Challenges in continuous air quality improvement: An insight from the contribution of the recent clean air actions in China

China's air quality has improved but great challenges of continuous improvement remain. The current understanding on the anthropogenic activities and climate dynamics on air quality improvement is insufficient. Here, we evaluate the impact of pollution control on air quality improvement after controlling for the effects of meteorological conditions. We found that notable urban air quality improvement with an average PM2.5 concentration reduction of 29% from 2015 to 2019 and an even greater reduction during heating seasons. Cities with higher pollution levels tend to exhibit a greater improvement even with fewer financial inputs, suggesting a higher cost efficiency in the improvement, and more financial inputs might be needed to achieve the continuous improvement. Our results demonstrate China's air quality improvement majorly due to the implementation of clean air policies. However, to ensure continuous improvement, greater financial inputs and more adaptive and place-based policies are required.