A three-step synergy analysis framework for carbon mitigation and pollution reduction in China

Promoting the coordinated governance of carbon emissions and air pollutants is of great significance for optimizing man-land relationship. However, how to systematically track the synergistic effect between carbon mitigation (CM) and pollution reduction (PR) still requires strengthening theoretical construction and empirical analysis. This study established a three-step synergy analysis framework consisting of emission synergy, spatial synergy and response synergy, to explore the synergy between CM and PR of China's 284 prefecture-level cities from 2006 to 2022. The results demonstrated that with 95.77 % of cities commonly reducing carbon emission intensity and PM_2.5 concentration, the coupling coordination degree between CM and PR increased from 0.4370 to 0.7384, transforming from a transition state to a moderate synergy state. Geographically, the emission synergy in the central region was inferior to that in the eastern and western regions. Although the spatial positive synergy between CM and PR strengthened especially in the southeastern coastal area, many cities in the north exhibited the spatial relationship of negative synergy and trade-off. By and large, agglomeration effect, structure effect, innovation effect and policy effect played a positive role in facilitating the synergy, but their impacts were heterogeneous at different quantiles of synergy level. With the improvement of synergy between CM and PR, it is crucial to increasingly strengthen structure and innovation effects, and appropriately optimize agglomeration and policy effects. These findings can provide novel thinking and pathways for coordinating the relationship between climate change and environmental quality.