: ATMOSPHERIC AEROSOL STUDIES pared in order to evaluate the performance of the various samplers. The comparisons were done separately for the coarse (> 2 pm EAD) and fine (<2 pm EAD) size fractions. The coarse-ffaction elemental concentrations for the ILVS were obtained by adding up the values from stages 2 and 3, whereby upper limit values were set equal to zero. Similarly, for the LPI samples, the data of stages 10 through 8 were added up to obtain the concentrations in the coarse fraction, and the sum of stages 7 through 1 provided the fine-fraction concentrations. Here also, upper limits were replaced by zeros in the summation. As two or three SFU samples were always col lected during one LPI sampling, the concentrations obtained from the SFU samples (in ng/m 3) were converted to volume-weighted averages for a two- or three-day period before comparing them with the LPI results. For each parallel sampling, the concentration ratios ILVS/SFU or LPI/SFU were calculated, and these ratios were then averaged per element and per size fraction over all parallel samplings for each site and for each campaign. However, when the percentage analytical standard deviation on an individual ratio was larger than about 30-35%, that ratio was excluded from the averaging. Also, evident outlier ratios were rejected. Table 2 Average ratio ILVS/SFU for variouselements and the aerosol mass (MS) at Nordmoen during the spring 1988 campaign Fine fraction Codrse fraction (< 2 pm EAD) (> 2 pm EAD) Element XT ± s [N/n]' x ± s [N/n] Na 0.93 ± 0.13 [19/2] 0.78 ± 0.14 [21/0] Mg 0.75 ± 0.26 [ 8/2] A1 1.00 ± 0.18 [20/1] 0.59 ± 0.10 [18/3] Si 0.98 ± 0.22 [18/3] 0.72 ± 0.11 [19/2] S 1.10 ± 0.13 [21/0] 0.73 ± 0.18 [12/3] K 1.14 ± 0.14 [20/1] 0.84 ± 0.19 [21/0] Ca 0.90 ± 0.15 [20/1] 0.81 ± 0.20 [21/0] Sc 0.95 ± 0.26 [7/0] 0.56 ± 0.12 [15/1] Ti 0.93 ± 0.21 [11/1] 0.67 ± 0.16 [18/1] V 1.10 ± 0.11 [20/1] 0.65 ± 0.17 [20/1] Mn 1.07 ± 0.10 [21/0] 0.64 ± 0.12 [20/1] Fe 1.04 ± 0.15 [21/0] 0.91 ± 0.30 [21/0] Cu 1.08 ± 0.28 [8/0] 0.72 ± 0.18 [ 5/0] Zn 1.03 ± 0.13 [21/0] 0.74 ± 0.23 [19/1] As 0.77 ± 0.22 [19/2] 0.90 ± 0.43 [14/3] Sb 1.03 ± 0.21 [20/1] 0.99 ± 0.35 [14/0] I 0.95 ± 0.19 [20/1] 0.85 + 0.31 [12/2] Cs 0.89 ± 0.25 [17/1] La 0.89 ± 0.24 [10/1] 0.58 ± 0.11-[18/2] Sm 1.03 ± 0.30 [12/0] 0.57 ± 0.09 [18/3] W 0.84 ± 0.27 [16/0] 0.96 ± 0.38 [15/0] Pb 1.10 ± 0.18 117/1] 0.78 + 0.26 [11/2] MS 1.00 ± 0.18 [18/3] *N+n is the number of samples for which the individual ratio had a percentage analytical standard deviationof less than 30-35%, N is the number of samples retained in the averaging and n is the number of rejected outliers. 274 W. MAENHAUT etal.: ATMOSPHERIC AEROSOL STUDIES The average ILVS/SFU ratios for Nordmoen 1988 are given in Table 2. For the fine fraction (thus the filters), virtually all average ratios are within the range 0.84- 1.14. The overall average ratio, obtained by averaging the mean ratios of all ele ments, is 0.99±0.10. Furthermore, the total number of rejected outliers (summed over all elements) remained limited to 5.1%. This excellent agreement between the filter data of ILVS and SFU implies that the air volumes were measured quite accu rately and that the two filters collected virtually identical particle populations. Conse quently, the cut-off (d50-value) for stage 3 of the ILVS was quite close to that for the coarse filter of the SFU, and the difference in pore size of the two filters had no impact on the elemental masses collected. For the coarse fraction, however, all aver age elemental ratios are systematically lower than 1. The overall average ratio (over all elements) is 0.75+0.13, and the total number of rejected outliers amounted to 7.4%. Particularly the typical crustal elements or elements with an important crustal component, such as Al, Si, Sc, Ti, V, Mn, La and Sm, exhibit low average ratios, i.e., between 0.56 and 0.72. These elements are predominantly associated with the coarse- aerosol mode (or have a very important coarse aerosol component). Therefore, the low ratios are most likely caused by a difference in upper cut-off value for the coarse fractions from the two samplers. For the ILVS, the coarse fraction is the sum of Table 3 Average ratio LPI/SFU for variouselements and the aerosol mass (MS) at Birkenes during the spring 1988 campaign Fine fraction Coarse fraction (< 2 pm EAD) (> 2 pm BAD) Element "X" ± s [N/nl* x ± s [N/n] Na 0.66 ± 0.15 17/0] 0.92 ± 0.12 [7/0] Al 0.79 ± 0.17 [7/0] 0.67 ± 0.15 [7/0] Si 1.20 ± 0.39 [6/0] 0.73 ± 0.25 [7/0] S 1.30 ± 0.19 [7/0] 1.00 ± 033 [7/0] Cl 0.98 ± 0.29 [5/1] 0.20 K 1.09 + [7/0] 0.85 ± 0.10 [6/1] Ca 0.67 ± 0.18 [7/0] 0.90 ± 0.18 [6/1] Sc 0.53 + 0.08 [7/0] Ti 0.61 ± 0.27 [4/0] 0.92 ± 0.35 [7/0] V 0.83 ± 0.19 [7/0] 0.65 ± 0.08 [7/0] Mn 1.06 ± 0.29 [6/1] 0.92 ± 0.07 [6/1] Fe 1.05 ± 0.36 [6/1] 1.02 ± 0.25 [7/0] Cu 1.15 ± 0.37 [3/1] Zn 1.21 ± 0.33 [6/1] 0.92 ± 0.15 [6/1] As 1.14 ± 0.36 [5/2] 1.39 + 0.45 [5/2] Br 0.89 ± 0.31 [5/2] Sb 0.84 ± 0.34 [6/1] 1.03 + 0.40 [7/0] I 0.48 ± 0.14 [7/0] Cs 0.77 ± 0.23 [3/1] La 0.50 ± 0.24 [4/0] 0.66 + 0.15 [6/1] Sm 0.31 ± 0.19 [6/0] 0.59 ± 0.13 [6/1] W . 1.00 ± 0.32 [5/0] Pb 1.24 ± 0.47 [5/2] 0.96 + 0.49 [4/1] MS . 0.82 ± 0.17 [5/0] "See footnote Table Z 275 7 21405 W. MAENHAUT etal.: ATMOSPHERIC AEROSOL STUDIES stages 2 and 3, and thus represents the aerosol size fraction between 2 and 10 pm BAD. In the case of the SFU, however, the upper cut-off of the coarse filter is not well defined, and is likely larger than 10 pm BAD. For certain typical anthropogenic elements, such as S, Cu, I and Pb, where the effect of difference in upper cut-off should be much less, the low ILVS/SFU ratios are explained by the fact that about Table 4 Average ratio LPI/SFU for variouselements at Nordmoen during the spring 1989 campaign Fine fraction Coarse fraction (< 2 pm EAD) (> 2 pm EAD) Element x ± s [N/n]* x + s [N/n] Na 1.17 ± 0.17 [5/0] 1.14 + 0.22 [5/0] Mg 0.66 + 0.06 [3/2] A1 0.85 ± 0.09 [5/0] 0.59 + 0.13 [5/0] Si 1.24 ± 033 [5/0] 0.71 + 0.25 [5/0] S 1.69 ± 0.15 [4/1] 0.64 + 0.07 [4/1] a 1.60 + 0.46 [4/1] K 134 ± 0.28 [5/0] 0.73 + 0.12 [4/1] Ca 1.07 ± 0.12 [5/0] 1.00 ± 0.27 [4/1] Sc 0.64 + 0.23 [5/0] Ti 0.80 ± 0.11 [4/1] 0.79 + 0.17 [4/1] V 1.21 ± 0.36 [4/1] 0.70 + 0.24 [5/0] Mn 1.52 ± 0.21 [4/1] 0.79 + 030 [5/0] Fe 132 ± 0.24 [5/0] 1.08 + 0.41 [4/1] Co 1.47 + 0.39 [4/1] Cu 0.58 ± 0.15 [3/0] Zn 1.86 ± 0.19 [5/0] 1.19 + 0.17 [5/0] As 0.83 + 0.05 [3/1] Br 1.09 ± 0.36 [4/1] Sb 1.34 ± 0.26 [3/2] I 0.80 + 0.23 [5/0] 0.53 + 0.13 [5/0] Ba 0.64 ± 0.07 [3/0] La 0.92 ± 0.14 [4/1] 0.73 t 0.25 [4/1] Sm 0.90 ± 0.26 [4/1] 0.87 + 0.30 [3/2] W 1.03 + 0.20 [2/2] Au 0.98 + 0.55 [4/0] Pb 1.85 ± 0.46 [5/0] 0.97 + 0.25 [5/0] "See footnote Table 2. 50% of the individual concentrations for stage 2 of the ILVS were upper limits (and thus set equal to zero in the summation of stages 2 and 3). The average LPI/SFU ratios for Birkenes 1988 and Nordmoen 1989 are presented in Tables 3 and 4, respectively. The agreement between LPI and SFU is clearly poorer than that between ILVS and SFU, but, in general, it is still quite reasonable. For Birkenes 1988, the overall average LPI/SFU ratios are 0.89±0.28 for the fine fraction and 0.88±0.20 for the coarse fraction, whereas the total number of rejected outliers amounted to 9.2% and 7.8%, respectively. For Nordmoen 1989, the overall average LPI/SFU ratios are 1.22+0.34 for the fine fraction (with 11% outliers reject- 276 W. MAENHAUT et al.: ATMOSPHERIC AEROSOL STUDIES ed) and 0.87+0.28 for the coarse fraction (15% outliers rejected). There are several possible explanations for these poorer results, including errors in the chemical anal ysis, inaccuracies in volume measurement, differences in collected particle size ranges between LPI and SFU, wall losses (in the LPI) and the fact that upper limits are replaced by zeros in summing up the data from the various stages for the LPI. The latter two effects will generate LPI/SFU ratios lower than one, and the last effect is definitely responsible for the low ratios of some crustal elements (i.e., Ca, Ti, La and Sm) in the fine fraction. Perhaps most difficult to explain are the high LPI/SFU ratios obtained for S, Zn and Pb for the fine fraction of Nordmoen 1989. Most of the ef fects just mentioned cause a systematic bias in the LPI/SFU ratio for all elements within one campaign (or at least within one size fraction). Total atmospheric concentrations The elemental concentrations (in ng/nv*) from the coarse and fine filter of each SFU sample were added up, and, for the total atmospheric concentrations thus obtained, median values were determined for each of the two sites and for each of the two campaigns. These medians are given in Table 5 for 27 elements. For the Table 5 Median total atmospheric concentrations (in ng/m3), as derived from the SFU samplings, at Birkenes and Nordmoen in spring 1988 and spring 1989 Birkenes Nordmoen Element 1988 1989 1989 1989 Na 170 161 140 128 Mg 81 66 Al 60 45 145 200 Si 190 80 420 438 S 440 270 340 196 Cl 34 87 46 43 K 45 34 98 77 Ca 42 18.4 80 53 Sc 0.0126 0.0079 0.023 0.030 Ti 5.7 214 11.4 10.7 V 0.81 0.26 0.86 0.69 Mn 4.8 3.1 4.9 3.9 Fe 43 33 107 111 Co 0.26 0.193 0.072 Cu 0.41 0.72 Zn 7.6 1.66 18.6 4.7 As 0.44 0.056 0.42 0.091 Br 2.6 0.56 22 21 Sb 0.28 0.052 0.27 0.073 I 20 1.14 1.16 0.70 Cs 0.188 0.078 0.130 0.024 La 0.075 0.049 0.139 0.137 Sm 0.0072 0.0078 0.0192 0.020 Eu 0.052 0.031 0.055 W 0.082 0.133 0.029 Au 0.0028 0.00121 0.00181 0.00067 Pb 3.8 0.86 11.4 4.2 277 W. MAENHAUT etal.: ATMOSPHERIC AEROSOL STUDIES typical soil dust elements (Al, Si, K, Ca, Sc, Ti, Fe, La, Sm), which were mainly associated with coarse particles as will be indicated below, the median concentrations are clearly higher at Nordmoen than at Birkenes. However, at each site, the concen trations in 1988 and in 1989 are rather similar to each other. A large fraction of the airborne soil dust is likely from southern Norwegian origin, particularly at Nordmoen. For the typical anthropogenic elements (S, Zn, As, Sb and Pb), on the other hand, the median concentration values are about a factor of 3 higher in 1988 than in 1989, and this for each site. Furthermore, within each campaign, rather similar concentra tions are observed at the two sites for S, As and Sb. This suggests that these three elements are mainly advected from source regions outside of Norway, and that the intensity of the transport and/or the transport pathways were different in the two campaigns. For Zn and Pb, the levels at Nordmoen are about a factor of three higher than those observed at Birkenes. This seems to point to a regional source for these Table 6 Mass median diameters (in pm BAD) for 27 elements and the aerosol mass (MS), as derived from the Birkenes 1988 and Nordmoen 1989 LPI samplings. A comparison is also made with values obtained from the PCI samplings (DUCASTEL et al.19) Birkenes Nordmoen Element 1988 PCI 1988 LPI 1989 PCI 1989 PCI 1989 LPI Na 3.1 3.2 Mg 3.2 4.0 23 3.3 4.1 Al 6.6 3.9 3.5 5.2 5.5 Si 3.2* 4.2" 3.0 6.1 5.4 S 0.43 0.50 0.53 0.58 0.50 Cl 4.2 4.3 3.2 3.4 3.0 K 1.2 2.1 4.3 4.2 3.0 Ca 3.6 4.5 3.2 5.0 4.9 Sc 4.9 5.5 Ti 4.5 4.7 5.1 5.5 5.6 V 0.42 0.49 0.86 1.2 0.81 Cr 1.9 Mn 1.3 1.9 1.7 4.0 3.2 Fe 3.1 3.8 3.9 5.5 4.8 Ni 1.4 1.9 2.2 Cu 1.6 2.0 4.2 23 2.5 Zn 0.62 0.74 0.94 0.78 0.78 As 0.52 0.38 Br 0.43 0.54 0.75 0.88 0.43 Mo 0.98 Z0 Sb 0.52 0.51 I 0.44 0.46 Cs 0.93 0.88 La 3.7 5.4 Sm 4.2 5.6 W 0.86 Z1 Pb 0.49 0.52 0.80 0.64 0.52 MS 0.75 "Sample No. 3 was excluded. 278 W. MAENHAUTet al.: ATMOSPHERIC AEROSOL STUDIES elements near Nordmoen. Probably incinerators and automotive emissions within the greater Oslo area are the main sources for Zn and Pb at Nordmoen. Finally, it is interesting to note that the concentration of the sea-salt marker element Na is only slightly higher at Birkenes than at Nordmoen, and this despite the fact that Birkenes is much closer to the open sea. For the Birkenes site, total concentrations of many atmospheric trace elements have been measured by a number of researchers since the early seventies (see AMUNDSEN,2 and references cited therein). AMUNDSEN2 carried out a long-term sampling campaign, which covered a full year (February 1985 -January 1986). In general, our median levels, observed at Birkenes during the 1988 campaign, are of the same order as those found in AMUNDSEN’s study. They also compare well with total concentrations derived from PCI samplings at the Birkenes site during a spring 1987 sampling campaign .3 Average size distributions From the LPI data average size distributions for each site were calculated. Fig. 1 presents the average size distributions obtained from the LPI samples of Birkenes 1988. It appears from this figure that even for the elements that are mainly associ ated with fine particles, such as S, Zn and I, only a small mass fraction is present in the size range below 0.1 pm EAD. This indicates that the high-temperature sources CL0S2 016 0.52 19 75 0062 016 052 19 7.6 0062 016 052 19 7.6 0932 0090 033 095 3.6 16 0032 0090 033 095 3 6 16 0032 0090 033 095 3 6 16 I I I I I I I I I I I II I II I II I I M I I Cl *25 Si *12 MS *20 Mg % 1.3 Mnx4 Co * 065 Vxl9 Br x 036 Sb x 027 AS x 015 Pb x 007 0001 — MM II II II II 1 2 3 4 5 7 8 9 10 23456789 10 1 23456789 10 STAGE NUMBER Fig. 1. Average size distributions, as derived from the Birkenes 1988 LPI samples. The data plotted are mean mass fractions and standard deviations, based on eight samples (for Si separate data are given for sample No. 3, and for all other samples; MS is the aerosol mass) 279 W. MAENHAUT etal.: ATMOSPHERIC AEROSOL STUDIES for these elements are at some oistance from the sampling sites, so that the very fine particles emitted by such sources had time to coagulate during atmospheric transport The average size distributions were used as a basis to calculate mass median di ameters (MMDs) for the different elements. The MMDs obtained are listed in Table 6 , together with the results from the PCI samples, as derived by DUCASTEL et al. -19 This table shows that there is generally good agreement between the MMD values derived from PCI and LPI samples taken in parallel. Also the average size distributions obtained from the parallel PCI and LPI samples resembled each other rather well. Table 6 further indicates that the MMDs of the various elements vary rather little from year to year, and are similar for the two sampling sites. Interesting ly, the biggest discrepancy in MMD values between Birkenes and Nordmoen is noted for Si and Mn. For these elements southern Norwegian anthropogenic sources are quite important at Birkenes ,3 but not at Nordmoen. On the basis of the average size distributions and average MMDs, the elements can be classified into three different groups. A first group of elements, including Na, Mg, Al, Si (at Nordmoen), Cl, Ca, Sc, Ti, Fe, Sm and La, exhibits a unimodal size distribution, with an MMD of about 3 to 5 pm EAD. This indicates that dispersion processes, such as soil dust dispersal or bubble bursting at the sea surface, are the sources of those elements. For Si (at Birkenes), K, Cr, Mn, Ni, Cu, Mo, Cs and W the distribution is rather flat or bimodal, suggesting that there is an important anthro pogenic contribution. S, V, Zn, As, Br, Sb, I, Pb and the aerosol mass are predomi nantly associated with <1 pm EAD particles, and exhibit MMDs in the range of 0.5 to 0.8 pm EAD, indicating that these elements (and the aerosol mass) originate mainly from high-temperature and/or combustion processes. * W. M. and G. D. acknowledge support from the Belgian "Nationaal Ponds voor Wetenschappe- lijk Onderzoek", the "Interuniversitair Instituut voor Kemwetenschappen", the "Instituut tot Aan- moediging van het Wetenschappelijk Onderzoek in Nijverheid en Landbouw", and the Impulse Program 'Global Change" supported by the Belgian State-Prime Minister’s Service, Science Polity Office. R. E. H. and T. A P. were funded by the Maj and Tor Nessling Foundation (Helsinki, Finland) and by the Academy of Finland. J. M. P. acknowledges funds from the Norwegian Minis try of the Environment Thanks are due to J. CAFMEYER for technical assistance. References 1. J. M. PACYNA, A SEMB, J. E. HANSSEN, Tellus, B36 (1984) 163. 