Power Plant Emissions and Adult Mortality: Evidence from U.S. Acid Rain Legislation

The burning of coal for electricity generation is a major source of pollution emissions in the United States, and historically a large contributor to airborne sulfur dioxide (SO2) levels. As part of the Clean Air Act Amendments of 1990, Congress created the Acid Rain program to reduce airborne sulfate levels. Estimated costs for the program are around $3 billion per year, while earlier calculations estimate the benefits to be around $120 billion per year, $100 billion of which comes in the form of avoided adult mortality. Health benefits of the program, however, are rough estimates, extrapolated by comparing modeled pollution reductions with estimates of health effects from isolated studies. Such estimates fail to account for common problems in measurement of environmental exposure such as avoidance behavior, prior health conditions, and selective migration toward and away from highly polluted areas.

We estimate a more reliable measure of the health effects of SO2, using the substantial short-run variation caused by regulation of power plants under the acid rain legislation. We find the first well-identified evidence of a link between air pollution and mortality among the prime working age population, those aged 35-65. A one part-per-billion reduction in ambient SO2 translates to 0.06 fewer deaths per 1,000 adult population, a decrease of approximately 1% of baseline mortality. Effects are largely driven by cardiovascular mortality. Our findings pass numerous robust checks, including using external deaths and false treatment period assignment to rule out confounding factors. We show no detectable effects for infants or young children. This suggests the mechanism is though prolonged exposure rather than contemporaneous emissions.