Abstract
We use the global Community Earth System Model to investigate the response of secondary pollutants (ozone O3, secondary organic aerosols SOA) in different parts of the world in response to modified emissions of primary pollutants during the COVID‐19 pandemic. We quantify the respective effects of the reductions in NOx and in volatile organic carbon (VOC) emissions, which, in most cases, affect oxidants in opposite ways. Using model simulations, we show that the level of NOx has been reduced by typically 40% in China during February 2020 and by similar amounts in many areas of Europe and North America in mid‐March to mid‐April 2020, in good agreement with space and surface observations. We show that, relative to a situation in which the emission reductions are ignored and despite the calculated increase in hydroxyl and peroxy radicals, the ozone concentration increased only in a few NOx‐saturated regions (northern China, northern Europe, and the US) during the winter months of the pandemic when the titration of this molecule by NOx was reduced. In other regions, where ozone is NOx‐controlled, the concentration of ozone decreased. SOA concentrations decrease in response to the concurrent reduction in the NOx and VOC emissions. The model also shows that atmospheric meteorological anomalies produced substantial variations in the concentrations of chemical species during the pandemic. In Europe, for example, a large fraction of the ozone increase in February 2020 was associated with meteorological anomalies, while in the North China Plain, enhanced ozone concentrations resulted primarily from reduced emissions of primary pollutants.
Highlights
With the development of the COVID-19 pandemic and the resulting slowdown in economic activity, first in China and in the rest of the world, anthropogenic emissions of primary pollutants were significantly altered after January 2020
In the model simulations presented we address this particular uncertainty by considering a case in which the high volatile organic carbon (VOC) emission reduction of Doumbia et al (2021) is adopted and a case in which no reduction in VOC and carbon monoxide (CO) emissions is applied
The response of photooxidants to the simultaneous reductions in nitrogen oxides (NOx), VOC, and CO emission has varied according to the geographic location and the time of the year
Summary
During the COVID-19 lockdown, the atmospheric concentration of primary pollutants (NOx, VOCs, CO, SO2) was considerably reduced. The concentration of secondary pollutants increased in NOxsaturated areas and decreased in NOx-limited areas. Global Changes in Secondary Atmospheric Pollutants During the 2020 COVID-19 Pandemic. Benjamin Gaubert , Idir Bouarar, Thierno Doumbia, Yiming Liu, Trissevgeni Stavrakou , Adrien Deroubaix , Sabine Darras, Nellie Elguindi , Claire Granier, Forrest Lacey , Jean-François Müller , Xiaoqin Shi , Simone Tilmes , Tao Wang, and Guy P. Brasseur Formal analysis: Benjamin Gaubert, Idir Bouarar, Yiming Liu, Trissevgeni Stavrakou, Adrien Deroubaix, Nellie Elguindi, Forrest Lacey, Jean-François Müller, Xiaoqin Shi, Simone Tilmes, Tao Wang, Guy P. Brasseur Methodology: Thierno Doumbia, Tao Wang, Guy P. Brasseur Resources: Thierno Doumbia, Yiming Liu, Trissevgeni Stavrakou, Sabine
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