9319119 Lamb Atmospheric trace gases frequently contact the surfaces of ice in many clouds, as well as the earth's surface in cold climatic regions. The nature of such heterogenous gas-ice interactions is still largely unknown, so specific experiments have been designed to gain insight into the corresponding molecular-scale mechanisms and to provide quantitative estimates of parameters used in atmospheric models. These experiments will acquire both kinetic and thermodynamic data as inorganic gases in the nitrogen, sulfur and chlorine families are allowed to contact ice particles under controlled conditions. The primary tool for this research will be a new, virtually wall-less, continuous flow reactor with an atmospheric pressure ionization-mass spectrometer interfaced to the reactor for on-line analysis of the gaseous reaction products. The chemical systems which will be studied include SO2 (sulfur dioxide) - O3 (ozone) - ice aerosols, HNO3 (nitric acid vapor) - ice or H2SO4 interpreted in ways that permit multiphase chemical phenomena in the atmosphere to be quantified and understood in terns of nature's fundamental processes.