The report is the result of a study of the emission of air pollutants by aircraft engines in the United States. The objectives of the study were to: (1) Determine the nature and extent of aircraft engine exhaust emissions. (2) Determine the effects or impact of aircraft engine exhaust emissions. (3) Evaluate approaches to reducing the emission of air pollutants by aircraft engines. (4) Evaluate approaches to governmental control of aircraft engine exhaust emissions. In achieving each of these objectives, an attempt was made to compile and analyze, as far as possible, all available relevant information. As a result, the report represents the current level of understanding of the nature, impact, and control of aircraft exhaust emissions. (Author)