Heterogeneous Chemical Processes of Importance in the Stratosphere

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9322740 Molina The objective of the proposed research is to improve the understanding of the processes responsible for chlorine activation in the stratosphere. These processes involve chemical reactions occurring on polar stratospheric cloud particles and on liquid sulfuric acid aerosols. It is important to have a detailed knowledge of the mechanisms of these heterogeneous reactions in order to make reliable predictions of future ozone depletion, particularly at high latitudes in the Northern Hemisphere. Some of the proposed experiments are designed to probe various aspects of the interaction of HCl (hydrochloric acid) vapor with ice surfaces: They include testing the solvation of HCl by monitoring its isotopic exchange with DCl; investigating the effects of surface morphology; exploring the extent of the uptake at very low HCl partial pressures; etc. The results should help to discriminate among the various HCl uptake mechanisms proposed so far, i.e. physical adsorption vs. formation of a liquid-like layer on the ice surface. Other proposed experiments consist of measurements of the reaction probabilities for chlorine activation processes on liquid H2SO4/(sulfuric acid) HNO3/(nitric acid) HCl/H2O(water vapor) solutions with compositions such as those predicted for aerosol particles in the high-latitude stratosphere. The results of these experiments are potentially of great importance for interpreting the unusually high levels of the ClO (chlorine monoxide) radical observed in some air parcels in the lower stratosphere.