The COVID-19 restrictions in 2020 caused significant changes in NO2 and O3 concentrations in China. This study uses a combined model-measurement approach to isolate the effects of the Chinese New Year (CNY), China's 2018–2020 Clean Air Plan (CAP), and the COVID-19 lockdown on NO2 and O3, also considering meteorological conditions. The impact on the multi-pollutant Health-based Air Quality Index (HAQI) is quantified. Results show that CNY, COVID-19 lockdown, and CAP reduced NO2, while meteorology increased it. The opposite trend was observed for O3. The combined effects drastically reduced multi-pollutant health risks, with meteorology negatively affecting Northeast China. The CAP's contribution highlights the effectiveness of air-quality regulations on NO2 reduction.

Fuzhen Shen, Michaela I. Hegglin, Yuanfei Luo, Yue Yuan, Bing Wang, Johannes Flemming, Junfeng Wang, Yunjiang Zhang, Mindong Chen, Qiang Yang, Xinlei Ge