Atmospheric Environment 44 (2010) 1831e1846

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Atmospheric Environment

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Review Oxygenated polycyclic aromatic hydrocarbons in atmospheric particulate matter: Molecular characterization and occurrence

Christophe Walgraeve a, Kristof Demeestere a, Jo Dewulf a, Ralf Zimmermann b,c, Herman Van Langenhove a,* a Research Group EnVOC, Department of Organic Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium b Lehrstuhl für Analytische Chemie, Abteilung für Analytische, Technische und Umweltchemie am Institut für Chemie, Universität Rostock, Dr.-Lorenz-Weg 1, D-18051 Rostock, Germany c Helmholtz-Zentrum München e Deutsches Forschungszentrum für Gesundheit und Umwelt, Institut für Ökologische Chemie, Ingolstädter Landstraße 1, D-85764 Oberschleißheim, Germany article info abstract

Article history: Particulate matter (PM) has become a major research issue receiving increasing attention because of its Received 30 March 2009 significant negative impact on human health. There are main indicators that next to the morphological Received in revised form characteristics of the particle, also the chemical composition plays an important role in the adverse 28 November 2009 health effects of PM. In this context, the rather polar organic fraction of PM is expected to play a major Accepted 2 December 2009 role, and advanced analytical techniques are developed to improve the knowledge on the molecular composition of this fraction. One component class that deserves major attention consists of the Keywords: oxygenated polycyclic aromatic hydrocarbons (PAHs). Those compounds are considered to be among the Particulate matter Polycyclic aromatic hydrocarbons key compounds in PM toxicity. This paper presents a comprehensive review focusing on the analysis, fate fi fl Oxygenated and behavior of oxygenated PAHs in the atmosphere. The rst part of the paper brie y introduces (i) the Oxidized main sources and atmospheric pathways of oxygenated PAHs, (ii) available physicalechemical properties Oxygenated PAH and (iii) their health effects. The second and main part of this paper gives a thorough discussion on the Analysis entire analytical sequence necessary to identify and quantify oxygenated PAHs on atmospheric PM. Concentrations Special attention is given to critical parameters and innovations related to (i) sampling, (ii) sample preparation including both extraction and clean-up, and (iii) separation and detection. Third, the state- of-the-art knowledge about the atmospheric occurrence of oxygenated PAHs is discussed, including an extended overview of reported concentrations presented as a function of sampling season and geographical location. A clear seasonal effect is observed with the median of the oxygenated PAHs concentrations during winter being a factor of 3e4 higher than during summer. However, the oxygen- ated PAH/parent PAH ratio is about 20 times higher during summer, indicating the importance of photochemical activity in the atmosphere. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction fine particles are responsible for visibility impairment (Cheung et al., 2005; Liu et al., 2008; Yang et al., 2007). Third, PM has In the last years, particulate matter (PM) has become worldwide a significant negative impact on human health (Billet et al., 2007; a major research issue receiving increasing attention because of Harri et al., 2005; Li et al., 2003a; Ma and Ma, 2002; Oliveira et al., several reasons. First, atmospheric PM affects climate processes, 2007; Schober et al., 2006; Vinitketkumnuen et al., 2002), as both directly by absorbing and scattering solar irradiation and highlighted by numerous recent epidemiologic studies (Nawrot indirectly by formation of cloud condensation nuclei (CCN) that et al., 2006; Nawrot and Nemery, 2007; Valavanidis et al., 2006a). may counterbalance global warming (Andreae et al., 2005; Bellouin Negative health effects include asthma, as well as increased respi- et al., 2005; Pio et al., 2007). Secondly, high mass concentrations of ratory and cardiovascular mortality and morbidity (Li et al., 2003b, 2004; Nemmar and Inuwa, 2008; Walker and Mouton, 2008). In Flanders, it has been estimated that out of the five healthy living months that each inhabitant losses because of environmental * Corresponding author. Tel.: þ32 9 264 59 53; fax: þ32 9 264 62 43. fi E-mail address: [email protected] (H. Van Langenhove). pollution 71% is attributed to the inhalation of PM10, i.e. ne URL: http://www.EnVOC.UGent.be particulate matter with an aerodynamic diameter of less than

1352-2310/$ e see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2009.12.004 1832 C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846

