The influence of the OH+NO2+M reaction on the NOy partitioning in the late Arctic winter 1992/1993 as studied with KASIMA

The northern hemispheric winter 1992/1993 is simulated with the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA). The model is a combination of an off-line model using analyses from the European Centre for Medium Range Weather Forecasts up to a pressure altitude of 10 hPa and a mechanistic prognostic model on top with an entire altitude range from 10 up to 120 km. The chemistry scheme included in the model represents the gas phase chemistry as well as heterogeneous reactions on polar stratospheric clouds and on liquid sulfate aerosols. We compare model results with global measurements performed by the instruments of the Upper Atmosphere Research Satellite. The model is able to simulate the global distribution of source gases and long-lived species as well as reactive species in good agreement with the observations. The most significant discrepancies occur inside the vortex where the calculated ozone mixing ratio is overestimated. Below the pressure altitude of 30 hPa inside the vortex the calculated NO2 mixing ratio is underestimated compared to the measurement. A sensitivity study with a new recommendation of the OH + NO2 + M rate constant using the full form of the falloff function for the pressure dependence has been performed. The mixing ratios of the NOy species differ by only about 5% due to the new recommended rate constant inside the vortex with no significant effect on the denoxification.