Global Changes in Secondary Atmospheric Pollutants During the 2020 COVID‐19 Pandemic

Gaubert, Benjamin ORCIDiD
Bouarar, Idir
Doumbia, Thierno
Liu, Yiming
Stavrakou, Trissevgeni ORCIDiD
Deroubaix, Adrien ORCIDiD
Darras, Sabine
Elguindi, Nellie ORCIDiD
Granier, Claire
Lacey, Forrest ORCIDiD
Müller, Jean‐François
Shi, Xiaoqin ORCIDiD
Tilmes, Simone ORCIDiD
Wang, Tao
Brasseur, Guy P. ORCIDiD

DOI: https://doi.org/10.23689/fidgeo-4427
Gaubert, Benjamin; Bouarar, Idir; Doumbia, Thierno; Liu, Yiming; Stavrakou, Trissevgeni; Deroubaix, Adrien; Darras, Sabine; Elguindi, Nellie; Granier, Claire; Lacey, Forrest; Müller, Jean‐François; Shi, Xiaoqin; Tilmes, Simone; Wang, Tao; Brasseur, Guy P., 2021: Global Changes in Secondary Atmospheric Pollutants During the 2020 COVID‐19 Pandemic. In: Journal of Geophysical Research: Atmospheres, 126, 8, DOI: https://doi.org/10.23689/fidgeo-4427. 
 
Gaubert, Benjamin; 1 National Center for Atmospheric Research Atmospheric Chemistry Observations and Modeling Laboratory Boulder CO USA
Bouarar, Idir; 2 Environmental Modeling Group Max Planck Institute for Meteorology Hamburg Germany
Doumbia, Thierno; 3 Laboratoire d’Aérologie Université de Toulouse CNRS UPS France
Liu, Yiming; 5 Department of Civil and Environmental Engineering The Hong Kong Polytechnic University Hong Kong China
Stavrakou, Trissevgeni; 6 Royal Belgian Institute for Space Aeronomy Brussels Belgium
Deroubaix, Adrien; 2 Environmental Modeling Group Max Planck Institute for Meteorology Hamburg Germany
Darras, Sabine; 4 Observatoire Midi‐Pyrénées Toulouse France
Elguindi, Nellie; 3 Laboratoire d’Aérologie Université de Toulouse CNRS UPS France
Granier, Claire; 3 Laboratoire d’Aérologie Université de Toulouse CNRS UPS France
Lacey, Forrest; 1 National Center for Atmospheric Research Atmospheric Chemistry Observations and Modeling Laboratory Boulder CO USA
Müller, Jean‐François; 6 Royal Belgian Institute for Space Aeronomy Brussels Belgium
Shi, Xiaoqin; 2 Environmental Modeling Group Max Planck Institute for Meteorology Hamburg Germany
Tilmes, Simone; 1 National Center for Atmospheric Research Atmospheric Chemistry Observations and Modeling Laboratory Boulder CO USA
Wang, Tao; 5 Department of Civil and Environmental Engineering The Hong Kong Polytechnic University Hong Kong China

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.


Plain Language Summary: With the reduction in economic activities following the COVID‐19 pandemic outbreak in early 2020, most emissions of air pollutants (i.e., nitrogen oxides [NOx], carbon monoxide [CO], sulfur dioxide [SO2], volatile organic carbon [VOC], black carbon [BC], organic carbon [OC]) have decreased substantially during several months in different regions of the world. This unintended global experiment offered a glimpse into a potential future in which air quality would be improved. Here, a global atmospheric model is used to assess the changes in the chemical composition of the atmosphere during the pandemic period and in the related chemical processes that lead to the formation of ozone (O3) and secondary organic aerosols (SOA). The study illustrates the nonlinearity of the air quality response to reduced NOx and VOC emissions, which depends on the chemical environment including the background level of nitrogen oxides. Meteorological variability can lead to anomalies in the concentration of chemical species with magnitudes that are as large or even larger than the perturbations due to COVID‐induced changes in the emissions.


Key Points:

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 NOx‐saturated areas and decreased in NOx‐limited areas

The response of the chemical system depends on the relative changes in NOx and VOC emissions, and is affected by weather variability