Does urban agglomeration aggravate regional haze pollution? Empirical evidence from urban agglomerations in the middle reaches of the Yangtze River in China

Under China's "new normal," urban agglomeration (UA) has become a new direction for urbanization and regional coordinated development. The urban agglomeration in the middle reaches of the Yangtze River (MRYR-UA) is one of the locations where the haze concentration surpasses the Chinese standard. This study analyzes panel data from 284 Chinese prefecture-level cities from 2005 to 2018 to undertake an empirical investigation based on the MRYR-UA as a quasi-natural experiment for its development planning strategy. The results show that the establishment of the MRYR-UA greatly reduced regional haze pollution. In this paper, social, economic, and natural factors are considered: industrial structure, human capital, and population density can reduce haze pollution, while openness exacerbates urban pollution, confirming the pollution haven hypothesis. The increase in wind speed and rainfall can reduce the concentration of haze. The mediating effect test shows that economic, technological, and structural effects can alleviate haze pollution in the MRYR-UA. The heterogeneity analysis reveals that the number of enterprises decreased in core cities but significantly increased in edge cities, indicating that core cities transferred industrial enterprises to edge cities under the pressure of environmental regulation, resulting in the internal transfer of pollution.