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Fingerprints of a New Normal Urban Air Quality in the United States
  • +2
  • Shobha Kondragunta,
  • Zigang Wei,
  • Brian McDonald,
  • Daniel Goldberg,
  • Daniel Tong
Shobha Kondragunta
National Oceanic and Atmospheric Administration (NOAA), National Oceanic and Atmospheric Administration (NOAA)

Corresponding Author:shobha.kondragunta@noaa.gov

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Zigang Wei
IM Systems Group, IM Systems Group
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Brian McDonald
NOAA Chemical Sciences Laboratory, NOAA Chemical Sciences Laboratory
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Daniel Goldberg
George Washington University, George Washington University
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Daniel Tong
GMU, GMU
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Abstract

Most countries around the world including the United States took actions to control COVID-19 spread that included social distancing, limiting air and ground travel, closing schools, suspending sports leagues, closing factories etc., leading to an abrupt shift in human activity. On-road NOx emissions from light and heavy duty vehicles decreased by 9% to 19% between February and March at the onset of lockdown in the middle of March in most of the US; between March and April, the on-road NOx emissions dropped further by 8% to 31% when lockdown measures were the most stringent. These precipitous drops in NOx emissions correlated well with tropospheric NO2 column amount observed by Sentinel 5 Precursor TROPOspheric Monitoring Instrument (S5P TROPOMI). Further, the changes in TROPOMI tropospheric NO2 across the continental U.S. between 2020 and 2019 correlated well with changes in on-road NOx emissions (r = 0.68) but correlated weakly with changes in emissions from the power plants (r = 0.35). These findings confirm the known knowledge that power plants are no longer a major source of NO2 in urban areas of the US. With increased unemployment rate in 2020 after the lockdown combined with telework policies across the nation for non-essential workers, the NO2 values decreased at the rate of 0.8 ┬Ámoles/m2 decrease per unit percentage increase in unemployment rate. Across the urban regions we found positive correlation between S5P TROPOMI NO2 and Suomi NPP Visible Infrared Imaging Radiometer Suite (VIIRS) aerosol optical depths indicating common source sectors for NO2 and aerosols/aerosol precursors.