An Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT)

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*** 9809962 McMurry The proposed work is a four-year study of the sulfur chemistry in the antarctic atmosphere, including two summer field seasons at South Pole station in 1998-99 and 2000-01. It is a major project, involving ten principal and senior investigators at five institutions with seven additional contributing investigators. The study has two broad-based goals: to substantially improve our current understanding of the oxidation chemistry of biogenic sulfur in the polar environment, and to improve the climatic interpretation of sulfur-based signals in antarctic ice core records. The decision to base the proposed study at South Pole came from the recognition that the atmospheric boundary layer in the interior would present a homogeneous and relatively simple environment from which to unravel the photochemically driven oxidation chemistry of dimethyl sulfide (DMS). It is based on and has evolved from a number of other sulfur studies during the last decade, including an earlier study at a coastal antarctic site by this group of investigators. Atmospheric sulfur chemistry is an important component in climate change issues because both naturally and anthropogenically emitted sulfur compounds form minute particles in the atmosphere (so-called aerosols) that reflect solar radiation, produce atmospheric haze and acid rain, and affect ozone depletion. Sulfate particles in the atmosphere may also act as condensation nuclei for water vapor and enhance global cloudiness. The primary natural sources of sulfur are volcanic emissions and DMS production by oceanic phytoplankton. On the millenial time scale the variability and natural background level of atmospheric aerosols can be reconstructed from the preserved paleorecords of sulfur oxidation products in ice cores. It is however necessary to understand how the physical and chemical environment of the oxidation process affects the relative concentrations of the oxidation products that become buried in the ice. This study requires simultaneous observations of a wide-ranging suite of sulfur species such as DMS and its oxidation products: sulfur dioxide, dimethyl sulfoxide, dimethyl sulfone, methane sulfonic acid, and sulfuric acid, as well as photochemically important compounds such as carbon monoxide, nitrous oxide, water vapor, and non-methane hydrocarbons. Secondary objectives will be to examine interior antarctic air samples for other significant DMS oxidation products such as sulfurous acid and methane sulfinic acid, and to assess the local variation in hydroxyl and perhydroxyl radicals, a measure of the oxidizing power of the atmosphere. This study will for the first time provide a quantitative picture of exactly which atmospheric sulfur compounds are advected into the antarctic interior, and a detailed picture of the sulfur chemistry that is active in the antarctic atmosphere. *** ??