How does the opening of high-speed railway affect the regional pollution gap in China? From the perspective of knowledge spillover

The rapid development of China's high-speed railway (HSR) has deeply affected the reorganization and reallocation of production elements, which has exerted a profound impact on the regional economic pattern. Existing research lacks attention to how HSR can impulse the regional pollution pattern. The operation of HSR serves a high-speed channel for knowledge spillover, which is an important mechanism to reshape the regional pollution pattern. Based on the data of 250 peripheral cities in China from 2004 to 2018, this paper utilizes a difference-in-differences model (DID) to investigate the impact of HSR opening on regional pollution gap, and provides a mechanism explanation from the perspective of knowledge spillover. It is found that the opening of HSR significantly helps to reduce the industrial pollution gap between HSR cities and central cities. The result remains unchanged after using instrumental variable method (IV) and a series of robustness tests. Heterogeneity tests show that the effect of HSR opening on narrowing the regional pollution gap is greater in the eastern region, areas with low pollution intensity and areas within the half-hour economic circle, and HSR service widens the pollution gap in the western region, areas with high pollution intensity and areas outside the one-hour economic circle. Further mechanism examinations reveal that HSR opening contributes to narrowing the regional pollution gap through knowledge spillover effects, and the knowledge spillover effects driving knowledge improvement to shrink the regional pollution gap is verified. This paper provides a new idea for the balanced regional development of cities in the aspect of environmental protection as well as empirical evidence for promoting environmental equity in China.