Spatio-Temporal Distribution of Chinese Cities’ Air Quality and the Impact of High-Speed Rail to Promote Carbon Neutrality

With China’s continuous urbanization and industrialization, the emissions in Chinese cities have become increasingly serious. Chinese government has set a goal to reach carbon peak and achieve carbon neutrality, endeavoring to gradually realize net-zero carbon dioxide (CO₂) emission. Moreover, the new transport technology has also been fast developed, represented by the quick expansion of the high-speed rail (HSR) system. Based on the Air Quality Index (AQI) of 286 Chinese cities over the 2016–2019 period, this paper first adopts the spatial auto-correlation analysis to quantify the spatio-temporal characteristics of Chinese cities’ AQI. Then, a spatial difference-in-differences (SDID) model is estimated to shed light on how Chinese cities’ air quality can be affected by HSR. Our paper identifies apparent spatio-temporal distribution patterns in Chinese cities’ air quality. Our empirical results that the HSR opening can help reduce emissions to improve the city’s air quality. Moreover, HSR opening in the adjacent city can also improve one city’s air quality (i.e., the neighboring effect). We also highlight and verify the mechanism of such a positive HSR impact on the city’s air quality. First, as a cleaner transport mode, HSR helps divert traffic from other more polluting modes (i.e., positive direct “transport substitution effect”). HSR also helps promote the city’s tertiary industry, leading to fewer emissions (i.e., positive indirect “industrial structure effect”). Our heterogeneous analyses further demonstrate that HSR is more effective to improve the air quality in eastern and western regions. But the neighboring effect is only obvious in eastern China as the cities are closer to each other in terms of economic relations and geographic locations.