\documentclass[10pt]{article}

\usepackage{fullpage}
\usepackage{setspace}
\usepackage{parskip}
\usepackage{titlesec}
\usepackage[section]{placeins}
\usepackage{xcolor}
\usepackage{breakcites}
\usepackage{lineno}
\usepackage{hyphenat}





\PassOptionsToPackage{hyphens}{url}
\usepackage[colorlinks = true,
            linkcolor = blue,
            urlcolor  = blue,
            citecolor = blue,
            anchorcolor = blue]{hyperref}
\usepackage{etoolbox}
\makeatletter
\patchcmd\@combinedblfloats{\box\@outputbox}{\unvbox\@outputbox}{}{%
  \errmessage{\noexpand\@combinedblfloats could not be patched}%
}%
\makeatother


\usepackage{natbib}




\renewenvironment{abstract}
  {{\bfseries\noindent{\abstractname}\par\nobreak}\footnotesize}
  {\bigskip}

\titlespacing{\section}{0pt}{*3}{*1}
\titlespacing{\subsection}{0pt}{*2}{*0.5}
\titlespacing{\subsubsection}{0pt}{*1.5}{0pt}


\usepackage{authblk}


\usepackage{graphicx}
\usepackage[space]{grffile}
\usepackage{latexsym}
\usepackage{textcomp}
\usepackage{longtable}
\usepackage{tabulary}
\usepackage{booktabs,array,multirow}
\usepackage{amsfonts,amsmath,amssymb}
\providecommand\citet{\cite}
\providecommand\citep{\cite}
\providecommand\citealt{\cite}
% You can conditionalize code for latexml or normal latex using this.
\newif\iflatexml\latexmlfalse
\providecommand{\tightlist}{\setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}%

\AtBeginDocument{\DeclareGraphicsExtensions{.pdf,.PDF,.eps,.EPS,.png,.PNG,.tif,.TIF,.jpg,.JPG,.jpeg,.JPEG}}

\usepackage[utf8]{inputenc}
\usepackage[greek,ngerman,english]{babel}



\usepackage{float}








\begin{document}

\title{Quantifying the impact of the COVID-19 lockdown on air quality in
downtown Toronto using open-path Fourier transform spectroscopy}



\author[1]{Yuan You}%
\author[1]{Brendan Byrne}%
\author[1]{Orfeo Colebatch}%
\author[1]{Dylan Jones}%
\author[2]{Jinwoong Kim}%
\author[3]{Richard Mittermeier}%
\author[4]{Felix Vogal}%
\author[1]{Kimberly Strong}%
\affil[1]{University of Toronto}%
\affil[2]{University of Toronto; Environment and Climate Change Canada}%
\affil[3]{Environment and Climate Change Canada}%
\affil[4]{Climate Research Division, Environment and Climate Change Canada}%


\vspace{-1em}



  
  \date{June 09, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
During the global COVID-19 pandemic, anthropogenic emissions of air
pollutants and greenhouse gases, especially traffic emissions in urban
areas, have declined significantly. Long-term measurements of trace gas
concentrations in urban areas can be used to quantify the impact of
emission reductions on local air quality. Open-path Fourier transform
infrared (OP-FTIR) spectroscopy is a non-intrusive technique that can be
used to simultaneously measure multiple atmospheric trace gases in the
boundary layer. This study investigates the reduction of surface CO, CO2
, and CH4 mole fractions during the lockdown in downtown Toronto,
Canada, which is the fourth largest city in North America. The mean
daily CO mole fraction anomaly (\selectlanguage{greek}Δ\selectlanguage{english}CO) for the period from March 14 to May
18, 2020 declined by 46 \selectlanguage{ngerman}± 16\% compared to the period before lockdown
from January 13 to March 13, 2020. The mean daily \selectlanguage{greek}Δ\selectlanguage{english}CO during the
lockdown also declined relative to the same period in previous years: by
50 \selectlanguage{ngerman}± 20\% relative to 2019 and by 44 ± 25\% relative to 2018. Changes in
the diurnal variations of CO, CO2 and CH4 during the lockdown are also
investigated and compared to 2019 and 2018. Both CO and CO2 show early
morning maxima on weekdays corresponding to rush hour. The change of the
amplitude of the diurnal variation in CO during the lockdown is
significant, compared to the period before lockdown. The differences in
the diurnal variation in CO during the same two periods in 2019 and 2018
are not significant. Ratios of CO/CO2 anomalies show seasonal
variations, which are also likely due to seasonal changes of emissions
from local sources. These results show that the COVID-19 lockdown in
Toronto modified surface mole fractions, diurnal variations, and ratios
of air pollutants monitored by OP-FTIR. In addition, measured CO mole
fractions are compared with simulated CO mole fractions by WRF-STILT to
assess the relationship between atmospheric measurements and urban
emissions from Toronto.%
\end{abstract}\selectlanguage{ngerman}%



\sloppy




\selectlanguage{english}
\FloatBarrier
\end{document}

