In response to the COVID-19 global pandemic, the state and local governments declared emergency and enforced lockdowns to slow the progress of infections in March 2020, which was expected to reduce pollutant emissions in the United States. Satellite observations of nitrogen dioxide (NO2) have been used to estimate nitrogen oxides (NOx) emissions due to COVID-19 lockdowns with reduced human activities. We applied a daily retrieval inversion method to derive the NOx emissions for March to May 2020, using the 3-D Regional chEmistry and transport Model (REAM) based on corrected TROPOMI observations onboard the Copernicus Sentinel-5P satellites. We monitored emission changes over the U.S. in correspondence to the enactments of varied virus control policies and social behavior changes in different major city areas. We find about 10% to 36% reduction of NOx emissions during the lockdown period in major U.S. cities compared to 40-50% decrease in large cities of China, reflecting the less restrictive nature of the stay-at-home orders. The U.S. NOx emission reduction during the lockdown period is more comparable to the reduction of NOx emission reduction in China from the pre-lockdown to post-lockdown period.

Lower than expected reduction of nitrogen oxides emissions during the COVID-19 pandemic over the United States

ACS Fall 2021

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