The City-Level Effects of the 1990 Clean Air Act Amendments
研究了1990年《清洁空气法》修正案是否导致加州1990-2000年间PM10浓度下降，发现城市层面的未达标认定解释了6%的浓度降低，而县级层面效应不显著。
This paper examines whether the 1990 Clean Air Act Amendments caused the decline in ambient concentrations of particulate matter (PM10</sub>) in California over the 1990-2000 period. Consistent with previous studies, we find that PM10</sub> nonattainment status at the county level is not a significant factor in explaining the reductions in PM10</sub>. However, when we allow for spatially heterogeneous treatment effects <i>within</i> nonattainment counties, and incorporate measures of community characteristics, climate, geography, transboundary pollution, and industrial composition and scale, we find that nonattainment designations at the city level account for a 6% reduction in ambient PM10</sub> concentrations.