Aerosol Science 34 (2003) 1061–1084 www.elsevier.com/locate/jaerosci Polycyclic aromatic hydrocarbon size distributions in aerosols from appliances of residential wood combustion as determined by direct thermal desorption—GC/MS Michael D. Haysa;∗, N. Dean Smitha, John Kinseya, Yuanji Dongb, Peter Kariherb aNational Risk Management Research Laboratory, U.S. Environmental Protection Agency, 109 Alexander Dr MD, E343-02 Air Pollution, Prevention and Control Division, Research Triangle Park, NC 27711, USA bARCADIS, Research Triangle Park, NC 27713, USA Received4 February 2003; receivedin revisedform 7 April 2003; accepted7 April 2003 Abstract In this work, a direct thermal desorption/gas chromatography/mass spectrometry (TD/GC/MS) method is implemented to determine the polycyclic aromatic hydrocarbon (PAH) composition (MW = 202–302 amu) in size-segregatedaerosols from residentialwoodcombustion. Six combustion tests are performedwith two commonly burnedwoodfuel species, Douglas-ÿr ( Pseudotsuga sp.) andwhite oak ( Quercus sp.). Atmospheric dilutionandcooling of the aerosol plume are simulatedin a newly designedwindtunnel,andthe resulting aerosols are size classiÿedwith an electrical low-pressure impactor (ELPI). ELPI stage dataspeciatedby TD/GC/MS were invertedandmodeledusinga log normal distributionfunction. Gravimetrically determined PM2:5 (ÿne particles with aerodynamic diameters [da] ¡ 2:5 m) emission rates (2.3–10:2g=kg) corroborate to matrix-correctedELPI mass measurements of stages 1–8 (2.7–11 :8g=kg). Fuel moisture content linearly 2 correlates (r =0:986) to the PM2:5 mass geometric mean diameter (dg). Combustion eDciency (CO2=CO) andtemperature, O 2 levels, and gas dilution temperature aFect particle size distributions; dg ranges from 313 to 662 nm, indicating an accumulation mode. Reconstruction and summation of inverted ELPI data allow for the quantiÿcation of 27 individual PAHs (and clusters of structural PAH isomers); PAHs characterize between 0.01 and0 :07 wt% of the PM2:5 mass. Benzo[a]pyrene predominates the PAH emissions. PAH size allocations (dg range = 171–331 nm) are out of phase with PM2:5 mass ones andshiftedto ÿner da. Higher andlower MW PAHs preferentially segregate to ÿne andcoarse da in that order. The ultraÿne mode contains on average greater than 80% of the total measuredparticle number concentration. Values of dg for particulate matter surface area distributionsare between 120 and330 nm. For these tests, PAH mass andPM surface area linearly correlate (r2 ¿ 0:913). Application of a simple function to consider adsorption and absorption ∗ Corresponding author. Tel.: +1-919-5413984; fax: +1-919-5410359. E-mail address: [email protected] (M.D. Hays). 0021-8502/03/$ - see front matter ? 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0021-8502(03)00080-6 1062 M.D. Hays et al. / Aerosol Science 34 (2003) 1061–1084 mechanisms makes apparent that (a) surface andcore compositions of PAH of identicalMW groups vary with combustion and(b) preferential surface adsorptionof lower MW PAH is possible. ? 2003 Elsevier Ltd. All rights reserved. Keywords: Thermal desorption; ELPI; PAH; Particulate matter 1. Introduction Substantial evidence links respirable particulate matter (PM) to human morbidity and mortality, especially in susceptible subpopulations (Dockery et al., 1993; Pope, 2000; Samet, Dominici, Curriero, Coursac, & Zeger, 2000). Deposition eDciency of PM in respiratory tract zones (tracheo- bronchial, pulmonary, nasopharyngeal, and thoracic) of humans is size dependent (Phalen et al., 1991; Swift, 1995; Balashazy, Hofmann, & Heistracher, 1999); ÿne particles (aerodynamic diameter, da, ¡2:5 m, PM2:5) for example are primarily conÿnedto the lower respiratory zones ( Tsuda, Rogers, Hydon, & Butler, 2002). Discrete size classiÿcations [coarse (da ¡ 10 m, PM10), ÿne, andultraÿne (da ¡ 0:1 m)] of PM of urban air induce diFerent biological toxicity in in vitro and in vivo models due in part to their chemical compositions varying by size (Diociaiuti et al., 2001; Hauser, Godleski, Hatch, & Christiani, 2001; OberdQorster, 2001). With several anthropogenic andbiogenic source types contributing to the airborne ÿne PM mixture, comprehension of the chemical composition by size on a source category basis is essential from air quality modeling, regulatory, and health standpoints. Aerosol time-of-Right-mass-spectrometry (ATOFMS) (Silva & Prather, 1997; Silva, Liu, Noble, & Prather, 1999), temperature-programmedthermal desorptionparticle beam mass spectrometry (TPTDP) (Tobias & Ziemann, 1999; Tobias et al., 2001) andoF-line analysis of impactor col- lection substrates (Kleeman, Schauer, & Cass, 1999, 2000) are examples of approaches usedto size segregate andchemically proÿle source emissions. On-line ATOFMS