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Programm und Abstracts der Sitzung UP 15

Photochemical reactions of trace compounds in snow

•Hans-Werner Jacobi, Thompson Annor, Emmanuel Quansah und 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.

Gas Exchange Experiments using time resolved UV-Spectroscopy

•Kai Degreif^1,2 und Bernd Jähne^1,2
1Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Im Neuenheimer Feld 368, D-69120 Heidelberg
²Institut für Umweltphysik, Im Neuenheimer Feld 229, D-69120 Heidelberg

The air sea gas exchange plays a key role in the development of the earth's climate. The oceans can act as a source or sink for climate relevant gases such as carbon dioxide, methane or dimethyl sulphide. Hydrodynamics in the viscous boundary layer at the free ocean surface and therefore the gas transfer across the interface are not well understood yet and require precise measurements with multiple tracers. UV-spectroscopy is introduced as a new technique for direct and fast measurements of multiple tracer concentrations both in the water and the atmosphere. Volatile aromatic hydrocarbons such as benzene, thiophene, pyridine and derivates and some other species can be measured. The new technique is attractive for two reasons: a) concentrations of volatile species dissolved in water can be measured directly in the water without the need for extraction and b) tracers with a wide range of physicochemical parameters, i.e. Schmidt number and solubility can be measured simultaneously so that a detailed experimental study of the influence of these parameters on air-water gas exchange becomes feasible. The experimental set up and analysis of the spectral data are described. First results from experiments in a 120 cm diameter circular wind-wave-facility in Heidelberg show the significant potentiality of the new technique.

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