Atmos. Chem. Phys. Discuss., 11, 6457-6492, 2011
www.atmos-chem-phys-discuss.net/11/6457/2011/
doi:10.5194/acpd-11-6457-2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Yields of hydrogen peroxide from the reaction of hydroxyl radical with organic compounds in solution and ice
T. Hullar and C. Anastasio
Department of Land, Air and Water Resources, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA

Abstract. Hydrogen peroxide (HOOH) is a significant oxidant in atmospheric condensed phases (e.g., cloud and fog drops, aqueous particles, and snow) that photolyzes to form hydroxyl radical (·OH). ·OH can react with organics in aqueous phases to form organic peroxyl radicals and ultimately reform HOOH, but the efficiency of this process in atmospheric aqueous phases, as well as snow and ice, is not well understood. We investigate HOOH formation from ·OH radical attack of 10 environmentally relevant organic compounds: formaldehyde, formate, glycine, phenylalanine, benzoic acid, octanol, octanal, octanoic acid, octanedioic acid, and 2-butoxyethanol. Liquid and ice samples with and without nitrate (as an ·OH source) were illuminated using simulated solar light, and HOOH formation rates were measured as a function of pH and temperature. For most compounds, the formation rate of HOOH without nitrate were the same as the background formation rate in blank water (i.e., illumination of the organic species does not produce HOOH directly), while formation rates with nitrate were greater than the water control (i.e., reactions of OH with the organic species forms HOOH). Yields of HOOH, defined as the rate of HOOH production divided by the rate of ·OH production, ranged from essentially zero (glycine) to 0.24 (octanal), with an average of 0.12 ± 0.05 (95% CI). HOOH production rates and yields were higher at lower pH values. There was no temperature dependence of the HOOH yield for formaldehyde or octanedioic acid between −5 to 20 °C and ice samples had approximately the same HOOH yield as the aqueous solutions. In contrast, HOOH yields in formate solutions were higher at 5 and 10 °C compared to −5 and 20 °C. Yields of HOOH in ice for solutions containing nitrate and either phenylalanine, benzoate, octanal, or octanoic acid were indistinguishable from zero. Our HOOH yields were approximately half that found in previous studies conducted using γ-radiolysis, but this difference might be due to the much lower (and more environmentally relevant) ·OH formation rates in our experiments.

Citation: Hullar, T. and Anastasio, C.: Yields of hydrogen peroxide from the reaction of hydroxyl radical with organic compounds in solution and ice, Atmos. Chem. Phys. Discuss., 11, 6457-6492, doi:10.5194/acpd-11-6457-2011, 2011.
 
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