München 2004 – wissenschaftliches Programm

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UP: Umweltphysik

UP 15: Poster: Die „Atmosph
äre“ im Labor

UP 15.1: Poster

Dienstag, 23. März 2004, 14:00–16:00, Schellingstr. 3

Photochemical reactions of trace compounds in snow — •Hans-Werner Jacobi, Thompson Annor, Emmanuel Quansah, and Otto Schrems — Alfred Wegener Institute for Polar and Marine Research Bremerhaven

Photochemical reactions can have important implications for the fate of impurities like inorganic and organic compounds or heavy metals present in natural snow covers. For example, under the influence of solar radiation surface snow serves as a source of NOx. Since the produced NOx is immediately emitted to the atmosphere this process changes the composition of the atmospheric boundary layer over snow-covered regions. Nevertheless, reaction mechanisms and rate constants of photochemical reactions in natural snow are not well known. Therefore, laboratory experiments were performed to investigate if photochemical reactions of further reactive compounds in snow are possible. Laboratory-made snow samples containing single impurities were illuminated with intense UV radiation. After the experiments, remaining amounts of the added compound were determined. We found that H2O2 and HCHO incorporated in artificial snow effectively decompose under the influence of UV radiation. The decompositions followed first-order decay rates indicating photolysis reactions. Such reactions probably lead to the formation of highly reactive radicals like OH or HO2 in the snow. Moreover, we compared the decay rates of H2O2, HCHO and nitrate in a series of experiments under similar conditions.