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Observations

NASA satellite measurements show global-scale reductions in tropospheric ozone in 2020 and again in 2021 during COVID-19

The COVID-19 pandemic created global scale reductions in anthropogenic sources of pollution including important tropospheric ozone precursors such as nitrogen oxides (NOx (NO+NO2 )) and Volatile Organic Compounds (VOC’s). There have been many publications describing the large reductions in pollutants and tropospheric ozone in spring-summer 2020. Their results, using ground-based measurements and model simulations have shown reductions in tropospheric ozone throughout the Northern Hemisphere (NH) averaging around 7% with regional variations ~5-15%.

These satellite results show several new additional features:

  1. The tropospheric ozone reductions in spring-summer 2020 have repeated again in spring-summer 2021 with almost identical drops in ozone;
  2. The Southern Hemisphere (SH) exhibits similar anomalous decreases around summertime;
  3. Much of the reductions in NH and SH tropospheric ozone occurred over ocean.
Inter-annual anomalies in tropospheric column ozone for March-August 2020 and March-August 2021

Figure 1: Inter-annual anomalies (based on 2016-2019 average) in tropospheric column ozone (in Dobson Units) for March-August 2020 (top panel) and March-August 2021 (bottom panel).

Northern Hemisphere:

  • EPIC+OMI+OMPS merged satellite data show anomalous decreases in NH tropospheric ozone in spring-summer 2020 that continue again in spring-summer 2021.
  • The decreases in ozone are deemed largely due to reductions in anthropogenic pollution including ozone precursors NOx and VOC’s during the COVID-19 pandemic.)

Southern Hemisphere:

  • The satellite data also show similar anomalous decreases in tropospheric ozone in the SH around summertime, indicating that decreased pollutant emissions resulted in less ozone being photochemically produced during the summer season.

Both Northern and Southern Hemisphere:

  • Average reductions in tropospheric ozone in spring-summer are ~7-8 %
  • Regional reductions vary ~5-15 %
  • Much of the reductions occur over ocean downwind of major pollution sources
Inter-annual anomalies (based on 2016-2019 average) in zonal mean tropospheric column ozone (in Dobson Units) for January 2016-August 2021

Figure 2: Inter-annual anomalies (based on 2016-2019 average) in zonal mean tropospheric column ozone (in Dobson Units) for January 2016-August 2021. Negative anomalies in the tropics in 2019 are not COVID-related, but instead caused by an exceptionally strong positive phase of the Indian–Ocean Dipole (IOD) that was the strongest on record since 2006).




Data Sources:

EPIC data are available via the NASA ASDC and local link from the NASA GSFC Code 614 homepage. OMPS is available locally via NASA GSFC Code 614. OMI data are available via NASA GSFC AVDC and locally from NASA GSFC Code 614. The merged satellite tropospheric column ozone used here is derived by statistical averaging of the original tropospheric column ozone from EPIC, OMPS, and OMI based on their individual daily coverage. Tropospheric column ozone is a residual measurement of satellite instrument total column ozone minus assimilated Microwave Limb Sounder (MLS) stratospheric column ozone from MERRA-2. MERRA-2 data can be found here.

Reference:

Ziemke, J. R., N. A. Kramarova, S. M. Frith, L.-K. Huang, D. P. Haffner, K. Wargan, L. N. Lamsal, G. J. Labow, R. D. McPeters, and P. K. Bhartia, NASA satellite measurements show global-scale reductions in tropospheric ozone in 2020 and again in 2021 during COVID-19, Geophys. Res. Lett., 49, https://doi.org/10.1029/2022GL098712, 2022.


09.2022



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