Covid-19 Shutdowns as an Unplanned Atmospheric Composition Experiment

Abstract:

The rapid spread of the novel coronavirus around the globe caused a dramatic cutback of human activities and triggered a large-scale unplanned experiment enabling us to examine the response of atmospheric composition to the shutdown measures. In some of the major epicenters of the outbreak, the temporary cleaning up of the air gave way to a gradual pollution rebound due to the restart of economic activities, like in China and India, whereas other countries were compelled to adopt strict measures as the pandemic evolves and new epidemic centers are emerging. Substantial, large-scale drops in pollutants levels and subsequent recoveries have been revealed by spaceborne observations from the Tropospheric Monitoring Instrument (TROPOMI) on board Sentinel-5 Precursor. TROPOMI provides daily global measurements of high accuracy for key trace gases since 2018. Here we use TROPOMI observations of nitrogen dioxide (NO₂), a key compound in atmospheric chemistry and an important precursor for ozone production and secondary aerosol formation. These observations allow us to track the day-by-day evolution of the NO₂ levels in major cities around the globe during the shutdowns and identify changes compared with the same period of the previous year. Our focus will be on China, where the pandemic emerged in January 2020, and thence strict lockdowns were enforced. We will compare the evolution of NO₂ observations from TROPOMI and from a dense network of in situ measurements, focusing on three strongly polluted regions, the Hubei province, the Yangtze River Delta and the Pearl River Delta. The variability of the observed columns due to meteorology will be further analyzed by conducting model simulations using the MAGRITTE v1.1 CTM at 0.5°x0.5° resolution over East China. The model will use updated anthropogenic emissions, taking into account the reductions during the shutdowns based on traffic and other economic activity data.