HR: 14:10h
AN: A13F-02    [Abstracts]
TI: Quantum Yields of OH in the Photolysis of Nitrite Anion and Nitrous Acid in Snow and Ice
AU: * Chu, L
EM: lchu@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
AU: Kundert, K L
EM: klkundert@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
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: The photodecomposition of nitrite anion and nitrous acid (together referred to as N(III)) generates OH radicals and NO in snow and ice. While concentrations of N(III) are much lower than those of nitrate in snow and ice, the photolysis of nitrite could be significant since, compared to nitrate, it absorbs at longer wavelengths (where actinic fluxes are higher) and it is photochemically more efficient, at least in solution. Both OH radical and NO could affect snow chemistry as well as the composition and chemistry of the atmospheric boundary layer. While nitrite and nitrous acid photolysis in aqueous solutions have been studied, the photochemical behavior of N(III) in snow and ice remains unknown. In this study, we first measured the quantum yields of OH radical (Φ(NO₂^-->OH)) from the photolysis of frozen and aqueous NO₂^- solutions using benzoate as a chemical probe for OH. These quantum yields are dependent upon both illumination wavelength as well as temperature. We have determined an expression for this dependence of Φ(NO₂^-->OH) using experiments conducted between 240 and 298 K with illumination at individual wavelengths between 302 to 390 nm at pH 6. We have also determined the photochemistry of N(III) at lower pH values where HNO₂, and perhaps H₂ONO⁺, are the dominant forms of N(III). The results from these experiments in solution at 274 K between pH 1.3 and 6.0 will be discussed, as well as their extrapolation to snow conditions. Finally, we use our results to compare the relative importance of the photolysis of N(III), nitrate, and hydrogen peroxide as sources of both OH and NO_x in the snowpack. From these results we can also predict the pseudo-steady-state concentrations of N(III) that should exist in sunlit snowpacks at different locations.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0317 Chemical kinetic and photochemical properties
DE: 0322 Constituent sources and sinks
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005