Comparing Tropospheric NO2 Retrievals from OMI and TROPOMI during the COVID-19 Lockdowns

Abstract:

The decreases in transportation use and power production during the COVID-19 lockdowns significantly reduced regional emissions of nitrogen dioxide (NO₂) into the atmosphere. Since 2004, the Ozone Monitoring Instrument (OMI) UV-VIS spectrometer onboard the NASA EOS Aura satellite has been making measurements of ozone and other trace gases including NO₂. In response to COVID-19, the NASA OMI team has developed a monitoring website to track changes in NO₂ globally (OMI NO₂ Monitoring Website ) using OMI tropospheric NO₂ data. We highlight and examine these analyses including timeseries and maps of NO₂ during the COVID-19 period in 2020 comparing these to baseline NO₂ data from 2015-2019. In 2017, the European Space Agency (ESA) launched the Tropospheric Monitoring Instrument (TROPOMI) instrument on the Sentinel-5 Precursor (S5P). TROPOMI provides similar trace gas measurements but at a much higher spatial resolution. We compare NO₂ measurements from the OMI and TROPOMI instruments during the COVID-19 period. In addition to the standard ESA NO₂ product, we also present our modified TROPOMI NO₂ retrievals using a similar algorithm to NASA’s V4 OMI NO₂ Standard Product. The main differences between the NASA and ESA TROPOMI NO₂ algorithms are in calculation of the Air-Mass Factors (AMF), including the implementation of a dynamic geometry dependent surface reflectivity (GLER), improvements to cloud and snow AMF corrections, and high resolution (0.25^o x 0.25^o ) a-priori NO₂ profiles from NASA’s Global Modeling Initiative (GMI) model replay runs. The decreases in NO₂ emissions due to COVID-19 lockdowns provide an excellent opportunity to compare NO₂ data from OMI and TROPOMI, highlight the importance of the long-term satellite NO₂ record from OMI, and demonstrate the benefit of higher resolution data from TROPOMI.