10 mm(MIRA-T, 2004). The mechanisms through which PM toxicity 2008; Borras and Tortajada-Genaro, 2007; Ciganek et al., 2004; and genotoxicity proceed are still a matter of discussion. Goriaux et al., 2006; Ho and Yu, 2004; Lima et al., 2005; Marr et al., There are major indications that next to the morphological 2006; Naumova et al., 2002; Ravindra et al., 2006a,b; Ryno et al., characteristics of the particle, also the chemical composition plays 2006; Schauer et al., 2003; Turrio-Baldassarri et al., 2003; Valava- an important role in the adverse health effects of PM (Karthikeyan nidis et al., 2006a; Wauters et al., 2008; Wingfors et al., 2001; Yusa and Balasubramanian, 2006; Kennedy, 2007; Kubatova et al., 2004; et al., 2006). This is mainly because of the well-known carcinogenic Li et al., 2003a,b, 2004; Lintelmann et al., 2005; Ma and Ma, 2002). and mutagenic properties of this group of compounds. In addition PM is an extremely complex matrix containing a wide range of to chronic health effects, PAHs are also reported to be responsible chemical species, including inorganic acids and salts, metals, water, for acute health effects e.g. through oxidative stress caused by and a complex mixture of low volatility organic compounds, all in oxidized PAH metabolites (Marie et al., 2009). Both the occurrence highly variable concentrations (Caseiro et al., 2007; Cincinelli et al., and the analytical techniques used for PAHs determination have 2007; Dabek-Zlotorzynska and McGrath, 2000; Di Filippo et al., been reported recently (Chang et al., 2006; Crimmins and Baker, 2005; Huang et al., 2006; Liu et al., 2007; Ochsenkuhn and Och- 2006; Lima et al., 2005; Poster et al., 2006; Pozzoli et al., 2004; senkuhn-Petropoulou, 2008; Simoneit et al., 2007; Tang et al., Ravindra et al., 2008) and will therefore be no subject of this review 2006). Airborne chemical and biological substances can interact paper. with and adsorb on the particles during transport, deposition and In contrast, focus will be put on PAHs derivatives formed collection. Because of the expected high importance of the chem- through atmospheric reactions with oxidative species such as ical composition of PM on its environmental and human health ozone, hydroxyl and nitrate radicals as well as UV induced photo- effects, intensive research is going on to elucidate the molecular reactions (Vione et al., 2006). These PAHs oxidation products are composition of the PM species. However, because of the high typically found in the intermediate polarity PM fractions and complexity of the matrix and the often trace concentrations of include a wide range of compounds that can be classified in nitro- adsorbed micropollutants, this is a challenging task requiring PAHs and oxygenated PAHs. Since both the formation, occurrence, highly advanced sensitive and selective multi-step analytical and chemical analysis of nitro-PAHs is recently reported (Brichac methods and instruments (Chow et al., 2007; Hays and Lavrich, et al., 2004; Delhomme et al., 2007; Dimashki et al., 2000; Hattori 2007). et al., 2007; Ishii et al., 2000a; Kuo et al., 2003; Nicol et al., 2001b; The chemical characterization of transition metals and inorganic Perrini et al., 2005; Prycek et al., 2007; Sienra and Rosazza, 2006b; species present on PM has been intensively investigated already for Vincenti et al., 2001; Xu and Lee, 2001; Zielinska and Samy, 2006), years (Baez et al., 2007; Canepari et al., 2006; Chang et al., 2008; this subgroup is not further considered in this work. Fujimori et al., 2007; Garcia et al., 2008; Karageorgos and Rapso- This paper particularly deals with oxygenated PAHs. In agree- manikis, 2007; Karthikeyan and Balasubramanian, 2006; Kumar ment with Lundstedt et al. (2007), oxygenated PAHs are PAHs et al., 2006; Ochsenkuhn and Ochsenkuhn-Petropoulou, 2008; oxidation products that can be divided into two sub-groups: oxy- Ocskay et al., 2006; Pachon and Vela, 2008; Park et al., 2008; Per- PAHs and hydroxylated PAHs. Oxy-PAHs contain one or more rino et al., 2008; Shah and Shaheen, 2008; Valavanidis et al., 2006a; carbonylic oxygen(s) attached to the aromatic ring structure and Vasconcellos et al., 2007; Wojas and Almquist, 2007; Zhang et al., consist of ketones and quinones. Hydroxylated PAHs are defined as 2007). Excellent recent reviews are presented by Fang et al. (2005), PAHs on which one or more hydroxyl groups are attached. Nieuwenhuijsen et al. (2007) and Smichowski et al. (2008). Strong indications of the toxicological importance of oxygenated However, mainly because of the analytical complexity, the molec- PAHs (Dellinger et al., 2001; Ishii et al., 2000b; Li et al., 2003b; ular characterization of the organic fraction of PM is much less Lundstedt et al., 2007; Machala et al., 2001; Ohyama et al., 2007; documented but has become a growing research issue in recent Pedersen et al., 2005; Reed et al., 2003; Squadrito et al., 2001; years (Alves et al., 2006, 2007; Feng et al., 2006; He et al., 2006; Takamura-Enya et al., 2006; Thomas et al., 2002; Umbuzeiro et al., Kubatova et al., 2002; Lewandowski et al., 2007; Oliveira et al., 2008a; Vione et al., 2004; Xia et al., 2004) have resulted in 2007; Wang and Kawamura, 2005; Ward et al., 2006). Widely used a growing interest in the chemical analysis, occurrence, fate and thermal combustion and optical transmission methods enable the behavior of these micropollutants on PM. Pioneering work in this determination of the organic carbon (OC), elemental carbon (EC), field has been done by Akimoto et al. (1997), Allen et al. (1997), and black carbon (BC) fractions, but this compound unspecific Barbas et al. (1996), Binabas et al. (1995), Choudhury (1982), Durant approach does not provide knowledge on the molecular composi- et al. (1996), Enya et al. (1997), Fraser et al. (1998), Galceran and tion of PM (Currie et al., 2002; Maricq, 2007; Viana et al., 2007). Moyano (1992, 1993, 1994, 1995, 1996), Hawthorne et al. (1992), Whereas PM consists for up to 50% of a complex mixture of organic Helmig et al. (1992a, b), Helmig and Harger (1994), Konig et al. compounds exhibiting a wide spectrum of physicalechemical (1983), Levsen (1988), Moyano and Galceran (1997), Moyano et al. properties (e.g. molecular weight and polarity), only approximately (1997), Ramdahl (1983), Schulze et al. (1984), and Wilson and 10e20% of the organic fraction has been chemically identified and McCurdy (1995). However, particularly since 2000, there is an quantified (Alves, 2008; Mazurek, 2002). This makes that the increased number of research papers dealing with this issue, but as molecular characterization of the organic fraction of PM has far as we know, the state-of-the-art hereabout is not reviewed yet. become one of the priority research issues in the field of environ- Therefore, the main literature sources for this paper consist of peer- mental analytical sciences (Alves, 2008). Therefore, the scope of reviewed research papers and reviews, indexed by ISI Web of this review article is to present the state-of-the-art knowledge on Science, and published from 2000 to 2008. the occurrence of selected organics on PM and to highlight recent In Section 2, an introductory overview is presented about (i) advances in the rapidly evolving analytical techniques needed to major physicalechemical properties of oxygenated PAHs, (ii) their gain new insights. main sources and atmospheric pathways, and (iii) their health Among the wide range of organic compounds that are associ- effects. The focus of this paper, i.e. the state-of-the-art and inno- ated with PM, the rather non-polar fraction has attracted most vations in the chemical analysis of oxygenated PAHs sorbed on PM, attention so far. Particularly, the identification and quantification of is highlighted in Section 3. Focus is put on (i) sample collection and polycyclic aromatic hydrocarbons (PAHs), and especially the 16 sampling artefacts, (ii) sample preparation including extraction, priority PAHs defined by The United States Environment Protection clean-up, preconcentration, and fractionation, and (iii) separation Agency (EPA) has been investigated intensively (Bente et al., 2006, and detection. In Section 4, current monitoring data on the C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846 1833 molecular composition and concentrations of oxygenated PAHs on Since vapor pressure is a crucial parameter affecting the parti- atmospheric PM are summarized, including information about tioning of organic compounds between the free gas phase and the sampling place and season. particulate phase in the atmosphere (see Fig. 1), and since the vapor pressure of oxygenated PAHs is well below 10 Pa at ambient conditions, it is clear that oxygenated PAHs have a higher tendency 2. Oxygenated PAHs: physicalechemical properties, to sorb onto particulate matter than their parent PAH compounds atmospheric pathways and health effects (Vione et al., 2004), as discussed more in detail in Section 2.2.

In Fig. 1, an overall schematic representation is given on (i) the 2.2. Sources and atmospheric pathways main sources of oxygenated PAHs, (ii) their atmospheric pathways as influenced by both atmospheric conditions and phys- In contrast to PAHs which are emitted directly from combustion icalechemical compound specific properties, and (iii) their health processes, the sources of oxygenated PAHs emission in the atmo- effects. sphere can be both by direct introduction and by tropospheric conversion of PAHs (Albinet et al., 2007b; Lemieux et al., 2004; 2.1. Physicalechemical properties Vu-Duc et al., 2007) or other precursor molecules (Webb et al., 2006; Schauer et al., 2004; Morel et al., 2006; Feilberg et al., 2002; Main physicalechemical properties that may be important Phousongphouang and Arey, 2003). towards the fate and behavior of oxygenated PAHs in both the Direct emission of both gaseous and PM associated oxygenated environment (e.g. partitioning between gaseous and particulate PAHs proceeds through incomplete combustion processes of a wide phases) and the human body (e.g. uptake and accumulation) are variety of materials. Major sources are the combustion of domestic summarized in Table 1 (supporting material). As is clear from the waste (Sidhu et al., 2005) and biomass (Gullett et al., 2003) such as table, experimental data about physicalechemical properties of pine wood (Fitzpatrick et al., 2007), European conifers, African oxygenated PAHs are rather scarce. Therefore, in cases where no hardwood, savannah grass, German and Indonesian peat (Iinuma experimental data are available, the table represents theoretical et al., 2007), rice and wheat (Hays et al., 2005) and the open data, as estimated by ACD Solaris Estimation from SciFinder Scholar burning and smoldering of building debris (Olson and Norris, based on algorithm calculations (Scifinder, 2007 ed.). This makes 2008). They are also compounds of diesel PM (Jakober et al., 2006; that these data should be dealt with care, and that fundamental Leoz-Garziandia et al., 2000a,b; Letzel et al., 2001; McDonald et al., research is needed on these properties for a better understanding of 2004; Murahashi, 2003; Sidhu et al., 2005; Wang et al., 2007; the environmental and toxicological behavior of oxygenated PAHs. Zielinska et al., 2004) and are emitted during gasoline combustion Oxygenated PAHs are typically characterized by higher molec- (Jakober et al., 2007; Oda et al., 2001; Rao et al., 2001), production ular weights and lower vapor pressures compared to their parent of charcoal (Re-Poppi and Santiago-Silva, 2002) and coal burning PAHs (Goldfarb and Suuberg, 2008; Howard and Meylan, 1997). (Bi et al., 2008; Simoneit et al., 2007).

