Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 5 2005 10.5194/acpd-5-9547-2005 http://www.atmos-chem-phys-discuss.net/5/9547/2005/ http://www.atmos-chem-phys-discuss.net/5/9547/2005/acpd-5-9547-2005.html http://www.atmos-chem-phys-discuss.net/5/9547/2005/acpd-5-9547-2005.pdf 9547 9580 2005-10-04 Liquid particle composition and heterogeneous reactions in a mountain wave Polar Stratospheric Cloud D. Lowe A. R. MacKenzie H. Schlager C. Voigt A. Dörnbrack M. J. Mahoney F. Cairo Environmental Science Dept., Lancaster University, Lancaster, UK Institute for Atmospheric Physics, DLR, Oberpfaffenhofen, Germany Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA Institute of Atmospheric Sciences and Climate of the National Research Council (CNR-ISAC), Rome, Italy Mountain wave polar stratospheric clouds (PSCs) were detected on 8 February 2003 above the Scandinavian Mountains by in-situ instruments onboard the M55 Geophysica aircraft. The observations of PSC particle composition, backscatter and chlorine activation are studied with a recently developed dynamical microphysical non-equilibrium box model. Results from the microphysical model, run on quasi-lagrangian trajectories, show that the PSC is composed of supercooled ternary (H₂O/HNO₃/H₂SO₄) solutions (STS) particles, which are out of equilibrium with the gas phase. The optical properties of the PSC can well be simulated with the model. Up to 0.15 ppbv Cl₂ can be released by the PSC within 2 h in reasonable agreement with the measured ClO_x concentrations, but high solar zenith angles prevent a direct comparison. Equilibrium calculations commonly used in large scale chemistry transport models poorly represent the measured PSC particle composition and chlorine activation under mountain wave conditions.