Heterogeneity and typology of the city-level synergy between CO2 emission, PM2.5, and ozone pollution in China

Air pollution and climate change are issues of worldwide concern. Synergizing air pollution control and climate mitigation have been an important national policy of China. This study develops bivariate and integrated synergy indexes (BSI and ISI) to investigate the synergy states between air pollution and CO2 emission. The synergy indexes are based on the correlation coefficient and established from exploiting the internal comparability of the data. Using the BSI and ISI, we evaluated the correlation and synergy states between air pollution (involving ambient PM2.5 and ozone) and CO2 emission in Chinese cities from 2015 to 2020. The results present the city-level trends and heterogeneities of synergy between air pollution and CO2 emission. The averaged value of BSIPM2.5-ozone, BSIPM2.5-CO2, and BSIozone-CO2 for all cities and assessing years were −0.239, −0.291, and −0.242, indicating a generally and globally weak synergy. The synergy states between air pollution and CO2 emission were relatively significant and complex in specific regions. Combined with the local spatial association and decoupling analysis, we further identified the primary variables and key areas for synergistic control. This study provides a systematic idea and case demonstration for city-level synergy assessment through transforming and expanding the data usage capacity. The method and process are applicable to various scales and regions, which would be of reference value for synergy assessments in other countries and regions.