Air-Snow Exchange of Nitric and Nitrous Acids at South Pole

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The proposed work is an addition to a four-year study of the sulfur chemistry in the antarctic atmosphere, including two summer field seasons at South Pole station, one in 1998-99 and the second to occur in 2000-01. Investigations of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) is a major project, involving ten principal and senior investigators at five institutions with seven additional contributing investigators. During the 1998-99 field season ISCAT scientists found levels of reactive nitrogen in the atmospheric boundary layer at South Pole station that greatly exceeded levels predicted from standard gas phase tropospheric chemistry models. Since it is highly unlikely that these nitrogen species could have been transported in from lower latitudes, it was supposed that there is a local source within the antarctic snow cover. This supposition has enormous consequences because it means that the snow does not act as a simple accumulator and integrator of atmospheric trace gases, and that observed concentrations in snow and ice cores cannot be simply taken as reflecting atmospheric conditions at the time the snow was falling. In the 2000-01 season the observational protocol of ISCAT will include an expanded nitrogen oxide chemistry. Nitric and nitrous acid will be measured both in the atmosphere and in the snow, with the reduced data available in near-real time to guide the ISCAT observational program.