classiÿes in real time the inor- ganic andorganic chemical species of individuallysizedparticles but is limitedto chemical species identiÿcation. From the standpoint of the organic chemical composition of nanoparticles within a deÿned size mode, TPTDP discriminates further than ATOFS but is only semi-quantitative to date. In comparison, impactor-based, oF-line methods are quantitative and can be applied to determine organic andelemental carbon, trace element, andwater-soluble ion (sulfate, nitrate, andammonium) concentrations within impactor-resolvedparticle size fractions. In airborne PM, size distributions of polycyclic aromatic hydrocarbons (PAHs) (see, for exam- ple, Allen et al., 1998 or OFenberg & Baker, 1999), some of which are employedas molecular markers for source apportionment, andoxygenatedPAHs ( Allen et al., 1997) were determined by impactor-based methods in past work. The thermal desorption/gas chromatography/mass spectrome- try (TD/GC/MS) approach of Falkovich andRudich(2001) , in particular, overcomes many of the signiÿcant analytical challenges associatedwith the examination of organics in the airborne PM. Their methodrequires no sample preparation, small sample mass, is rapid,sensitive, andaccurate and would, on a temporal basis, oFer better resolution of episodic air pollution events. As eForts in- tensify to develop air quality models that consider size-based particle chemistry, the development of precise size-resolved source proÿles is desirable. To the best of our knowledge, size distribution data of individual organic species from carbon-based emission sources using the thermal desorption (TD) M.D. Hays et al. / Aerosol Science 34 (2003) 1061–1084 1063 technique are virtually nonexistent. These data are needed to advance air quality model predictions of air parcels pollutedwith size-distributedchemicalmixtures. In this work, a direct(TD/GC/MS) methodis utilizedto determinethe PAH composition in size-segregatedPM from RWC, a major ÿne PM source. In the US alone, RWC emits PM to the atmosphere at a rate of 1:1 × 106 metric tons=yr, andup to 30% of the atmospheric PM Rux in the winter months in certain regions can be attributedto RWC ( Nolte, Schauer, Cass, & Simoneit, 2001). In emerging countries, it is a signiÿcant source of ÿne PM in poorly ventilatedindoorair ( Oanh, Nghiem, & Phyu, 2002). These particles by mass (≈ 95%) have da ¡ 400 nm, are rich in organic carbon (¿ 70%), chemically complex, adversely impact health (Larson & Koenig, 1994; Pintos, Franco, Kowalski, Oliveira, & Curado, 1998) andare mutagenic ( Oanh et al., 2002). Because this toxicity andthe PAHs in PM may be linked( Schoey, 1998; Vinggaard, Hnida, & Larsen, 2000), we closely examine the size distribution of a wide molecular weight range (202–302 amu) of PAHs from RWC. Relative PAH concentrations can vary with combustion andwoodfuel conditions;thus, wood combustion appliances, Rame phases, andfuels of diFerentmoisture contents andspecies ( Quercus sp. and Pseudotsuga sp.) were studied. 2. Experimental 2.1. Fuels Two woodfuel species, Douglas-ÿr ( Pseudotsuga sp.) andwhite oak ( Quercus sp.), were selected for testing. These fuels rankedamong the top 10 in a nationwide(UnitedStates) availability indexfor residential wood burning (Fine, Cass, & Simoneit, 2001). Fuel sources were collectedfrom northern Durham County, NC (oak) andreceivedfrom Myren Consulting of Colville, WA (Douglas-ÿr). Wet oak samples were gatheredandsplit on the dayof testing. Wet oak logs were stored(if necessary) in stacks outside, intact, and uncovered. Dry oak samples were split upon delivery and stored inside the woodstove laboratory. The Douglas-ÿr samples at two moisture levels were shipped in large wooden crates, where they remaineduntil testing. On each fuel subsample, moisture contents (Table 1) were measuredas receivedusing ASTM methodsD2961, D3302, D3173. Pre-burn fuel compositions with ASTM methodD3176 were also obtainedon each fuel subsample andshowedvirtually identical atomic mass wt/wt values. Found: C, 42.2–42.8; H, 6.6–6.8; N, ¡ 0:5; O, 50.4–51.3; S, ¡ 0:05; Cl, 20–33 ppm. All values are given as percentages unless notedotherwise. 2.2. Fuel combustion Six combustion experiments were performedin a wood-ÿredtestfacility detailedbyothers ( Purvis, McCrillis, & Kariher, 2000; Gullett, Touati, & Hays, 2003). The facility houses residential ÿreplace (MRC42A; Majestic, Ontario, Canada) and noncatalytic woodstove (3100; Quadraÿre, Colville, WA) appliances, both of which were engaged here. The woodstove was freestanding, fabricated from steel andhada glass windowin the front door.The zero-clearance ÿreplace containeda log grate andglass door.These units were typical of those currently available to consumers in US markets andtestedin previous