The Impact of the Clean Air Act on Particulate Matter in the 1970s

We examine whether counties designated as out of attainment with the National Ambient Air Quality Standards (NAAQS) under the 1970 CAA experienced larger reductions in total suspended particulates (TSP) during the 1970s than attainment counties. We answer this question using the official designation of nonattainment status which, between 1972 and 1978, was by Air Quality Control Region. Data from balanced panels of TSP monitors in operation 1969–1978 and 1971–1978 are used to examine the impact of nonattainment status on TSP. We also examine that impact using the definition in the literature, which designates a county as out of attainment if any of its monitors violated the NAAQS.On average, using the official designation, TSP fell by more than 9 μg/m3 more in nonattainment than attainment counties, controlling for county and year fixed effects, county population, employment, and per capita income. The average treatment effect is 10.2 μg/m3 and 9.1 μg/m3 using the 1969 and 1971 panels, respectively. Using the definition of nonattainment in the literature yields similar, albeit slightly smaller, average treatment effects: 6.0 μg/m3 and 7.7 μg/m3 using the1969–1978 and 1971–1978 panels, respectively.