The impact of the COVID-19 epidemic on anthropogenic emissions in the Beijing-Tianjin-Hebei region of China based on 3DVar sectoral emission inversion.

The coronavirus disease 2019 (COVID-19) epidemic can be regarded as a significant means of sustained emission reduction over a considerable time period. In this work, we developed and verified a three-dimensional variational initial conditions assimilation and sectoral emission inversion method that combines the integrated source apportionment method and the extremely randomised trees method (ICIS). This study focused on the fine particulate matter (PM2.5) and ozone (O3) concentrations of the Beijing-Tianjin-Hebei (BTH) region simulated by a Community Multiscale Air Quality Modelling System (CMAQ) with data from before and during the COVID-19 epidemic. The area-averaged root mean square errors of PM2.5 and O3 were reduced by 45 % and 29 %. A comparison results using ICIS revealed that the total emissions of PM2.5, nitrogen oxides (NOX), and volatile organic compounds (VOCs) during the COVID-19 epidemic were approximately 77 %, 88 %, and 81 %, of those in the pre-epidemic period. The results of the study indicate that the PM2.5 concentration in Beijing decreased by 5.78 μg/m3 during the epidemic, with the residential, industry, and transportation sectors contributing 39 %, 28 %, and 26 %. An increase in the O3 concentration of 0.05 μg/m3 was observed, which was attributed to changes in the contribution of the transportation sector.