2. C. E. AMUNDSEN, Langtransport av luftforurensninger studert ved analyse av filterpr0ver fra Birkenes, Thesis, University of Trondheim, Norway, 1987. 3. P. CORNILLE, W. MAENHAUT, J. M. PACYNA, Nucl. Instr. Methods, B49 (1990) 376. 4. L O. HAGEN, T. C. BERG, E. JORANGER, S. LARSEN, T. OFSTAD, NILUs overvakingsprogrammer for SET. Statjonsbeskrivelser pr. 1.5.1990, NILU Report OR 56/90, Norwegian Institute for Air Research, Lillestrpm,.. Norway, 1990. 5. T. A CAHILL, L. L. ASBAUGH, J. B. BARONE, R. A. ELDRED, P. J. FEENEY, R. G. FLOCCHINI, C. GOODART, D. J. SHADOAN, G. W. WOLFE, J. Air Pollut. Control Assoc., 27 (1977) 675. 6. N. Z. HEIDAM, Atmos. Environ., 15 (1981) 891. 7. W. JOHN, S. HERING, G. REISCHL, G. SASAKI, S. GOREN, Atmos. Environ., 17 (1983) 373. 280 W. MAENHAUT et al.: ATMOSPHERIC AEROSOL STUDIES 8 . R. HILLAMO, unpublished. 9. R. I. MITCHELL, J. M. PILCHER, Ind. Eng. Chem., 51 (1959) 1039. 10. S. BAUMAN, P. D. HOUMERE, J. W. NELSON, Nucl. Instr. Methods, 181 (1981) 499. 11. A BERNER, Staub-Reinhalt. Luft, 32 (1972) 315. 12. A BERNER, C. LURZER, J. Phys. Chem., 84 (1980) 2079. 13. R. E. HILLAMO, E. I. KAUPPINEN, Aerosol Sci. Technol., 14 (1991) 33. 14. W. MAENHAUT, W. H. ZOLLER, J. Radioanal. Chem., 37 (1977) 637. 15. P. SCHUTYSER, W. MAENHAUT, R. DAMS, Anal. Chim. Acta, 100 (1978) 75. 16. W. MAENHAUT, A SELEN, P. VAN ESPEN, R. VAN GRIEKEN, J. W. WINCHESTER, Nucl. Instr. Methods, 181 (1981)399. 17. W. MAENHAUT, H. RAEMDONCK, Nucl. Instr. Methods, B1 (1984) 123. 18. W. MAENHAUT, J. VANDENHAUTE, Bull. Soc. Chim. Belg., 95 (1986) 407. 19. G. DUCASTEL, W. MAENHAUT, R. HILLAMO, T. PAKKANEN, J. M. PACYNA in: Heavy Metals in the Environment, International Conference, Edinburgh, September 1991, Vol. 1, J. G. FARMER (Ed.), CEP Consultants Ltd., Edinburgh, 1991, p. 270. SOURCES AND PHYSICO-CHEMICAL CHARACTERISTICS OF THE ATMOSPHERIC AEROSOL IN SOUTHERN NORWAY Tuomo A. Pakkanen*, Risto E. Hillamo and Petri Keronen Finnish Meteorological Institute, Air Quality Department, Sahaajankatu 22 E, SF-00810 Helsinki, Finland Willy Maenhaut and Geert Ducastel University of Ghent, Institute for Nuclear Sciences, Proeftuinstraat 86, B-9000 Ghent, Belgium and Jozef M. Pacyna Norwegian Institute for Air Research, P.O. Box 64, N-2001 Lillestrdm, Norway submitted to Atmospheric Environment ABSTRACT An intensive aerosol sampling campaign was carried out at Birkenes and Nordmoen, southern Norway, between April 11 and May 4, 1988. Several sampling instruments were used, including two-stage filter samplers (SFU) and Berner low-pressure impactors (LPI). The samples were analyzed for up to 45 components by instrumental neutron activation analysis, particle-induced X-ray emission, inductively coupled plasma mass spectrometry and ion chromatography. The atmospheric concentrations were found to be similar at the two sampling sites, separated by a distance of about 250 km. During long-range transport episodes, the pollutant concentrations were 20 - 50 times higher than during background periods. Detailed information about the aerosol and element mass size distributions was obtained from the LPI samples. The aerosol fine particle mode clearly shifted to larger particle sizes when the average relative humidity was higher than 80% during sampling. The fine to total elemental concentration ratios were found to be similar for the SFU and LPI. Conventional methods and a new method based on size distributions gave similar results in assessing of local and/or regional sources of aerosols. The interelemental concentration ratios in air masses of different geographical origin were studied and some similarities were found to ratios measured in southern Sweden. Keywords: atmosphere, aerosol, elements, elemental ratios, sources of aerosols, impactors, size distributions 1. INTRODUCTION During the 1980s, long-range transport (LRT) of pollutants was studied intensively at various receptor sites in southern Scandinavia (Lannefors et al., 1980; Lannefors et al., 1983; Martinsson et al., 1984; Oblad and Selin, 1986; Amundsen et al., 1987; Swietlicki et al., 1989; Comille et al., 1990; Amundsen et al., 1992). These studies showed that the highest pollution levels were associated with air masses originating from the British Isles and eastern and central Europe. In Denmark, Keiding et al. (1986, 1988) and Kronborg et al. (1987) have studied local emissions. LRT models for sulphur (OECD 1979; Eliassen and Saltbones, 1983) and trace elements (Pacyna et al., 1984, 1989) have been developed to study the links between the distant European source areas and the receptor sites in Scandinavia. Rahn and Lowenthal (1984) proposed regional signatures for atmospheric aerosols in the eastern U.S. and, in a similar manner, Swietlicki et al. (1989) determined elemental sector signatures for air masses coming to southern Sweden. This paper presents results from an intensive 23-day atmospheric aerosol sampling campaign conducted during spring, 1988, at Birkenes and Nordmoen, in southern Norway. To ensure the quality of the results versatile sampling and analysis was made. Berner low-pressure impactor was used to measure elemental size distributions which are important parameters in assessing health effects, deposition velocities and origins of aerosol components. Possible sources of various aerosol constituents as well as interelemental concentration ratios in air masses originating from various parts of Europe are discussed. Results of ionic species and more detailed description of the sampling methods are presented elsewhere (Hillamo et al., 1992). -2- 2. EXPERIMENTAL 2.1. Aerosol sampling The aerosol sampling was performed at two locations in southern Norway, i.e., at Birkenes (58°23 ’ N, 8°15 ’ E) and Nordmoen (60° 16' N, 11°06’ E), during the period from 11 April to 4 May, 1988. Birkenes is a rural site situated close to the southernmost tip of Norway. Nordmoen is located 40 km to the north of Oslo and is occasionally influenced by the atmospheric emissions from sources in the Oslo region. The location of the sampling sites and some important regional point sources are presented in Fig. 1. Table 1 gives an overview of the sampling instrumentation used. At the two sites, filter sampling was conducted with a stacked filter unit (SFU). Details about this sampling method and its performance are described in Cahill et al. (1977), Heidam (1981) and John et al. (1983). The sample collection started at about 8:00 in Birkenes and at about 16:00 local time in Nordmoen. Both SFUs collected 24 h samples on two 47-mm diameter Nuclepore polycarbonate filters: an 8.0-pm pore size prefilter and a 0.2-pm pore size back-up filter. The 50% cut-off diameter of the prefilter was about 2 pm equivalent aerodynamic diameter (EAD). At Birkenes there was no sampling on the last day of the campaign (3rd-4th May). The collection of samples 15 and 20 at Nordmoen and of sample 13 at Birkenes failed and, as a result, the total number of valid SFU samples is 21 for both sampling sites. The air flow rate through the SFUs was about 7 litres per min (corresponding total air volume: 10 m3) for the first 7 Birkenes samples and the first 6 Nordmoen samples, but was increased to about 12 litres per min (total air volume: 17 m3) for the remaining samples. This increase in the air flowrate causes some decrease in the 50% cut-off diameter of the prefilter (John et al., 1983). However, it seemed to have only a minor effect on the data obtained, since, for example, the fine to total ratio for S remained virtually unchanged. At Birkenes, a Hauke low pressure impactor (LPI) designed by Berner (Berner, 1984; Berner and Ltirzer, 1980) was used to collect 48 or 72 h samples on poreless Nuclepore polycarbonate film. The substrates collecting coarse particles (EAD >2 pm) were greased with Apiezon L vacuum grease (Hillamo and Kauppinen, 1991). The air volume sampled was about 70 m3 for the 48 h samples and 100 m3 for the 72 h samples. The 50% cut-off diameters of the 10 impactor stages at the nominal flow rate of 25 litres per minute were 0.034, 0.064, 0.092, 0.17, 0.35, 0.57, 1.0, 2.0, 4.0 and 8.0 pm EAD for stages 1 through 10, and the 50% cut-off diameter of the pre-stage was 16 pm EAD. The values for the compressible flow stages (stages 1-6: cut-offs 0.034-0.57 pm EAD) were calibrated experimentally by Hillamo and Kauppinen (1991). Table 2 shows the correspondance between the SFU and LPI samples. At Nordmoen, a so-called impactor low volume sampler (ILVS) was utilized to collect samples in parallel with the SFU. This ILVS contains a 0.4-pm pore size Nuclepore filter, which is preceded by three impaction stages with 50% cut-off points of 2, 6 and 10 pm EAD, respectively, and the device is operated at a flow rate of 15 litres per min. More details about the ILVS are given by Hillamo et al. (1992). -3- 2.2. Analysis The gravimetric, ion chromatograph (IC) and inductively coupled plasma mass spectrometry (ICP-MS) analyses were performed at the Norwegian Institute for Air Research in Norway, and the particle induced X-ray emission (PIXE) and instrumental neutron activation analysis (INAA) measurements were carried out at the Institute of Nuclear Sciences, University of Ghent, Belgium. The analysis schedule and the elements analyzed with each technique are presented in Table 3. While with PIXE and INAA a non-destructive instrumental analysis was carried out (Schutyser et al., 1978; Maenhaut et al., 1981; Maenhaut and Raemdonck, 1984), the ICP-MS analysis involved an acid dissolution step with 0.2 molar nitric acid (Pakkanen et al., 1993) prior to analysis. The ICP-MS measurements were carried out with a VG Plasmaquad instrument using an ordinary scan procedure. Quantification was performed using three acid matched standard solutions. In each of the analytical techniques appropriate blank corrections were carried out. From the blank corrected elemental masses, the particle masses deduced from weighing, and from the volume of flue gas sampled, particulate elemental concentrations in the flue gas (expressed in gg/Nm3) and particle compositions were then derived. The results were combined to produce the final data set used in this paper. However, the dissolution for ICP-MS samples being somwhat inefficient for certain elements, the ICP- MS data was used only to complement other methods with results for Mg, Rb, Mo, Ba and Bi and partly for Cu and Cd. 3. RESULTS AND DISCUSSION 3.1. SFU fine particle mass and elemental concentrations The median concentrations and the 25 and 75 percentile concentrations of selected components in the Birkenes and Nordmoen SFU fine (<2 gm BAD) particle samples are presented in Table 4. For most elements the concentrations were similar at the two sampling sites, with the differences being largest for K, V, Mn, Zn, I, Pb, and for the crustal elements Al, Si and Fe. The median values in Table 4 are similar to those reported in previous aerosol studies for southern Scandinavia (Lannefors et al., 1980; Lannefors et al., 1983; Martinsson et al., 1984; Oblad and Selin, 1987; Amundsen et al., 1987, 1992; Swietlicki et al., 1989; Comille et al., 1990). This suggests that the atmospheric particulate elemental concentrations did not exhibit drastic changes over the past decade. At Nordmoen, very good agreement was observed between the fine particle filter data from the parallel SFU and ILVS samples, but the agreement for the coarse particle fraction was not. as good (Maenhaut et al., 1993a). The daily concentration variation (time trend) of nine typical anthropogenic elements in the Birkenes and Nordmoen SFU fine particle samples is presented in Fig. 2. This figure shows that the concentrations were elevated for samples 4,5 and 6 (episode I) and for samples 16-23 (episode II). The air mass back trajectories (provided by the Norwegian Meteorological Institute, Oslo) showed that the air masses were coming from the British Isles during episode I, but for episode II the back trajectories moved slowly from N-E to S-W, indicating that most of the sampled material had a mixed origin. The time trends for the fine particle mass and various elements were generally fairly parallel at Birkenes and Nordmoen. As these two sampling sites are located at a distance of about 250 km from each other, this parallellism indicates that most of the fine particle pollution elements were long-range transported and did not deposit effectively. However, some differences between the two sites did exist for certain elements, and these differences probably resulted from local and/or regional contributions. The electrical aerosol analyzer and condensation nucleus counter measurements indicated, -4- however, that the aerosols sampled during the campaign had not been generated in the immediate vicinity of the sampling sites. 