The Impacts of COVID-19 Lockdowns on NO2 as Measured by Sentinel-5P TROPOMI: impacts of Weather and Implications for Emissions and Chemistry

Abstract:

Soon after the start of the lockdown in China, the impact of the COVID-19 measures were dramatically demonstrated by the NO₂ observations of the Sentinel-5P TROPOMI instrument. Huge reductions in NO₂ tropospheric columns were observed, up to 40% for the Chinese cities. When the virus spread around the world, and lockdowns were implemented in many countries, large reductions were observed in Europe (Italy, Spain, France), in North America, South America, India and other parts of the world. The 2020 lock-down situation was compared with pre-lockdown measurements and data from 2019. With the high spatial resolution of TROPOMI we can further distinguish the center of the cities from the industrial areas and major highways, providing additional information on the sectors contributing to the NO₂ pollution.

These observations raise several important questions. How is the reduction in the column amount related to the concentration reduction at the surface? How much of the reduction may be attributed to changes in emissions as a result of the covid-19 measures? When comparing 2020 with 2019, what is the impact of the changes in weather on the relative difference? How do uncertainties in the TROPOMI NO2 retrievals influence the results? How are the concentrations changes related to emission changes, and how are other aspects of pollution (aerosols, ozone, VOCs) influenced?

In our we will briefly review the NO₂ reductions observed by TROPOMI (OMI) in 2020. We will show results from our analysis over Europe, and will provide examples of recent research addressing the questions raised above.