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IMPACTS OF ANTHROPOGENIC EMISSIONS IN THE SOUTHEASTERN U.S. ON HETEROGENEOUS CHEMISTRY OF ISOPRENE-DERIVED EPOXIDES LEADING TO SECONDARY ORGANIC AEROSOL FORMATION
Impact/Purpose:
The underlying hypothesis of this study is that anthropogenic emissions enhance isoprene SOA formation through the heterogeneous chemistry of isoprene-derived epoxides, possibly leading to light-absorbing SOA in the southeastern U.S. The specific objectives to evaluate this hypothesis include: (1) Leveraging our ongoing Look Rock, TN, field site during the community-led Southern Oxidant & Aerosol Study (SOAS) in summer 2013 to evaluate how isoprene SOA formation chemistry varies between regional and urban influenced air masses; (2) Evaluate the effects of relative humidity, aerosol acidity, and seed aerosol type on the heterogeneous chemistry of isoprene-derived epoxides leading to SOA and how this might yield light-absorbing aerosol constituents (i.e., brown carbon); (3) Evaluate gaseous yields of epoxides from isoprene oxidation under varying initial levels of nitric oxide.
Description:
The proposed activities will yield the formulation of parameterizations that can be incorporated into SOA models that will lead to improvement in the ability to simulate isoprene SOA formation in the southeastern U. S. Specific results include: (1) characterization of reaction pathways that control the oxidation of isoprene in the southeastern U. S. and quantitative assessment of the impact of anthropogenic emissions on these pathways; (2) discover the links between isoprene oxidation, anthropogenic influences, and formation of isoprene-derived SOA; (3) determine the importance of RH, aerosol water content, pre-existing PM, and aerosol acidity on isoprene SOA formation enhanced by anthropogenic emissions; and (4) characterization of isoprene-derived SOA constituents leading to light-absorbing brown carbon. These results will provide improvements that are essential so that air quality models can be used with increased confidence in predicting organic PM2.5.