Spatial and temporal characteristics of air pollutants and their health effects in China during 2019-2020.

This work presents the temporal and spatial characteristics of the major air pollutants and their associated health risks in China from 2019 to 2020, by using the monitoring data from 367 cities. The annual average PM, PM, NO, SO, CO, and O concentrations decreased by 10.9%, 13.2%, 9.3%, 10.1%, 9.4%, and 5.5% from 2019 to 2020. National average PM concentration in 2020 met the standard of 35 μg/m, and that of O decreased from 2019. COVID-19 lockdown affected NO level dramatically, yet influences on PM and O were less clear-cut. Positive correlations between PM and O were found, even in winter in all five key regions, e.g., Jing-Jin-Ji (JJJ), FenWei Plain (FWP), Yangtze River Delta (YRD), Pearl River Delta (PRD) and Chengdu-Chongqing Region (CCR), indicating importance of secondary production for both PM and O. Large seasonal variability of PM-SO correlation indicates a varying role of SO to PM pollution in different seasons; and generally weak correlations in winter between PM and NO or SO reveal the complexity of secondary formation processes to PM pollution in winter. Multilinear regression analysis between PM and SO, NO and CO demonstrates that PM is more sensitive to the change of NO than SO in JJJ, FWP, PRD and CCR, suggesting a priority of NO emission control for future PM reduction. Furthermore, the new World Health Organization Air Quality Guidelines (WHO AQG2021) were adopted to calculate the excess health risks (ER) as well as the health-risk based air quality index (HAQI) of the pollutants. Such assessment points out the severity of air pollution associated health risks under strict standards: 40.0% of days had HAQI>100, while only 14.4% days had AQI>100. PM ER was generally larger than O ER, but O ER in low PM region (PRD) and during summer became more serious. Notably, NO ER became even more important than PM due to its strict limit of WHO AQG2021. Overall, our results highlight the increasing importance of O in both air quality evaluation and health risk assessment, and the importance of coordinated mitigation of multiple pollutants (mainly PM, O and NO) in protecting the public health.