Abstract: The Chinese government is actively promoting the construction of national-level urban agglomerations, but there has been limited attention on their potential role in pollution reduction and carbon emission decrease in the academic circles. Based on the panel data from 19 urban agglomerations in China from 2005 to 2021, this study conducts an empirical study using a difference-in-differences model. The findings show that the national urban agglomeration policy has a pollution reduction and carbon reduction effect, which becomes more pronounced as the policy is implemented for a longer period of time. The driving range of pollution reduction and carbon reduction by central cities is within a radius of 350 to 450 kilometers. The national urban agglomeration policy promotes pollution reduction by increasing the number of environmental practitioners and improving energy utilization efficiency, and promotes carbon reduction by promoting industrial restructuring. However, the mechanisms of pollution reduction and carbon reduction have not demonstrated synergistic effects. The effect of national-level urban agglomeration policies on pollution reduction and carbon reduction is heterogeneous. The urban agglomerations in Chengdu-Chongqing and Central Plains exhibit significant effects on pollution reduction and carbon reduction, while the Harbin-Changchun urban agglomeration shows a significant effect on pollution increase. The central and western cities, the cities with a permanent resident population of over 3 million, and the cities with strong government governance efforts in pollution reduction and carbon reduction demonstrate more significant effects on pollution reduction. The pollution reduction and carbon emission reduction effects of national-level urban agglomeration policies exhibit spatial spillover characteristics, and these spillover effects are more significant compared to the direct effects. Therefore, it is recommended that local governments should accelerate the formulation of urban agglomeration development plans, establish a long-term mechanism driven by the dual goals of pollution reduction and carbon emission reduction, and implement a regional cooperative emission reduction mechanism, jointly promoting the high-quality environmental and economic development in urban agglomerations.

Key words: national-level urban agglomeration policies, pollution reduction and carbon emission decrease, difference-in-differences method, spillover effects