Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 4 2005 10.5194/acpd-5-7361-2005 http://www.atmos-chem-phys-discuss.net/5/7361/2005/ http://www.atmos-chem-phys-discuss.net/5/7361/2005/acpd-5-7361-2005.html http://www.atmos-chem-phys-discuss.net/5/7361/2005/acpd-5-7361-2005.pdf 7361 7386 2005-08-24 The impact of ice uptake of nitric acid on atmospheric chemistry R. von Kuhlmann M. G. Lawrence Max-Planck-Institute for Chemistry, Department of Airchemistry, Mainz, Germany now at: German Aerospace Center (DLR), Bonn, Germany The potential impact of the uptake of HNO₃ on ice on the distribution of NO_y species, ozone and OH has been assessed using the global scale chemistry-transport model MATCH-MPIC. Assuming equilibrium uptake according to dissociative Langmuir theory results in significant reductions of gas phase HNO₃. Comparison to a large set of observations provides support that significant uptake of HNO₃ on ice is occurring, but the degree of the uptake cannot be inferred from this comparison alone. Sensitivity simulations show that the uncertainties in the total amount of ice formation in the atmosphere and the actual expression of the settling velocity of ice particles only result in small changes in our results. The largest uncertainty is likely to be linked to the actual theory describing the uptake process. The inclusion of non-methane hydrocarbon chemistry buffers the overall effect of neglected uptake of HNO₃ on ice. The calculated overall effect on upper tropospheric ozone concentrations and the tropospheric methane lifetime are moderate to low. These results support a shift in the motivation for future experimental and theoretical studies of HNO₃-ice interaction towards the role of HNO₃ in hydrometeor surface physics.