H₂O₂ in Solid Precipitation

Abstract

H₂O₂ concentrations up to 20 µeq/l were found in snow from alpine regions. To extract useful information for atmospheric chemistry models, the snow concentration has to be translated into atmospheric concentrations. To do so, two questions have to be answered first: 1) The stability of H₂O₂ snow and ice, 2) the scavenging ratio c_air/c_snow and its dependence upon the formation of the snow.

To investigate the first question, we measured during winter 1985/1986 the H₂O₂ in snow profiles at the experimental snow field of the Snow and Avalanche Research Institute, Weissfluhjoch-Davos, Switzerland, situated at an altitude of 2500 m.a.s.l. The results show a degradation of H₂O₂ in the snow with increasing age. The degradation is linked to the exposure of the snow to sunlight. The second question has only recently been adressed by measuring the H₂O₂ concentration in the gas phase, fog droplets and precipitation during a winter precipitation event. The H₂O₂ concentration in the fog droplets and the precipitation is determined by both, the gasphase concentration and chemical reactions occuring in the cloud droplets.