Studies of the Production of Molecular Halogens in Arctic Snowpacks and on Sea Ice Surfaces

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This project would involve field experiments at Barrow, AK, aimed at improving understanding of the oxidation of the sea salt halides, chloride and bromide, into the molecular halogens, Cl2, BrCl, and Br2. In the Arctic at spring time there is a dramatic phenomenon characterized by the complete loss of ozone from the lowest layer of the atmosphere, along with near-complete loss of atmospheric elemental mercury. The elemental mercury is oxidized to short-lived products that then deposit to the surface, where it can enter and damage sensitive ecosystems. These ozone depletion episodes (ODEs) and mercury depletion episodes (MDEs) are known to occur as a result of halogen atom chemistry. However, the details of the halogen reactions that lead to the ODEs and MDEs are still unknown, limiting the ability to develop models that describe these processes, and how they might change in the future. It is thought that the processes that release molecular halogens are related to the presence of seasonal, or first-year (relatively thin and relatively saline), sea ice. The Arctic is currently experiencing a rapid decrease in the extent of multi-year sea ice, with associated increases in the extent of first-year sea ice. Thus the investigator hypothesizes that this halogen chemistry, and the associated potential impacts on atmospheric composition and deposition of mercury, will increase to the extent that the current trend in sea ice loss continues. To improve understanding of the fundamental processes associated with the production of molecular halogens in the Arctic, the investigator proposes an experiment involving exposures of natural snow samples and excised sea-ice samples in a snow chamber to potentially important atmospheric oxidants and measurement of the product molecular halogens. The investigator would also simultaneously conduct measurements of the concentrations of these compounds within the natural snowpack. He would then construct a detailed photochemical model of the chemistry involved with ODEs and MDEs, that could then be incorporated into larger scale Earth System climate and chemistry models to help enable reliable simulations of the future state of the Arctic atmosphere. The project would support a postdoctoral researcher and a graduate student. Numerous outreach activities would be supported through the Purdue Climate Change Research Center, interactions with the local community in Barrow, visits to schools, and through collaboration with adventure and children's book writer Peter Lourie on the web site arcticstories.net.