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\begin{document}

\title{Diesel passenger vehicle shares influenced COVID-19 changes in urban
nitrogen dioxide pollution}



\author[1]{Gaige Hunter Kerr}%
\author[1]{Daniel L. Goldberg}%
\author[2]{K. Emma Knowland}%
\author[2]{Christoph A. Keller}%
\author[3]{Dolly Oladini}%
\author[4]{Iyad Kheirbek}%
\author[3]{Lucy Mahoney}%
\author[5]{Zifeng Lu}%
\author[6]{Susan Anenberg}%
\affil[1]{George Washington University}%
\affil[2]{Universities Space Research Association (USRA)/GESTAR, Columbia, MD, USA}%
\affil[3]{C40 Cities, London, England, UK}%
\affil[4]{C40 Cities Climate Leadership Group Inc., New York, NY, USA}%
\affil[5]{Systems Assessment Center, Energy Systems Division, Argonne National Laboratory, Lemont, IL, USA}%
\affil[6]{Department of Environmental and Occupational Health, Milken Institute School of Public Health, The George Washington University, Washington, DC, USA}%


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  \date{May 25, 2024}


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\begin{abstract}
Diesel-powered vehicles emit several times more nitrogen oxides than
comparable gasoline-powered vehicles, leading to ambient nitrogen
dioxide (NO2) pollution and adverse health impacts. The COVID-19
pandemic and ensuing changes in emissions provide a natural experiment
to test whether NO2 reductions have been starker in Europe, a region
with larger diesel passenger vehicle shares. Here we use a
semi-empirical approach that combines in-situ NO2 observations from
urban areas and an atmospheric composition model within a machine
learning algorithm to estimate business-as-usual NO2 during the first
wave of the COVID-19 pandemic in 2020. These estimates account for the
moderating influences of meteorology, chemistry, and traffic. Comparing
the observed NO2 concentrations against business-as-usual estimates
indicates that diesel passenger vehicle shares played a major role in
the magnitude of NO2 reductions. European cities with the five largest
shares of diesel passenger vehicles experienced NO2 reductions
\textasciitilde{}2.5 times larger than cities with the five smallest
diesel shares. Extending our methods to a cohort of non-European cities
from the C40 Cities network reveals that NO2 reductions in these cities
were generally smaller than reductions in European cities, which was
expected given their small diesel shares. We identify potential factors
such as the deterioration of engine controls associated with older
diesel vehicles to explain spread in the relationship between cities'
shares of diesel vehicles and changes in NO2 during the pandemic. Our
results provide a glimpse of potential NO2 reductions that could
accompany future deliberate efforts to phase out or remove passenger
vehicles from cities.%
\end{abstract}%



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