Disentangling Effects of Anthropogenic Emission Reductions and Meteorology on Air Pollution Changes and Associated Health Risks during the COVID-19 Lockdown in China

The Covid-19 restrictions in 2020 have led to obvious reductions in air pollutant emissions in China. Meanwhile, not only anthropogenic emissions but also meteorological conditions can contribute to variations in air pollutant concentrations and related health risks, especially for NO2. Here, quantification of the isolated anthropogenic emission changes including the effects of the Chinese New Year (CNY), Chinas Clean Air Plan (CAP) over the 2018 to 2020 period, and the Covid-19 lockdown was attempted by using a combined model-measurement approach based on in-situ observations and the Copernicus Atmosphere Monitoring Service Reanalysis (CAMSRA). The contribution of prevailing meteorological conditions to the emission changes was evaluated by applying a machine learning method. To comprehensively evaluate the health risks from the resulting variations in air pollutants under the Covid lockdown, a multiple-air-pollutant health index was compared between two scenarios with and without the Covid restrictions. The results show that anthropogenic NO2 emissions declined by -26.7% and -15.7% under the impact of the CNY and the CAP across China, respectively. Excluding the combined effects of the CAP and CNY, the average anthropogenic emissions of NO2 across China during the CNY in 2020 and the Total Covid period were reduced by -11% and -37.9%, respectively. During the Total Covid period, meteorological conditions led to NO2 increases of 7.8% when compared to climatological 2015-2019 conditions. Meanwhile, the Health-based Air Quality Index (HAQI) was reduced by -22.9% in most cities across China during the Total Covid period. Our results show that meteorological conditions prevailing in 2020 led to an adverse effect on air pollution in China, while air quality regulations introduced by the Chinese government over the 2018-2020 period have led to significant improvements in air quality. Neglecting these opposite drivers (as done in most previous studies) thus would have led to an underestimate and overestimate of the effect of the Covid lockdown on NO2 reductions and the HAQI, respectively.