US COVID-19 Shutdown Demonstrates Importance of Background NO2 in Inferring NOx Emissions From Satellite NO2 Observations

Zhen Qu; Daniel J Jacob; Rachel F Silvern; Viral Shah; Patrick C Campbell; Lukas C Valin; Lee T Murray

doi:10.1029/2021GL092783

US COVID-19 Shutdown Demonstrates Importance of Background NO₂ in Inferring NO_x Emissions From Satellite NO₂ Observations

Geophys Res Lett. 2021 May 28;48(10):e2021GL092783. doi: 10.1029/2021GL092783. Epub 2021 May 18.

Authors

Zhen Qu¹, Daniel J Jacob¹, Rachel F Silvern^{2

3}, Viral Shah¹, Patrick C Campbell^{4

5}, Lukas C Valin⁶, Lee T Murray⁷

Affiliations

¹ School of Engineering and Applied Science Harvard University Cambridge MA USA.
² Department of Earth and Planetary Sciences Harvard University Cambridge MA USA.
³ Now at The National Academies of Sciences, Engineering, and Medicine Washington DC USA.
⁴ Center for Spatial Information Science and Systems/Cooperative Institute for Satellite Earth System Studies George Mason University Fairfax VA USA.
⁵ Office of Air and Radiation, Air Resources Laboratory National Oceanic and Atmospheric Administration College Park MD USA.
⁶ Office of Research and Development United States Environmental Protection Agency, Triangle Research Park Durham NC USA.
⁷ Department of Earth and Environmental Sciences University of Rochester Rochester NY USA.

Abstract

Satellite nitrogen dioxide (NO₂) measurements are used extensively to infer nitrogen oxide emissions and their trends, but interpretation can be complicated by background contributions to the NO₂ column sensed from space. We use the step decrease of US anthropogenic emissions from the COVID-19 shutdown to compare the responses of NO₂ concentrations observed at surface network sites and from satellites (Ozone Monitoring Instrument [OMI], Tropospheric Ozone Monitoring Instrument [TROPOMI]). After correcting for differences in meteorology, surface NO₂ measurements for 2020 show decreases of 20% in March-April and 10% in May-August compared to 2019. The satellites show much weaker responses in March-June and no decrease in July-August, consistent with a large background contribution to the NO₂ column. Inspection of the long-term OMI trend over remote US regions shows a rising summertime NO₂ background from 2010 to 2019 potentially attributable to wildfires.