Atmospheric fate and behaviour (Section 2.2)

Atmospheric conversions, e.g. by UV induced photoreactions and reactions with ozone, nitrate and hydroxyl radicals (Section 2.2)

PAHs Oxygenated Sources (Section 2.2) PAHs Health effects (Section 2.3) Incomplete combustion processes: Free gas phase Free gas phase mutagenic, cytotoxic, biomass,domestic carcinogenic, endocrine waste, coal and disrupting effects and/or building debris oxidative damage (redox burning, traffic, cycling) charcoal production Sorbed on PM Sorbed on PM

Partitioning mainly determined by atmospheric conditions (e.g. temperature) and compound specific properties (e.g. vapor pressure, melting and boiling point, water solubility, molecular weight (Section 2.1)

Fig. 1. Schematic representation of the main sources of oxygenated PAHs, their atmospheric pathways, and their health effects. 1834 C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846

Besides direct formation, oxygenated PAHs can be formed out of authors concluded that compounds having a molecular weight PAHs via photochemical reactions and reactions with hydroxyl below 202 g/mol are mainly present in the free gas phase (>50%) radicals, nitrate radicals and ozone. Given the partitioning of PAHs while those containing more than 4 aromatic rings are mostly between the gas phase and PM, transformation processes can take (>90%) associated with the particulate phase. This is in agreement place in both phases. Reactions involving hydroxyl radicals (during with Liu et al. (2006) who also found that 4- to 5-ring oxygenated day) and nitrate radicals (during night) are considered to play PAHs (except for 4H-cyclopenta[def]phenanthren-4-one) are a major role in gas phase reactions whereas ozone and photolysis predominantly (>95%) associated with particles. Fig. 2 also are expected to play only a secondary role (Vione et al., 2004). demonstrates that, especially in winter seasons, oxygenated PAHs Particle associated PAHs containing more than five rings are less clearly have a higher tendency to sorb onto PM (>95% if molar susceptible to reaction with gaseous reactive radicals. Nevertheless, weight exceeds 200 g/mol) than their parent PAHs having a lower they can also undergo a wide variety of transformation processes, molecular weight. Furthermore, in contrast to PAHs, seasonal but often with slower kinetics than in the gas phase. Especially effects show to play a significant role in the gas/particle partition- direct photolysis and photolysis in the presence of photosensitizers ing of oxygenated PAHs and nitro-PAHs. Although ambient (e.g., quinones or aromatic carbonyls) play a significant role for temperature may be a crucial factor in this context, only the gas/ these compounds. The wide electron delocalization of PAHs enables particle partitioning of phenanthrene-9-carboxaldehyde (R2 ¼ 0.43) them to absorb sunlight, so that irradiation under atmospheric and 3-nitrophenanthrene (R2 ¼ 0.50) could be correlated with conditions may lead to photooxidation (Vione et al., 2006). temperature (Albinet et al., 2008a). Particularly for quinones, the Quantitative data on the relative importance of secondary atmospheric distribution between the gas and particle phase is versus primary formed oxygenated PAHs are scarce. Recently, recently investigated by Eiguren-Fernandez et al. (2008a). Whereas Eiguren-Fernandez et al. (2008b) estimated the secondary forma- phenanthrene-9,10-dione was only detected in the PM phase, other tion of phenanthrene-9,10-dione in the Los-Angeles basin. Different investigated quinones (1,2-napthoquinone, 1,4-napthoquinone and sites were sampled along the dominant wind trajectory and anthracene-9,10-dione) showed significant fractions in both pha- correlation coefficients between phenanthrene-9,10-dione (sorbed ses. Distribution ratios (PM-phase/free gas phase) between 0.01 on PM) and phenanthrene (both in the gas phase and sorbed on and 3 were observed and were site dependent. PM) were used to have an indication on the importance of secondary formed phenanthrene-9,10-dione. As a result, the authors concluded that ca. 90% of the phenanthrene-9,10-dione 2.3. Human health effects present in the downwind site was secondary formed during transport. With respect to their human health effects, oxygenated PAHs are Next to the aforementioned introduction and formation path- considered to be more toxic than their parent PAHs because of their ways, the fate of oxygenated PAHs in the atmosphere is largely direct mutagenic potency, whereas PAHs require first an enzymatic affected by their partitioning between the free gas phase and PM. activation (Yu, 2002). The mechanisms underlying their toxicity are According to a general rule of thumb given by Howard and Meylan complex and far from fully understood (Cho et al., 2005; Lampi (1997), chemicals having a vapor pressure less than 1.3 10 6 Pa et al., 2006; Lundstedt et al., 2007). Even the potencies of have a non significant fraction in the free gas phase, and are thus oxygenated PAHs may vary from compound to compound and with totally sorbed onto PM. Experimental data specifically dealing with the various toxicological end points studied. the partitioning of oxygenated PAHs between both phases are Metzger et al. (2004) reported that cardiovascular disease rather limited so far, but this issue has become a matter of recent complaints can be associated with oxygenated hydrocarbons research interest. The fraction of oxygenated PAHs that is associated (considered as a group of compounds) concentration levels in PM. with the particulate phase is strongly dependent on compound Next, oxygenated PAHs are considered as suspected endocrine specific physicalechemical characteristics (equilibrium conditions) disrupting chemicals (Sidhu et al., 2005) having estrogenic and exemplified by e.g. the vapor pressure and molecular weight (see anti-estrogenic activity and higher cytotoxicity than their parent Table 1, supporting material), next to mass transfer kinetics. PAHs (Kishikawa et al., 2004a). Midpolarity fractions (extracted Recently, Albinet et al. (2008a) reported PM associated fractions of with pressurized (liquid) water of 100e150 C) from wood smoke a wide set of oxygenated PAHs, PAHs and nitro-PAHs as a function PM displayed high cytotoxicity corresponding to methoxyphenols of molecular weight and sampling season (Fig. 2). Overall, the and oxygenated PAHs (Kubatova et al., 2004).

Fig. 2. PAHs, oxygenated PAHs and nitro-PAHs partitioning according to their molecular weight during winter and summer sampling campaigns (Albinet et al., 2008a). C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846 1835

