| Summary: | Heterogeneous reactions on polar stratospheric clouds (PSCs), such asClONO2+HCl—Cl2+HNO3, are important for an understanding of the production of active chlorine species (HOCl,Cl2) and Antarctic ozone depletion.H2O-ice forms the Type II PSCs and the nature ofH2O-ice surfaces under stratospheric conditions may affect the heterogeneous chemistry. This review focuses on recent measurements ofH2Oadsorption kinetics on ice,H2Odesorption kinetics from ice,H2Osurface diffusion on ice andH2Odiffusion into ice. These measurements reveal that the ice surface is extremely dynamic under polar stratospheric conditions. For example, the residence time for anH2Omolecule on an ice surface at 188 K is only ~20 milliseconds before desorption and only ~0.4 milliseconds before diffusion into the ice bulk. The dynamic nature of the ice surface may significantly affect the adsorption, solvation, diffusion and reaction of the chlorine reservoir molecules (ClONO2, HCl). The dynamic ice surface may also serve as a model for the surfaces of other molecular solids.
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