HR: 16:35h
AN: A22G-03    [PDF]
TI: Quantum Yields of OH From the Photolysis of HOOH in Ice
AU: * Chu, L
AF: Atmosphere Science Program, Department of Land, Air, and Water Resources, University of California, One Shields Avenue, Davis, CA 95616-8627 United States
AU: Anastasio, C
EM: canastasio@ucdavis.edu
AF: Atmosphere Science Program, Department of Land, Air, and Water Resources, University of California, One Shields Avenue, Davis, CA 95616-8627 United States
AB: Hydrogen peroxide (HOOH) is a common constituent of snow and cirrus ice clouds. Based on its behavior in aqueous solution, photolysis of HOOH on snow/ice should form hydroxyl radical (OH), a process that might be significant as a loss of HOOH as well as a source of OH. In turn, the formation of OH should lead to the oxidation of organic carbon and halides and subsequent release of these oxidation products (e.g., carbonyls, carboxylic acids, and reactive molecular halogens). Determining the importance and rate of OH generation from HOOH photolysis on snow and ice requires knowing the quantum yields for this process as a function of temperature and other environmental variables (e.g., pH and ionic strength). Since these values have not been previously measured, our goal in this work was to determine these quantum yields (i.e., $\Phi$$_{HOOH->OH}$). Our first step was to measure the molar absorptivities of HOOH between 274 K to 298 K so that we could extrapolate to ice temperatures. There was no temperature dependence of the HOOH molar absorptivity in our measurements, suggesting that the HOOH molar absorptivity is similar in the quasi-liquid layer of ice at low temperatures. Our initial experiments measuring $\Phi$$_{HOOH->OH}$ as a function of temperature (243 - 268 K) show that the values roughly follow the same temperature dependence previously reported for aqueous solution (Zellner et al., 1990). In addition to these results we will also report how $\Phi$$_{HOOH->OH}$ varies as a function of ionic strength and pH. The implications of our measurements for ice particle and snowpack chemistry will also be discussed. Zellner, R.; Exner, M.; Herrmann, H. J. Atmos. Chem. 1990, 10, 411.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0317 Chemical kinetic and photochemical properties
DE: 0322 Constituent sources and sinks
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting