Simulations of Polar Stratospheric Clouds and Denitrification Using Laboratory Freezing Rates

During the 1999-2000 Arctic winter, the SAGE III Ozone Loss and Validation Experiment (SOLVE) provided evidence of widespread solid-phase polar stratospheric clouds (PSCs) accompanied by severe denitrification. Previous simulations have shown that a freezing process occurring at temperatures above the ice frost point is necessary to explain these observations. In this work, the nitric acid freezing rates derived from laboratory measurements are used in the Integrated MicroPhysics and Aerosol Chemistry on Trajectories (IMPACT) model to calculate both PSC microphysical properties and their net effect on the denitrification process. A range of cases have been explored, including whether the solid-phase PSC particles are composed of nitric acid dihydrate or trihydrate, whether the homogeneous freezing process occurs in the bulk or on the surface of stratospheric particles, and uncertainties in the derived freezing rates. Finally, the possibility that meteoritic debris enhances the freezing rate has also been examined. The results of these winter-long simulations have been compared with key PSC and denitrification measurements made during the SOLVE campaign. The cases that best reproduce the measurements will be highlighted, with a discussion of the implications for our understanding of solid PSC formation mechanisms.