The content of this book are lectures and research papers presented at the NATO Advanced Study Institute on -Chemistry of the Unpolluted and Polluted Troposphere-held from September 28 to October 10, 1981, on the Island of Corfu, Greece. The realization of the scientific event was made possible by the sponsorship of the NATO Scientific and Environmental Affairs Division. We must express our gratitude first to this Institution for the important assistance and cooperation we received. For additional assistance we are much obliged to our distinguished co sponsors: Carl Zeiss Werk, Oberkochen, FRGj Biotronik GmbH, Frankfurt, FRGj Bodenseewerk Perkin Elmer u. Co GmbH, Ueberlingen, FRGj and TSI Deutschland Inc., Aachen, FRG. To Mr. Dimitris Bouas, the Director of the Grand Hotel Glyfada, we would like to express our thanks and appreciation for the excellent services. The Center of Environmental Protection of the University of Frankfurt, FRG, conducted the NATO Advanced Study Institute because of the rapidly increased interest in the problems of air chemistry and air pollution. This development has contributed in recent years to a significant expansion of knowledge in the field of atmospheric chemistry, where several of the classic disciplines like meteorology, physics and chemistry have joined in combined research. The Advanced Study Institute offered an ideal opportunity to give a comprehensive survey of the present knowledge in this relatively new field of atmospheric science.