Particularly, toxicological effects of quinones and their reduction Next to that, more volatile oxygenated PAHs might be suscep- products like semiquinones and hydroquinones received major tible towards vaporization losses during sampling. For example, attention (Taguchi et al., 2007, 2008). Quinones might be key Leoz-Garziandia et al. (2000a) found losses for anthracene-9,10- compounds in PM toxicity (Li et al., 2003b). This is mainly because dione ranging from 40 to 50% during high volume sampling (4 h, of their ability to undergo enzymatic and non-enzymatic redox 70 m3) on quartz fiber filters at 20e30 C. cycling with their corresponding semiquinones and thereby producing reactive oxygen species (ROS). These ROS, particularly 3.2. Sample preparation: extraction and clean-up . superoxide anion radicals (O2 ), hydroxyl radicals (HO ) and their for oxygenated PAHs analysis derivatives like hydrogen peroxide can cause severe oxidative stress through formation of oxidized cellular macromolecules, In Fig. 3 (and Table 2, supporting material) an overview is given including lipids, proteins and DNA. According to Chung et al. of the different techniques which are used for the extraction and (2007), oxidative stress is described as a condition under which analysis of oxygenated PAHs in PM samples. Two major groups of increased production of free radicals, ROS and oxidant related extraction techniques can be distinguished: solvent based tech- reactions result in damage to cells. This damage induces biological niques and the more recently applied thermal extraction tech- responses such as inflammation and apoptosis. Recently, Kubatova niques. Information on the solvent (mixtures) used for extraction is et al. (2006) showed that individual oxygenated PAHs like 1,8- given together with clean-up steps. dihydroxyanthracene-9,10-dione and anthracene-9,10-dione may contribute to pulmonary disease and oxidative DNA damage caused 3.2.1. Solvent based methods by wood smoke PM. Solvent extraction is the most widely used technique to transfer Reported health effects indicate that oxygenated PAHs are organic target compounds like oxygenated PAHs from the filter toxicologically highly relevant and belong to the key compounds to material into a liquid phase that is used for further analysis. Hereby, be measured in atmospheric PM. This necessitates innovative Soxhlet and ultrasonic extraction (USE) are the more traditional multi-step analytical techniques and advanced equipment, as dis- and most widely used solvent extraction techniques for PM cussed in detail in Section 3. analysis. With respect to Soxhlet extraction, dichloromethane or mixtures of dichloromethane with methanol or acetone are 3. Analytical sequence for oxygenated PAHs determination commonly used for the extraction of oxygenated PAHs from PM on particulate matter matrices (PM2.5,PM7,PM10, total suspended particles (TSP), size segregated PM) and recoveries between 20 and 120% are reported 3.1. Sampling artefacts for oxygenated PAHs (Harrad et al., 2003). Solvent consumption varies between 40 and 100 ml per analysis. A major drawback of the Soxhlet-method is the Sampling of particulate matter for chemical organic analysis long extraction time ranging from 8 h to 24 h. Ultrasonic extraction commonly proceeds through collection on glass, quartz or teflon offers the advantage over Soxhlet extraction by a dramatically (PTFE) fiber filters. Herefore, either low or high volume samplers reduction of the extraction time ranging from 15 min to 1.5 h. are used, operating for 2e48 h at flow rates from 1 m3/h to 1.8 m3/h Although USE is typically performed with common solvents (or and from 25 m3/h to 100 m3/h, respectively. During sampling, PAHs mixtures, see Table 2), solvent selection might be crucial. Lintel- and oxygenated PAHs may react with ozone, hydroxyl and nitrate mann et al. (2006) found that recoveries and precision significantly radicals similar as in the atmosphere, which may produce sampling improved by using ethylacetate as an extraction solvent for USE of artefacts. In order to minimize under or overestimation of benzo[a]pyrenediones compared to toluene-methanol solvent concentrations and possible health effects, ozone denuders are mixtures. Next, temperature was observed to be a critical param- sometimes used for ozone removal from the air stream prior to eter. The extraction efficiency of phenanthrene-9,10-dione, chrys- collection of the particles on the filter. Liu et al. (2006) investigated ene-5,6-dione and 4-oxa-benzo[def]chrysene-5-one increased sampling artefacts on oxygenated PAHs collected by low volume with increasing temperature during USE with ethylacetate, in sampling with and without a manganese oxide ozone denuder. contrast to the benzo[a]pyrenediones (especially benzo[a]pyrene- Because of their different behavior, distinction has to be made 7,8-dione and benzo[a]pyrene-11,12-dione) probably because of between the mainly particle associated 4- to 5-ring oxygenated thermal degradation of the latter compounds. Given the instability PAHs and the mainly gaseous 2- to 3-ring oxygenated PAHs. of benzo[a]pyrenediones, it is advisable to avoid high temperatures Concentrations of mainly particle associated oxygenated PAHs like (ice cooling during USE), to eliminate oxygen (reduction steps 11H-benzo[a]fluorene-11-one, 11H-benzo[b]fluorene-11-one, 7H- under nitrogen) and to use protic solvents (acetonitrile instead of benzo[de]anthracene-7-one and benzo[a]anthracene-7,12-dione methanol). Reported recoveries for USE range from 35% to 132%, showed to be 10e40% higher without ozone denuder. So, ozone depending on the compound and method of analysis. Kishikawa induced formation prevailed over ozone mediated degradation. As et al. (2004a) investigated several solvents for USE of hydroxylated an exception, the concentration of 4H-cyclopenta[cd]pyrene-3-one PAHs (2-naphthol, 1-naphthol, 2-hydroxydibenzofuran, 2-hydrox- was 10% lower without ozone denuder, showing the higher relative yfluorene, 9-hydroxyphenanthrene and 1-hydroxypyrene) and susceptibility to ozonation; and 6H-benzo[cd]pyrene-6-one was found that ethanol has a maximum extractability among several found to be stable against ozonation. The average concentrations other solvents like methanol, acetonitrile, hexane, acetone and (measured on filters) of the more volatile oxygenated PAHs, i.e. 2- ethylacetate. Castells et al. (2003) found that 9H-fluorene-9-one to 3-ring compounds (napthalene-1,4-dione; 9H-fluorene-9-one; shows an important interference when USE with dichloromethane anthracene-9,10-dione) and 4H-cyclopenta[def]phenanthrene-4- is used, although no further details are given by the authors. In one, were 1.3e2.4 times higher in denuded samples compared to general, solvent consumption for USE varies between 8 and 200 ml the non-denuded ones, indicating that catalytic formation of these per analysis. oxygenated PAHs at the denuder surface dominated over ozone Recently, Rissanen et al. (2006) have used an automatic USE induced degradation. The use of an MnO2 ozone denuder is by technique. This dynamic sonication assisted extraction method consequence not suitable for the analysis of more gaseous (DSAE) allows adding new solvent to the extraction vessel during oxygenated PAHs. USE while simultaneously removing compound loaded solvent 1836 C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846

Extraction Clean-up Solvent extraction

None Soxhlet Filtration USE Centrifugation DSAE Column chromatography PLE SPE MWE HPLC SFE LLE Thermal extraction

CPP

DTD Derivatisation

Separation

GC GCxGC LC-GC LC

Detection

ECD FID MS MS/MS F UV/UV-VIS Chemiluminescence

QMS ITMS TOFMS

Fig. 3. Analytical sequence for oxygenated PAHs analysis from PM samples. (USE: ultrasonic extraction; DSAE: dynamic sonication assisted extraction; PLE: pressurized liquid extraction; MWE: microwave extraction; SFE: supercritical fluid extraction; CPP: curie point pyrolysis; DTD: direct thermal desorption; SPE: solid phase extraction; LLE: liquid- eliquid extraction; ECD: electron capture detector; FID: flame ionization detector; MS: mass spectrometry; UVeVIS: ultraviolet and visible light spectroscopy; F: fluorescence detector; QMS: quadrupole MS; ITMS: ion trap MS; TOFMS: time of flight MS; GC: gas chromatography; (HP)LC: (high performance) liquid chromatography). from the extraction vessel. Although the total extraction time is elevated pressure keeps the solvent below its boiling point, thus 40 min, solvent consumption is low (22 ml of an acetone-hexane enabling safe and rapid extractions. Albinet et al. (2006) used PLE for (1:1) mixture per analysis) when compared to conventional USE. extracting a set of 9 oxygenated and 17 nitro-PAHs by using More innovative solvent extraction techniques like pressurized dichloromethane as the extraction solvent at 120 C and 14 MPa. liquid extraction (PLE or accelerated solvent extraction, ASE), Recoveries between 5% (napthalene-1-carboxaldehyde) and 83% supercritical fluid extraction (SFE) and microwave extraction (MWE) (benzo[b]fluorenone) were obtained. Although PLE has promising are developed in order to reduce both the extraction time and solvent potential, Lintelmann et al. (2005) reported chemical degradation or consumption, to increase extraction efficiency, and to improve rearrangement of PAH-quinones during PLE at temperatures and automatization. Those techniques have recently been investigated pressures less than 100 C and 10.7 MPa, respectively. Different for oxygenated PAHs extraction from PM samples. PLE increases the solvents were used including methanol, toluene, and a mixture of efficiency of the extraction process by using conventional solvents hexane and acetone, but irreproducible results from spiked quartz (dichloromethane, acetonitrile, methanol, ethylacetate, toluene) at fiber filters were obtained and recoveries were below 80%. Further elevated temperatures (50e200 C) and pressures (0.3e21 MPa). work is needed in order to determine more precisely the application Increased temperature accelerates the extraction kinetics, and potential of PLE for oxygenated PAHs extraction. C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846 1837