3.2. Low-pressure impactor (LPI) results and elemental size distributions During this campaign, nine LPI samples were collected at Birkenes, but the first sample was not subjected to PIXE and INAA. Maenhaut et al. (1993a) compared the concentration data from the LPI samples with those from the parallel SFU samples, and they concluded that the agreement was reasonably good in both the fine and coarse size fractions. The comparison for fine particles is presented in Table 5. The elemental size distributions were evaluated for eight LPI samples, but in this paper we only discuss some features of them. Fig. 3 (from Ducastel et al., 1991) shows average size distributions (or mean mass fractions) for selected elements as derived from the eight LPI samples. On the basis of their size distributions the elements could be classified into three groups: 1. Elements with most of their mass in fine particles: S, V, Zn, As, Br, Sb, I, Pb 2. Elements with roughly equal amounts of their mass in fine and coarse particles: K, Mn, Cu, (Mo, Cs, W) 3. Elements with most of their mass in coarse particles: Na, Mg, Al, Si, Cl, Ca, Sc, Ti, Fe, La, Sm All elements from group 1 are known to be emitted in large quantities by various anthropogenic high-temperature sources, but S, Br and I have also large natural (i.e., marine) sources. The group 2 elements, Cu, K and Mn have anthropogenic fine particle sources and crustal rock is a natural coarse particle source for these elements. In group 2 there are also Mo, Cs and W which are in parenthesis because the concentrations of these elements were close to or below the detection limits and therefore the uncertainty in their size distributions is large. The elements of group 3 are mainly of coarse particle crustal and/or marine origin. MICRON inverted (Wolfenbarger and Seinfeld, 1990; 1991) size distributions for selected elements in the LPI sample 9 (represents part of the LRT episode II) are given in Figures 4a and 4b. Figures 4c and 4d show size distributions of selected elements for LPI sample 2, which represents a situation of rather low concentration of pollutant elements. The LPI sample 2 exhibited a high sodium concentration and clearly represented air from marine origin. Table 6 presents the average concentration percentage from total and average mass median diameters (MMD:s) with the corresponding standard deviations or arithmetic differences for the largest , fine particle mode and for the largest coarse particle mode as obtained using TWOMEY algorithm (Winklmayr et al., 1990) on the MICRON inverted LPI data. All the elements examined had one or two modes for fine (BAD <2 pm) and one or two modes for coarse (EAD >2 pm) size fractions. Sometimes, there was a minor mode with center at about 0.08 pm EAD, but probably this mode was in most cases the result of coarse particle bounce off. Support for such explanation was provided by the fact that the elemental ratios to aluminium in that very fine mode were rather similar to the ratios in the particle fraction larger than 4 pm EAD. In certain cases (see sections 3.4 and 3.5), however, this very fine mode appeared to have been created by local and/or regional sources. Table 6 indicates that in spite of the number of modes (normally 3 or 4) the sum of largest fine particle mode and largest coarse particle mode usually accounted for more than 80% from the total -5- concentration. Exceptions are V, As and I for LRT samples and Sb for the other samples. In accordance with the results of Tang et al. (1978) higher average relative humidities (80 and 85% for the LRT samples and 47 - 75% for the rest of the samples) resulted in higher fine particle MMD:s (see Table 6 ). However, it is not known if, and to what extent, the much higher concentrations in the LRT samples (Table 4) may have increased the fine particle MMD:s for these samples. 3.3. Fine to total elemental concentration ratios in the SFU and LPI samples The average values for the fine to total aerosol concentration ratios of selected elements in the Birkenes LPI and SFU samples and in the Nordmoen SFU samples are given in Table 7. For the anthropogenic elements (group 1 in section 3.2) the SFU ratios were similar at both sampling sites with only arsenic and vanadium having slightly lower ratios in Nordmoen. The lower ratio for V in Nordmoen was likely due to higher concentrations of coarse particle crustal rock in Nordmoen, which also explains the differences found for Al, Si, Mn and Fe. Ratios for Cu were lower in Birkenes which may mean that near Nordmoen there was (were) local and/or regional fine particle Cu source(s). The average fine to total concentration ratios of elements in Birkenes were normally similar for SFU and LPI the difference being greatest for Ca and Au. The Au concentrations were low which resulted in large errors in the analysis and probably caused the large SFU-LPI difference. 3.4. Local and regional sources of sampled aerosols Mn The concentration of fine particle Mn at Birkenes is high in samples 3, 8 and 14. These elevated Mn concentrations are found in air masses coming from north and/or north-west of Birkenes which is in accordance with the observations of Comille et al. (1990). The probable origin of this manganese is the regional Mn and Fe industries (see Fig. 1). Also, SFU sample 4 in Nordmoen has a high Mn concentration and the back trajectories suggest that this Mn came from the same Mn source region as mentioned above. Zn and Pb Compared to concentrations in Birkenes samples, zinc and lead concentrations are 3-9 times higher in Nordmoen for samples 1, 2, 3, 4, 9, 17 and 18 which indicates that local and/or regional Pb and Zn sources affected the Nordmoen measurements. The Nordmoen to Birkenes ratios for fine and coarse particle Zn, Pb, Al and Fe generally followed each other for samples 1,2, 3, 4 and 9. Since coarse particle profiles for Al and Fe are indicative of crustal rock, it is probable that the source of additional Zn and Pb in Nordmoen is contaminated local soil or more likely road dust. Another fact supporting this assumption is that the fine to total aerosol ratios of Al and Fe were rather low for the above samples which indicates that there was not much coal fly ash present. Pacyna et al. (1989) also found local zinc in Nordmoen, but assumed that two municipal incinerators near Oslo were responsible. According to the back trajectories, it is likely that these incinerators are responsible for the observed Zn and Pb in samples 17 and 18. -6 - Br and I The median SFU fine particle Nordmoen to Birkenes ratio is 0.84 for Br and 0.62 for I which indicates that these elements are somewhat more abundant at the coastal Birkenes site. The parallel LPI and SFU measurements in Birkenes were compared by Maenhaut et al. (1993a) and the results for some elements are shown in Table 5. Collection of gaseous compounds at filters, except those made of teflon (Harrison and Sturges, 1983) and evaporation from filters (Sturges and Harrison, 1986) can be expected for Br. Nevertheless, results for Br in Table 5 show rather good agreement for LPI and SFU. Separate collections were not made for gaseous composites and it is not known to what extent vapor phase Br was present. The average ratios in Table 5 are rather close to unity, but I shows a low value of 0.48. Large amounts of gaseous Br and I are known to evolve from the sea in spring time (Sturges and Harrison, 1986; Sturges 1990). A possible explanation for the low ratio of I in Table 5 is that during the campaign there was gaseous I present in Birkenes and that SFU nuclepore filters and/or the particulate material on the filters collected gaseous I, but the LPI sampler did not. Another possible explanation is that a part of. the collected particulate I evaporated from the LPI impaction samples. However, one can more likely expect evaporation from the filter samples than from the LPI as was the case for nitrate when teflon filters were used (John et al., 1988). As and Sb Median Nordmoen to Birkenes ratios for fine particle SFU samples were 0.74 for As and 0.76 for Sb, indicating that these elements had somwhat higher concentrations at the coastal Birkenes site. A very large difference was observed for SFU samples 3, 4 and 5: compared to Nordmoen, the SFU As and Sb concentrations were three-fold higher in Birkenes for sample 4 (Sb also for sample 3) and 2 to 5 fold lower for sample 5. Moreover, impactor sample 2 (LPI 2) in Birkenes showed a three-fold lower concentration for As, and ten-fold lower for Sb than the corresponding Birkenes SFU samples 3 and 4. It is unlikely that these observations were due to analytical errors since some other elements analysed by INAA (K, V and Mn) showed good agreement for this comparison. Also, for all other samples the agreement between LPI and SFU results was much better for As and Sb. According to Nriagu (1988) coal combustion, smelters and refuse incinerators are important sources for fine particle As and Sb. Nevertheless, one possible explanation for the above observations is that there was a cloud of gaseous As and Sb moving with the air masses from south-west to north-east. If so, it can also be suggested that gaseous As and Sb, similarly to gaseous Br and I, were collected by the fine particle filter and/or the particulate material on the filter of SFU sample 4. Although this hypothesis is based on data from only few samples, there is some evidence in the literature indicating that the assumption is possible. Austin and Millward (1988) proposed that a large unknown vapour source for Sb exists and that perhaps the oceans are this source. Biovolatilization has been demonstrated for As (Cox and Alexander, 1973, Johnson and Braman, 1975) and Sb undergoes biomethylation in the aquatic environment in the same manner as arsenic (Andreae et. al., 1981). The SFU samples 3 and 4 and the corresponding LPI sample 2 were strongly influenced by marine aerosols as indicated by the huge amount of Na in these samples. Thus, there is the possibility that the observed additional As and Sb originated from the sea. Impactor collection was not performed in Nordmoen and therefore, it was not possible to determine if similar LPI - SFU disagreement occured at Nordmoen for the SFU sample 5. -7- Si Silicon is present in extremely high concentrations as fine particles for SFU samples 6 and 7 from Birkenes. The Si size distribution for the corresponding LPI sample (LPI-3) is totally different from those of the other LPI samples (Fig. 3). This fine particle Si most likely originates from silicon industries in southern Norway (Comille et al., 1990; see also Fig. 1). K Potassium was sometimes present in high concentrations in the fine particle mode. Contributions from crustal rock, using Al as reference (Mason, 1966), and from sea spray (ref. element Na) were subtracted from the total fine particle K and thus fine K, originating from sources other than above mentioned, was obtained. In Birkenes and Nordmoen the mean percentage of this additional fine K for samples 1 to 9 was 43% and 70%, respectively and the percentage range was 0-82% and 38-93%, respectively. Coal fly ash is not expected to be responsible for this additional K since K and Al have a similar ratio in crustal rock and fine particle coal fly ash (Kauppinen and Pakkanen, 1990). Most of this additional K likely originated from biomass burning (Stevens, 1985; Calloway et. al., 1989) and/or from incinerators (Dzubay et al., 1988). 3.5. Relative size distributions method (RSD method) for estimating aerosol sources Elemental ratios to aluminium and to sodium are used for evaluation of elemental enrichment factors for crustal rock particles and marine aerosols, respectively. These enrichment factors are useful for bulk samples or coarse particles since atmospheric aluminium and sodium mostly exist as coarse particles. These two elements are in rather low concentrations in fine particles which increases uncertainty in the analysis of these elements in fine aerosol fractions. Moreover, the fine particle aluminium and sodium may no more originate from crustal dust and sea but from other sources (e.g. combustion processes). Compared to the above enrichment factors the RSD method is more useful when fine particles and aerosol sources are studied. The RSD curves for LPI samples are calculated as follows: - the concentration of element E in stage 5 is multiplied by a factor that makes this concentration equal to the concentration of a reference element in stage 5 - the concentrations of E in the other stages are multiplied by the same factor - the ratios of the obtained normalized concentrations of E to the reference element concentrations are calculated for each stage (ratio is 1 for stage 5) In other words: i) the concentrations of element E in all the LPI stages are multiplied by a factor that makes the concentrations of E and the reference element in stage 5 equal, and ii) ratio of the normalized E concentrations to reference element concentrations are calculated for each stage. Stage 5 (50% cut-off = 0.37 pm EAD) was selected as the normalization point because the concentrations of pollutant elements are high for this stage and the relative analysis errors are at their minimum. Sulphur was selected as the reference element since i) sulphur was usually present as measurable concentrations in all LPI stages, and ii) the shape of sulphur size distributions (see Figures 4a and 4d) is such that the obtained RSD values are usually higher than one. However, depending on the sampling site and analysis methods available, some other element may be more useful as reference. For instance, Dodd et al. (1991) used Se and Maenhaut et al. (1993b) used total mass as reference component, but for 8 21405 -8- a different context. Figures 5a, 5b and 5c show RSD values for selected elements with S as reference element (=RSD(S) values). Fig. 5a represents the LRT episode I where the air masses came from the British Isles (LPI sample 3) and Fig. 5b represents LRT episode II with air coming from Central Europe (LPI sample 9). Fig. 5c (LPI sample 2) describes a situation where local sources of certain elements affected strongly the RSD(S) curves of these elements. To verify the influence of local sources to the RSD(S) curves the normalized Pb to sulphur ratio curves (nPb/S curves) were calculated for three different LPI samples collected in June, 1987, in the centre of Helsinki, capital of Finland. These nPb/S curves, presented in Fig. 5d, appeared to be nearly identical and reached values between 8 and 15 for coarse particles which was 2 - 3 times higher values than those of Cd and V. The'influence of local sources (car traffic) was even more dramatic for fine particles: for LPI stage 2 (50% cut- off = 0.069 Jim) these curves showed values 20 - 32 and for stage 1 (50% cut-off = 0.042 pm) the values were 120 - 240, which was 20 - 50 times higher values than for the other measured elements in these LPI samples. Thus, a sign of local sources is high RSD(S) values for fine particles and slightly elevated RSD(S) values for coarse particles. In Fig. 5b Mn has very high nMn/S values of 184 and 80 for stages 1 and 2, respectively. Also in the figures 5a and 5c Mn has high nMn/S values compared to several other elements. As presented above, high RSD(S) values for fine particles is a sign of local sources. In Fig. 5a the curves of K and Mn follow each other closely from stage 1 to stage 9. Also in Fig. 5b there are similarities between the nK/S and nMn/S curves, with Mn curve being steeper on both sides. These steeper wings of the RSD(S) curve of Mn may mean that the Mn source(s) is closer to the sampling site and/or is stronger than the K source(s). In Fig. 5c the nK/S values of stages 1 and 2 are missing (K values were below detection limits) but K and Mn follow each other closely in the stages 3 - 7. It really looks like similarly to Mn also K had local fine particle sources. In the Figures 5b and 5c I has high values for fine particles. Sturges and Harrison (1986) have shown that during spring time gaseous I compounds are released from sea and it is possible that these I compounds are involved. The crustal rock and sea salt elements Al, Si, Ca, Fe, Ti, Na and Cl form their own group of similar (high ratios for coarse particles) RSD(S) curves but these elements, being mostly of natural origin, are not inspected here. Cu, K and Mn have rather high values for coarse particles because of contribution from crustal rock. Crustal rock consists also of V which can be seen in the slightly elevated nV/S values in Fig. 5b. The nZn/S curves have a special (typical?) shape in the Figures 5a and 5c and also LPI samples 5 and 7 and to some extent also LPI sample 4 showed similar nZn/S curves. Often the nZn/S curves were clearly different from the other RSD(S) curves which might be an indication of different sources (probably local and/or regional source as discussed in section 3.4). In Fig. 5c (LPI sample 2) for stage 9, Sb has a value of 12 which is high compared to the other pollutant elements. Moreover, for stages 1 and 2 Sb shows high nSb/S values of 38 and 15, respectively, which were the highest nSb/S values during this campaign. The case of Sb is discussed also in section 3.4 and there we speculate that gaseous Sb compounds may have been involved. Elements with similar RSD(S) curves for fine (stages 1-6) and coarse (stages 7 - 10) particles are grouped in Table 8. Although the RSD(S) curves are somewhat different in the different LPI samples the groups of elements in Table 8 are similar for fine particles. As, Br, I, Sb, and V are in the same group in all three samples. Occasionally, the behaviour of K, Mn, Pb, S and Zn differs from group 1 elements. Overall, the RSD method was capable to reveal the same local and/or regional sources as discussed in the section 3.4. The reason for -9- this special capability of the RSD method is probably based on phenomena like physical and chemical state of components, condensation rates of different gases and coagulation rates of particles of different composition and size. Meteorological parameters may also affect the RSD curves and thus make the interpretation more complicated. To give a more reliable explanation for the RSD(S) curves, a much larger number of these curves should be inspected. 