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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
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2022
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Source: Atmospheric Chemistry and Physics, 22(20), 13753-13782
[PDF-14.79 MB]
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Journal Title:Atmospheric Chemistry and Physics
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Description:Abstract. Quantification and attribution of long-term tropospheric ozone trends are critical for understanding the impact of human activity andclimate change on atmospheric chemistry but are also challenged by thelimited coverage of long-term ozone observations in the free tropospherewhere ozone has higher production efficiency and radiative potentialcompared to that at the surface. In this study, we examine observedtropospheric ozone trends, their attributions, and radiative impacts from1995–2017 using aircraft observations from the In-service Aircraft for aGlobal Observing System database (IAGOS), ozonesondes, and a multi-decadalGEOS-Chem chemical model simulation. IAGOS observations above 11 regions inthe Northern Hemisphere and 19 of 27 global ozonesonde sites have measuredincreases in tropospheric ozone (950–250 hPa) by 2.7 ± 1.7 and 1.9 ± 1.7 ppbv per decade on average, respectively, with particularlylarge increases in the lower troposphere (950–800 hPa) above East Asia,the Persian Gulf, India, northern South America, the Gulf of Guinea, andMalaysia/Indonesia by 2.8 to 10.6 ppbv per decade. The GEOS-Chemsimulation driven by reanalysis meteorological fields and the mostup-to-date year-specific anthropogenic emission inventory reproduces theoverall pattern of observed tropospheric ozone trends, including the largeozone increases over the tropics of 2.1–2.9 ppbv per decade and aboveEast Asia of 0.5–1.8 ppbv per decade and the weak tropospheric ozone trends above North America, Europe, and high latitudes in bothhemispheres, but trends are underestimated compared to observations.GEOS-Chem estimates an increasing trend of 0.4 Tg yr−1 of thetropospheric ozone burden in 1995–2017. We suggest that uncertainties inthe anthropogenic emission inventory in the early years of the simulation(e.g., 1995–1999) over developing regions may contribute to GEOS-Chem'sunderestimation of tropospheric ozone trends. GEOS-Chem sensitivitysimulations show that changes in global anthropogenic emission patterns,including the equatorward redistribution of surface emissions and the rapidincreases in aircraft emissions, are the dominant factors contributing totropospheric ozone trends by 0.5 Tg yr−1. In particular, we highlightthe disproportionately large, but previously underappreciated, contributionof aircraft emissions to tropospheric ozone trends by 0.3 Tg yr−1,mainly due to aircraft emitting NOx in the mid-troposphere and upper tropospherewhere ozone production efficiency is high. Decreases in lower-stratosphericozone and the stratosphere–troposphere flux in 1995–2017 contribute to anozone decrease at mid-latitudes and high latitudes. We estimate the change intropospheric ozone radiative impacts from 1995–1999 to 2013–2017 is+18.5 mW m−2, with 43.5 mW m−2 contributed by anthropogenicemission changes (20.5 mW m−2 alone by aircraft emissions),highlighting that the equatorward redistribution of emissions to areas withstrong convection and the increase in aircraft emissions are effective forincreasing tropospheric ozone's greenhouse effect.
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Source:Atmospheric Chemistry and Physics, 22(20), 13753-13782
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ISSN:1680-7324
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Rights Information:CC BY
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Compliance:Submitted
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