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CONTRIBUTIONS OF TOLUENE AND Α -PINENE TO SOA FORMED IN AN IRRADIATED TOLUENE/Α-PINENE/NOX/AIR MIXTURE: COMPARISON OF RESULTS USING 14C CONTENT AND SOA ORGANIC TRACER METHODS
Citation:
OFFENBERG, J. H., C. W. LEWIS, M. LEWANDOWSKI, M. JAOUI, T. E. KLEINDIENST, AND E. O. EDNEY. CONTRIBUTIONS OF TOLUENE AND Α -PINENE TO SOA FORMED IN AN IRRADIATED TOLUENE/Α-PINENE/NOX/AIR MIXTURE: COMPARISON OF RESULTS USING 14C CONTENT AND SOA ORGANIC TRACER METHODS. ENVIRONMENTAL SCIENCE AND TECHNOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 41(11):3972-3976, (2007).
Impact/Purpose:
1. The PM chemistry code will be modified to maximize its speed to the extent possible when used in an air quality model. 2. Laboratory and computational chemistry studies will be carried out to assess the extent chemical reactions taking place within PM2.5 affect PM2.5 mass concentrations and compositions. These studies will include free radical, transition metal, and polymerization reactions. 3. The PM chemistry model will be modified to take into account reactions in the aerosols as well as other important chemical processes that significantly affect the ambient concentrations and compositions of PM2.5. 4. The performance of the PM chemistry model within the CMAQ model will be evaluated by comparing model predictions with field data measurements. 5. Special PM chemistry studies will be carried out in collaboration with OAQPS.
Description:
An organic tracer method, recently proposed for estimating individual contributions of toluene and α-pinene to secondary organic aerosol (SOA) formation, was evaluated by conducting a laboratory study where a binary hydrocarbon mixture, containing the anthropogenic aromatic hydrocarbon, toluene, and the biogenic monoterpene, α-pinene, was irradiated in air in the presence of NOx to form SOA. The contributions of toluene and α-pinene to the total SOA concentration, calculated using the organic tracer method, were compared with those obtained with a more direct 14C content method. In the study, SOA to SOC ratios of 2.07 ± 0.08 and 1.41 ± 0.04 were measured for toluene and α-pinene SOA, respectively. The individual tracer-based SOA contributions of 156 µg m-3 for toluene and 198 µg m-3 for α-pinene, which together accounted for 82% of the gravimetrically determined total SOA concentration, compared well with the 14C values of 182 and 230 µg m-3 measured for the respective SOA precursors. While there are uncertainties associated with the organic tracer method, largely due to the chemical complexity of SOA forming chemical mechanisms, the results of this study suggest the organic tracer method may serve as a useful tool for determining whether a precursor hydrocarbon is a major SOA contributor.