Score contribution per author:
α: calibrated so average coauthorship-adjusted count equals average raw count
We assess the US Clean Air Act standards for fine particulate matter (PM2.5). Using high-resolution data, we find that the 2005 regulation reduced PM2.5 levels by 0.4 μg/ m3 over five years, with larger effects in more polluted areas. Standard difference-in-differences overstates these effects by a factor of three because time trends differ by baseline pollution, a bias we overcome with three alternative approaches. We show that the regulation contributed to narrowing Urban-Rural and Black-White PM2.5 exposure disparities, but less than difference-in-differences suggest. Pollution damages capitalized into house prices, however, appear larger than previously thought when leveraging regulatory variation.