Die Atmosphäre als Photochemischer Reaktor

Abstract

The troposphere is a very large photochemical reactor, which transforms enormous quantities of trace gases and aerosols. Future increases of anthropogenic and natural emissions and aerosol formation will continue to change the status of the troposphere and the climate. Here the self-cleansing capability of the troposphere plays a decisive role. The tropospheric oxidation is initiated through a series of oxidants, especially by the hydroxyl radical, OH, but also by ozone, O3, and the nitrate radical, NO3. By their reaction with trace gas molecules, OH radicals are not consumed, but regenerated in catalytic cycles, where the concentration of nitrogen oxides plays a dominant role. This mechanism is general applicable to simple examples of the photochemical reaction system of the troposphere: most reactions of OH radicals with atmospheric trace gas molecules (e.g. methane, anthropogenic or biogenic emitted organic compounds) lead to chain reactions, which regenerate OH radicals. It clarifies that the degradation of trace gas species in a NO-containing atmosphere is irrevocably connected with the production of ozone. It also shows that the self-cleansing capability and consequently air quality and climate change of the troposphere are crucially influenced by the tropospheric photochemistry and the emissions. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.