3.6. Interelemental ratios 3.6.1. Interelemental ratios to excess V in southern Norway In order to study interelemental ratios for air masses of different geographical origins, a sector division similar to that used by Amundsen et al. (1992) was employed for Birkenes and is shown in Fig. 6. For Nordmoen the sectors were drawn to be as similar as possible to the Birkenes sectors. Vanadium not associated to crustal rock (excess vanadium = VX) was chosen as a reference element since no major local contribution was found for this element at the sampling sites. A drawback of using VX as a reference is the correction for crustal rock contribution which may cause additional error. Elemental to VX fine particle mass ratios and the corresponding sectors and samples are presented in Table 9. Only samples with one or two dominating sectors were included. The ratios presented in Table 9 are based on only a few samples and are thus preliminary. A common feature of data in Table 9 is that the ratios were clearly higher in the air masses coming from W, NW, N or NE (sectors 8,1 and 2). This is because major vanadium sources, such as burning of fuel oil to produce electricity and heat, are situated south of the sampling sites. The contribution of local sources of K, Zn and Pb in Nordmoen is obvious when the ratios for sectors 8+1 and 1+2 are compared between the two sites. At each site, sectors 5 and 6 had similar ratios, the difference being largest for S, Zn, As, Br and Sb. Also, sectors 5 and 6 had similar ratios at the two sites due to the high episodic concentrations of these elements in samples 5, 6 , 22 and 23 which masked the local differences. Combined sectors 1 and 8 had much higher ratios of K, Zn (Nordmoen), As, Br, I, and excess Mn (MnX) and Pb (Nordmoen) when compared to combined sectors 1 and 2. Especially for Nordmoen there was a strong local (or regional) contribution for several elements when the combined sector 1+8 samples were collected. In Birkenes, the sector 3 ratios for most of the elements fall between the values found in northerly and southerly air masses, which is acceptable considering the location of emission source regions. For Nordmoen, the trajectories of sector 3 samples were spread to sectors 2 and 4 and passed close to Oslo. Nevertheless, the Nordmoen "sector 3" data is included in Table 9 for comparison. The Nordmoen-Birkenes difference for sector 3 data is especially large for K, Zn, Pb and Bi. Since K and Zn are known to be emitted from refuse incinerators it may be possible that also Bi originated from this source. 3.6.2. Comparison of interelemental ratios in air masses coming from U.K. to southern Norway and to southern Sweden The preliminary interelemental ratios measured in this work for the United Kingdom (Table 9, sector 6 ) and the Great Britain signature of Swietlicki et al. (1989) are compared in Table 10. The original elemental ratios to nickel of Swietlicki et al. were recalculated as elemental ratios to vanadium. In this work, VX and MnX was used, but this had very little impact since the crustal rock contribution to fine particle mode was small for the measured sector 6 values. Sector 6 ratios were similar in Birkenes and Nordmoen and these values were combined to -10- obtain the arithmetic average of four samples. Swietlicki et al. (1989) presented their signatures as a geometric mean of single ratios, but this causes only a small difference. In this work, the elemental ratios to VX were typically consistent for all four samples, but one outlier had to be excluded from the As/VX and Sb/VX ratios. Also, Na/VX ratios showed large variability and therefore this ratio is presented in brackets in Table 10. Ratios for Cd and Cr are based on only two samples and are purely indicative. For the important tracer elements Mn, Cu, Ni, Zn, Br and Pb, the ratios measured in this work were strikingly similar to those of Swietlicki et al. (1989). 3.6.3. Comparison of interelemental ratios in emissions in U K. and in air masses coming from U.K. to Norway In Table 11, interelemental ratios measured in this work (1988) in Norway for air masses originating from UK are compared to element emission ratios in UK in 1979 (Pacyna, 1983). There is a difference of nine years for this comparison but with the exception of lead, the emissions are believed to be rathenunchanged within this nine years period. The agreement is within a factor of 2 for As, Cu, Mn and Pb, but Sb and Zn agree poorly. The local emissions of Sb and Zn near Birkenes and Nordmoen, discussed earlier in this paper, may be one important reason for the disagreement. 4. CONCLUSIONS During the eighties, the concentration levels of several pollutant elements have been rather stable in southern Scandinavia. In this work, the long-range transport episodes from U.K. and from Central and eastern Europe were found to increase the concentrations of pollutant elements to a level 20-50 times higher than the background concentrations. The size distributions of the investigated elements, measured using Berner low-pressure impactors, usually showed one or two modes in the fine particle range and one or two modes in the coarse particle range. Relative humidity values higher than about 80% resulted in significant increase of the MMD:s of the largest fine particle mode. The SFU samplers used at the two sampling sites and the LPI sampler used at Birkenes site showed similar average values for elemental fine particle to total aerosol ratios. Use of conventional methods showed that important local and/or regional sources of Si, K, Mn, Zn, Br, I, As, Sb and Pb existed in southern Norway. The existence of most of these sources could be verified by use of the relative size distributions method (RSD method). Interelemental ratios in air masses of different geographical origin were calculated for the two sampling sites. The elemental ratios in air masses coming from U.K. to southern Norway (this work) and to southern Sweden (Swietlicki et al., 1989) were strikingly similar for several pollutant elements. Also, for some elements the emission ratios in U.K. were similar to the interelemental ratios measured in this work for air masses coming from U.K.. -11- ACKNOWLEDGEMENTS The measurements presented in this paper were financially supported by a grant from Norges allmennvitenskapelige forskningsrad (NAVF) and by the Maj and Tor Nesslings foundation. W.M. and G.D. acknowledge support from the Belgian "Nationaal Ponds voor Wetenschap- pelijk Onderzoek", the "Interuniversitair Instituut voor Kemwetenschappen", the "Instituut tot Aanmoediging van het Wetenschappelijk Onderzoek in Nijverheid en Landbouw", and the Impulse Programme "Global Change" supported by the Belgian State - Prime Minister ’s Service - Science Policy Office. Thanks are also due to Dr. Sylvain M. Joffire for his constructive comments and to Mr. Jan Cafmeyer for technical assistance. REFERENCES Amundsen C.E., Hanssen J.E., Rambaek J.P., Semb A. and Steinnes E. 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(1990) Excess particulate and gaseous bromine at a remote coastal location. Atmospheric Environment 24A, 167-171. Swietlicki E., Hansson H.-C., Svantesson B. and Asking L. (1989) European source region identification of long range transported aerosol. In: Swietlicki E., European Source Region Identification of Long Range Transported Ambient Aerosol Based on PIXE Analysis and Related Techniques. Thesis, LUTFD2/(TFKF-1015), Department of Nuclear Physics, Lund University, Lund, Sweden, pp. 79-117. Tang I.N., Munkelwitz H.R. and Davis J.G. (1978) Aerosol growth studies - IV. Phase transformation of mixed salt aerosols in a moist atmosphere. J. Aerosol Sci. 9, 505-511. Winklmayr W., Wang H.-C. and John W. (1990) Adaptation of the Twomey algorithm to the inversion of cascade impactor data. AerosolSci. Technol. 13, 322-331. Wolfenbarger J.K. and Seinfeld J.H. (1990) Inversion of aerosol size distribution data. J. AerosolSci. 21, 227-247. Wolfenbarger J.K. and Seinfeld J.H. (1991) Regularized solutions to the aerosol data inversion problem. SIAM J. Sci. Stat. Comp. 12, 342-361. Table 1. The sampling instrumentation and duration of the sampling periods Site Sampler Duration Birkenes stacked filter unit (SFU) 24 h Hauke 25/0.015 low pressure impactor (LPI) 48 or 72h electrical aerosol analyzer, TSI model 3030 continuous Nordmoen stacked filter unit (SFU) 24 h filter sampler with two pre-impactors (ILVS) 24 h condensation nucleus counter, TSI model 3020 continuous Table 2. Corresponding SFU and LPI samples for Birkenes Date SFU LPI April 11 1 1 12 2 1 13 3 2 14 4 2 15 5 3 16 6 3 17 7 3 18 8 4 19 9 4 20 10 5 21 11 5 22 12 6 23 13 6 24 14 6 25 15 7 26 16 7 27 17 8 28 18 8 29 19 9 30 20 9 May 1 21 9 2 22 Table 3. The analysis schedule and the elements analyzed with each technique. Sampler Analysis method Species measured SFU gravimetric (fine particles only) mass PIXE elements INAA elements 1C (only Birkenes fine particles) so 4-s, nh 4-n , no 3-n ICP-MS (only Birk. fine particles) elements ILVS gravimetric mass PIXE elements INAA elements 1C (only fine particles) so 4-s, nh 4-n ICP-MS (only fine particles) elements LPI gravimetric mass PIXE elements INAA elements 1C (some samples only) so 4-s, nh 4-n , no 3-n ICP-MS (some samples only) elements Analysis method Species analyzed PIXE Si, P, S, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Se, Rb, Sr, Zr, Pb INAA Na, Mg, Al, Cl, K, Sc, V, Cr, Mn, Co, Ga, As, Br, Mo, Ag, Cd, In, Sn, Sb, I, Cs, Ba, La, Ce, Sm, Eu, Lu, W, Au, Th ICP-MS Li, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Rb, Sr, Mo, Cd, Sn, Sb, Cs, Ba, La, TI, Pb, Bi, Th 1C NH4-N, S04-S, no 3-n Table 4. The 25, 50 and 75 percentiles of the aerosol mass and elemental concentrations in the fine fraction of SFU (ILVS samples for Mg, Cu, Rb, Mo, Cd, Ba, Bi, S04-S, N03-N and NH4-N at Nordmoen) samples at Birkenes and Nordmoen. Aerosol mass concentration in pg/m 3 and elemental concentrations in ng/m 3. Birkenes Nordmoen Ele. 25 50 75 25 50 75 Na 39 50 125 31 64 84 Mg 7 10 49 2.7 5.7 9.5 Al 10 13 35 18 23 41 Si <29 45 74 50 65 123 S 261 371 1210 194 264 1318 Cl <47 <60 <79 <15 20 27 K 15 24 45 27 45 72 Ca 8 13 17 13 15 23 Sc <0.02 <0.02 <0.03 <0.008 <0.008 0.008 Ti <1.0 <2.1 2.1 <1.2 1.6 2.7 V 0.26 ■ 0.56 2.3 0.14 0.37 1.7 Cr <2.2 <2.7 <3.8 <2.3 <2.9 <3.9 Mn 1.2 2.2 3.9 0.8 1.4 3.0 Fe 7 13 24 11 26 35 Co <0.2 <0.3 <0.3 <0.12 <0.12 0.12 Ni <0.5 <0.63 0.63 <0.5 <0.5 <0.8 Cu <0.5 <0.6 0.81 <0.4 0.46 0.82 Zn 2.6 5.9 9.5 4.1 13 20 Ga <0.2 <0.2 <0.5 <0.1 <0.2 <0.3 As 0.21 0.33 0.62 0.14 0.31 0.74 Se <0.3 <0.4 <0.5 <0.4 <0.4 <0.5 Br 1.7 2.6 4.3 1.3 2.2 4.7 Rb <0.4 <0.4 0.61 <0.1 0.22 0.42 Mo 0.09 0.13 0.28 <0.02 0.02 0.18. Cd <0.8 <0.9 <1.2 <0.06 0.06 0.29 In <0.007 <0.008 <0.013 <0.005 <0.005 <0.007 Sb 0.09 0.25 0.43 0.07 0.23 0.55 1 1.4 1.8 2.7 0.8 1.1 2.0 Cs 0.13 0.17 0.23 0.08 0.10 0.13 Ba 0.16 0.26 0.61 <0.1 0.20 0.56 La <0.03 <0.03 0.031 0.02 0.04 0.04 Sm <0.003 <0.005 0.005 <0.003 <0.004 0.005 W <0.06 <0.08 0.08 <0.06 <0.07 <0.11 Au 0.0019 0.0022 0.0028 <0.002 <0.002 0.0028 Pb 1.8 3.6 7.0 1.8 9.3 19 Bi 0.020 0.038 0.082 <0.002 <0.002 0.007 mass 3.1 4.5 12.6 2.7 4.7 13.0 so 4-s 95 340 1170 180 250 1310 N03-N DL: detection limit *: no data Table 5. Average fine particle LPI to SFU ratios and associated standard deviations for selected elements at Birkenes (from Maenhaut el al., 1992) Element x ± s [N] Na 0.66 ± 0.15 [7] Al 0.79 ± 0.17 7 Si 1.20 ± 0.39 6 S 1.30 ± 0.19 7 K 1.09 ± 0.20 7 Ca 0.67 + 0.18 7 Ti 0.61 ± 0.27 4 V 0.83 ± 0.19 7 Mn 1.06 ± 0.29 6 Fe 1.05 ± 0.36 6 Cu 1.15 + 0.37 3 Zn 1.21 ± 0.33 6 As 1.14 + 0.36 5 Br 0.89 ± 0.31 5 Sb 0.84 ± 0.34 6 I 0.48 ± 0.14 7 Cs 0.77 ± 0.23 3 La 0.50 + 0.24 4 Sm 0.31 + 0.19 6 Pb 1.24 ± 0.47 [5' mass 0.82 + 0.17 [5] "N is the number of samples used in the comparison. Table 6. Average mass median diameters (MMD) and average concentration percentage from total (conc.%) and corresponding standard deviations (std) for largest modes of fine and coarse particles as obtained using TWOMEY algorithm on LPI data. Results are separately for the LRT-episodes (LPI samples 3 and 9; average relative humidities 80 and 85%) and for LPI samples 2, 4, 5, 6, 7 and 8 (average relative humidities 47 - 75%). Instead of std:s the FtiEt9tet^iff erence is presented for the two LRT samples. Number of inspected samples is LPI samples 2, 4, 5, 6, 7 and 8 LPI samples 3 and 9 (LRT samples) average RH = 47 - 75% average RH = 80 and 85% elem. MMD std [#] conc.% std [#] MMD conc.