| Abstract
| - Hydrogen peroxide (HOOH) in ice and snow is an important chemical tracer for the oxidative capacities ofpast atmospheres. However, photolysis in ice and snow will destroy HOOH and form the hydroxyl radical(•OH), which can react with snowpack trace species. Reactions of •OH in snow and ice will affect thecomposition of both the overlying atmosphere (e.g., by the release of volatile species such as formaldehydeto the boundary layer) and the snow and ice (e.g., by the •OH-mediated destruction of trace organics). Tohelp understand these impacts, we have measured the quantum yield of •OH from the photolysis of HOOHon ice. Our measured quantum yields (Φ(HOOH → •OH)) are independent of ionic strength, pH, andwavelength, but are dependent upon temperature. This temperature dependence for both solution and ice datais best described by the relationship ln(Φ(HOOH → •OH)) = −(684 ± 17)(1/T) + (2.27 ± 0.064) (whereerrors represent 1 standard error). The corresponding activation energy (Ea) for HOOH (5.7 kJ mol-1) ismuch smaller than that for nitrate photolysis, indicating that the photochemistry of HOOH is less affected bychanges in temperature. Using our measured quantum yields, we calculate that the photolytic lifetimes ofHOOH in surface snow grains under midday, summer solstice sunlight are approximately 140 h at representativesites on the Greenland and Antarctic ice sheets. In addition, our calculations reveal that the majority of •OHradicals formed on polar snow grains are from HOOH photolysis, while nitrate photolysis is only a minorcontributor. Similarly, HOOH appears to be much more important than nitrate as a photochemical source of•OH on cirrus ice clouds, where reactions of the photochemically formed hydroxyl radical could lead to therelease of oxygenated volatile organic compounds to the upper troposphere.
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