You are here:
POLYCYCLIC AROMATIC HYDROCARBON (PAH) SIZE DISTRIBUTIONS IN AEROSOLS FROM APPLIANCES OF RESIDENTIAL WOOD COMBUSTION AS DETERMINED BY DIRECT THERMAL DESORPTION - GC/MS
Citation:
Hays**, M D., N D. Smith*, J S. Kinsey*, Y. Dong, AND P. H. Kariher. POLYCYCLIC AROMATIC HYDROCARBON (PAH) SIZE DISTRIBUTIONS IN AEROSOLS FROM APPLIANCES OF RESIDENTIAL WOOD COMBUSTION AS DETERMINED BY DIRECT THERMAL DESORPTION - GC/MS. JOURNAL OF AEROSOL SCIENCE. Pergamon Press Ltd., New York, NY, 34(8):1061-1084, (2003).
Description:
The paper describesd a direct thermal desorption (TDS) approach to determine the PAH composition (MW = 202-302 amu) in size-segregated aerosols from residential wood combustion (RWC). Six combustion tests are performed with two highly available wood fuel varieties, 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). Charger particle loss is accounted for utilizing a novel approach to inversion. Gravimetrically determined PM2.5 (fine particles with aerodynamic diameters < 2.5 micrometers) emission rates (2.3-10.2 g/kg) and matrix-corrected ELPI mass measurements for stages 1-8 (2.7-11.8 g/kg) correspond. Fuel moisture content linearly correlates to the PM2.5 mass geometric mean diameter. Combustion efficiency (CO2/CO) and temperature, O2 levels, and gas dilution temperature affect particle size distributions; geometric mean diameters range from 313 to 662 nm, indicating an accumulation mode. Reconstruction and summation of inverted ELPI data allow for the quantification of 27 individual PAEs (and clusters of structural PAH isomers); PAHs characterize between 0.01 and 0.07 wt% of the PM2.5 mass. Intra- and inter-laboratory comparisons among PAH profiles of RWC indicate that the TDS-ELPI combination performs adequately. Benzo[a]pyrene predominates the PAH emissions. PAH size allocations (geometric mean diameter range = 171-331 nm) are out of phase with PM2.5 mass ones and shifted to finer aerodynamic diameters. Higher and lower MW PAHs preferentially segregate to fine and coarse aerodynamic diameters in that order. The ultrafine mode contains, on average, greater than 80% of the total measured particle number concentration. Values of geometric mean diameter for particulate matter surface area distributions are between 120 and 330 nm. For these tests, PAH mass and PM surface area linearly correlate. Application of a simple function to consider adsorption and absorption mechanisms makes apparent that a) surface and core compositions of PAH of identical MW groups vary with combustion and b) preferential surface adsorption of lower MW PAH is possible. Implications of these results on health effects and source apportionment issues are discussed.