% S f 0.419 ±0.034 [6] 86 ±10 [6] 0.838 ±0.081 82 ±2 c 2.95 ±0.72 [6] 10 ±10 [6] 3.94 ±1.50 4 ±3 sum 96 86 K f 0.354 ±0.063 [6] 32 ±18 [3] 0.915 ±0.166 47 ±1 c 4.92 ±1.21 [6] 59 ±26 [3] 5.08 ±0.83 43 ±4 sum 91 90 V f 0.321 ±0.061 [5] 56 ±11 [5] 0.714 ±0.161 50 ±2 c 5.39 ±0.72 [5] 26 ±11 [5] 4.13 ±0.03 16 ±2 sum 82 66 Mn f 1.11 ±0.25 [4] 51 ±7 [5] 1.07 ±0.43 41 ±2 c 5.57 ±0.37 [5] 43 ±9 [5] 4.50 ±0.71 49 ±11 sum 94 90 Fe f 1.16 ±0.34 [5] 14 ±5 [6] 0.808 ±0.283 20 ±1 c 5.61 ±1.14 [6] 81 ±7 [6] 4.98 ±1.04 79 ±1 sum 95 99 Cu f 0.851 ±0.300 41 ±13 c - - 5.02 ±1.52 55 ±11 sum - 96 Zn f 0.597 ±0.210 [5] 65 ±15 [5] 1.21 ±0.24 51 ±10 c 4.55 ±1.11 [6] 15 ±6 [5] 4.34 ±1.37 29 ±17 sum 80 80 As f 0.333 ±0.086 [4] * 0.955 ±0.136 63 ±3 c 4.00 ±0.81 [4] * 4.52 ±0.22 12 ±5 sum * 75 Sb f 0.297 ±0.042 [6] 39 ±8 [4] 0.724 ±0.109 69 ±4 c 4.97 ±0.71 [5] 23 ±15 [6] 3.87 ±0.04 17 ±10 sum 62 86 I f 0.390 ±0.024 [5] 66 ±15 [5] 0.726 ±0.144 60 ±8 c 2.24 ±0.29 [4] 15 ±9 [5] 4.13 ±0.10 9 ±4 sum 81 69 Pb f 0.324 ±0.083 [5] 70 ±21 [4] 0.650 ±0.293 73 ±6 c 3.56 ±1.13 [4] 15 ±2 [4] 3.47 ±1.40 20 ±12 sum 85 93 #: number of samples f: largest fine particle (BAD < 2 pm) mode c: largest coarse particle (BAD > 2 pm) mode sum: sum of largest fine and largest coarse mode for percentage from total concentration no data *: concentrations could not be well calculated with the TWOMEY algorithm Table 7. Average fine to total concentration ratios and associated standard deviations for the Birkenes LPI and SFU samples and for the Nordmoen SFU samples (the number of samples is indicated in brackets). Note: the fine to total ratios for the LPI samples were defined as the ratio of the particle or element mass in the fine fraction (sum of stages 1 through 7) to the total particle or element mass (sum of stages 1 through 10). Birkenes Nordmoen LPI SFU SFU Ele. x ± s [N] x±s [N] x±s [N] Na 0.29 ±0.11 [8 0.37± 0.11 [21] 0.39± 0.10 [21] Mg 0.24 ±0.11 6 0.37± 0.08 [3 Al 0.26 ±0.10 8 0.25± 0.11 21 0.16± 0.04 [21 Si 0.30 ±0.27 8 0.31 ± 0.23 15 0.20± 0.10 [21 S 0.88 ±0.05 8 0.84± 0.07 20 0.87± 0.07 [21 Cl 0:52 ±0.34 8 0.56± 0.18 [9 K 0.48 ±0.12 8 0.48± 0.13 20] 0.48± 0.10 [21 Ca 0.14 ±0.04 8 0.22± 0.10 16] 0.20± 0.07 [21 Sc 0.16 ±0.05 6 0.18± 0.04 [7 Ti 0.15 ±0.04 61 0.21 ± 0.08 8] 0.17± 0.08 [12 V 0.77 ±0.09 8 0.71 ± 0.11 20] 0.55± 0.19 [21 Mn 0.51 ±0.08 8 0.51 ± 0.08 20] 0.33± 0.10 21 Fe 0.28 ±0.09 8 0.30± 0.13 21] 0.24± 0.07 [21 Co 0.52 ±0.30 5 0.58± 0.10 11] 0.44± 0.06 [10: Ni 0.91 ±0.21 5 Cu 0.42 ±0.14 4 0.41 ± 0.14 7] 0.71 ± 0.28 [9" Zn 0.77 ±0.06 8 0.71 ± 0.13 [18] 0.74± 0.10 [21 j Ga 0.80 ±0.39 6 As 0.85 ±0.06 8 0.85± 0.12 [17] 0.73± 0.18 [17] Se 0.76 ±0.19 8 Br 0.87 ±0.15 8 Mo 0.66 ±0.20 7 In 0.93 ±0.18 6 0.50± 0.09 [3 Sb 0.77 ±0.13 8 0.79± 0.15 [1 7 0.81 ± 0.08 [14 I 0.90 ±0.09 8 0.88± 0.04 [1 6 0.89± 0.05 [15 Cs 0.75 ±0.17 4 0.74+ 0.06 5 0.66± 0.05 [7 La 0.26 ±0.13 6 0.28+ 0.11 8 0.26± 0.10 [20 Sm 0.18 ±0.07 r8 0.23± 0.08 [8 0.17± 0.05 [15 Eu 0.67 ±0.16 8 0.55± 0.07 5 0.47± 0.07 [7 W 0.70 ±0.17 7 0.53± 0.11 [1 1 0.43± 0.07 [14 Au 0.67 ±0.28 [8 0.25± 0.12 6 Pb 0.90 ±0.07 8 0.77± 0.05 [1 0 0.78± 0.07 [141 mass .0.77 ±0.12 7] 0.71 ± 0.13 [23]* : from ILVS data Table 8. Grouping of elements with similar RSD(S) values for fine and coarse particles. Fine particles Group BLPI-3 BLPI-9 BLPI-2 F1 As,Br,l,Pb,S,Sb,V,Zn As,Br,l,K,Sb,V l,K,Sb F2 K, Mn S,(Fe) S F3 Pb,Zn,(Cu) Mn,(As,V) F4 Mn Coarse particles Group BLPI-3 BLPI-9 BLPI-2 C1 I.Pb.S.V As,Br,l,Pb,S,Sb,V s,v C2 As.Br.Sb Zn As, I C3 Cu,K,Mn,Zn Cu,K,Mn Sb 04 K C5 Mn.Zn Table 9. Average elemental ratios to excess vanadium for fine particles as obtained from the SFU samples (ILVS samples for NH4-N, Mg, Mo, Ba and Bi at Nordmoen). Sector(see Fig.6) 1+8 1+2 3# 5 6 Samples 1,2,3 12-16 17,18# 22,23 5,6 nh 4-n Birk 990. D 600. D 610 740 440 Nord 340. D 980 1170. # 420 500 Mg Birk „ (390) 17. D (14) - (11) Nord 320. D - (6.7) # 2.4 4.6* S Birk 3100 1400. D 760 740* 160 Nord 3200 (2800) 1740. # 495 250 K Birk (150) (55) 47 21* 15 Nord 620 (130) 197.# 17 17 Ca Birk (150) (47) 25 4.3* (7.1) Nord 290 (75) 50. # 4.6 5.4 D MnX Birk 32. D (6.4) (2-9) 1.1* 0.67 Nord (8.0) (3.0) 2.5# (1.2) (0.82) Fe Birk 49 (55) 36 12* (12) Nord 360 (69) 79.# 10.5 (11) Ni Birk _ _ - 0.28* 0.38 Nord - - 0.34 0.34 Cu Birk 0.69 0.37* 0.39 Nord - - 1.5# 0.43 (0.36) Zn Birk 14. D (12) 10.4 7.6* 5.1 Nord 85 (24) 89. D# 8.7 (4.9) As Birk (2.6) (0.75) (0.56) 0.38* 0.09 [ Nord 2.3 (1.1) 1.12# 0.27 0.17 Br Birk 18 (11) (3.8) 1.8* 0.73 Nord 48. D (9.2) (8.5) # 1.9 (1.1) Mo Birk 0.66 - 0.25 0.1* (0.092] Nord - - (0.27) # 0.041 (0.037] Cd Birk _ _ _ _ Nord 2.4 D - 0.86# 0.12* 0.05* Sb Birk 1.5 D 0.31 D 0.31* 0.26* 0.09 [ Nord 1.3 (0.79) 0.78# 0.24 (0.18) 1 Birk 20 (8.1) (2.4) 1.1* 0.75 Nord 16 (12) 4.3# 0.48 (0.65) Ba Birk 0.79 1.1 D 0.38 0.13* 0.16 Nord 2.3 D - 0.96# 0.36 D 0.03* Pb Birk (10) 6.2 6.2* 4.2 Nord 125. D 16. D 33.# (9.8) (5.5) Bi Birk 0.31 (0.040) 0.022* 0.15 Nord 0.09 D " 0.32# - 0.004' Birk : Birkenes value(s) below detection limit(s) Nord : Nordmoen *: value based on one measurement only no parentheses or code : lowest value larger than 75% of the highest (): lowest value 50-75% of the highest D : lowest value less than 50% of the highest # : trajectors for sector 3 at Nordmoen were slightly spread to sectors 2 and 4 Table 10. Comparison of elemental ratios to vanadium or excess vanadium (VX) in air masses coming from the British Isles for this work as measured for the SFU samples (number of samples in brackets) and for the Great Britain signature of Swietlicki et al. (1989). Ratios of Mg, Mo, Ba and Bi are from ILVS samples for Nordmoen. This work Swietlicki etal. (1989) sector 6 sector G Elem. ratios to VX ratios to V Na (34) [4] 145 S 208 [4] 431 K 16 [4] 24.9 Ca 6.3 [4] 12.0 Ti 0.56 [4] 1.09 Mn 0.75 [4] 0.62 Fe 12 [4] 9.4 Ni 0.36 [4] 0.41 Cu 0.38 [4] 0.36 Zn 5.0 [4] 4.9 Br 0.91 [4] 1.07 Pb 4.8 [4] 4.9 Mg 8.6 [3] Cr (0.65) [21 As 0.15 [3] Se 0.18 [3] Mo 0.065 [4] Cd (0.10) [2] Sb 0.17 [3] 1 0.70 [4] Ba 0.12 [3] Bi 0.10 [3] nh 4-n 470 [4] Table 11. Comparison of interelement ratios, as measured in air masses coming from the U.K. to Norway, with estimated interelement emission ratios in the U.K. Measured in this Estimated emission work in Norway, ratios in U.K. in 1979 in 1988 (Pacyna, 1983) AsAZ 0.15 0.078 CuAZ 0.38 0.28 MnAZ 0.75 0.49 PbAZ 4.8 4.8 Sb/V 0.17 0.019 Zn/V 5.0 1.7 9 21405 9* Figure 1. The sampling sites, Birkenes and Nordmoen, and some regional aerosol sources. ------u---- V(B):100 — V(N):100 ------♦— Mn(B):20 —o— Mn(N):20 ------* ---- Br(B) 0.01 ------A— Br(N) ------e— l(B):5 0.001 T ------0— I(N):5 0.0001 H—I—I—I—t- H—I—I—I—I—I—I MCO'JlO'OMOO'O'-WtOtlflONeOO'O^Nn SAMPLE NUMBER 2b 1000 T I M I I m m I M I I ! I I M I I IN MI I m M I I ------■------S(B):10 —a------100 - • | | | | S(N):10 ------1------Zn(B) ------0------Zn(N) ------* ------As(B) ------A------As(N) ------e------Sb(B):5 1! i&N-MTi 11 —°— Sb(N):5 0.01 - ii 111111 in 11 n ! IThM-m j 1111111111 Pb(B):5 Pb(N):5 0.001 -i—i—i—i—i—i—i—i—i—i—i—i—i—)—i—i—i—i—i—i CNicO^LOONCOOOr— (NCO^LO'ONCOOOr-CNcO r— i— F— F— r— r— f— «— CN CN CN CN SAMPLE NUMBER Figures la and 2b. Time trends of selected elements for Birkenes and Nordmoen SFU samples (B stands for Birkenes and N for Nordmoen). 0062 016 052 0062 0.16 052 1.9 7.6 6062 016 052 1.8 0032 0090 033 0 95 3.8 0032 0090 033 OSS 36 0032 0080 032 095 3 8 iili I i ii ii i i if TTTTTT C! x 25 MS *20 No s 5.8 Si S3 * 12 V *L9 Br * 636 Cu x 01 ULjJj. Mill 1 1 I I 1 I I if I 12345678910 1 23456789 10 1 2 3 5 6 7 8 9 10 STAGE NUMBER Figure 3. Average size distributions, as derived from the LPI samples (mean mass fractions and standard deviations). For Si separate data are given for sample no. 3. MS is the aerosol mass. (Figure is taken from Ducastel et al., 1991. m/dlog(Dp), ng/m3 dm/dlog(Dp), n g / concentration The Figure and LPI-9 LPI-2 — 1991) left Particle Particle As 4. hand Size 0,1 0.1 was scales, distributions and used Diameter, Diameter, 4a 4c the respectively. in 1 1 the right evaluation of hand yu,m selected /zm 10 10 Inversion legends * • of - - • - elements 3000 4000 0.4 0.5 1.2 1000 1.0 the code correspond curves. for MICRON LPI . LPI-9 LPl-2 ------ to samples Particle Particle Mn the (Wolfenbarger 0.1 0.1 left 9 (a hand Diameter, Diameter, 4b 4d and and b) 1 and 1 and the Seinfeld, 2 right /zm /xm ------(c 10 10 and K hand 1990 . d). • • • * • - ■ 200 300 400 500 800 900 600 700 1100 ' ------a----- V/SX202 —n — Mn/Sx249 ------4------Zn/Sx84 —®— As/SlOOO ------A------Sb/S1590 —&— 1/5x405 ------e------Pb/Sx22.5 ------O— Br/Sx331 K/SX16 Particle diameter, pm ------■----— V/SX1495 — Mn/Sxl280 ------♦---- Zn/Sxl42 — As/Sx2140 ------* ---- Sb/Sx2750 ------A— 1/5x1960 ------e— Pb/Sxl23 — Br/Sx830 ------X—— K/Sx59 ------X—— Cu/Sx3740 Particle diameter, pm Figures 5a and 5b. Selected RSD(S)-curves for LPI-3 and LPI-9. ------1------V/Sx880 Mn/Sx3C0 Zn/Sx230 ------0------As/Sx5200 ------X------Sb/Sx 11300 ------6------1/5x880 Pb/Sx310 ------0------K/Sx62 Fe/Sxl90 Particle diameter, pm Helsinki, summer 1987 Pb/Sxl65 Pb/Sxl86 Pb/Sxl47 Particle diameter, pm Figure 5c. Selected RSD(S>cuives for LP1-2. Figure 5d. Three nPb/S-curves for samples collected in Helsinki, summer 1987. Figure 6 . Sector division for Birkenes (from Amundsen et al., 1992). Nuclear Instruments and Methods in Physics Research B75 (1993) 249-256 MMB North-Holland Beam Interactions with Materials & Atoms Evaluation of the applicability of the MOUDI impactor for aerosol collections with subsequent multielement analysis by PIXE W. Maenhaut a, G. Ducastel a, R.E. Hillamo b and T.A. Pakkanen b “ Institute for Nuclear Sciences, Proeftuinstraat 86, B-9000 Cent, Belgium b Finnish MeteorologicalInstitute, Sahaajankatu 22 E, SF-00810 Helsinki, Finland The micro-orifice uniform deposit impactor (MOUDI) is an 8-stage impactor with cut-sizes down to 0.056 pm and which allegedly provides uniform aerosol deposits for the various stages. In the present study it was examined how uniform the aerosol deposits really are for each impaction plate, and whether the uniformity is sufficient for a Straightforward PIXE analysis. This was done by collecting several samples of ambient aerosol with the MOUDI and by determining the deposition pattern of various elements on the foils through a linear PIXE scan across each impaction foil. It was found that the deposits are far from uniform at the millimeter level for the stage numbers up to 6. Despite this, concentration data can easily be obtained by PIXE from such samples, provided that the analyzed area is carefully selected and' appropriate correction factors for the nonuniformity are employed. Some size distribution data are presented. A comparison is also made of the size distribution data and detection limits that result from employing the MOUDI in combination with PIXE with those obtainable by PIXE analysis of some other types of cascade impactois. 1. Introduction PIXE analysis of some other types of cascade im pactors. In recent years Marple and coworkers [1] have developed a so-called micro-orifice uniform deposit impactor (MOUDI), which has several features that 2. Methods are not normally found in other cascade impactors. This device allows one to collect ultrafine particles as 2.1. Sample collection small as 0.056 pm while keeping the pressure drop moderate, and, for each stage, the particles are de Ten different impaction stages and a so-called inlet posited uniformly over the entire impaction plate by stage are available for the MOUDI. Some design and rotating the impaction plate relative to the nozzles. operation parameters for these stages, as given by The latter characteristic is very advantageous when a Marple et al. [1], are listed in table 1. Although there technique such as X-ray fluorescence (XRF) or parti are 10 impaction stages, only eight of them (any eight) cle-induced X-ray emission (PIXE) is used for elemen can be used in the MOUDI rotator. In this work we tal analysis. In the present study it was examined how employed a MOUDI with impaction stages numbers 2 uniform the aerosol deposits actually are for each through 8, and number 10. The MOUDI can be used impaction plate, and whether the uniformity is suffi with two different sizes of impaction plates, designed cient for a straightforward PIXE analysis. To this end, to accept 37- or 47-mm diameter substrates. For our several samples of ambient aerosol were taken with the collections we used impaction plates for 47-mm sub MOUDI, and the elemental profiles on the collection strates, and as impaction foils we employed 47-mm surfaces from the various stages were determined. Nor diameter Apiezon-coated Nuclepore polycarbonate fil malization factors for converting the results from a ters of 8 pm pore size. According to Marple et al. [1], partial analysis of the surfaces into data for the entire collection of the particulate material requires a 2.8-cm aerosol deposit for each stage were calculated. Some diameter surface for the inlet and stage 1, and 2.7 cm atmospheric concentrations and size distributions de for all other stages. rived from the MOUDI samples are presented. Fur The aerosol collections were conducted on the roof thermore, the size distribution data and detection lim of the Finnish Meteorological Institute, Helsinki, and its that result from employing the MOUDI in combina the sampling time for each collection was typically tion with PIXE are compared to those obtainable by about 24 h. Six samples, numbered HI through H6, 0168-583X/93/S06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved IV. ENVIRONMENTAL SAMPLES 250 W. Maenhaut et aL / Applicability of the MOUDI impactor Table 1 spectra were converted into concentrations in ng per Some design and operation parameters for the stages from m3 and per stage. In the latter calculation, use was the MOUDI, as given by Marple et al. [1] made of “normalization factors for nonuniform deposi Stage Nominal As calibrated Nozzle Number tion on the foils”, as will be discussed below. cut point a cut point a diameter of [pm] [pm] [cm] nozzles 3. Results and discussion Inlet 18 18 1.71 1 i 10.0 9.9 0.889 3 2 5.6 6.2 0.380 10 3.1. Uniformity of the particulate deposit for the various 3 3.2 3.1 0.247 10 stages of the MOUDI impactor 4 1.8 1.8 0.137 20 5 1.00 1.00 0.072 40 From a visual inspection of the aerosol deposits on 6 056 056 0.040 80 the various stages of the MOUDI samples it was al 7 032 0.32 0.0140 900 ready apparent that the deposit is clearly not uniform 8 0.18 0.18 0.0090 900 on a submillimeter scale, and for some stages even not 9 0.100 0.097 0.0055 2000 on a millimeter scale. To examine the heterogeneity 10 0.056 0.057 0.0052 2000 quantitatively, the elemental concentration (in ng/cm 2) a Data are equivalent aerodynamic diameters for 50% collec of each step of each impaction foil for each of the four tion efficiency and are based on a flow rate of 30 1/min at analyzed samples and for those elements that were standard atmospheric temperature and pressure. measured with best precision (between five and nine elements per foil) was divided by the average elemental concentration over the aerosol deposit part of the were collected. For one of the samples (i.e., H3) the scanned foil. The ratios thus obtained were then for stages were not rotated with respect to each other, but each step first averaged over the five to nine elements the other five samples were taken with the rotating of the foil, and these average ratios were subsequently MOUDI. for each step averaged over the four sample foils from the same stage number, thereby adjusting for slight 22. P1XE analysis differences in start position of the scan for each of these foils. Considering that the profiles should be The various impaction foils from four of the six symmetric with respect to the center of the foil, the last samples (i.e., from sample no. HI and nos. H4-H6) averages from the two corresponding steps at the same and a number of blank foils were mounted on a special distance from the center were again averaged. The PIXE target frame, so that each foil could be analyzed final profiles, thus obtained for each stage, are shown over its entire width in 2 mm steps. The PIXE analyses in fig. 1 for stages 2-5 and in fig. 2 for stages 6-8 and were carried out with the Gent PIXE setup using a 2.4 10. It is quite evident from these figures that the MeV uniform proton beam of rectangular shape (2 mm uniformity of the particle deposits is only good for wide X 5 mm high). A total of 18 PIXE bombardments stages 