H2O2 and HCHO in Polar Snow and Their Relation to Atmospheric Chemistry

Abstract

Our ability to infer past atmospheric concentrations of hydrogen peroxide (H202) and formalde-hyde (HCHO) from concentrations measured in polar firn and ice cores is limited by our la.ck of understanding of the atmosphere-snow transfer functions for the two species. Continuous H2 02 records going ba.ck into the last century have been obtained from Dye 3 and Summit in central Greenland and Siple in west Antarctica, with some measurements preserved back into the last gla.ciation. HCHO records also extend ba.ck into the last gla.ciation in these sa.me cores. Surface-snow and pit studies clearly show that H20 2 and HCHO concentrations in snow change in the days to weeks after the snow is deposited. It is thought that buried layers reflect seasonal average values, mediated by the a.mount and seasonal pattern of water accumulation and the temperature. Observed surface air concentrations of H20 2 a.nd HeHO at Summit, Greenland in summer are about 3-4 times tliose predicted by photochemical modeling; evaporation from the snow may explain the discrepancy. Development of process models of phase exchange in the snow and firn is essential for interpreting the ice core records of H20 2 a.nd HCHO in terms of trends in the oxidizing power of the atmosphere.