The report estimates the benefits and costs of historical air pollution control programs under the Clean Air Act by comparing the differences between two scenarios: a scenario which reflects historical economic and environmental conditions observed with the Clean Air Act in place and a hypothetical scenario which projects the economic and environmental conditions which would have prevailed without the federal, state, and local programs developed pursuant to the goals of the 1970 and 1977 Clean Air Acts.

Using a sophisticated array of computer models, EPA found that by 1990 the differences between the scenarios were so great that, under the so-called "no-control" case, an additional 205,000 Americans would have died prematurely and millions more would have suffered illnesses ranging from mild respiratory symptoms to heart disease, chronic bronchitis, asthma attacks, and other severe respiratory problems. In addition, the lack of Clean Air Act controls on the use of leaded gasoline would have resulted in major increases in child IQ loss and adult hypertension, heart disease, and stroke. Other benefits which could be quantified and expressed in dollar terms included visibility improvements, improvements in yields of some agricultural crops, improved worker attendance and productivity, and reduced household soiling damage.

When the human health, human welfare, and environmental effects which could be expressed in dollar terms were added up for the entire 20-year period, the total benefits of Clean Air Act programs were estimated to range from about $6 trillion to about $50 trillion, with a mean estimate of about $22 trillion. These estimated benefits represent the estimated value Americans place on avoiding the dire air quality conditions and dramatic increases in illness and premature death which would have prevailed without the 1970 and 1977 Clean Air Act and its associated state and local programs. By comparison, the actual costs of achieving the pollution reductions observed over the 20 year period were $523 billion, a small fraction of the estimated monetary benefits.

While the estimated net benefits may seem large, they reflect the huge differences between actual historical air quality achieved in the U.S. and a model-predicted world without the Clean Air Act in which seven metropolitan areas in the U.S. would have had higher concentrations of particulate matter (a critical pollutant responsible for much of the adverse human health consequences) than Bangkok, Thailand. Six metropolitan areas would have been worse than Bombay, India; two would have been worse than Manila, Philippines; and one U.S. metropolitan area would even have been worse than Delhi, India (one of the most polluted cities in the world).

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