05 Jul 2022
05 Jul 2022
Status: this preprint is currently under review for the journal ACP.

Global tropospheric ozone trends, attributions, and radiative impacts in 1995–2017: an integrated analysis using aircraft (IAGOS) observations, ozonesonde, and multi-decadal chemical model simulations

Haolin Wang1,2, Xiao Lu1,2, Daniel J. Jacob3, Owen R. Cooper4,5, Kai-Lan Chang4,5, Ke Li6, Meng Gao7, Yiming Liu1,2, Bosi Sheng1, Kai Wu8, Tongwen Wu9,10, Jie Zhang9,10, Bastien Sauvage11, Philippe Nédélec11, Romain Blot11, and Shaojia Fan1,2 Haolin Wang et al.
  • 1School of Atmospheric Sciences, Sun Yat-sen University, and Key Laboratory of Tropical Atmosphere-Ocean System, Ministry of Education, Zhuhai, China
  • 2Guangdong Provincial Observation and Research Station for Climate Environment and Air Quality Change in the Pearl River Estuary, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China
  • 3Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
  • 4Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 5NOAA Chemical Sciences Laboratory, Boulder, CO, USA
  • 6Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Science and Engineering, Nanjing University of Information Science and Technology, Nanjing, China
  • 7Department of Geography, State Key Laboratory of Environmental and Biological Analysis, Hong Kong Baptist University, Hong Kong, China
  • 8Department of Land, Air, and Water Resources, University of California, Davis, CA, USA
  • 9CMA Earth System Modeling and Prediction Centre, Beijing, China
  • 10State Key Laboratory of Severe Weather, Beijing, China
  • 11Laboratoire d’Aérologie (LAERO), Université Toulouse III - Paul Sabatier, CNRS, Toulouse, France

Abstract. Quantification and attribution of long-term tropospheric ozone trends are critical for understanding the impact of human activity and climate change on atmospheric chemistry, but are also challenged by the limited coverage of long-term ozone observations in the free troposphere where ozone has higher production efficiency and radiative potential compared to that at the surface. In this study, we examine observed tropospheric ozone trends, their attributions, and radiative impacts from 1995–2017 using aircraft observations from the In-Service Aircraft for a Global Observing System database (IAGOS), ozonesondes, and a multi-decadal GEOS-Chem chemical model simulation. IAGOS observations above 11 regions in the Northern Hemisphere and 19 of 27 global ozonesonde sites have measured increases in tropospheric ozone (950–250 hPa) by 2.7 ± 1.7 and 1.9 ± 1.7 ppbv decade-1 on average, respectively, with particularly large increases in the lower troposphere (950–800 hPa) above East Asia, Persian Gulf, India, northern South America, Gulf of Guinea, and Malaysia/Indonesia by 2.8 to 10.6 ppbv decade-1. The GEOS-Chem simulation driven by reanalysis meteorological fields and the most up-to-date year-specific anthropogenic emission inventory reproduces the overall pattern of observed ozone trends, including the large ozone increases over the tropics of 2.1–2.9 ppbv decade-1 and above East Asia of 0.5–1.8 ppbv decade-1, and the weak ozone trends above North America, Europe, and high-latitudes in both hemispheres, but trends are underestimated compared to observations. GEOS-Chem estimates an increasing trend of 0.4 Tg year-1 of the tropospheric ozone burden in 1995–2017. We suggest that uncertainties in the anthropogenic emission inventory in the early years of the simulation (e.g., 1995–1999) over developing regions may contribute to GEOS-Chem’s underestimation of ozone trends. GEOS-Chem sensitivity simulations show that changes in global anthropogenic emission patterns, including the equatorward redistribution of surface emissions and the rapid increases in aircraft emissions, are the dominant factors contributing to tropospheric ozone trends by 0.5 Tg year-1. In particular, we highlight the disproportionately large, but previously underappreciated, contribution of aircraft emissions to tropospheric ozone trends by 0.3 Tg year-1, mainly due to aircraft emitting NOx in the mid- and upper troposphere where ozone production efficiency is high. Decreases in lower stratospheric ozone and the stratosphere-troposphere flux in 1995–2017 contribute to an ozone decrease at mid- and high-latitudes. We estimate the change in tropospheric ozone radiative impacts from 1995–1999 to 2013–2017 is +18.5 mW m-2, with 43.5 mW m-2 contributed by anthropogenic emission changes (20.5 mW m-2 alone by aircraft emissions), highlighting that the equatorward redistribution of emissions to areas with strong convection and the increase in aircraft emissions are effective for increasing tropospheric ozone’s greenhouse effect.

Haolin Wang et al.

Status: open (until 16 Aug 2022)

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  • RC1: 'Comment on acp-2022-381', Anonymous Referee #2, 04 Aug 2022 reply

Haolin Wang et al.

Haolin Wang et al.


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Short summary
We report significant global tropospheric ozone increases in 1995–2017 based on extensive aircraft and ozonesonde observations. Using GEOS-Chem multi-decadal global simulations, we find that changes in global anthropogenic emissions, in particular the rapid increases in aircraft emissions, contribute significantly to the increases in tropospheric ozone and resulting radiative impact.