Comment on acp-2021-534

Abstract

The aim of this paper is two-fold: to provide guidance on how to best interpret TROPOMI trace gas retrievals and to highlight how TROPOMI trace gas data can be used to understand event-based impacts on air quality from regional to city-scales around the globe. For this study, we present the observed changes in the atmospheric column amounts of five trace gases (NO2, SO2, CO, HCHO and CHOCHO) detected by the Sentinel-5P TROPOMI instrument, driven by reductions of anthropogenic emissions due to COVID-19 lockdown measures in 2020. We report clear COVID-19-related decreases in NO2 concentrations on all continents. For megacities, reductions in column amounts of tropospheric NO2 range between 14 % and 63 %. For China and India supported by NO2 observations, where the primary source of anthropogenic SO2 is coal-fired power generation, we were able to detect sector-specific emission changes using the SO2 data. For HCHO and CHOCHO, we consistently observe anthropogenic changes in two-week averaged column amounts over China and India during the early phases of the lockdown periods. That these variations over such a short time scale are detectable from space, is due to the high resolution and improved sensitivity of the TROPOMI instrument. For CO, we observe a small reduction over China which is in concert with the other trace gas reductions observed during lockdown, however large, interannual differences prevent firm conclusions from being drawn. The joint analysis of COVID-19 lockdown-driven reductions in satellite observed trace gas column amounts, using the latest operational and scientific retrieval techniques for five species concomitantly is unprecedented. However, the meteorologically and seasonally driven variability of the five trace gases does not allow for drawing fully quantitative conclusions on the reduction of anthropogenic emissions based on TROPOMI observations alone. We anticipate that in future, the combined use of inverse modelling techniques with the high spatial resolution data from S5P/TROPOMI for all observed trace gases presented here, will yield a significantly improved sector-specific, space-based analysis of the impact of COVID-19 lockdown measures as compared to other existing satellite observations. Such analyses will further enhance the scientific impact and societal relevance of the TROPOMI mission.

Authors 15

1. Pieternel Felicitas Levelt

   Royal Netherlands Meteorological Institute · Delft University of Technology

   Affiliation as printed

   Royal Netherlands Meteorological Institute (KNMI), De Bilt, 3731GA, The Netherlands

   University of Technology Delft (TU Delft), Delft, 2628 CN, the Netherlands

2. Deborah Stein Zweers corresponding

   Royal Netherlands Meteorological Institute

   Affiliation as printed

   Royal Netherlands Meteorological Institute (KNMI), De Bilt, 3731GA, The Netherlands

3. Ilse Aben Aachen Netherlands Institute for Space Research

   Space Research Organisation Netherlands

   Affiliation as printed

   Netherlands Institute for Space Research (SRON), Utrecht, 3584 CA, The Netherlands

4. Maïté Bauwens

   Royal Belgian Institute for Space Aeronomy

   Affiliation as printed

   Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, 1180, Belgium

5. Tobias Borsdorff corresponding Aachen Netherlands Institute for Space Research

   Space Research Organisation Netherlands

   Affiliation as printed

   Netherlands Institute for Space Research (SRON), Utrecht, 3584 CA, The Netherlands

6. Isabelle De Smedt corresponding

   Royal Belgian Institute for Space Aeronomy

   Affiliation as printed

   Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, 1180, Belgium

7. Henk J. Eskes corresponding

   Royal Netherlands Meteorological Institute

   Affiliation as printed

   Royal Netherlands Meteorological Institute (KNMI), De Bilt, 3731GA, The Netherlands

8. Christophe Lerot corresponding

   Royal Belgian Institute for Space Aeronomy

   Affiliation as printed

   Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, 1180, Belgium

9. Diego Loyola corresponding

   Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

   Affiliation as printed

   German Aerospace Centre (DLR), Oberpfaffenhofen, Wessling, 82234, Germany

10. Fabian Romahn

    Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)

    Affiliation as printed

    German Aerospace Centre (DLR), Oberpfaffenhofen, Wessling, 82234, Germany

11. Trissevgeni Stavrakou

    Royal Belgian Institute for Space Aeronomy

    Affiliation as printed

    Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, 1180, Belgium

12. Nicolas Theys

    Royal Belgian Institute for Space Aeronomy

    Affiliation as printed

    Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, 1180, Belgium

13. Michel Van Roozendaël

    Royal Belgian Institute for Space Aeronomy

    Affiliation as printed

    Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, 1180, Belgium

14. Pepijn Veefkind corresponding

    Royal Netherlands Meteorological Institute · Delft University of Technology

    Affiliation as printed

    Royal Netherlands Meteorological Institute (KNMI), De Bilt, 3731GA, The Netherlands

    University of Technology Delft (TU Delft), Delft, 2628 CN, the Netherlands

15. Tijl Verhoelst corresponding

    Royal Belgian Institute for Space Aeronomy

    Affiliation as printed

    Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, 1180, Belgium