Source Apportionment of PM2.5 in the Southeastern United States Using Solvent-Extractable Organic Compounds as Tracers

TLDR

A chemical mass balance receptor model using particle‑phase organic compounds as tracers was applied to apportion primary source contributions to fine particulate matter and organic carbon in the southeastern United States and to assess their seasonal variability. Source contributions to PM2.5 were calculated from monthly composite samples collected at four urban and four rural/suburban sites in Alabama, Florida, Georgia, and Mississippi during April, July, October 1999 and January 2000, with organic compounds identified and quantified by gas chromatography/mass spectrometry and used as molecular markers in the CMB model. Wood combustion, diesel exhaust, meat cooking, and gasoline‑powered vehicle exhaust were the dominant contributors to PM2.5 organic carbon, together accounting for about 89 % of PM2.5 mass when secondary aerosol formation is included, with higher wood combustion in October and January and greater unexplained organic carbon in July likely due to secondary organic aerosol.

Abstract

A chemical mass balance (CMB) receptor model using particle-phase organic compounds as tracers is applied to apportion the primary source contributions to fine particulate matter and fine particulate organic carbon concentrations in the southeastern United States to determine the seasonal variability of these concentrations. Source contributions to particles with aerodynamic diameter ≤2.5 μm (PM2.5) collected from four urban and four rural/suburban sites in AL, FL, GA, and MS during April, July, and October 1999 and January 2000 are calculated and presented. Organic compounds in monthly composite samples at each site are identified and quantified by gas chromatography/mass spectrometry and are used as molecular markers in the CMB model. The major contributors to identified PM2.5 organic carbon concentrations at these sites in the southeastern United States include wood combustion (25−66%), diesel exhaust (14−30%), meat cooking (5−12%), and gasoline-powered motor vehicle exhaust (0−10%), as well as smaller but statistically significant contributions from natural gas combustion, paved road dust, and vegetative detritus. The primary sources determined in the present study when added to secondary aerosol formation account for on average 89% of PM2.5 mass concentrations, with the major contributors to PM2.5 mass as secondary sulfate (30 ± 6%), wood combustion (15 ± 12%), diesel exhaust (16 ± 7%), secondary ammonium (8 ± 2%), secondary nitrate (4 ± 3%), meat cooking (3 ± 2%), gasoline-powered motor vehicle exhaust (2 ± 2%), and road dust (2 ± 2%). Distinct seasonality is observed in source contributions, including higher contributions from wood combustion during the colder months of October and January. In addition, higher percentages of unexplained fine organic carbon concentrations are observed in July, which are likely due to an increase in secondary organic aerosol formation during the summer season.