7, 8 and 10, and, then, even for these stages were done across each foil (along a line passing through there is a tendency for higher elemental concentrations the center of the 27-28 mm diameter circular aerosol at the outer edge of the circular deposit. deposit). The beam current was typically 40 nA, and In applying our deposition patterns in other studies the preset charge per bombardment (step) was usually on MOUDI samples, it should be realized that the 7.5 pC. All measurements were done with a so-called results from any inhomogeneity study are dependent “funny filter” in front of the Si(Li) detector. Details on on the size of the probe used. At the millimeter or the experimental PIXE setup have been given else submillimeter level, the heterogeneities are most likely where [2-4]. The spectra from the individual steps even more accentuated. These finer details will have across each impaction foil and sum spectra, obtained been smoothed out by the size of our PIXE beam by summing up the spectra from the various steps collimator and to some extent also by our various across the aerosol deposit itself for each foil, and also averaging procedures. the spectra from the blank foils, were fitted by the computer program AXIL-84 [5]. Twenty-three ele 3.2. Calculation of atmospheric concentrations for the ments (i.e., Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, various stages of the MOUDI Mn, Fe, Ni, Cu, Zn, As, Br, Rb, Sr, Zr, and Pb) were included in these fits. After applying proper blank Unless the impaction foils of the MOUDI are bom corrections, the peak areas from the individual steps barded with a beam that fully envelopes the aerosol for each foil were converted into concentrations (in deposit (which is rather unfeasible in PIXE), the size units of ng/cm 2). Similarly, the data from the sum of this deposit has to be known. In the paper of Marple W. Maenhaut et al /Applicability of the MOUDI impactor 251 et al. [1], it is indicated that the collection of the Corporation [6], the company that commercializes the particulate material requires a 2.8-cm diameter surface MOUDI impactor, contains no information on the for the inlet and stage 1, and 2.7 cm for all other deposit diameters. Therefore, we derived these diam stages, but no further precision on the deposit diame eters from a visual inspection of the MOUDI samples ter is given. Also the instruction manual from MSP and from the PIXE data for our scans, including the Stage 2 Stage 3 10 11 12 13 14 15 16 17 10 11 12 13 14 15 16 17 16 Stage 4 Stage 5 9 10 11 12 13 14 15 16 17 10 11 12 13 14 15 16 17 Step number Fig. 1. Average deposition profiles, as derived from our linear PIXE scans through the center of the MOUDI impaction foils, for stages 2 through 5. The width of each step on the foil is 2.075 mm. See text for more details. IV. ENVIRONMENTAL SAMPLES 252 W. Maenhaut et aL / Applicability of the MOUDI impactor profiles displayed in figs. 1 and 2. The diameters thus should be carefully selected. Furthermore, in convert obtained are given in table 2, together with our esti ing the data from ng per cm2 and per m3 into results in mate of the total (maximum) error on this determina ng/m 3, a correction for the nonuniform deposition tion and with the deposit areas calculated from them. pattern should be applied. In this work, we derived the Because of the nonuniform deposition of the aerosol concentrations from the sum spectra, obtained by sum particles for most of the stages, the bombarded area ming up the spectra from the various steps across the Stage 6 Stage 7 10 11 12 13 14 15 16 17 10 11 12 13 14 15 16 17 Stage 8 Stage 10 9 10 11 12 13 14 15 16 17 16 9 10 11 12 13 14 15 16 17 Step number Fig. 2. Average deposition profiles for stages 6 through 8, and 10. See caption of fig. 1 for details. W. Maenhaut et al / Applicability of the MOUDIimpactor 253 aerosol deposit itself in our linear scan of each foil. In calculated “normalization factors” as follows: Each such sum spectrum, each step is given equal weight, step position was given its proper geometric weight whereas the steps at increasing distance from the cen (the square of the distance from the center), this weight ter of the foil should be given weights that are propor was multiplied by a nonuniformity weight factor for tional to the square of that distance. We therefore that step, as derived from fig. 1 or 2, and the products MnxtOO Stage number Fig. 3, Elemental size distributions for sample H4. The concentration in ng/m 3 for each stage is plotted versus the stage number. IV. ENVIRONMENTAL SAMPLES 254 W. Maenhaut el al /Applicability of the MOUDI impactor Table 2 and a backup filter, and the cut point of the last Diameter and area of the particle deposit for the MOUDI impaction stage (no. 1) is 0.25 pm BAD. Because of impactor stages, as determined in this work, and normaliza the fact that the aerosol particles are deposited in each tion factors for our PIXE analysis stage in one single small spot, which is easily fully Stage Diameter [cm] Area [cm2] Normalizations enveloped by a PIXE beam, this impactor is ideally number factor suited for PIXE analysis. In our PIXE analysis of samples collected with this impactor we utilize a circu 2 2.28 [0.10]a 4.08 1.078 lar 0.54 cm2 beam for stages 7 and 6 (and the filter 3 2.33 [0.06] 4.26 1.056 4 243 [0.06] 4.64 1.134 stage), and a 0.177 cm2 beam for stages 5 through 1. 5 245[0.06] 4.71 1.107 The Berner impactor is an 11-stage, multijet, 25 1/min 6 276 [0.06] 5.98 1.040 low-pressure cascade impactor, with cut points for the 7 2.88 [0.04] 651 1.004 last two stages of 0.030 and 0.015 pm EAD according 8 257 [0.04] 5.19 1.043 to the manufacturer [10]. However, Hillamo and Kaup- 10 268[0.04] 5.64 1.050 pinen [12] found from experimental measurements that 1 The data in brackets are our estimate of the total (maxi the real cut points deviate significantly from those mum) error on the diameter. specified by the manufacturer [10], in particular for the last five impaction stages. According to Hillamo and Kauppinen [12], the cut points for the last two stages thus obtained were summed over the entire deposit are 0.062 and 0.032 pm EAD, respectively. The panic diameter, and this sum was then divided by a similar ulate material is deposited in the various stages as a sum but calculated using nonuniformity weight factors ring of up to over 200 spots on annular impaction foils equal to 1. The normalization factors are given in the of 70 mm diameter, and, as a result, it is impossible to last column of table 2. Despite the various maxima and envelope all spots from one foil with a PIXE beam. In minima in several of the profiles from figs. 1 and 2, the our PIXE analysis of such samples, we use a quarter normalization factors are rather close to 1 for most of section of the annular foil and bombard such sections the stages. The major exceptions are stages 4 and 5, for with a beam size of 0.54 cm2 for the second, third, which the profiles exhibit a very large dip in the center. fourth and fifth stage (the first stage is never analyzed Using our normalization factors and the deposit areas, by us), and of 0.177 cm2 for all other stages. The the ng per cm2 and per m3 data derived from the sum number of spots enveloped by the beam varies from 1 spectra were converted in ng/m 3 values for each stage. to 8, depending on the stage, and this represents on As an example, the size distribution data thus obtained average 4% of the total number of spots on each for selected elements in sample H4 are displayed in fig. annular foil. Thus, the advantage of the 25 times 3. higher flow rate for the Berner impactor in comparison with the PIXE International impactor is totally nulli 3.3. Comparison of the size distribution data and detec fied in the PIXE analysis by the fact that only l/25th tion limits that result from employing the MOUDI in of the total aerosol deposit is bombarded. The only combination with PIXE with those obtainable by PIXE remaining advantages of the Berner impactor over the analysis of some other types of cascade impactors PIXE impactor are then that the sections of the foils that are not analyzed by PIXE can be analyzed by It is of interest for PIXE workers to see what the other techniques and that it has more stages at the advantages or disadvantages are of the MOUDI when lower end of the particle size range. The MOUDI compared with some other types of cascade impactors impactor shares the last characteristic, and it also al that are used in combination with PIXE. Here, we lows in theory (that is, if the deposits would be really discuss some aspects of such comparison with the PIXE uniform) that the foils are split up in several sections International cascade impactor [7,8] and with the for different techniques. Furthermore, in the PIXE Berner low-pressure impactor model 25/0.015 [9,10]. analysis of the foils one can use a large beam size, The PIXE cascade impactor comes in two models, i.e., which covers a substantial fraction of the deposit (e.g., 1-1 and I-1L, the difference being that two low-pres a 1 cm2 beam covers about 20% of the deposit), so that sure stages with cut points of 0.12 and 0.06 p.m equiva advantage is taken of the 30 times higher flow rate. lent aerodynamic diameter (BAD) have been added to In order to make a quantitative comparison of the the latter one. However, it was found by various re detection limits that are obtainable in a PIXE analysis searchers (e.g., ref. [11D that the two low-pressure of the MOUDI with those of the PIXE analysis of the stages do not function properly. Therefore, the model PIXE impactor and of the Berner impactor, we adopted I-1L will not be discussed. Model 1-1 is a single-orifice the same sampling time (24 h) for each impactor type, impactor operating at a nominal flow rate of 1 1/min; identical impaction foil material (i.e., 1.5 p.m Kimfol it has seven impaction stages (numbered 7 through 1) polycarbonate film), the beam sizes mentioned above W. Maenhaut et al. / Applicability of the MOUDI impactor 255 Serious drawbacks of both the MOUDI and the PCI and BLPI Berner impactors, relative to the PIXE impactor, are that they are at least 5 times more expensive, that they PCI and BLPI are more bulky and require a much more powerful MOUDI pump, thereby being less portable and more difficult to use for field work at remote locations, and that they are made of metal, so that there is a much larger risk of contamination (the PIXE impactor, on the other hand, is made of conductive plastic). 4. Conclusions It is evident from the present study that the MOUDI impactor does not provide uniform particle deposits for the stages 2 through 6 (and most likely also not for stage 1). The uniformity of the deposits is only good for stages 7 through 10. This implies that a PIXE analysis of stages 2 through 6 can only yield results that are representative for the entire aerosol deposit if a 28-mm diameter uniform beam is used (which is not really feasible) or if the analyzed fraction is carefully selected and the deposition pattern of the aerosol particles on the impaction foil is taken into consideration. The latter option was selected in the present work, and the 7TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT NaAlP O Ca Ti Cr Fe Hi Zn Ge Se RbYNb final concentrations were obtained from the sum spec KScVMnCoCuGaAsBr Sr Zr Mo trum from a linear scan through the center of the foil. Element The same approach can easily be adopted by other Fig. 4. Detection limits for the FIXE analysis of FIXE Inter PIXE workers and our normalization factors can even national cascade impactor (PCI) samples, Berner low-pressure be employed, provided that the height of the beam is impactor (BLPI) samples, and MOUDI impactor samples. not too much different from the 5 mm height used in The top curve applies to the stages 7 and 6 of the PCI and to this study. In order to increase the preset charge per the third, fourth and fifth stage of the BLPI (analysis with a unit of time (without resorting to increase in beam 0.54 cm2 beam size). The middle curve applies to stages 5 current density) it is suggested to employ a uniform through 1 of the PCI and to the last six stages of the BLPI rectangular (or square) beam that is larger than our (analysis with a 0.177 cm2 beam size). It is assumed that the detection of the element is based on the Ka line, except for 2X5 mm beam. For example, a 7X7 mm beam or a Ba and Pb where the La line is used. See the text for further 10x5 mm beam could be used. details. The nonuniformity of the particle deposits has the effect that an XRF analysis of MOUDI samples will be much more problematic than a PIXE analysis. Al for the PIXE and Berner impactors, and a 0.5 cm2 though the beam sizes are typically much larger in beam size for the MOUDI impactor, and a 600 s XRF than in PIXE, they will not fully envelop the bombardment per stage with our PIXE setup at a deposit. More important, the exciting X-ray beams in beam current density of 300 nA/cm 2 (this corresponds XRF are far from uniform, so that appropriate correc to a 90 p.C preset charge for a 0.5 cm2 beam size). tion factors will be hard to determine and will be quite Furthermore, we based the detection limit calculation dependent upon the actual excitation / detection geom on the 3(Background) 1/2 criterion, and neglected the etry used. contribution from blank variability. The PIXE detec tion limits that correspond with all these conditions are displayed in fig. 4. For the reason given above, the Acknowledgements values for the PIXE and Berner impactors are virtually the same. Of the two beam sizes used for bombarding W.M. and G.D. acknowledge support from the Bel the foils from these impactors, the smaller one obvi gian “Nationaal Fonds voor Wetenschappelijk Onder- ously provides the lowest detection limits, and the zoek”, the “Interuniversitair Instituut voor Kemweten- detection limits for the MOUDI are a factor of 1.6 schappen ”, the “Instituut tot Aanmoediging van het lower than these values. Wetenschappelijk Onderzoek in Nijverheid en Land- IV. ENVIRONMENTAL SAMPLES 256 W. Maenhaut etal. /Applicability of the MOUDI impactor bouw”, and the Impulse Programme “Global Change” [4] W. Maenhaut and H. Raemdonck, Nucl. Instr. and Meth. supported by the Belgian State - Prime Minister’s B1 (1984) 123. Service - Science Policy Office. R.E.H. and T.A.P. [5] W. Maenhaut and J. Vandenhaute, Bull. Soc. Chim. were funded by the Maj and Tor Nessling Foundation Belg. 95 (1986) 407. (Helsinki, Finland) and by the Academy of Finland. [6] Instruction Manual for Model 100 Micro-orifice Uniform Deposit Impactor (MOUDI), MSP Corporation, 1313 Thanks are due to J. Cafmeyer for technical assistance. Fifth Street, SE, Suite 206, Minneapolis, MN 55414, USA (1989). [7] S. Bauman, P.D. Houmere and J.W. Nelson, Nucl. Instr. and Meth. 181 (1981) 499. References [8] PIXE Intenational Corporation, P.O. Box 2744, Tallahas see, Florida 32316, USA. [9] A. Berner and C. Lurzer, J. Phys. Chem. 84 (1980) 2079. [1] V.A. Marple, K.L. Rubow and S.M. Behm, Aerosol Sci. [10] Instruction manual for Hauke low pressure impactor, Technol. 