Presented here are authoritative and up-to-date assessments of the homogenous and heterogenous chemical and physical processes occuring in the troposphere and stratosphere, especially during the "ozone hole" event. The book begins with an overview of atmospheric chemistry, followed by reviews of relevant homogenous reactions in the gas phase and the microphysics and physical chemistry of heterogenous processes that occur on, or in aerosols, rain and ice. Low temperature laboratory studies are compared with related fieldwork measurements, particularly in relation to the formation and composition of polar stratospheric clouds. Also discussed are measurements in glacial ice. Finally chemical modelling of the troposphere and stratosphere, including heterogenous processes, is reviewed.