Supercritical solvent extraction is another advanced extraction Kishikawa et al. (2004a) investigated different types of SPE technique which is used for the extraction of oxygenated PAHs from cartridges to selectively extract hydroxylated PAHs from USE fluids PM. In this context, a two step SFE technique for both oxygenated and to remove interfering compounds prior to HPLC analysis. With Ò and nitro-PAHs from PM has been developed by Castells et al. BondElut NH2, the highest recoveries were obtained between 91% (2003).Inafirst step, the filter is extracted with pure CO2 (45 C, (9-hydroxyphenanthrene) and 103% (2-naphthol), with an intraday 15.2 MPa) in order to remove non-polar compounds such as and interday precision ranging from 0.9 to 3.0% and from 1.3 to aliphatic hydrocarbons and some PAHs (between 10 and 20% of the 4.8%, respectively. total amount extracted). However, by using pure CO2 as an For some compounds liquideliquid extraction (LLE) is used for extraction fluid, recoveries for rather polar compounds like clean-up. For example, Feilberg et al. (2002) isolated 3-nitro-7H- oxygenated and nitro-PAHs are dramatically low. The limiting benzo[de]anthracene-7-one from an USE fluid by means of LLE factor of SFE is the ability of the extraction fluid to overcome (recovery ¼ 90%). Further purification was done by HPLC fraction- matrixeanalyte interactions rather than the solubility of these ation using a Nucleosil Si-50-5 stationary phase with a gradient of polar analytes in the SFE fluids. To overcome this limitation, cyclohexane-toluene. a modifier is necessary (Castells et al., 2003). Therefore, the second step consists of an extraction with toluene-modified CO2 (5:95 v/v; 3.2.2. Derivatisation reactions 90 C, 35.5MPa) to selectively extract the oxygenated PAHs and Sub-groups of oxygenated PAHs are characterized by different nitro-PAHs from the matrix. Recoveries between 87 and 99% were functionalities (hydroxylated PAHs, oxy-PAHs, nitro-containing obtained within a 35 min period. In contrast to USE, no further oxy-PAHs) and therefore need different derivatision approaches. sample purification was needed. The total solvent consumption was Oxy-PAHs are mostly analysed in their underivatized form, reduced to 12 mL (elution and rinsing of the C18 trap) compared to although some authors used a derivatization method in order to 75 mL for USE. In another application of SFE (40.5 MPa, 150 C) improve the detectability. Recently, Chung et al. (2006) and Cho dichloromethane was used as a modifier to CO2 (Shimmo et al., et al. (2004) developed a derivatization technique for PAH-quinones 2004a, 2004b). This method proved to be useful to determine in order to improve the sensitivity of their GCeMS analysis. These a variety of compounds ranging from non-polar compounds compounds were converted to their diacetyl derivatives using zinc (n-alkanes, hopanes, steranes, PAHs, alkyl-PAHs) to more polar ones and acetyl acetate. Performing this derivatization step significantly (n-alkan-2-ones, n-alkanals, oxygenated PAHs) in PM samples. decreased the limit of detection (LOD, signal/noise ¼ 3) ranging Microwave extraction for oxygenated PAHs analysis is so far only from 0.002 ng/m3 (acenaphthenequinone) to 280 ng/m3 (phenan- used by McDonald et al. (2002) using dichloromethane as the threne-9,10-dione) without derivatization to maximum 0.008 ng/m3 solvent for the extraction of xanthone, acenapthoquinone and 1H- (napthalene-1,2-dione) after derivatization. Some quinones phenalene-1-one. However, no further details about solvent (acenapthylene-1,2-dione, 2-methylanthracene-9,10-dione, 2,3- volume and extraction time are given. dimethylanthracene-9,10-dione, napthacene-5,12-dione, benz[a] Overall, when determining recoveries, distinction has to be anthracene-7,12-dione and anthracene-9,10-dione), however, could made between matrix dependent and matrix independent recov- not be completely converted to their diacetate derivatives and did eries. With respect to the latter, Lintelmann et al. (2005) compared not show lower detection limits. Although fluorescence detection is both recoveries obtained with USE. Matrix independent recoveries one of the most sensitive and selective methods for PAHs analysis, on spiked blank quartz fiber filters ranged from 29% (benzo[a]pyr- most oxy-PAHs and especially quinones cannot be detected with ene-7,8-dione) to 87% (4-oxa-benzo[def]chrysene-5-one), whereas fluorescence (Lintelmann et al., 2005). Therefore, Delhomme et al. matrix dependent recoveries between 49% (benzo[a]pyrene-7,8- (2008) very recently investigated post column derivatization (with dione) and 92% (4-oxa-benzo[def]chrysene-5-one) were achieved. a zinc catalyst) of oxygenated PAHs (including ketones, diketones This effect was explained by the stabilizing effect of the matrix and and pyrones) to their corresponding hydroxylated PAHs, as a sample its constituents on the reactive PAH-diones, and/or by degradation derivatization technique for LC with fluorescence detection. of the analytes by the heated and thus activated quartz filters that However, LOD values between 1.0 (9-hydroxyxanthene) and 1.4 ng were used to determine the matrix independent recoveries. (1,4-dihydroxynapthalene) reported for this method are high Within a limited number of studies, analysis is performed on the compared to 14 pg and 8 pg, respectively, obtained with the LC- crude extracts as obtained after solvent extraction or following MS-MS method. On the contrary, Kishikawa et al. (2004b) devel- a single filtration or centrifugation. However, a more intensive oped a highly sensitive and selective method for the determination clean-up is most often needed prior to chromatographic analysis. of phenanthrene-9,10-dione using HPLC with pre-column Both liquid open column chromatography (from 20 mm 2.1 mm derivatization and fluorescence detection. Using benzaldehyde as I.D. to 30 cm 1 cm I.D.) on anhydrous silica gel, alumina, alumina- a derivatizing reagent in the presence of ammonium acetate, silica, or silica impregnated with silver nitrate, and flash chroma- phenanthrene-9,10-dione was converted into 2-phenyl-1H-phe- tography on silica are used. Sometimes online LC-chromatography nanthro[9,10-d]imidazole (reaction yield: 80%), exhibiting a strong is implemented into the analytical method for the fractionation of fluorescence. The LOD was 1.0 pg. Interday and intraday precision SFE fluids. More advanced clean-up steps like solid phase extraction ranged from 3.1 to 4.5% and 2.3e3.2%, respectively. (SPE) are alternatives for further fractionation of the extracts. Unlike oxy-PAHs, which are seldom derivatised, hydroxylated In this context, Albinet and co-workers developed a two-step PAHs are mostly converted to their trimethylsilyl (TMS) analogues SPE procedure after PLE of PM10 samples. The procedure allows using N,O-bis-trimethylsilyltrifluoroacetamide (BSTFA) plus tri- extract-purification that is suitable for both oxygenated and nitro- methylchlorosilane and pyridine, at a temperature of 70 C. The PAHs (Albinet et al., 2006, 2007a,b, 2008a,b). In the first step the derivatization time typically amounts 3 h. The silylated extract can extract was loaded on an alumina SPE cartridge, which was be analysed by a quadrupole mass spectrometer using EI (70 eV) as subsequently eluted with dichloromethane to remove both the ionization technique (Simoneit et al., 2007; Wang et al., 2007). macromolecules and polar interfering compounds. In the second Hydroxylated PAHs can also be analysed directly by GCeMS and as step the aliphatic fraction was separated from the aromatic one on methyl ethers, but better response factors are obtained with the a silica SPE cartridge. Elution with n-pentane removed the alkanes TMS derivatives (Simoneit et al., 2007). whereas the target compounds were obtained by elution with With respect to nitro-containing oxy-PAHs, Tang and co- a mixture of pentane and dichloromethane (65/35, v/v). workers (Hayakawa et al., 