The impact of regional integration on PM2.5 concentrations—Quasi-natural experimental evidence from city economic coordination committee

It is of great significance to explore the causality between regional integration (RI) and PM_2.5 pollution within urban agglomerations in the current pursuit of ecological civilization construction and high-quality development. Using panel data of 285 prefecture-level cities in China from 2003 to 2016, this study considers the expansion of the city economic coordination committee in Yangtze River Delta (YRDECC) as a quasi-natural experiment of RI, and use a difference-in difference method to explore the effect and inner mechanisms of RI on PM_2.5 concentration. After a descriptive analysis of the spatial-temporal variation trend of the PM_2.5 concentration in the Yangtze River Delta urban agglomeration, the empirical results show that RI helps to alleviate 4.8% of the PM_2.5 concentration overall. For the original cities, the reduction effect on the PM_2.5 concentration is 5.2%, for the new cities, however, RI exacerbates 2.1% of the local PM_2.5 concentration. A series of robustness tests confirm the validity of the baseline results, and further indicate that the effect of RI remains significant in the long term and starts to increase from the third year. Furthermore, the reduction effect of RI on PM_2.5 concentration is more pronounced in cities with larger scales, more developed economies, and higher degrees of marketization. The mechanism analysis shows that industrial transfer, population migration and technological innovation are significant channels of RI that affect PM_2.5 concentrations. The conclusions of this paper provide a new path to alleviate PM_2.5 pollution and achieve ecological conservation and high-quality development in the city cluster area.