A systematic assessment of city-level climate change mitigation and air quality improvement in China

China is facing dual challenges of air pollution and climate change. By using city-level data, we comprehensively assessed air quality and CO2 emission changes from 2015 to 2019 for 335 Chinese cities. We selected important regions for air pollution control and categorized all cities into different classes according to their development levels. Our novel approach revealed new insights on different patterns of changes of PM2.5, O3, and CO2 by region and city class. We found that PM2.5 concentrations decreased remarkably due to mandatory city-level reduction targets, especially in the Beijing-Tianjin-Hebei (−27%) region. Nonetheless, O3 concentrations and CO2 emissions increased in 91% and 69% of Chinese cities, respectively. Observed CO2 emission reductions in more developed cities were mainly due to prominent energy intensity reduction and energy structure improvement. Our study indicates a lack of synergy in air pollution control and CO2 mitigation under current policies in China. To address both challenges holistically, we suggest setting mandatory city-level CO2 emission reduction targets and reinforcing clean energy and energy efficiency measures. [Display omitted] •City-level trends in PM2.5, O3, and CO2 were not consistent in China from 2015 to 2019.•Air quality varied by region not city class; CO2 emissions varied by city class not region.•Mandatory city-level reduction targets were effective in reducing PM2.5 concentrations.•China should set mandatory city-level CO2 emissions reduction targets based on development levels.