Air quality impacts of COVID-19 lockdown measures detected from space using high spatial resolution observations of multiple trace gases from Sentinel-5P/TROPOMI

Abstract

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.

Variability of nitrogen oxide emission fluxes and lifetimes estimated from Sentinel-5P TROPOMI observations

“…The significantly higher emissions in February 2019 compared to 2020 are probably mainly caused by two factors, first a strong synoptic meteorological variability in Europe and, second, February is also a month with typically persistent cloud cover, resulting in a reduced number of TROPOMI observations which will reveal more natural variability. Similar findings are also described in Bauwens et al (2020) and Levelt et al (2021). For the months May and October 2020, when Covid-19 restrictions were in place, the calculated NO x emissions in Madrid are 43 % and 63 % lower than in 2019.…”

Peculiar COVID-19 effects in the Greater Tokyo Area revealed by spatiotemporal variabilities of tropospheric gases and light-absorbing aerosols

“…This indicates that biogenic emissions dominate HCHO even within our urban region. Pieces of evidence in TROPOMI HCHO reductions as a consequence of the COVID-related mobility restrictions have been reported only for China (Ghahremanloo et al, 2021), while meteorology likely drove most of the HCHO variations in India (Levelt et al, 2022). However, even in Wuhan, while the reduction in NO 2 reached about 83 %, the decrease in HCHO was only 11 %.…”

Impact of COVID-19 Measures on the Air Quality Monitored for the State of Himachal Pradesh: A Google Earth Engine Based Study

“…For CO, secondary production by methane oxidation and (biogenic) hydrocarbons accounts for at least 60% of the total atmospheric CO, followed by contributions from biomass burning and fossil fuel use [20]. Anthropogenic CO emissions originate from the industry, transportation, and residential sectors and account for about 30% of the global emissions [4].…”

“…Retrievals provide information on the lower atmosphere/tropospheric level or total column that amounts to these gases because the spectra contain limited information on their vertical distribution in the atmosphere. TROPOMI observations thus provide a two-dimensional representation of the three-dimensional atmosphere [20]. The vertical profiles of each trace gas vary and significantly depend on the emissions' height and the trace gases' atmospheric lifetime (see Table 1).…”