The Impact of Metro Systems on Smog Reduction: Evidence from Chinese Cities

This study uses data from 2009 to 2023 and a difference-in-differences model to analyze the impact of metro construction on smog pollution in Chinese cities. The results show that metro significantly reduces smog levels, with the effect remaining robust after several sensitivity checks. Mechanism analysis suggests that the reduction in smog is driven primarily by alleviating road traffic congestion, promoting transit-oriented development, and generating technological spillovers. Further heterogeneity analysis reveals that cities with higher metro coverage and those with an industrial base experience more significant reductions in smog, while service-oriented cities show weaker effects. The study provides valuable insights for policymakers, offering empirical evidence to optimize urban transportation and environmental policies in the fight against smog. These findings contribute to the broader understanding of how metro systems can support sustainable urban development and improve air quality.