This paper examines how political partisanship shaped both the designation and
resolution of county-level nonattainment (NA) status for total suspended particulates
under the Clean Air Act. Logistic models show that adding emissions, industrial com-
position, political leadership, and EPA regional effects to pollution measures increases
in-sample accuracy from 81% to 88%, indicating that designations reflected more than
air-quality metrics. Among 1978 NA counties, Cox models with time-varying coeffi-
cients show that Republican-led states attained earlier in the mid-1980s, while counties
with larger annual exceedances transitioned more slowly; both effects diminished over
time. These results highlight evolving political and scientific drivers of NA decisions.
Air Quality Impacts of Metro Rail in Mumbai
with Palak Suri
In this paper, we study the effects of the introduction of Metro Line 1 in Mumbai
on air pollution. We use data on daily average levels of nitrogen dioxide (NO2), sulfur dioxide (SO2), and particulate matter (PM10) from manual ground monitoring stations in an event study framework to identify the changes in pollution levels following the opening of Metro Line 1. We find a robust and significant reduction in the level of NO2 and no evidence of changes in PM10 and SO2. We also find declines in the level of Aerosol Optical Depth measured using satellite data at 1 km resolution and the daily maximum level NOx measured by an automatic monitoring station. We can not rule out that the decline in pollution following the opening of Line 1 is due to a combined effect of Line 1 and the Eastern Freeway flyover, the last segment of which opened a week after Line 1.