The Air Pollution Pilot Study of the NATO Committee on the Challenges of Modern Society (CCMS) designed a program to demonstrate and encourage the development of long-range air quality management programs. To demonstrate the application of these techniques to different situations, a series of actual assessment studies was undertaken. Initially, case studies were carried out by the pilot (U.S.) and the co-pilots (Germany and Turkey) in three locations--Ankara, Turkey; Frankfurt, Germany; and St. Louis, United States. This report describes the air pollution assessment study in St. Louis, United States. This report includes the assessment of sulfur oxide and particulate pollution and the assessment of carbon monoxide, nitrogen oxides, hydrocarbon, and oxidant pollution.