Collaborative Research: Impact of Snow Photochemistry on Atmospheric Radical Concentrations at Summit, Greenland

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Blake0220862In the past few years there has been an explosion of scientific interest in the chemical processing occurring in sunlit snow. Rather than simply acting as a passive sink for the products of tropospheric reactions, the snowpack has been shown to be one of the most photochemically active, and strongly oxidizing, regions of the entire troposphere. The group of investigators assembled for this proposal has played a central role in this revolution in our thinking about the role of the snowpack in atmospheric chemistry. One key finding has been that photolysis of snow chromophores initiates the release of a number of important trace gases. Initial modeling suggests that photolysis of a number of these gases (HCHO, HOOH, CH3CHO and HONO) results in an enormous production of HOx (i.e., OH and HO2), which in turn causes a large enhancement of these radicals in the snowpack and in the air just above the snow. Because oxidation by OH is the main sink for many tropospheric gases, including some of those important for climate change and stratospheric O3 depletion, this enhancement in HOx might significantly perturb tropospheric chemistry. Snowpack chemistry likely also modifies the chemical records of atmospheric composition ultimately preserved in glacial ice. While recent work has shown that photochemical and physical processes in the snowpack can impact the chemistry and composition of both the atmosphere and snowpack, these processes are, in general, poorly understood. This is especially true for the processes that produce and consume OH and HO2. The research will elucidate the processes that produce and consume OH and HO2 radicals within and above sunlit snow over a wide range of environmental conditions, thereby improving our understanding of fast photochemistry within this unique environment.