2001; Tang et al., 2004, 2003) developed 1838 C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846 a chemiluminescence method for the quantification of nitro-7H- artefacts. It has been found that phenanthrene-9,10-dione is con- benzo[de]anthracene-7-one isomers (1-, 2-, 3- and 10-nitro-7H- verted into 9H-fluorene-9-one by elimination of one CO entity benzo[de]anthracene-7-one). An online reduction column with an during injection, resulting in a 9H-fluorene-9-one overestimation Pt/Rh catalyst converts the nitrobenzanthrone isomers into their and phenanthrene-9,10-dione underestimation (Liu et al., 2006; amino derivatives. After concentration and introducing the Sklorz et al., 2007a,b). Concerning the ionization method used in chemiluminescence reagent solution (acetonitrile solution con- GCeMS analysis, electron ionization (EI, 70 eV) is the most widely taining bis(2,4,6-trichorophenyl)oxalate and hydrogen peroxide), used method for oxygenated PAHs analysis. Recently, however, LODs ranged from 5.5 pg (1-nitrobenzanthrone) to 9.6 ng Albinet and co-workers have successfully used negative ion (2-nitrobenzanthrone). chemical ionization (NICI) with methane as a reagent gas for the detection of 17 nitro- and 9 oxygenated PAHs (Albinet et al., 2006, 3.2.3. Thermal methods 2007a,b, 2008a,b). Because NICI is a soft ionization technique, it Next to solvent extraction, there is a recent tendency to explore may offer some advantages with respect to the detection limit due the potential of direct thermal desorption (DTD) of oxygenated to the lower fragmentation compared with EI. Linearity was PAHs from PM samples (Chow et al., 2007; Hays and Lavrich, 2007; investigated using a daily seven point calibration curve and coef- Neusüss et al., 2000; Ochiai et al., 2007; Schnelle-Kreis et al., 2005a, ficients of correlation were better than 0.99. LODs for the target 2007). Advantages are reduced extraction times (9 mine5 h), the oxygenated PAHs ranged from 0.01 pg (9H-fluorene-9-one) to elimination of solvent use, which fits within the concept of green 2.60 pg (anthracene-1,4-dione). analytical chemistry, and the elimination of the sample preparation GCeMS analysis of raw PM-extracts may cause problems in steps. Reduction of analyte losses and memory effects by desorp- terms of uncertainty of confirmation or even undetectability of tion of the sample within the GC injector are also important some target oxygenated PAHs, due to interfering compounds from advantages. Low limits of quantification (LOQs, signal/noise ¼ 10) the matrix. In this context, Nicol et al. (2001a) developed an are achieved more easily but care should be taken when analyzing advanced GC tandem ion trap-mass-spectroscopy (ITMS) method compounds that degrade during thermal desorption like phenan- (GC-MS-MS) on crude extracts in order to improve the detection threne-9,10-dione which forms 9H-fluorene-9-one due to CO limits. Tandem MS is an approach which reduces the background elimination. As an example, Schnelle-kreis and co-workers (Ochiai caused by complex matrices by excluding all ions except the parent et al., 2007; Schnelle-Kreis et al., 2005a, 2007, 2005b) investigated ion, which then can be fragmented to produce an unique product DTD for the extraction of oxy-PAHs and several other component ion mass spectrum. Linearity was investigated in a calibration range classes (hopanes, linear alkylbenzenes, nitriles, methylesters, from 10 to 1000 pg/ml for 11 oxygenated PAHs and coefficients of n-alkan-2-ones, n-alkanes and PAHs) from PM2.5. Two small quartz correlation between 0.95 and 0.99 were obtained. The MSeMS filter pieces (2.1 27 mm), each representing 1.1 m3 of sampled air, method offers a significant decrease in limits of detection ranging were placed into a GC injector liner, after which a mixture of from 1 (indane-1-one; 9H-fluorene-9-one) to 60 (10H-anthracene- isotope labeled compounds was added as an internal standard. The 9-one) pg compared to a GCeMS method showing LODs between 1 liners were put in a cold injector and temperature was increased up (indane-1-one) and 290 (7H-benzo[de]anthracene-7-one) pg. to 320 Cat1C/s. Analysis was performed by GC-TOFMS or GCeMSeMS also has been used by Tsapakis et al. (2002) and GCxGC-TOFMS. Feilberg et al. (2002) for the quantification of 12 oxy-PAHs and Curie point pyrolysis gas chromatography mass spectrometry 3-nitro-7H-benzo[de]anthracene-7-one, respectively. (CPP-GC-MS) is an alternative thermal desorption technique that Since the chromatographic resolution in one-dimensional GC is reduces the analysis time through elimination of the sample often too limited to provide separation for the large number of preparation steps. Neusüss et al. (2000) developed a CPP-GC-MS semi-volatile PAH-derivates (among which oxygenated PAHs) method, where particles are collected on two pieces of ferromag- present in ambient PM samples, multidimensional techniques like Ò netic foils (Pyrofoil ) placed on the impactor stages of a Berner type comprehensive two-dimensional gas chromatography (GCxGC) low-pressure cascade impactor. Through radio frequency induction have recently gained interest for improving the separation power the Fe/Ni ferromagnetic foil is rapidly (20 ms) heated to the Curie and peak capacity (Hamilton et al., 2004; Kallio et al., 2003; Ochiai point of 590 C to hold this temperature for 3 s. At this point et al., 2007; Schnelle-Kreis et al., 2005b). Schnelle-Kreis et al. ferromagnetism of the metal changes to paramagnetism and the (2005b) combined TD with GC-TOFMS and GCxGC-TOFMS for the flash evaporating compounds are introduced into the GC column by analysis of semi-volatile organic compounds in PM2.5 and could helium and detected with a quadrupole mass spectrometer using EI provide a variation in time of the daily summarized concentrations ionization. In contrast to solvent extraction (toluene-dichloro- of oxygenated PAHs, besides several other groups of organic methane, (1:1)) where an aerosol mass of 27 mg was used, CPP-GC- compounds including n-alkanes, n-alkan-2-ones, n-alkanoic acid MS only needed 95 mg to perform a complete analysis. Besides the methyl esters, acetic acid esters, n-alkanoic acid amides, nitriles, advantages of the CCP-method, the main limitation is that various linear alkylbenzenes and 2-alkyl-toluenes, hopanes, PAHs and species might be thermally unstable and are not measured by the alkylated PAHs. In the DTD-GC-TOFMS chromatograms, about 1500 method. As such, only 4 oxygenated PAHs could be quantitatively compounds could be separated, partially by peak deconvolution, determined: 9H-fluorene-9-one (or isomer); 1H-phenalene-1-one from which 200 compounds were quantified and semiquantified on (or isomer); anthracene-9,10-dione; and 1,8-napthalicanhydride. a daily basis. In contrast to the one-dimensional method, more than 10 000 compounds were detected in the same samples analysed by 3.3. Separation and detection of oxygenated PAHs DTD-GCxGC-TOFMS. This increase in peak capacity by a factor of 6 shows clearly the advantages of comprehensive GCxGC for the 3.3.1. Gas chromatography methods analysis of highly complex matrices like PM. Gas chromatography coupled to mass spectrometry (GCeMS) is Although mass spectrometric detection is the method of choice a common analytical technique for the separation and detection of for the detection of oxygenated PAHs in PM samples, Castells et al. oxygenated PAHs which are sufficiently thermostable and that have (2003) investigated electron capture detection (ECD, 63Ni) for the a vapor pressure higher than napthacene-5,12-dione (5.65 10 7 Pa; measurement of 5 oxygenated PAHs. However, a lower selectivity in 25 C) (Table 1, supporting material) However, some compounds detection when compared to GC-MS-selected ion monitoring (SIM) are not suitable for GC-analysis due to formation of analytical was observed. In some cases, higher concentrations were obtained C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846 1839

