ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-8205-2012 A comparison of the chemical sinks of atmospheric organics in the gas and aqueous phase Epstein S. A. 1 Nizkorodov S. A. 1 Department of Chemistry, University of California, Irvine, Irvine, CA, USA 12 09 2012 12 17 8205 8222 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/8205/2012/acp-12-8205-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/8205/2012/acp-12-8205-2012.pdf

Photochemical reactions represent the main pathway for the removal of non-methane volatile organic compounds (VOCs) in the atmosphere. VOCs may react with hydroxyl radical (OH), the most important atmospheric oxidant, or they can be photolyzed by actinic radiation. In the presence of clouds and fog, VOCs may partition into the aqueous phase where they can undergo aqueous photolysis and/or reaction with dissolved OH. The significance of direct aqueous photolysis is largely uncertain due to the lack of published absorption cross sections and photolysis quantum yields. In light of this, we strive to identify atmospherically relevant VOCs where removal by aqueous photolysis may be a significant sink. The relative importance of different photochemical sinks is assessed by calculating the ratios of the removal rates inside air parcels containing cloud and fog droplets. This relative approach provides useful information in spite of the limited aqueous photolysis data. Results of this work should help guide researchers in identifying molecules that are the most likely to undergo aqueous OH oxidation and photolysis. For example, we find that out of the 27 atmospherically relevant species investigated, the removal of glyceraldehyde and pyruvic acid by aqueous photolysis is potentially an important sink. We also determine the relative magnitudes of these four chemical sinks for the set of relevant organic compounds.

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