Governance matters: Urban expansion, environmental regulation, and PM2.5 pollution.

Increasing PM2.5 pollution in urban expansion threatens citizens' health. Environmental regulation has proven to be an effective tool to directly combat PM2.5 pollution. However, whether it can moderate the impacts of urban expansion on PM2.5 pollution, in the context of rapid urbanization, is an interesting and unexplored topic. Therefore, this paper constructs a Drivers-Governance-Impacts framework and explores in depth the interactions among urban expansion, environmental regulation, and PM2.5 pollution. Based on 2005-2018 sample data from the Yangtze River Delta region, the estimation results of the Spatial Durbin model imply that (1) urban expansion has an inverse U-shaped association with PM2.5 pollution. The positive correlation may reverse when the ratio of urban built-up land area hits 0.21. (2) Of the three environmental regulations, investment in pollution control has little impact on PM2.5 pollution. Pollution charges and public attention exhibit a U-shaped and inverted U-shaped relationship with PM2.5 pollution, respectively. (3) In terms of moderating effects, pollution charges can exacerbate PM2.5 pollution from urban expansion, while public attention can inhibit it through its monitoring role. Therefore, we suggest that cities adopt differentiated strategies of urban expansion and environmental protection according to their urbanization levels. Meanwhile, appropriate formal regulation and strong informal regulation will help improve air quality.