Abstract
Abstract. 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 +6 to +7 Dobson units (DU) (i.e., ∼15 %–20 % of average background ozone), with the largest increase (∼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 +6 to +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 ∼+3 DU decade−1 or greater during 2005–2016 compared to about +1.2 to +1.4 DU decade−1 for 1979–2005. The GMI simulation and satellite data also reveal a tropospheric ozone increases in ∼+4 to +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 ∼+3 DU decade−1 over the N Atlantic and NE Pacific.
Highlights
Over the last several decades there have been substantial regional changes in emissions and concentrations of global pollutants, including precursors of tropospheric ozone, as documented by many studies (e.g., Granier et al, 2011; Parrish et al, 2013; Young et al, 2013; Cooper et al, 2014; Lee et al, 2014; Zhang et al, 2016; Heue et al, 2016; Lin et al, 2017)
Biomass burning emissions for prior years have interannual variability from regional scaling factors based on the Total Ozone Mapping Spectrometer (TOMS) aerosol index (Duncan et al, 2003) imposed on a climatology derived from Global Fire Emissions Dataset (GFED)-4s, similar to the approach used in Strode et al (2015)
Studies suggest that ozone in the troposphere has increased globally throughout much of the 20th century due largely to increases in anthropogenic emissions
Summary
Over the last several decades there have been substantial regional changes in emissions and concentrations of global pollutants, including precursors of tropospheric ozone, as documented by many studies (e.g., Granier et al, 2011; Parrish et al, 2013; Young et al, 2013; Cooper et al, 2014; Lee et al, 2014; Zhang et al, 2016; Heue et al, 2016; Lin et al, 2017). The model simulations and OMI/MLS satellite measurements employed by Zhang et al (2016) indicated the largest increases in tropospheric ozone extending from the Near East to India and SE Asia and further eastward over the Pacific Ocean. The results by Zhang et al (2016) appear consistent with the Bulletin of the American Meteorological Society BAMS State of the Climate Report for the year 2016, which indicates about a 21.8 Tg increase in OMI/MLS tropospheric ozone when averaged over 60◦ S–60◦ N between October 2004 and December 2016, with the largest contribution to global trends (about +3 to +4 DU decade−1 for OMI/MLS) originating from the same India and the East and Southeast Asia region. S1–S4) that discusses validation of OMI/MLS, TOMS, and OMPS TCO, and comparisons of decadal changes or trends between ozonesonde and OMI/MLS TCO
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