Laboratory Studies of Polar Tropospheric Chemistry

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Motivated by field observations which demonstrate the importance of atmosphere-aerosol and atmosphere-surface interactions to the polar troposphere, two sets of heterogeneous chemistry laboratory experiments involving ice and seawater substrates will be performed. First, to identify the source of troposheric active bromine, processes which liberate bromide from frozen seawater will be studied. Reactive uptake coefficients of gas-phase molecules capable of oxidizing bromide, including hypobromous acid, hypochlorous acid, chlorine and ozone, will be measured from 233 to 258 K in a flow tube which has its inner walls coated with frozen artificial seawater solutions. The goal from these experiments is to assess the relative efficiencies of these molecules to oxidize bromide. Motivated by the possibility of autocatalytic bromide oxidation, the yield of bromine chloride and bromine from artificial seawater solutions which are exposed to hypobromous acid will be determined. The second focus will be upon measuring the surface coverages of nitric acid, hydrogen peroxide and formaldehyde on ice surfaces over the same temperature range. Previous laboratory studies have been performed at substantially lower temperatures, motivated by polar stratospheric cloud chemistry. The goal of this project is to investigate the chemistry at the temperatures where gases are scavenged in the boundary layer by ice aerosols and the ice surface, and to better understand the atmosphere-ice transfer function which determines the chemical composition of ice cores.