Uncertainties in modelling heterogeneous chemistry and Arctic ozone depletion in the winter 2009/2010
Stratospheric chemistry and denitrification are simulated for the Arctic winter 2009/2010 with the Lagrangian Chemistry and Transport Model ATLAS. A number of sensitivity runs is used to explore the impact of uncertainties in chlorine activation and denitrification on the model results. In particular, the efficiency of chlorine activation on 5 different types of liquid aerosol versus activation on nitric acid trihydrate clouds is ex-amined. Additionally, the impact of changes in reaction rate coefficients, in the particle number density of polar stratospheric clouds, in supersaturation, temperature or the ex-tent of denitrification is investigated. Results are compared to satellite measurements of MLS and ACE-FTS and to in-situ measurements onboard the Geophysica aircraft 10 during the RECONCILE measurement campaign. It is shown that even large changes in the underlying assumptions have only a small impact on the modeled ozone loss, even though they can cause considerable differences in chemical evolution and den-itrification. In addition, it is shown that chlorine activation on liquid aerosols alone is able to explain the observed magnitude and morphology of the mixing ratios of active 15 chlorine, reservoir gases and ozone.