Atmos. Chem. Phys. Discuss., 13, 10905-10937, 2013
© Author(s) 2013. This work is distributed
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Direct photolysis of carbonyl compounds dissolved in cloud and fog droplets
S. A. Epstein, E. Tapavicza, F. Furche, and S. A. Nizkorodov
Department of Chemistry, University of California, 1102 Natural Sciences 2, Irvine, CA 92697-2025, USA

Abstract. Gas phase photolysis is an important tropospheric sink for many carbonyl compounds, however the significance of direct photolysis of carbonyl compounds dissolved in cloud and fog droplets is uncertain. We develop a theoretical approach to assess the importance of aqueous photolysis for a series of carbonyls that possess carboxyl and hydroxyl functional groups by comparison with rates of other atmospheric processes. We use computationally and experimentally derived Henry's law parameters, hydration equilibrium parameters, aqueous hydroxyl radical (OH) rate constants, and optical extinction coefficients to identify types of compounds that will not have competitive aqueous photolysis rates. We also present molecular dynamics simulations of atmospherically relevant carbonyl compounds designed to estimate gas and aqueous phase extinction coefficients. In addition, experiments designed to measure the photolysis rate of glyceraldehyde, an atmospherically relevant water soluble organic compound, reveal that aqueous quantum yields are highly molecule-specific and cannot be extrapolated from measurements of structurally similar compounds. We find that only three out of the 92 carbonyl compounds investigated, pyruvic acid, 3-oxobutanoic acid, and 3-oxopropanoic acid, may have aqueous photolysis rates that exceed the rate of oxidation by dissolved OH. For almost all carbonyl compounds lacking α, β conjugation, atmospheric removal by direct photolysis in cloud and fog droplets can be neglected.

Citation: Epstein, S. A., Tapavicza, E., Furche, F., and Nizkorodov, S. A.: Direct photolysis of carbonyl compounds dissolved in cloud and fog droplets, Atmos. Chem. Phys. Discuss., 13, 10905-10937, doi:10.5194/acpd-13-10905-2013, 2013.
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