Geographic Resolution in Environmental Policy: EPA's Shift from Regions to Counties Under the Clean Air Act

A large literature uses nonattainment status under the U.S. Clean Air Act (CAA) to measure regulatory stringency and to instrument for air pollution in studies of the impact of the CAA on health and other endpoints. Since 1978 U.S. Environmental Protection Agency (EPA) has regulated ambient air quality at the county level; however, prior to 1978 nonattainment status was imposed on Air Quality Control Regions, contiguous counties that comprise an airshed. This is not the definition of nonattainment used in the literature. Using county-level data, we examine the impacts of EPA’s definition of nonattainment status for TSP, CO, ozone, and SO2 in 1972 on ambient air quality and manufacturing employment between 1969 and 1976 and EPA’s definition of nonattainment in 1978 on air quality and manufacturing employment between 1975 and 1988. Nonattainment status in 1972 had no significant impact on either ambient TSP or on the ratio of dirty manufacturing to total employment between 1969 and 1976. We do, however, find significant impacts on ambient TSP using 1978 nonattainment status, and significant impacts of TSP, CO, ozone and SO2 nonattainment in 1978 on the fraction of employment in dirty manufacturing industries from 1975 to 1988. We discuss the implications of these findings for EPA’s decision regarding the geographic level at which to regulate air pollution.