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\begin{document}

\title{Ozone Anomalies in the Free Troposphere during the COVID-19 Pandemic}



\author[1]{Idir Bouarar}%
\author[2]{Benjamin Gaubert}%
\author[1]{Guy P. Brasseur}%
\author[3]{Wolfgang Steinbrecht}%
\author[4]{Thierno Doumbia}%
\author[2]{Simone Tilmes}%
\author[5]{Yiming Liu}%
\author[6]{Trissevgeni Stavrakou}%
\author[1]{Adrien Michel Deroubaix}%
\author[7]{Sabine Darras}%
\author[8]{Claire Granier}%
\author[9]{Forrest Gerhart Lacey}%
\author[10]{Jean-François Müller}%
\author[1]{Xiaoqin Shi}%
\author[11]{Nellie Elguindi}%
\author[12]{Tao Wang}%
\affil[1]{Max Planck Institute for Meteorology}%
\affil[2]{National Center for Atmospheric Research (UCAR)}%
\affil[3]{Deutscher Wetterdienst}%
\affil[4]{Laboratoire d'Aerologie, University de Toulouse, CNRS, UPS}%
\affil[5]{Sun Yat-sen University,}%
\affil[6]{Royal Belgian Institute for Space Aeronomy}%
\affil[7]{Observatoire Midi-Pyrenees}%
\affil[8]{University of Toulouse}%
\affil[9]{National Center for Atmospheric Research}%
\affil[10]{Royal Belgian Institute for Space Aeronomy (BIRA-IASB)}%
\affil[11]{Centre national de la recherche scientifique}%
\affil[12]{The Hong Kong Polytechnic University}%


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  \date{June 17, 2024}


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\begin{abstract}
Using the CAM-chem Model, we simulate the response of chemical species
in the free troposphere to changes in emissions of primary pollutants
during the COVID-19 pandemic. 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 ozone observations. 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. In the Southern Hemisphere,
COVID-19 related ozone reductions by 4 to 6\% were masked by comparable
ozone increases due to other changes in 2020.%
\end{abstract}%



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