14 (1991) 434. Hauke KG, Postfach 103, A4810 Gmunden, Austria [2] W. Maenhaut, A. Selen, P. Van Espen, R. Van Grieken (1984). and J.W. Winchester, Noel. Instr. and Meth. 181 (1981) [11] H. Raemdonck, W. Maenhaut and M.O. Andreae, Nucl. 399. Instr. and Meth. B3 (1984) 446. [3] W. Maenhaut, R. Cornells, J. Cafmeyer and L. Mees, [12] R.E. Hillamo and E.I. Kauppinen, Aerosol Sci. Technol. Bull. Soc. Chim. Belg. 90 (1981) 1115. 14 (1991) 33. STUDY OF FORMATION OF COARSE PARTICLE NITRATE AEROSOL Tuomo A. Pakkanen Finnish Meteorological Institute Air Quality Department Aerosol Research Group Sahaajankatu 22 E SF-00810 Helsinki, Finland Submitted to Atmospheric Environment 10 21405 1 ABSTRACT The results of the analyses of 6 aerosol samples collected using a Berner low-pressure impactor (BLPI) device during the Nordic HN03/N03" and NH3/NH4+ gas/particle intercomparison excercise in Helsinki (11 - 22 May 1992) are reported. Formation of coarse particle nitrate was studied by evaluating the various ion balances of the measured water soluble ions (NH/, Na+, K+, Mg2*, Ca2*, Cl", N03" and S042") in addition to the detrmination of the mass size distributions of Na+, Ca2+, Cl" and N03" species. Atmospheric coarse particle N03‘ was found to be formed in the atmosphere when HN03 reacted with sea and soil derived coarse particles. The fraction of nitrate on coarse sea and soil derived particles followed the measured concentrations and size distributions of these two coarse particle types: the ratio of soil to sea particles increased with increasing particle size as did the fraction of nitrate on the soil particles. The reaction with sea salt particles resulted in the evaporation of Cl" as HC1. The presence of non sea salt S042" probably indicates that H2S04 and/or S02 reacted with sea salt contributing to the Cl' loss. Overall the percentage of evaporated Cl" decreased with increasing particle size suggesting a surface reaction mechanism. HC1 evaporation was nearly complete for the 1 - 2 pm equivalent aerodynamic particle diameter (BAD) size fraction indicating that all major sea derived chlorides, NaCl, MgCl2, CaCl2 and KC1, may react with acidic species in the atmosphere. Ion balances for the measured ions showed an anion deficit for coarse particles above 2 pm BAD. Most of this deficit was probably due to carbonate ions that were not analysed in this work. Key word index: impactor, size distribution, ions, nitrate, sea salt, soil particles, coarse particles INTRODUCTION No important primary coarse particle nitrate sources are known to exist. However, several research groups have found atmospheric nitrate in coarse aerosol samples. Thus, the nitrate found in such samples must have formed on and/or attached to these coarse particles in the atmosphere. This formation or attachment can occur when nitrate containing fine particles and/or gaseous nitrogen species interact with atmospheric coarse particles. Willeke and Whitby (1975) reported that fine particles do not interact appreciably with coarse particles in the atmosphere indicating that coarse nitrate probably originates from atmospheric reactions of gaseous nitrogen species with existing coarse particles. The emission of nitrogen oxides from traffic is the most important precursor of atmospheric nitrate aerosol. A significant part of these nitrogen oxides is transformed to gaseous nitrous and nitric acids in the atmosphere (Harrison et al., 1994). Several research groups have shown (Martens et al., 1973; Harrison and Pio, 1983; Wall et al., 1988; Solomon et al., 1992 and Harrison et al., 1994) that coarse particle nitrate can be formed in the atmosphere through reaction of gaseous nitric acid with coarse sea salt particles (reaction 1). Inspection of individual atmospheric coarse particles has shown that nitrate is frequently found as a surface coating of atmospheric sodium chloride particles (De Bock et al., 1994). Therefore, NaCl usually represents sea salt in reaction 1. HN03(g) + NaCl(s) -> NaN03(s) + HCl(g) 1. 2 In the San Francisco Bay area this reaction may almost go to completion (Martens et al., 1973). In contrast to volatile ammonium nitrate, a major constituent of atmospheric fine particles (Stelson and Seinfeld, 1982; Yoshizumi and Hoshi, 1985; Wexler and Seinfeld, 1990; Ottley and Harrison, 1992; Pio et al., 1992; Harrison and Msibi, 1994), the coarse sodium nitrate formed in reaction 1 is stable in the atmosphere (Yoshizumi and Hoshi, 1985) and thus serves as a permanent removal pathway for nitrate. Reaction 1 occurs especially when maritime and polluted continental air masses are mixed (Harrison and Pio, 1983). Calculations by Russell and Cass (1986) indicate that transport of nitric acid to the surface of sea salt particles is the governing factor for reaction 1. In the experiments of Wolff (1984) and Dasch and Cadle (1990) the existence of atmospheric coarse nitrate was explained by the reaction of gaseous nitric acid with coarse soil particles. It is still unclear exactly what happens when nitric acid interacts with soil particles but one possibility is that it reacts (2) with calcium carbonate (Harrison and Kitto, 1990): 2HN03(g) + CaC03(s) -> Ca(N03)2(s) + H20(aq) + C02(g) 2. Studies by Clarke and Karani (1992) indicate that calcium carbonate is a major constituent in the atmosphere which provides evidence to support the existence of reaction 2. Some other less abundant carbonates like, for instance MgC03, may also react with nitric acid. Mamane and Gottlieb (1992) performed laboratory experiments to study the heterogeneous reactions of nitric acid and nitrogen dioxide with sea salt and different types of soil particles. This study indicated that both gases reacted with sea salt and various soil particles in the dark. Under ultraviolet radiation, the formation of nitrate on sea salt particles increased but remained nearly unchanged on the soil particles. The studies of Harrison et al. (1994) support the possibility for an atmospheric reaction (3) between nitrogen dioxide and marine sodium chloride: 2N02(g) + NaCl(s) -> ClNO(g) + NaN03(s) 3. Size distributions of aerosol components can provide valuable information of the composition of aerosol particles in different particle ranges. Various types of cascade impactor devices (Savoie and Prospero, 1982; Harrison and Pio, 1983; Wall et al., 1988; John et al., 1990; Dasch and Cadle, 1990; Ottley and Harrison, 1992) and inspection of a large number of individual aerosol particles (Bruynseels et al., 1988; Wu and Okada, 1994; De Bock et al., 1994) have been used as methods to determine nitrate particle size distributions. The nitrate mass size distribution for coarse particles seems to be often associated with the surface area distribution of the sea salt aerosol (Savoie and Prospero, 1982; Harrison and Pio, 1983; Bruynseels and Van Grieken, 1985; Wall et al., 1988; Ottley and Harrison, 1992). Such a situation may be explained by a surface reaction of nitric acid (or nitrogen dioxide) with sea salt particles. In this work atmospheric aerosols were collected using a Berner low-pressure impactor device (BLPI) (Berner and Ltirzer, 1980), a size segregation method that allows measurement of size distributions of aerosol components. Various ion balances between the measured water soluble anions and cations were employed to study the formation of coarse nitrate aerosol at the sampling site. The relative importances of nitrate formation on sea salt and soil particles were estimated. 3 EXPERIMENTAL Sampling Sampling was performed during the Nordic HN03/N03" and NH3/NH4+ gas/particle intercomparison in Helsinki, Finland, 11-22 May, 1992 (Pakkanen et al., 1994), where atmospheric gases and aerosols were measured using different types of filter packs and denuder systems. In addition, size segregation methods, Berner low-pressure impactor and virtual impactor, were used for aerosol measurements. The sampling site was the roof (20 m above ground level) of the Finnish Meteorological Institute building which is situated two kilometers from the sea coast and seven kilometers to the east from the centre of Helsinki. In this paper, the concentration data for inorganic ions obtained using an 11-stage Berner low- pressure impactor (BLPI, Model 25/0.015) are discussed. The particle size calibration of the BLPI instrument was based on the experimental work of Hillamo and Kauppinen (1991) and Wang and John (1988). The particle size range collected was 0.03-15 Jim but discussion here is limited to the water soluble inorganic ions in the coarse particle'stages 7, 8, 9 and 10. The stages 7 to 10 correspond to particle size fractions of about 1-2, 2-4,4-8 and 8-15 pm BAD, respectively. Stage 11 is a pre-stage that was not analysed. The upper limit of the size range was determined by the impactor of the PM 10-type inlet (Liu and Pui, 1981). Sampling durations were 24h for BLPI samples 1 and 2 and 48h for samples 3 to 6 . The BLPI collection substrates were made of polycarbonate film and the coarse particle substrates were greased to minimize particle bounce-off (Hillamo and Kauppinen, 1991). The HN03 concentrations were determined from denuder systems and filter packs (Pakkanen et al., 1994). Chemical analysis The BLPI samples were prepared for analysis as described earlier for metals (Pakkanen et al., 1993). The samples were cut using cleaned scissors into four or five pieces that were placed in clean 10 ml transparent polypropylene test tubes fitted with screwed caps. Five ml of distilled and deionised water (Milli-Q water) was added and the samples were shaken by hand and treated in an ultrasonic bath at about 35°C for 20 min. The samples were then visually examined to determine whether the aerosol deposits were removed from the surface of the substrate pieces. The desorption procedure was repeated until there were no visible spots left on the substrates. For certain impaction stages (particle size fractions), the deposit sites sometimes remained slightly visible because of staining due to soot. Concentrations of water soluble NH4+, Na+, K+, Mg2*, Ca2+, Cl", N03" and S042" ions in the BLPI samples were analysed after a storage time of about three weeks. The instrument used to perform the analysis was a Waters ion chromatographic (IC) system equipped with a Waters HPLC pump Model 501. A borate/gluconate eluent was used for IC analysis. Contamination control In the case of BLPI samples, low procedural blank values are especially important since the sample is divided into ten separate particle size fractions in the sampling instrument. The minimisation of blank values included washing the BLPI, contamination free preparation of collection substrates, careful storing of substrates, impactor and collected samples and discarding the edges of collection substrates before the dissolution procedure. The inner parts of the BLPI were washed in an ultrasonic bath with Milli-Q water and isopropanol and immediately dried with filtered, pressurised air. After the drying procedure impactors were quickly assembled or loaded with substrates on a clean bench and sealed with parafilm or an airproof stopper to prevent contamination. Unloading of the samples was carried out on a clean bench as quickly as possible in order to reduce the contamination risk. A sharp, custom II 21405 55C 4 made stainless steel punch was used to prepare the collection substrates. The punch was carefully cleaned with Milli-Q water and isopropanol before use. The collection substrates were prepared by pressing the clean punch through the unopened plastic package of polycarbonate substrate sheets. After pressing, the substrates together with the separating papers were immediately removed into a washed, airtight plastic box. The clean impactors and collected samples were stored in an airtight container in a cold (+5°C), dark room. Before analysis the samples were cut in four or five pieces using cleaned scissors. To avoid possible contamination from the punch and impactor, the edges of the pieces were cut off using scissors before transfer to the test tubes. The forceps and scissors used for sample handling were frequently wiped with clean tissue paper (Kimwipes) wetted with isopropanol. Eight to ten layers of paper were used to prevent leaching of contaminants from finger tips. Just before use, the test tubes and IC sample cups were rinsed several times with fresh Milli-Q water. RESULTS AND DISCUSSION Concentration data and mass size distributions A summary of the measured concentrations of Cl", NO/, S042", NH4+, Na+, K+, Mg2* and Ca2+ for the individual coarse particle impactor stages 7, 8, 9 and 10 in the six BLPI samples is presented in Table 1. The results presented are all for water soluble ions as neq/m 3. The atmospheric HN03 concentrations during the sampling periods of the BLPI samples 1-6 were 9.50, 6.43, 14.50,9.14,12.36, and 17.64 nmol/m 3, respectively (Pakkanen et al., 1994). The HN03 values are not utilised in this work but they can be compared to the corresponding coarse particle N03" as measured by the BLPI instrument (=sum of nitrate in stages 7, 8, 9 and 10): 9.48, 4.19, 7.73, 10.60, 4.34, and 10.97 nmol/m 3, respectively for samples 1 to 6 . As the charge of NO/ ion is -1 the above concentrations are identical to neq/m 3 and can be compared to the data in Table 1. In BLPI samples 1, 2, 3, 4 and 5 the Na+ and NO/ coarse particle size distributions are similar but in sample 6 coarse particle NO/ peaks at a larger particle size than coarse particle Na+. This is illustrated in Figures 1 and 2. Fig. 1 presents the Na+, Ca2+, Cl" and NO/ coarse particle mass size distributions for the samples BLPI-1 and BLPI-6 . Fig. 2 presents the measured NO//Na* ratios for stages 7 to 10 for all six samples and shows clearly that sample 6 differs from the others. Some general features of the measured size distributions can be seen for the coarse particles: Na+ and NO/ peak at nearly the same particle size except for BLPI-6 Cl" peaks at a slightly smaller particle size than Ca2+ Ion balances for the measured ions Ion balances of the measured ions for all BLPI-stages 1 - 10 in the six samples are indicated in Fig. 3. For the coarse particle stages 7-10 there is a cation excess that increases with increasing particle size. For stages 9 and 10 the cation excess observed is likely to be due to Ca2+ because in all six measurements Ca2+ was the most abundant cation (as equivalents) in stage 10 and in four cases in stage 9. The most common atmospheric anions not measured in this work are carbonate and organic anions. Clarke and Karani (1992) state that CaC03 is a major atmospheric constituent and the usual form of atmospheric carbonate. In their coarse particle samples Wall et al. (1988) found a small anion deficit that they estimated as carbonate. In this work it is likely that most of the deficit can be explained as carbonate. Another important atmospheric ion, the hydrogen ion, H+, was also not measured in this work. However, the hydrogen ion is not believed to be present in coarse particles because atmospheric soil particles are basic or neutral and sea salt particles are neutralised by evaporation of hydrochloric acid. 5 Some characteristics of seawater and sea salt aerosols Even though the ion concentrations and concentration ratios of ions are fairly stable in the oceans there can be some