þ with GC-ECD than with GCeMS, which is probably due to the molecular ions [M þ H] whereupon they were subjected to frag- presence of compounds that interfered in the ECD. mentation in the collision cell. Fragment ions due to CO and/or þ þ þ A quite novel analytical strategy is the online coupling of sample CO þ H ([M þ H-28] ,[Mþ H-28-28] ,[MþH-28-29] ) elimination þ preparation with subsequent separation and detection in order to were obtained for the quinones, whereas a CO2þH(Mþ H-45] ) further decrease the manual sample pretreatment steps. As such, entity was lost during 4-oxa-benzo[def]chrysene-5-one fragmen- Shimmo and co-workers (Shimmo et al., 2004a,b) developed an tation. These fragmentation schemes were used for the multiple online coupled supercritical fluid extractioneliquid chromatogra- reaction monitoring mode (MRM). Quantification and method phyegas chromatographyemass spectrometry (SFEeLCeGCeMS) validation was done by external calibration because of the technique for the analysis of non-polar compounds (n-alkanes, unavailability of isotopically labeled PAH-diones or other suitable hopanes and steranes), PAHs and alkyl-PAHs, n-alkan-2-ones, n- internal standards. Linearity was investigated in the range between alkanals and oxygenated PAHs on PM. Overall, the method provided 80 and 3250 pg and coefficients of correlation were better than 0.99 a fractionation of the SFE extracts in terms of polarity, and reduced (n ¼ 6). Ion suppression was not significant, showing that inter- the number of peaks in the chromatogram. This resulted into fering matrix constituents are successfully separated during sample a better peak identification and quantification and thus in more preparation and chromatographic separation. LOQs ranged reliable data. between 1 and 58 pg. Although most of the oxygenated PAHs detection is performed 3.3.2. Liquid chromatography methods with MS, fluorescence detection give some advantages for some Although GC methods for oxygenated PAHs analysis are the sub-groups of oxygenated PAHs. Kishikawa et al. (2004a) developed most widely reported, LC offers several advantages, especially a method for the determination of 6 hydroxylated PAHs (2-napthol, when the target compounds are thermally labile, have low vapor 1-napthol, 2-hydroxydibenzofuran, 2-hydroxyfluorene, 9-hydrox- pressures or have highly polar functional groups (Delhomme et al., yphenanthrene and 1-hydroxypyrene) using HPLC with fluores- 2008; Lintelmann et al., 2005, 2006; Valavanidis et al., 2006b). cence detection without any derivatization. Calibration curves were With respect to the ionization mode, typically a choice is made made by spiking particulate matter with standard hydroxylated between atmospheric pressure chemical ionization (APCI), atmo- PAHs solutions to obtain a range of injected measures between spheric pressure photo ionization (APPI) or electrospray ionization 3.6 pg and 2.9 ng. Coefficients of correlation were higher than 0.994 (ESI). Grosse and Letzel (2007) investigated these ionization tech- (n ¼ 3), and detection limits ranged from 1.1 pg (2-hydroxy- niques both in the positive and negative mode for 30 oxygenated fluorene) to 37 pg (9-hydroxyphenanthrene). PAHs under which several PAH-acids, PAH-lactones, (di)hydroxyl- Overall, because of the trace concentrations of oxygenated PAHs ated PAHs, (di)keto-PAHs and mixed functional group PAHs in the atmosphere, the complex matrix in which they occur, and the (hydroxyl, keto, carboxyl groups). The ESI source showed to be not large number of samples needed for an extensive evaluation of useful for the detection of most aromatic compounds. APPI and their occurrence, fate and behavior, the focus in future analytical APCI gave better results and several substances are detectable with research should be on the further development and optimization of both sources using positive and/or negative detection mode (PAH- sensitive and selective analytical methods with a high sample acids, hydroxylated PAHs, dihydroxylated PAHs, PAH ketones, PAH throughput. Innovative sample preparation methods like PLE, SFE diketones, mixed functional group PAHs). Some were exclusively MAE combined with a selective sample clean-up, next to thermal detectable in positive ionization mode (keto-PAHs, PAH-lactones); desorption methods should be further exploited because of their some only in negative mode (hydroxylated PAHs). In conclusion, limited solvent use, fast extraction, and high recoveries. Next to APCI was preferred because of its higher efficiency due to its that, sensitive and selective techniques such as advanced mass simultaneous analyte protonation and deprotonation via solvent spectrometric detection have indicated to be preferable for the ions produced by the electrons in APCI. analysis of oxygenated PAHs on PM matrices, because of their When separation of oxygenated PAHs is performed using LC, ability to distinguish the target compounds from the complex PM tandem MS has recently become the detection method of choice extract. Third, automated systems providing online lab-analysis of (Delhomme et al., 2008; Lintelmann et al., 2005, 2006). Tandem MS oxy-PAHs are desirable when long-term monitoring studies are offers the advantage of producing selective fragmentation patterns, conducted. At the end, there is a need for profound comparative which provides more power for structural information, identifica- studies taking into account both the analytical performance and the tion and quantification. In this context, Delhomme et al. (2008) financial aspects of different techniques. compared ESI with APCI as the ionization method in a triple quadrupole mass spectrometer. The target compounds involved 16 4. Oxygenated PAHs on atmospheric PM samples: reported oxygenated PAHs including 5 ketones and pyrones and 11 dike- concentrations tones. Poor results were obtained in both ESIþ and ESI because most of the oxygenated PAHs could not be detected, while for Research on the occurrence, fate and behavior of oxygenated others the LOD values were relatively high (4e8 ng, see Table 2). In PAHs has received major attention only in the last decade. In Table 3 contrast, using APCI, LODs were decreased to pg order of magni- (supporting material), an overview of reported concentrations is tude. For one subset of oxy-PAHs, i.e. ketones and pyrones, APCIþ given. The table contains literature data from 2000 till 2008 and is was the preferred ionization method (LODs: 2e14 pg), whereas organized as a function of the basic PAHs structures. Information on diketones gave better sensitivity in APCI- (LODs: 3.8e24 pg). The sample matrix, sampling place, sampling period (winter, fall, LC-MS/MS method was externally calibrated for the 16 oxygenated spring, summer) and detected concentrations is included. Infor- PAHs with standard solutions ranging from 0.1 to 10 ng. Good mation about the sampling period is given to highlight seasonal linearity was observed with coefficients of correlation varying from differences that might be linked to changing atmospheric condi- 0.98 (benz[b]fluorene-11-one) to 0.9997 (chromone). tions, and that may affect the oxygenated PAHs fate and behavior Lintelmann and co-workers developed an HPLC-MS/MS method (Fig. 2). Certified concentrations for oxygenated PAHs in standard using a triple quadrupole MS for the analysis of 12 oxygenated PAHs reference materials (SRM) are relatively scarce, but available data in PM-extracts (Lintelmann et al., 2005, 2006). APCIþ was applied on concentrations of oxygenated PAHs in SRM 1649a (urban dust), with an ammonium acetate buffer because of the non-polar char- reported by Albinet et al. (2006) and Cho et al. (2004), are included acter of the target compounds. All substances gave rise to pseudo in the table. Considering the information given in the table and 1840 C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846 recent literature information, at least 3 points deserve special et al., 2007a, 2008a). During these monitoring campaigns, 9H-flu- attention with respect to the occurrence of oxygenated PAHs in the orene-9-one, anthracene-9,10-dione and napthalene-1-carbox- atmosphere. aldehyde represented respectively 20e70%, 10e60% and 10e40% of First, concentration levels of oxygenated PAHs in the environ- the total oxygenated PAHs concentration (Albinet et al., 2008a). ment are in the pg/m3 to lower ng/m3 range depending on the During winter, also 7H-benz[de]anthracene-7-one (0.15e2.05 compound of interest, sampling period and sampling place. To get ng/m3) proved to be a major compound. Also sampling place a more overall view on the oxygenated PAHs concentrations on PM, characteristics can have a significant effect on the observed all data in Table 3 were pooled to calculate the 25th, 50th (median) oxygenated PAHs concentrations. Albinet et al. (2007a) compared and 75th percentiles. For individual oxy-PAHs, 50% of the reported the concentrations (both in gas phase and on PM) of 8 different concentrations are in the range between 80 and 960 pg/m3 oxy-PAHs in the Marseille area and found 3 to 13 and 2e8 times (median: 270 pg/m3 ; n ¼ 689), whereas for individual hydroxylated higher concentrations in the urban and sub-urban environment, PAHs, 50% of the reported concentrations are between 13 pg/m3 and respectively, compared to those measured in rural environments. 14 100 pg/m3 (median: 90 pg/m3; n ¼ 31). By selecting the ring Relatively high concentrations of pyrene-1-carboxaldehyde were number as a grouping factor, results presented in Fig. 4A indicate found in Santiago de Chile during both winter (2.66e4.66 ng/m3) that up to 5 times higher concentrations for 3-ring oxygenated PAHs and spring (2.60e3.58 ng/m3), with the highest in the Providencia are measured, compared with 2-, 4- and 5-ring oxygenated PAHs. sampling site close to a street. This may be an indication that Compared to PAHs and other PAH derivatives, oxygenated PAHs oxygenated PAHs can be a marker for PM from automobiles (Sienra, concentration levels measured during both winter and summer 2006a). Similarly, hydroxylated PAHs are considered to be charac- campaigns in French alpine valleys (Chamonix and Murienne) were teristic for coal combustion processes (together with PAHs) (Wang of the same order of magnitude as those of PAHs, while nitro-PAHs et al., 2007). This might explain why Simoneit et al. (2007) detected concentrations were one to two orders of magnitude lower (Albinet hydroxylated PAHs in winter, but only in cities in northern China (Beijing and Taiyuan) where coal burning is common practice. In order to get a more general view about the concentration levels of oxygenated PAHs in comparison to their parent PAHs, the data in A 1800 Table 3 were used to calculate the concentration ratio between the 1600 individual oxygenated PAHs and their parent PAHs, provided that fi fi 1400 both types of analytes were quanti ed in the same eld study. 1200 Overall, the ratio of the oxygenated PAH versus corresponding PAH concentration ranged between 0.0002 and 27 with a 25th, 50th and 1000 75th percentile of 0.09, 0.70 and 2.62, respectively. This indicates 800 (pg/m³) that this ratio might be largely dependent on the type of compound; 600 the sampling place and sampling season (see further in this Concentration 400 section). 200 Second, with respect to the matrix, it was found by Albinet and 0 co-workers that about 90% of the PAHs, oxygenated PAHs and nitro- 2 (n=80) 3 (n=328) 4 (n=285) 5 (n=27) PAHs are associated with fine particles (PM1.3) during winter (Albinet et al., 2008b). For the finest particles (PM0.39), fractions of B 1600 oxygenated PAHs (56%) and nitro-PAHs (63%) were significantly 1400 higher than for PAHs (45%). This indicates that the more toxic oxygenated PAHs and nitro-PAHs can penetrate deeper into the 1200 respiratory tract. During summer, lower fractions, i.e. 80% for PAHs 1000 and oxygenated PAHs and 60% for nitro-PAHs were associated with 800 fine particles. Fig. 4B, showing the 25th, 50th and 75th percentiles

