The U.S. Environmental Protection Agency (EPA) promulgates the National Ambient Air Quality Standards (NAAQS) on the basis of scientific information contained in air quality criteria issued under Section 108 of the Clean Air Act. Emphasis is placed on the presentation of health and environmental effects data; however, other scientific data are presented and evaluated in order to provide a better understanding of the nature, sources, distribution, measurement, and concentrations of O3 and related photochemical oxidants and their precursors in the environment. Volume III contains discussion of toxicological effects, human health effects, extrapolation of animal toxicologial data to humans, and an integrative summary of ozone health effects.