In this project, we investigate the effect of urban rail transit expansions in Chinese cities on air quality. We also compare the magnitude of effects across cities and identify the factors behind the potentially heterogeneous effects. By identifying these factors, this project is expected to help policy makers predict the effects of potential new rail systems or expansions on air pollution.
We investigate whether urban rail transit expansion improves air quality, compare the magnitude of effects across cities, and explain any variation across cities. We collect and merge five major data sets: (1) hourly air quality data for all monitoring stations in China since Jan 2013 from the Minister of Environmental Protection; (2) timing of subway building/expansion in all cities from various news sources; (3) detailed weather information from the China Meteorological Administration; (4) polluting industry activity data from Renmin University of China; and (5) city characteristics data from city or provincial yearbooks. We use a difference-in-differences approach that exploits cross-city variation in the timing of the opening or expansion of subway lines. In addition, we investigate the factors behind the possible heterogeneous effects across cities, such as weather, industrial activities, and city characteristics. We expect this study to help policy makers improve the efficacy of subway lines at alleviating air pollution.
The research objectives of this study include:
1) statistically estimating the extent to which subway building/expansions in Chinese cities have improved air quality;
2) identifying the heterogeneous effects of subway expansion on air quality across cities and the driving factors of the heterogeneous effects;
3) delineating the implications of our study for cost-benefit analysis of subway expansion.
