Greening thy neighbor: The impact of cross-border high-speed rail network positions on transboundary air pollution in China

Existing studies mainly examine the environmental effects of high-speed rail (HSR) at the regional level, with limited attention to administrative border areas where pollution externalities interact with jurisdictional fragmentation. This study introduces the concept of cross-border HSR network position (CHSRNP) to capture the relational position of border counties relative to neighboring provinces. We construct three indicators: cross-border HSR degree (CHSRD), cross-border HSR closeness (CHSRC), and cross-border HSR betweenness (CHSRB), and build a unique panel of 626 Chinese provincial border counties from 2007 to 2020. Using a two-way fixed effects model, we find that higher CHSRNP significantly reduces PM 2.5 concentrations in border counties. A one-standard-deviation increase in CHSRD, CHSRC, and CHSRB reduces PM 2.5 concentrations by approximately 0.72%, 0.75%, and 0.63%, respectively. Further analyses show that higher CHSRNP is accompanied by stronger interregional economic linkages and less land supplied by local governments to air-polluting firms. Higher CHSRNP is also generally associated with smaller pollution gaps between border counties and more developed areas. These findings highlight how cross-regional transport networks can reshape the functional role of administrative border areas and provide a new geographical perspective for understanding transboundary pollution governance and environmental inequality.