Global-scale reductions in free tropospheric ozone in 2020-2022 associated with decreased pollution due to COVID-19 and impact on trends

Abstract

NASA satellite measurements show that ozone reductions throughout the Northern Hemisphere (NH) free troposphere reported for spring-summer 2020 during the COronaVIrus Disease 2019 (COVID-19) pandemic have occurred again in spring-summer 2021.  The satellite measurements show that tropospheric column ozone (TCO) (mostly representative of the free troposphere) for 20oN-60oN during spring-summer for both 2020 and 2021 averaged ~3 Dobson Units (DU) (or ~7-8%) below normal.  These ozone reductions in 2020 and 2021 were the lowest over the 2005-2021 record.  We also include satellite measurements of tropospheric NO2 that exhibit reductions of ~10-20% in the NH in early spring-to-summer 2020 and 2021, suggesting that reduced pollution was the main cause for the low anomalies in NH TCO in 2020 and 2021.  Reductions of TCO ~2 DU (7 %) are also measured in the Southern Hemisphere in austral summer but are not associated with reduced NO2.  We also extend our analyses to show that year 2022 spring-summer anomalies in NH tropospheric NO2 and free tropospheric ozone from the satellite measurements still remained below pre-COVID levels.