China's Urban Agglomerations as Drivers of Synergistic Pollution and Carbon Reduction

Wang Ruxiao¹Fengcun Feng^2*Zainab Khalid^3*Ubair Nisar^4*

• ¹Shandong University of Technology, Zibo, China
• ²Zhejiang A and F University, Hangzhou, China
• ³Southeast University, Nanjing, China
• ⁴Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir, Srinagar, India

This study examines whether China’s national-level city cluster policy enhances the synergistic governance of urban pollution reduction and carbon reduction in terms of both “quantity reduction” and “efficiency improvement.” Using panel data from 274 prefecture-level and above cities for the period 2006–2023, the policy is treated as a quasi-natural experiment, and a difference-in-differences (DID) model—augmented by mediating and moderating effect analyses—is employed to estimate its impacts. The results show that the policy significantly reduces PM₂.₅ concentrations and CO₂ emissions in pilot cities while improving governance efficiency. Mechanism analysis identifies three key drivers: green technology innovation, knowledge spillovers, and industrial structure upgrading. Heterogeneity tests reveal that quantitative effects are stronger in hub cities, while efficiency gains are more pronounced in non-resource-based cities; differences between hub and non-hub cities are insignificant for efficiency, and resource endowment differences are insignificant for quantity. This study contributes to the literature in three ways. First, it constructs a dual-dimensional assessment framework to jointly evaluate “quantity reduction” and “efficiency improvement” in synergistic pollution and carbon governance. Second, it uncovers the mechanism pathways through which the city cluster policy operates. Third, it identifies heterogeneous effects across different city types. The findings confirm the dual promotion effect of the policy, the validity of mediating mechanisms, and the existence of regional heterogeneity. Policy implications include maintaining and moderately expanding the pilot programme, institutionalizing joint prevention and control mechanisms, fostering green innovation through talent and technology support, and tailoring city cluster development strategies to local conditions.