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\begin{document}

\title{Tropospheric NO\_2 and O\_3 response to COVID-19 lockdown restrictions
at the national and urban scales in Germany}



\author[1]{Vigneshkumar Balamurugan}%
\author[1]{Jia Chen}%
\author[1]{Xiao Bi}%
\author[2]{Zhen Qu}%
\author[1]{Johannes Gensheimer}%
\author[3]{Ankit Shekhar}%
\author[4]{Shrutilipi Bhattacharjee}%
\author[2]{Frank Keutsch}%
\affil[1]{Technical University of Munich}%
\affil[2]{Harvard University}%
\affil[3]{ETH Zurich}%
\affil[4]{National Institute of Technology Karnataka}%


\vspace{-1em}



  
  \date{June 15, 2024}


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\begin{abstract}
This study estimates the influence of anthropogenic emission reductions
on nitrogen dioxide (NO\_2) and ozone (O\_3) concentration changes
during the COVID-19 pandemic period using in-situ surface and
Sentinel-5p (TROPOMI) satellite column measurements and GEOS-Chem model
simulations. We show that, as a result of reductions in anthropogenic
emission in eight German metropolitan cities, meteorology corrected mean
in-situ (\textbackslash{}\& column) NO\_2(2020,corr) concentrations
decreased by 23 \selectlanguage{ngerman}± 4.7 \% (\& 16.4 ± 7.2 \%) between March 21 and June
30, 2020, whereas meteorology corrected mean in-situ O\_3(2020,corr)
concentration increased by 4 ± 8.8 \% between March 21 and May 31, 2020,
and decreased by 3 ± 8.7 \% in June 2020, compared to 2019 (uncertainty
represents the 1 \selectlanguage{greek}σ \selectlanguage{english}of mean changes of eight metropolitan cities). The
impacts of meteorology on in-situ and TROPOMI NO\_2 concentration
changes during the lockdown compared to 2019 are relatively small (+0.4
\% and -0.6 \%, respectively), while those on in-situ O\_3 concentration
changes are more significant (+3.6 \% and -13.5 \% for March 21 to May
31, 2020 and June 2020, respectively). A NO\_X saturated ozone
production regime in German metropolitan cities in March to May explains
the increased O\_3(2020,corr) concentration in response to the decreased
NO\_2(2020,corr) concentration. This implies that future reductions in
NO\_X emissions are likely to increase ozone pollution in these cities
if appropriate mitigation measures are not implemented. TROPOMI
NO\_2(2020,corr) concentrations decreased nationwide during the stricter
lockdown period, except for North-West Germany, which can be attributed
to enhanced NO\_X emissions from agricultural soils.%
\end{abstract}%



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