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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/acp-2020-685
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-685
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  18 Sep 2020

18 Sep 2020

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This preprint is currently under review for the journal ACP.

Global Impact of COVID-19 Restrictions on the Surface Concentrations of Nitrogen Dioxide and Ozone

Christoph A. Keller1,2, Mathew J. Evans3,4, K. Emma Knowland1,2, Christa A. Hasenkopf5, Sruti Modekurty5, Robert A. Lucchesi1,6, Tomohiro Oda1,2, Bruno B. Franca7, Felipe C. Mandarino7, M. Valeria Díaz Suárez8, Robert G. Ryan9, Luke H. Fakes3,4, and Steven Pawson1 Christoph A. Keller et al.
  • 1NASA Global Modeling and Assimilation Office, Goddard Space Flight Center, Greenbelt, MD, USA
  • 2Universities Space Research Association, Columbia, MD, USA
  • 3Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York, YO10 5DD, UK
  • 4National Centre for Atmospheric Science, University of York, York, YO10 5DD, UK
  • 5OpenAQ, Washington, DC, USA
  • 6Science Systems and Applications, Inc., Lanham, MD, USA
  • 7Municipal Government of Rio de Janeiro, Rio de Janeiro, Brazil
  • 8Secretaria de Ambiente, Quito, Ecuador
  • 9School of Earth Sciences, The University of Melbourne, Australia

Abstract. Social-distancing to combat the COVID-19 pandemic has led to widespread reductions in air pollutant emissions. Quantifying these changes requires a business as usual counterfactual that accounts for the synoptic and seasonal variability of air pollutants. We use a machine learning algorithm driven by information from the NASA GEOS-CF model to assess changes in nitrogen dioxide (NO2) and ozone (O3) at 5756 observation sites in 46 countries from January through June 2020. Reductions in NO2 correlate with timing and intensity of COVID-19 restrictions, ranging from 60 % in severely affected cities (e.g., Wuhan, Milan) to little change (e.g., Rio de Janeiro, Taipei). On average, NO2 concentrations were 18 % lower than business as usual from February 2020 onward. China experienced the earliest and steepest decline, but concentrations since April have mostly recovered and remained within 5 % to the business as usual estimate. NO2 reductions in Europe and the US have been more gradual with a halting recovery starting in late March. We estimate that the global NOx (NO + NO2) emission reduction during the first 6 months of 2020 amounted to 2.9 TgN, equivalent to 5.1 % of the annual anthropogenic total. The response of surface O3 is complicated by competing influences of non-linear atmospheric chemistry. While surface O3 increased by up to 50 % in some locations, we find the overall net impact on daily average O3 between February–June 2020 to be small. However, our analysis indicates a flattening of the O3 diurnal cycle with an increase in night time ozone due to reduced titration and a decrease in daytime ozone, reflecting a reduction in photochemical production.

The O3 response is dependent on season, time scale, and environment, with declines in surface O3 forecasted if NOx emission reductions continue.

Christoph A. Keller et al.

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Christoph A. Keller et al.

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Short summary
This study combines surface observations and model simulations to quantify the impact of COVID-19 restrictions on air quality across the world. The presented methodology removes the compounding impacts of meteorology on air pollution. Our results indicate that surface concentrations of nitrogen dioxide, an important air pollutant emitted during the combustion of fossil fuels, declined by up to 60 % following the implementation of COVID-19 containment measures.
This study combines surface observations and model simulations to quantify the impact of...
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