EMS Annual Meeting Abstracts
Vol. 18, EMS2021-447, 2021
EMS Annual Meeting 2021
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

What are drivers of the tropospheric ozone reduction during spring 2020?

Benjamin Gaubert1, Idir Bouarar2, Guy P. Brasseur1,2,9, Thierno Doumbia3, Sabine Darras4, Adrien Deroubaix2, Claire Granier3,5, James Hannigan1, Duseong Jo1, Forrest Lacey1, Yiming Liu6, Jean-François Müller7, Ivan Ortega1, Xiaoqin Shi2, Trissevgeni Stavrakou7, Wolfgang Steinbrecht8, Simone Tilmes1, and Tao Wang9
Benjamin Gaubert et al.
  • 1National Center for Atmospheric Research, Atmospheric Chemistry Observations & Modeling Laboratory, United States of America (gaubert@ucar.edu)
  • 2Environmental Modeling Group, Max Planck Institute for Meteorology, Germany.
  • 3Laboratoire d’Aérologie, Université de Toulouse, CNRS, UPS, France.
  • 4Observatoire, Midi-Pyrénées, France.
  • 5NOAA Chemical Sciences Laboratory/CIRES, University of Colorado, USA.
  • 6School of Atmospheric Science, Sun Yat-sen University, China.
  • 7Royal Belgian Institute for Space Aeronomy, Belgium.
  • 8Deutscher Wetterdienst, Germany.
  • 9Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, China.

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 anthropogenic emissions and meteorological anomalies, including a discussion on long-term changes from the chemical climatology. 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. 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 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. Zonally averaged ozone concentrations in the free troposphere during Northern Hemisphere spring and summer were 5 to 15 % lower than 19-year climatological values, in good quantitative agreement with observations from ozonesondes and ground-based remote sensing from the Network for the Detection of Atmospheric Composition Change (NDACC). About one third of this anomaly is attributed to the drastic reduction in air traffic during the pandemic, another third to reductions in surface emissions, the remainder to 2020 meteorological conditions, including the exceptional springtime Arctic stratospheric ozone depletion. The overall COVID-19 reduction in mean northern hemisphere tropospheric ozone in June is less than 5 ppb below 400 hPa, but reaches 8 ppb at 250 hPa.

How to cite: Gaubert, B., Bouarar, I., P. Brasseur, G., Doumbia, T., Darras, S., Deroubaix, A., Granier, C., Hannigan, J., Jo, D., Lacey, F., Liu, Y., Müller, J.-F., Ortega, I., Shi, X., Stavrakou, T., Steinbrecht, W., Tilmes, S., and Wang, T.: What are drivers of the tropospheric ozone reduction during spring 2020?, EMS Annual Meeting 2021, online, 6–10 Sep 2021, EMS2021-447, https://doi.org/10.5194/ems2021-447, 2021.

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