A regression discontinuity evaluation of the policy effects of environmental regulations

A regression discontinuity design was applied to measure the short- and long-term policy effects of the air quality improvement plan implemented for the G20 Hangzhou summit. The analysis considered the effects across 11 prefecture-level cities in Zhejiang, China. Five meteorological indicators (temperature, humidity, pressure, wind speed and rainfall) were employed as control variables. Using these control variables, the short- and long-term policy effects were measured in terms of the changes in the air quality index (AQI) and pollutant concentrations (PM2.5, PM10, CO, SO2, NO2 and O3) 1 year and 2.5 years after policy implementation. The results reveal significant short- and long-term effects of the environmental plan on air quality improvement in cities in Zhejiang. The policy effects of the plan for the G20 summit were stronger in Hangzhou than in other prefecture-level cities. In Hangzhou, the short-term policy effects were stronger than the long-term effects, especially in terms of the decreasing AQI, PM2.5 and PM10 levels. Similar regulations should continue to be implemented for lasting improvements in regional air quality.