Collaborative research: Quantifying the Sensitivity of Antarctic Snowpack Nitrate to Primary NOx Sources and Photodenitrification: Implications for the Ice Core Record

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The processes that form, transport and recycle the reactive forms of nitrogen in the atmosphere are important in global air quality, atmospheric nutrient deposition, and for controlling the long term oxidation capacity of the atmosphere. The NOx gases (NOx = NO + NO2) are also important greenhouse gases. The ultimate goal being pursued in this modeling study is the understanding of past (polar) atmospheric composition, and through a better accounting of the variability of contemporary atmospheric reactive nitrogen compounds as may be discerned from measurements of nitrate concentrations retained in snow, firn and ice cores on the Antarctic continent. The approach will use a inverse chemical transfer model (adjoint GEOS-Chem) to test the sensitivity of nitrate deposition to Antarctic ice from various possible sources. By integrating a snowpack radiative transfer subroutine into the chemical transport model, comparisons of calculated with observed fluxes of snowpack NOx at some observed inland and coastal Antarctic sites are to be used to parameterize photdenitrification rates. An additional question to be investigated with the developed modeling tools is what fraction of the nitrate concentration undergoing photolysis at the snow surface is recycled back to the atmosphere, or else preserved in the accreting ice.