Intricate synergistic effects between air pollution and carbon emission: An emerging evidence from China

Due to global climate change and intensifying anthropogenic pollution, China confronts the dual challenge of controlling particulate matter 2.5 μm (PM_2.5) pollution and reducing carbon emissions. Quantifying the characteristics of PM_2.5 concentrations and CO₂ emissions, as well as identifying the driving factors and synergistic effects of PM_2.5 reduction and CO₂ mitigation, are crucial steps in promoting sustainable urban development and achieving the Sustainable Development Goals (SDGs) in China. In this study, we selected 168 cities as our case-study, and quantified spatial characteristics of PM_2.5 concentrations and CO₂ emissions from 2015 to 2020 in China. Then we analyzed driving factors affecting the spatial heterogeneity of PM_2.5 reduction and CO₂ mitigation applying Multi-scale Geographically Weighted Regression (MGWR) model. By employing coupling coordination degree (CCD) model, we further detected the spatiotemporal evolution patterns of the synergistic effects between PM_2.5 reduction and CO₂ mitigation in key Chinese cities. The result showed that: (a) From 2015 to 2020, PM_2.5 concentrations experienced a significant reduction from 59.78 μg/m³ to 49.83 μg/m³, while CO₂ emissions increased from 44.88 × 10⁶ t in 2015 to 45.77 × 10⁶ t in 2020; (b) Green economy efficiency (gee), government attention (gover), and environmental regulation (envir) demonstrate the most pronounced synergistic effect on pollution reduction and carbon mitigation, with the drivers exhibiting obvious spatial heterogeneity; (c) The overall coupling coordination level of PM_2.5 pollution and CO₂ emissions in China dropped from 0.49 in 2015 to 0.46 in 2020, and the coupling coordination grade in northern cities was notably higher than that in southern cities. The result enhances our understanding of spatiotemporal patterns of synergistic effects between PM_2.5 reduction and CO₂ mitigation, and provides the theoretical basis for policy decision-making to realize pollution decrease and carbon neutral and regional environment governance.