# Trends in global tropospheric ozone inferred from a composite record of TOMS/OMI/MLS/OMPS satellite measurements and the MERRA-2 GMI simulation

Past studies have suggested that ozone in the troposphere has increased globally throughout much of the 20th century due to increases in anthropogenic emissions and transport. We show, by combining satellite measurements with a chemical transport model, that during the last four decades tropospheric ozone does indeed indicate increases that are global in nature, yet still highly regional. Satellite ozone measurements from Nimbus-7 and Earth Probe Total Ozone Mapping Spectrometer (TOMS) are merged with ozone measurements from the Aura Ozone Monitoring Instrument/Microwave Limb Sounder (OMI/MLS) to determine trends in tropospheric ozone for 1979–2016. Both TOMS (1979–2005) and OMI/MLS (2005–2016) depict large increases in tropospheric ozone from the Near East to India and East Asia and further eastward over the Pacific Ocean. The 38-year merged satellite record shows total net change over this region of about inline-formula+6 to inline-formula+7 Dobson units (DU) (i.e., inline-formula∼15 %–20 % of average background ozone), with the largest increase (inline-formula∼4 DU) occurring during the 2005–2016 Aura period. The Global Modeling Initiative (GMI) chemical transport model with time-varying emissions is used to aid in the interpretation of tropospheric ozone trends for 1980–2016. The GMI simulation for the combined record also depicts the greatest increases of inline-formula+6 to inline-formula+7 DU over India and East Asia, very similar to the satellite measurements. In regions of significant increases in tropospheric column ozone (TCO) the trends are a factor of 2–2.5 larger for the Aura record when compared to the earlier TOMS record; for India and East Asia the trends in TCO for both GMI and satellite measurements are inline-formula $M7inlinescrollmathml\sim +normal 3$ 26pt10ptsvg-formulamathimg48252b8ccd0db32d6368a886837c21fe acp-19-3257-2019-ie00001.svg26pt10ptacp-19-3257-2019-ie00001.png  DU decadeinline-formula−1 or greater during 2005–2016 compared to about inline-formula+1.2 to inline-formula+1.4 DU decadeinline-formula−1 for 1979–2005. The GMI simulation and satellite data also reveal a tropospheric ozone increases in inline-formula $M12inlinescrollmathml\sim +normal 4$ 26pt10ptsvg-formulamathimg4f60ad4e973b9f30ced144d4a3c2d22d acp-19-3257-2019-ie00002.svg26pt10ptacp-19-3257-2019-ie00002.png to inline-formula+5 DU for the 38-year record over central Africa and the tropical Atlantic Ocean. Both the GMI simulation and satellite-measured tropospheric ozone during the latter Aura time period show increases of inline-formula $M14inlinescrollmathml\sim +normal 3$ 26pt10ptsvg-formulamathimg7dc3024f2fd36743d11bfc91c32d0e58 acp-19-3257-2019-ie00003.svg26pt10ptacp-19-3257-2019-ie00003.png  DU decadeinline-formula−1 over the N Atlantic and NE Pacific.

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Ziemke, Jerry R. / Oman, Luke D. / Strode, Sarah A. / et al: Trends in global tropospheric ozone inferred from a composite record of TOMS/OMI/MLS/OMPS satellite measurements and the MERRA-2 GMI simulation. 2019. Copernicus Publications.

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