This research project was undertaken to investigate the products of selected hazardous air pollutants (HAPs) as they react in the atmosphere. Many hazardous or potentially hazardous organic compounds are emitted into the atmosphere and are subject to chemical change by photolysis, or by reaction with a number of highly reactive species including free radicals ozone, and nitrogen oxides. It is important to understand both the fate and the persistance of a HAP in order to assess its health significance. However, for many HAPs, the major atmospheric reaction products have not been identified. The first phase of this study entailed a literature survey to determine what reaction product information was available for an initial selection of 15 target HAPs. In the second phase of the research, a number of the target HAPs were studied in Battelle's 17.3 cu m smog chamber to determine major reaction products and to derive an estimate of atmospheric lifetime. Those HAPs examined experimentally include propylene oxide, epichlorohydrin, toluene, acrylonitrile, trichloroethylene, benzene, p-dichlorobenzene, aniline, nitrobenzene, chlorobenzene, o-cresol, and phenol. Following the chamber studies, the third phase of the research was devoted to development of field-compatible sampling and analysis methods for those HAP reaction products which: (1) represent a potential hazard and (2) for which current methods are unavailable or unsuitable.