deviations for the corresponding parameters in more isolated seas, as for example in the Baltic Sea, where the fraction of fresh water is large. These deviations can be due to anthropogenic sources and variable ion content in the water of different rivers feeding into the sea. The concentrations of the most important ions in oceans are presented in Table 2 as ion charge equivalents. In seawater the most abundant ions are Cl" and Na+ whereas the concentration of the important atmospheric ions, NH4+ and N03", is negligible. In this work the concentration ratios of ions in ocean water (Table 2) were used in several calculations because they are believed to represent a good average of the slightly different ratios in various parts of the Baltic Sea. Bochert (1965) describes four stages of fractional recrystallization of seawater when water evaporates from sea salt droplets in the atmosphere: 1. CaC03 and dolomite, 2. CaS04, 3. NaCl and, 4. Na^Q,, K2S04, MgS04, KC1 and MgCl2. Studies of individual atmospheric coarse particles have indicated that NaCl, CaS04 and combinations of other seawater recrystallisation products can be found in the atmosphere (De Bock et al., 1994). CaC03 and CaS04 can originate also from soil derived sources (De Bock et al., 1994). In addition to fairly pure sea salts the recrystallization can produce mixed salts and their aqueous solutions in droplets (De Bock et al., 1994). Comparison of the measured Na*/(N0 3'+Cl ) ratios to the corresponding seawater ratio In seawater the amount of N03" is negligible and therefore, the Na+/Cl" ratio, 0.85, represents the original Na7(N03"+Cl") molar ratio in seawater. In their work Wall et al. (1988) estimated that all coarse particle Na+ originated from sea salt. Assuming that all coarse Na+ is sea derived and that reaction 1 dominates in the atmosphere, a certain fraction of sea salt Cl" is replaced by N03" and the measured Na+/(N03"+Cl") ratios should indicate the seawater ratio. Fig. 4 describes the Na7(N03"+Cl") ratios of ion charge equivalents for the sum of the coarse particle stages 7 to 10 in all the BLPI samples 1 to 6. The first five samples show ratios similar to the seawater ratio, but sample 6 exhibits a low ratio of 0.46. Distortion from the ratio of 0.85 is an indication of additional sources and/or atmospheric reactions of Na+ and/or N03" and/or Cl". Some coarse Na+ may originate from soil or combustion sources and some coarse Cl" or N03" may evaporate but these cases would result in ratios higher than 0.85. On the other hand, Na+ should not evaporate in atmospheric conditions. Thus, the low ratio of sample 6 is probably due to additional enhancement of coarse particle N03" and/or Cl" concentrations. Wolff (1984) and Dasch and Cadle (1990) have reported that atmospheric HN03 can react with coarse soil particles. This reaction is the likely reason for the observed low Na+/(N03'+Cl") ratio in sample 6. Of the ions measured in this work, Ca2+ is the best indicator of soil derived particles. Sample 6 had the highest Ca2+ concentrations and the lowest NaV(N03"+Cl") ratios, which indicates that HN03 reacted with CaC03 or other soil particles in the atmosphere before the collection of sample 6. Clearly, in BLPI sample 6 the nitrate size distribution (Figures 1 and 2) is shifted to particle sizes larger than that of Na+. For the samples 1 - 5 it seems that the reaction of HN03 with sea salt dominated. The case of sample 1 has been earlier discussed by Hillamo et al. (1993) in terms of size distributions of (Na+ + Mg2*) and (Cl" + N03") which drew the same conclusion as this work, ie reaction of HN03 with sea salt dominated for sample 1. The measured Na7(N03"+Cl") ratios are different for the individual impactor stages (Fig. 5). Note that the contribution from stage 10 for the sum of stages 7 to 10 is small. Fig. 5 shows that the NaV(N03"+Q") ratios decrease with increasing particle size except for BLPI-1. Thus, 6 considering that the original seawater Na7(N03"+Cl") ratio is 0.85, in stages 9 and 10 there is some additional N03" originating from the reaction of HN03 with soil particles and the fraction of this soil derived nitrate increases with increasing particle size. Stage 10 of sample 6 has the lowest Na7(N03"+Cl") ratio (0.23) and the lowest Na7Cl" ratio (0.82). The Na7Cl" ratio lower than the sea water ratio (0.85) may indicate that some HC1, originating from reaction 1 or from other sources, also reacted with coarse soil particles. In contrast to stages 9 and 10, the measured Na7(N03"+Cl") ratios for stage 7 are above the seawater ratio for BLPI-samples 2, 3, 4 and 5. The likely explanations are: i) atmospheric sulphuric acid and/or sulphur dioxide reacted with sea salt aerosol producing Na2S04 (Harrison and Pio, 1983; Sievering et al., 1991; DeBock et al., 1994) and ii) stage 7 is influenced by fine particles and therefore, Na+ ions originating from sources other than sea salt may be important (e.g. combustion sources). Evaporation ofHCl from coarse sea salt particles: evidence of reaction of sea derived MgCl2, CaCl2 and KCl with atmospheric acidic species The measured Na+/Cl" ratios reveal the fraction of HC1 evaporated from sea salt aerosol in the different coarse particle stages (Fig. 6). Assuming that all coarse Na+ is sea derived, the original amount of sea salt CT is 1.18xNa + and the amount of evaporated HC1 is equal to the difference between original and measured coarse particle Cl". The HCI evaporation is probably principally caused by reaction 1, but as indicated above, the reaction of sulphuric acid with sea salt can displace CT. This possibility is evident since there was non sea-salt S042" present in all samples. Nevertheless, the fraction of evaporated chloride decreases with increasing particle size suggesting that surface reactions were the most important evaporation mechanisms in this study. This behaviour is similar to that observed by Harrison and Pio (1983) for northern England and Wall et al. (1988) for California. Evaporation percentages varied between about 87 - 100, 60 - 82, 37 - 55 and 0-37 for the stages 7, 8, 9 and 10, respectively. The zero evaporation percentage for stage 10 in BLPI 6 can be explained as a measurement error or, more likely, as indication of the reaction of HCI with coarse soil particles. In stage 7 of BLPI sample 5 the measured Cl" concentration was at the level of the blank value indicating total Cl" loss. Similarly, Martens et al. (1973) reported that in southern California the sea salt chloride can be nearly totally evaporated. This observation implies that chloride associated with the sea salt ions Mg2* and/or Ca2+ and/or K+ can also evaporate when HN03 and/or H2S04 reacts with sea salt aerosol. The possible reaction of MgCl2 with acidic atmospheric gases has been discussed by Hillamo et al. (1993). Coarse NOj connected with sea salt and soil particles The possibility of some reaction, between HCI and coarse soil particles has been discussed above, however, if this assumption is not valid then excess (or additional) coarse particle N03" , expressed here as XN03", is present if the sum of measured nitrate and chloride is higher than the original amount of chloride in sea water: XN03" = N03* + Cl" - 1.18xNa + (1.18xNa + is the original amount of sea salt Cl") XN03" shows the min imum amount of N03" originating from reaction of HN03 (and possibly N02) with coarse particles other than sea derived, e.g. soil particles. Figure 7 gives the fraction of XN03" from total measured N03"+CT. Except for BLPI-1 it seems that the fraction of XN03* increases with increasing particle size. This behaviour is reasonable since as the 7 particle sizes increase from stage 7 to stage 10 the relative amount of sea salt decreases while that of soil particles increases. Especially for stages 9 and 10 in BLPI-6 the reaction of HN03 with soil particles is important with most of N03' being connected with soil particles. This fact is clearly observed in the size distributions (or ratios) of Na+ and N03" in BLPI sample 6 (Figures 1 and 2) where N03" peaks at particle size larger than Na+. The total sum of nitrate and chloride is below the original sea salt amount in five cases for stage seven and in two cases for stage 8. This can be explained by the reaction of H2S04 and/or S02 with sea salt and/or existence of additional Na+ sources. Assuming that 1) all Na+ originates from sea, 2) that HC1 does not react with coarse soil particles and that 3) sulphur species do not react with coarse sea salt particles, the amount of N03" associated with soil particles can be calculated as indicated above for XN03". This calculation was performed and all XN03" was attributed to soil particles. The results are presented in Fig. 8 as the fraction of N03" present in soil particles. If the reaction of HN03 with soil particles occurs it is clear that on stages 7 and 8 there should also be some N03" on soil particles which seems not to be the case in Fig. 8. The likely uncertainties of this calculation, reaction of H2S04 and/or S02 with sea salt and/or existence of additional Na+ sources, tend to make the fractions of N03* on soil particles too low. Thus, the actual fractions of NO/ associated with soil particles are believed to be somewhat higher than those presented in Fig. 8. In their work Wall et al. (1988) attributed all coarse particle NH4+ to NH4N03. In this work NH4N03 may also have been present since some coarse particle NH4+ was found (Table 1). However, compared to concentrations of Na+, Cl" and N03" the NH4+ concentration was low, especially for stages 8 and 9. Stage 7 is influenced by fine particles and some (NH4)2S04 is very likely present. Overall it is assumed that in this work the presence of NH4+ in coarse particles does not significantly influence the NO/ distribution between sea and soil particles for stages 7, 8 and 9. In stage 10 the relative concentration of NH4+ was relatively high which may affect the N03" speciation data of Fig. 8 for this stage. Wall et al. (1988) published data about N03" speciation in coarse particles but their results are for the coarse particle mode without any further size segregation. Their results indicate that most of coarse particle N03" is associated with sea salt which is in agreement with our results. Unfortunately the size classified N03" distribution between sea and soil particles could not be compared to other measurements since such data was not available in the literature. CONCLUSIONS On the southern coast of Finland atmospheric coarse particle nitrate can be formed in the atmosphere by the reactions of nitric acid with both sea salt and soil particles. The fraction of nitrate associated with soil particles increases with increasing particle size and seems to follow the relative abundancies of coarse sea salt and soil particles. In some cases the reaction with soil particles can dominate. The data presented in this work suggest that HC1 may also react with coarse soil particles in the atmosphere. Cl" is depleted from sea salt and gaseous HC1 is formed when HN03 and H2S04 react with sea salt particles in the atmosphere. The Cl" loss decreases with increasing particle size indicating surface reaction mechanisms for the reactions. The Cl" loss can be complete for smaller sea salt particles (about 1-2 pm BAD in this work) which gives evidence for the reaction of atmospheric acidic species with sea derived MgCl2, CaCl2 and KC1. 8 In southern Finland atmospheric coarse particles can contain considerable amounts of some anion(s) not measured in this work. It is assumed that carbonate and/or some organic anions are responsible for the anion deficit observed. ACKNOWLEDGEMENTS Thanks are due to Dr. Risto Hillamo for his valuable comments about the manuscript, which positively influenced this work. The assistance from the members of the aerosol research group and the laboratory group at the Finnish Meteorological Institute is acknowledged. This work was partially funded by the Nordic Council of Ministers and the Academy of Finland (SILMU-programme). REFERENCES Berner A. and Liirzer C. (1980) Mass size distributions of traffic aerosols at Vienna. J. Phys. Chem. 84, 2079-2083. Bochert H. (1965) Chemical Oceanography,; Academic Press: London, 1965 Bruynseels F. and Van Grieken R. (1985) Direct detection of sulfate and nitrate layers on sampled marine aerosol by laser microprobe mass analysis. Atmos. Environ. 19, 1969-1970 Bruynseels F., Storms H. and Van Grieken R. (1988) Characterization of North Sea aerosols by individual particle analyses. 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Minimum, average and maximum concentration values (neq/m 3) for the measured ions in the impactor stages 7, 8, 9 and 10 of the BLPI samples 1-6. stage 7 stage 8 stage 9 stage 10 ion min ave max min ave max min ave max min ave max Cl' 0 0.20 0.57 0.43 1.27 2.52 0.72 1.66 3.31 0.23 0.44 0.83 no 3- 0.76 1.70 2.88 1.73 3.40 5.08 1.25 2.24 3.49 0.32 0.55 1.04 S042' 1.13 2.00 3.47 0.96 1.70 2.81 0.73 1.24 1.86 0.43 0.58 0.88 NH/ 0.27 0.78 1.59 0.13 0.30 0.49 0.14 0.23 0.34 0.11 0.17 0.25 Na+ 1.07 2.05 4.17 1.70 3.50 6.71 1.22 2.34 4.49 0.27 0.49 1.10 ' K+ 0.05 0.12 0.18 0.12 0.20 0.33 0.15 0.23 0.41 0.04 0.11 0.22 Mg2+ 0.32 0.54 0.96 0.64 1.03 1.64 0.59 0.92 1.33 0.26 0.38 0.51 Ca2+ 0.52 0.79 1.52 1.49 2.43 5.62 2.13 4.37 10.1 1.37 3.07 6.27 Table 2. Concentrations of the most important sea water ions in the oceans as ion charge equivalents in one kilogram of sea water. cations eq/kg sea water anions eq/kg sea water Na+ 0.475 cr 0.560 Mg2+ 0.108 S042- 0.056 Ca2+ 0.020 HC03-+C032- 0.003 K+ 0.010 7 8 9 10 BLPl-stage BLPI-6 7 8 9 10 BLPl-stage Flg.l. Size distributions for Na, Ca, Cl and NOS Ions In the coarse particle stages of BLPI samples 1 and 6. ------■— BLPI-1 - BLPI-2 ——4------BLPI-3 ----- 0------BLPI-4 ------* — BLPI-5 ------6 — BLPI-6 0.5 BLPl-stage Fig. 2. N03/Na ratios for the corresponding water soluble Ions In the coarse particle stages of the BLPI samples. -----■--- BLPI-1 - BLPI-2 S 2.5 BLPI-3 2 2 ----- o— BLPI-4 ----- * --- BLPI-5 ----- A— BLPI-6 BLPl-stage Fig. 3. Catlons/anlons ratios for the measured Ions In the Individual BLPI-stages. Carbonate, hydrogen Ion and organic Ions were not measured. ratio in sea water: 0.85 BLPI sample number Fig. 4. Na/(CI+N03) ratios of ion charge equivalents for the sum of the coarse particle stages 7,8,9 and 10 in each BLPI sample. BLPI-1 BLPI-2 BLPI-3 BLPI-4 BLPI-5 BLPI-6 BLPI-stage Fig. 5. Na/(N03+CI) equivalent ratios for the corresponding Ions In the coarse particle BLPI-stages. In sea water the ratio Is 0.85. ----- ■— BLPI-1 - BLPI-2 ----- «--- BLPI-3 —o— BLPI-4 ----- A--- BLPI-5 ----- A— BLPI-6 BLPl-stage Flq. 6. (1.18xNa-CI)/l .18xNa ratios of water soluble Ions representing fraction of Cl evaporated from sea salt. 0.8 t ----- ■--- BLPI-1 0.6 -■ - BLPI-2 0.5 •• ---♦ ■ BLPI-3 <0.4---. ----- o— BLPI-4 0.3 ------* --- BLPI-5 ----- A— BLPI-6 0.1 - BLPl-stage Fig. 7. (N03+CI-1.18xNa)/(N03+CI) ratios of water soluble Ions representing the fraction of additional (excess from sea salt) NOS + Cl. <9 0.8 BLPI-2 BLPI-3 o 0.6 BLPI-4 BLPI-5 R 0.2 BLPI-6 BLPI-stage Fig. 8. (N03+CI-1,18xNa)/N03 ratios of water soluble ions representing the fraction of nitrate connected to soil particles.