(pg/m³) 600 of the oxygenated PAHs concentrations listed in Table 3, represents

Concentration a broader view on the oxygenated PAHs occurrence on different 400 particle size fractions. Based on the available data, the median of 200 the oxygenated PAHs concentrations on the total suspended 0 particles is a factor 1.3 and 3.2 higher than that on PM10 and PM2.5, TSP (n=63) PM10 (n=82) PM2.5 (n=229) respectively. More intensive size-fractionated PM sampling and analysis on fixed places and periods might be necessary to gain 2500 C more insight in the oxygenated PAHs distribution between 2000 different PM sizes. Third, clear seasonal trends can be observed not only in the 1500 oxygenated PAHs gas/particle partitioning (see Section 2.2) but also in their concentration levels. Overall, concentrations in summer are 1000 lower than in other periods of the year (Fig. 4C). Whereas the median value of the individual oxygenated PAHs concentrations (pg/m³) 500 during winter (n ¼ 165) is a factor of 1.5 and 1.8 smaller than

Concentration during fall (n ¼ 25) and spring (n ¼ 176) respectively, it is about 0 3e4 times higher than during summer (n ¼ 285). Similarly, the Winter Spring Summer Fall 75th percentile in the winter is 5 times higher than in summer. (n=165) (n=176) (n=285) (n=25) This might be explained by seasonal modulated emissions like residential heating (domestic and communal) and traffic(Albinet Fig. 4. The 25th, 50th, 75th percentiles of the individual oxygenated PAHs concen- trations on PM (pg/m3) listed in Table 3. Data are presented as a function of ring et al., 2008a). For example, about 3 times higher hydroxylated number (Fig. 4A); sampled matrix (Fig. 4B); and sampling season (Fig. 4C). PAHs concentrations were measured in Nanjing (China) in winter C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846 1841 than in summer, probably due to the enhanced coal burning for physicalechemical properties is needed to gain better insight in the house heating and because of the formation of atmospheric behavior of oxygenated PAHs in the environment and in the human inversion layers in the cold season (Wang et al., 2007). With body. respect to the latter, the effect of atmospheric dispersion is shown Accurate and precise analysis of oxygenated PAHs in atmo- by Albinet et al. (2008a) by comparing their results obtained spheric PM is a challenging multi-step task. At first, attention should during sampling campaigns in two Alpine valleys: the Maurienne be paid to avoid sampling artefacts during low or high volume valley and the smaller Chamonix valley. Concentrations in the sampling of PM. Therefore, technical developments such as ozone Chamonix valley were twice as high as compared to those in denuders are evaluated in current research. Second, like in other the wider Maurienne valley, although more international heavy fields of environmental analysis, traditional extraction techniques duty traffic is run in the latter. are Soxhlet and ultrasonic extraction. However, investigating the Seasonal variations in atmospheric conditions and processes potential and applications of innovative solvent extraction tech- might be another possible explanation for the observed seasonal niques such as pressurized liquid extraction, microwave extraction, differences in oxygenated PAHs concentrations. For example, Lin- and supercritical fluid extraction for oxygenated PAHs analysis is telmann et al. (2006) did not measure increased PM associated subject of international on-going research. In quite recent years, oxygenated PAHs concentrations in summer, although this could be also thermal desorption techniques are investigated, with the main expected from increased photochemical activity and higher ozone advantage of eliminating the laborous sample preparation steps. concentrations. This is in agreement with the results of Koeber et al. Next, separation is mostly done using gas chromatography with (1999) who measured higher concentrations of benzo[a]pyrene- mass spectrometry detection using electron impact ionization. 1,6-dione; benzo[a]pyrene-3,6-dione and benzo[a]pyrene-6,12- However, also in this part of the analytical sequence innovations dione in winter than in summer. Moreover, these authors found such as (i) the use of LC based separation, (ii) the use of multidi- a significant correlation between the normalized benzo[a]pyr- mensional chromatography (e.g. GCxGC, LCeGC) and mass spec- enediones concentration (i.e. the ratio of the benzo[a]pyrenedione trometry (tandem MS), and (iii) the online coupling of sample and the total carbon concentration) and the solar irradiation preparation and separation/detection, are intensively explored (W/m2) during winter (R2 ¼ 0.79, n ¼ 19), but no correlation was nowadays. found with other meteorological data (temperature, relative Because of the trace concentrations of oxygenated PAHs in the humidity, wind velocity, wind direction) nor with the benzo[a] atmosphere, the complex matrix in which they occur, and the large pyrene or ozone concentration. During summer, the correlation number of samples needed in monitoring studies, main merit is between solar irradiation and benzo[a]pyrenediones was not clearly attributed to sensitive and selective analytical methods with significant, although higher concentrations were obtained for a high sample throughput. daytime samples. Next to the temperature effect on the oxygenated The recent character of this research field, and the rather short PAHs partitioning (Fig. 2) between gas and particulate phase term monitoring studies dealing with oxygenated PAHs in the (Albinet et al., 2008a), a possible explanation for the observed atmosphere, makes that it is rather preliminary to draw overall seasonal effects might be that higher concentrations of oxidative conclusions with respect to the behavior of these micropollutants species and/or sunlight (inducing photolytical processes) during in the atmosphere. However, some first important indicative summer oxidizes the oxygenated PAHs to smaller not yet identified tendencies, e.g. with respect to the oxygenated PAHs occurrence decomposition products (Koeber et al., 1999). The importance of as a function of type of target compound (or ring number), photochemical activity during summer is also supported by sampled matrix, and seasonal differences, are discussed in this considering the ratio of the individual oxygenated PAH concen- paper. tration listed in Table 3 versus that of the corresponding parent Major challenges for future research include (i) the gain of PAH. During winter, 50% of the ratios are between 0.006 and 0.16 a better insight into the physicalechemical properties of oxygen- (median: 0.08; n ¼ 19), whereas this oxygenated PAH/PAH ratio is ated PAHs, (ii) the further innovation and validation of trace about 20 times higher during summer (50% of the ratios is between analytical methods for identification and quantification of atmo- 0.54 and 3.6; median: 1.75; n ¼ 48). spheric oxygenated PAHs, and (iii) the set-up of systematic moni- However, starting from these important indications to be learnt toring studies to better understand the effects of particular sources, from the available data so far, further research is certainly needed atmospheric processes, and geographic location on the occurrence to better understand the effect of complex atmospheric processes of oxygenated PAHs in the atmosphere, and to better understand and conditions on the oxygenated PAHs concentrations. Therefore, their effects on human health. there is an actual need on more systematic monitoring studies to gain improved insight in the occurrence of atmospheric oxygenated Acknowledgements PAHs in relation to both meteorological conditions on the one hand and health effects on the other hand. Fig. 2 was reprinted from Atmospheric Environment 42, Albinet, A., Leoz-Garziandia, E., Budzinski, H., Villenave, E., Jaffrezo, J.L., 5. Conclusions Nitrated and oxygenated derivatives of polycyclic aromatic hydro- carbons in the ambient air of two French alpine valleys - Part 1: Because of the high potential mutagenic and toxic effects of Concentrations, sources and gas/particle partitioning. 43-54 (2008) oxygenated PAHs, the occurrence, fate and behavior of this group of with permission from Elsevier. This work was supported by the atmospheric organic micropollutants deserve major attention. Both PARHEALTH-project (Health effects of particulate matter in relation direct emission processes and photochemical PAHs conversions to physicalechemical characteristics and meteorology; SE/HE/01A result into the introduction of oxygenated PAHs in the atmosphere, PARHEALTH) funded by the Belgian federal government. typically at pg/m3 to ng/m3 concentration levels. Because of their low volatility (typically less than 0.2 Pa at 25 C), oxygenated PAHs are predominantly sorbed on fine particulates (PM) and aerosols. Appendix. Supplementary material These may enter the human lung and blood systems and induce severe oxidative stress. More research on both primary and Supplementary data associated with this article can be found in secondary sources of oxygenated PAHs and particularly on their the online version at doi:10.1016/j.atmosenv.2009.12.004. 1842 C. Walgraeve et al. / Atmospheric Environment 44 (2010) 1831e1846

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