Three-dimensional model simulations of SF6 with mesospheric chemistry

Multiannual integrations with the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) have been performed using meteorological analyses of vorticity and divergence up to 10 hPa to analyze the influence of a simplified SF6 mesospheric chemistry on estimation of mean age of air and to compare profiles of SF6 mixing ratios observed in the stratosphere with model simulations. The chemical degradation scheme includes electron attachment of SF6 and subsequent reactions of SF6- such as photodetachment and charge transfer with ozone. Several combinations of reaction rate constants and electron profiles have been tested. Good agreement with observations is found for inert SF6 transport. However, when mesospheric loss is included in the model, significant deviations are found for polar winter observations above 25 km. Chemical loss by electron attachment without reactions yielding SF6 again is not compatible with observations. The atmospheric lifetime of SF6 spans 400 to 10,000 years, depending on the assumed loss mechanism and the value for the electron density in the stratosphere.