Polycyclic aromatic hydrocarbon size distributions in aerosols from appliances of residential wood combustion as determined by direct thermal desorption - GC/MS

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-segregated aerosols from residential wood combustion. Six combustion tests are performed with two commonly burned wood fuel species, Douglas-fir (Pseudotsuga sp.) and white oak (Quercus sp.). Atmospheric dilution and cooling of the aerosol plume are simulated in a newly designed wind tunnel, and the resulting aerosols are size classified with an electrical low-pressure impactor (ELPI).. ELPI stage data speciated by TD/GC/MS were inverted and modeled using a log normal distribution function. Gravimetrically determined PM2.5 (fine particles with aerodynamic diameters [d(a)] < 2.5 mum) emission rates (2.3-10.2 g/kg) corroborate to matrix-corrected ELPI mass measurements of stages 1-8 (2.7-11.8 g/kg). Fuel moisture content linearly correlates (r(2) = 0.986) to the PM2.5 mass geometric mean diameter (d(g)). Combustion efficiency (CO2/CO) and temperature, O-2 levels, and gas dilution temperature affect particle size distributions; dg ranges from 313 to 662 nm, indicating an accumulation mode. Reconstruction and summation of inverted ELPI data allow for the quantification of 27 individual PAHs (and clusters of structural PAH isomers); PAHs characterize between 0.01 and 0.07 wt% of the PM2.5 mass. Benzo[a]pyrene predominates the PAH emissions. PAH size allocations (d(g) range = 171-331 nm) are out of phase with PM2.5 mass ones and shifted to finer d(a). Higher and lower MW PAHs preferentially segregate to fine and coarse da in that order. The ultrafine mode contains on average greater than 80% of the total measured particle number concentration. Values of dg for particulate matter surface area distributions are between 120 and 330 nm. For these tests, PAH mass and PM surface area linearly correlate (r(2) greater than or equal to 0.913). Application of a simple function to consider adsorption and absorption mechanisms makes apparent that (a) surface and core compositions of PAR of identical MW groups vary with combustion and (b) preferential surface adsorption of lower MW PAH is possible. (C) 2003 Elsevier Ltd. All rights reserved.