The Department of Atmospheric and Oceanic Sciences has a longstanding tradition of experimental and theoretical research in atmospheric chemistry and physics. The department is indeed built around a 9-story high precipitation shaft used by Hans Pruppacher to study the growth of water drops. Today the Atmospheric Physics and Chemistry program consists of six nationally and internationally recognized faculty who work together with a number of researchers and graduate students. The research areas cover many of today’s most pressing environmental problems. The investigation of chemical processes in the atmosphere will advance the understanding the formation of the stratospheric ozone hole and smog in urban areas. The genesis and growth of aerosol and cloud particles, as well as their interaction with atmospheric radiation is one of the most uncertain aspects of the global climate and the anthropogenic greenhouse effect. The research activities range from computer modelling to experiments in various laboratories. to field measurements and satellite observations.