Bulk Composition, Structure, and Dynamics of the Atmosphere. Photochemical Processes and Elementary Reactions. Chemistry of the Stratosphere. Chemistry of the Troposphere: The Methane Oxidation Cycle. Ozone in the Troposphere. Hydrocarbons, Halocarbons, and Other Volatile Organic Compounds. The Atmospheric Aerosol. Chemistry of Clouds and Precipitation. Nitrogen Compounds in the Troposphere. Sulfur Compounds in the Atmosphere. Geochemistry of Carbon Dioxide. The Evolution of the Atmosphere. References. Appendix: Supplementary Tables.