Analysis of impact mechanism of the Yangtze River Delta integration upon county-level air pollution

The Yangtze River Delta (YRD) is one of China’s most economically dense regions with the most dynamic county-level economies. The YRD’s success in addressing air pollution at the county level directly affects the ecological security of the Yangtze River Economic Belt. This study utilizes panel data of 151 counties in the YRD from 2003 to 2022. It regards the expansion of members of the YRD Urban Economic Coordination Council as a quasi-natural experiment. This study analyzes the influence of regional integration on county-level air pollution using the difference-in-differences approach, the synthetic difference-in-differences methodology, and spatial econometrics. Our findings indicate that: (1) regional integration can significantly reduce air pollution at the county level; (2) the environmental impact of regional integration is heterogeneous, influenced by regional differences, administrative constraints, and industrial foundations; and (3) regional integration reduces air pollution through advancing industrial structure and technological innovation, along with spatial spillover impacts. Therefore, policymakers should attach importance to air quality governance in counties, deepen regional integration strategies, optimize industrial structures, enhance technological innovation, and strengthen collaborative environmental governance to continuously promote regional sustainable development.