Substantial nitrogen oxides emission reduction from China due to COVID-19 and its impact on surface ozone and aerosol pollution

Abstract

A top-down approach was employed to estimate the influence of lockdown measures implemented during the COVID-19 pandemic on NO_x emissions and subsequent influence on surface PM_2.5 and ozone in China. The nation-wide NO_x emission reduction of 53.4% due to the lockdown in 2020 quarter one in China may represent the current upper limit of China's NO_x emission control. During the Chinese New Year Holiday (P2), NO_x emission intensity in China declined by 44.7% compared to the preceding 3 weeks (P1). NO_x emission intensity increased by 20.3% during the 4 weeks after P2 (P3), despite the unchanged NO₂ column. It recovered to 2019 level at the end of March (P4). The East China (22°N - 42°N, 102°E - 122°E) received greater influence from COVID-19. Overall NO_x emission from East China for 2020 first quarter is 40.5% lower than 2019, and in P4 it is still 22.9% below the same period in 2019. The 40.5% decrease of NO_x emission in 2020 first quarter in East China lead to 36.5% increase of surface O₃ and 12.5% decrease of surface PM_2.5. The elevated O₃ promotes the secondary aerosol formation through heterogeneous pathways. We recommend that the complicated interaction between PM_2.5 and O₃ should be considered in the emission control strategy making process in the future.

Keywords: Aerosols; Control strategy; Covid-19; NO(x) emissions; Ozone.