The effect of subway development on air pollution: Evidence from China

This paper investigates the relation between subway development and air pollution. Using yearly data from 160 Chinese cities from 2014 to 2017 and the spatial difference-in-differences (SDID) method, we obtain four findings. First, air pollution has a positive spatial spillover effect, and the impact of subway development will be overestimated if this spillover effect is not considered. Second, we find that increasing the mileage of subways will reduce the level of air pollution. Third, the development of subways has different impacts on various air pollutants. Subway system development can reduce the concentrations of PM2.5 and PM10 but has no obvious impacts on SO2, NO2, CO and O3. Fourth, different development modes for the subway system have different impacts on reducing air pollution. Increasing the mileage, lines and stations of subways could decrease the levels of air quality index (AQI) and PM2.5, but increasing the mileage and stations of subways have negative but nonsignificant effects on PM10. Thus, policymakers should focus on actively advocating for green transportation and the rational planning of subway system networks.