ABSTRACT
Toxic air pollutants are trace chemical compounds present in the air that are harmful to humans. Concern for toxic air pollutants was first expressed in the Clean Air Act of 1977. Toxic air pollutants are also distinguished because their effects extend over limited areas around sources of each pollutant. Strictly speaking this is true for benzene, which causes cancer in laboratory animals, but benzene is emitted in trace quantities from most combustion processes, including automobile engines. The other distinguishing characteristic of toxic air pollutants is that both emissions and ambient concentrations are low compared to the emissions and concentrations of criteria pollutants. Typically toxic air pollutant emissions are measured in pounds rather than tons per year, and the health effects which can result are caused by very small concentrations. The hazardous or toxic air pollutants that are expected to be emitted by a proposed project are the hazard.
