Seminar Physik und Chemie der Atmosphäre (Abstract)

Photochemical processes in surface snow

Hans-Werner Jacobi
Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven

hwjacobi@AWI-Bremerhaven.DE

11.1.2002, 13.00 c.t.
Raum N3380 Several measurements at Arctic and Antarctic sites have demonstrated that unexpected photochemical reactions occur in irradiated surface snow. The results of these reactions are most obvious in the interstitial air of the surface snow. Nitrogen oxides (NO_x) and HONO are emitted by the snow depending on the radiation level. Experiments with artificial snow showed that nitrate dissolved in the snow acts as the NO_x precursor. However, a detailed mechanism is still lacking. Moreover, snow can be a temporary reservoir for compounds like hydrogen peroxide (H₂O₂) and formaldehyde (HCHO), which are emitted or deposited depending on temperature and atmospheric concentration. Even at higher latitudes these exchange processes between the atmospheric boundary layer and the underlying snow surface lead to enhanced photochemical activity comparable to tropical conditions where the radiation level is significantly higher. However, the exchange is also important for the interpretation of ice core profiles. Physical transfer models for H₂O₂ and HCHO have been developed and used for the analysis of firn profiles. Corresponding one-dimensional models, which also include photochemical processes at the surface, are needed for a successful interpretation of further trace gas profiles.