Research ArticleCLIMATOLOGY

Aircraft observations since the 1990s reveal increases of tropospheric ozone at multiple locations across the Northern Hemisphere

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Science Advances  21 Aug 2020:
Vol. 6, no. 34, eaba8272
DOI: 10.1126/sciadv.aba8272
  • Fig. 1 Map of the 11 study regions.

    The flight tracks are also indicated in the boxes with western North America in gray, eastern North America in green, Europe in blue, Northeast China/Korea in red, southeast United States in brown, northern South America in purple, Gulf of Guinea in salmon, the Persian Gulf in black, India in orange, Southeast Asia in cyan, and Malaysia/Indonesia in magenta.

  • Fig. 2

    Annual trends of median ozone (nmol mol−1 decade−1) for two columns definition in the troposphere. Trends in the free troposphere (700 to 250 hPa) are shown in (A) and trends in the tropospheric column (950 to 250 hPa) are shown in (B). The trends are calculated between 1994 and 2016 above western North America (gray), eastern North America (green), Europe (blue), Northeast China/Korea (red), southeast United States (brown), South America (purple), Gulf of Guinea (salmon), India (orange), and Southeast Asia (cyan); between 1998 and 2016 above the Persian Gulf (black); and between 1995 and 2016 above Malaysia/Indonesia (magenta). For South America, the lower limit of the columns is at 600 hPa for data availability. Large squares indicate trends with P values less than 0.05; open large squares indicate trends with P values between 0.05 and 0.1, and open small squares indicate P values greater than 0.1.

  • Fig. 3 Annual trends and distribution of the 50th and 95th percentiles of ozone (nmol mol−1 decade−1) at intervals of 50 hPa.

    The trends (A and B) are calculated between 1994 and 2016 above western North America (gray), eastern North America (green), Europe (blue), Northeast China/Korea (red), southeast United States (brown), South America (purple), Gulf of Guinea (salmon), India (orange), and Southeast Asia (cyan); between 1998 and 2016 above the Persian Gulf (black); and between 1995 and 2016 above Malaysia/Indonesia (magenta). Squares indicate trends with P values less than 0.05. Open squares indicate trends with P values between 0.05 and 0.1. The zero trend value is indicated with a vertical black bar. The annual profiles of absolute values of ozone (C and D) are for the recent period 2011–2016 above the same 11 regions. For reference, the 70 nmol mol−1 value is indicated with a vertical black line, which corresponds to the U.S. National Ambient Air Quality Standards for ozone and is the annual fourth-highest daily maximum 8-hour average concentration averaged over 3 years.

  • Fig. 4 Histograms of ozone at three levels in the troposphere and for three key tropical regions, India, Southeast Asia, and Malaysia.

    (A) The periods 1994–2004 (blue) and 2011–2016 (orange) are shown above all three sites, with the exception that the earlier period is limited to 1995–2000 above Malaysia/Indonesia because of data availability. (B) Also shown are the annual trends of the first and fifth percentiles above all 11 regions, at vertical intervals of 50 hPa. Squares indicate trends with P values less than 0.05. Open squares indicate trends with P values between 0.05 and 0.1.

  • Fig. 5 Latitudinal distribution of NOx emissions from fossil fuel and biomass burning along with the emissions differences between 1994–1998 and 2012–2016.

    The emissions are shown in Tg NO year–1 for 1994–1998 in blue and 2012–2016 in orange (left). The emissions differences between the two time periods are shown in % (right). For both panels, the latitude band resolution is 5°.

  • Fig. 6 RF due to ozone above the 11 regions and globally.

    The circles and bars show the average RF and its range of uncertainty for the 11 regions. The squares and bars show the global average RF and its range of uncertainty from IPCC (2013) (2), and the stars and bars show the global average RF and its range of uncertainty from the work of Myhre et al. (8).

Supplementary Materials

  • Supplementary Materials

    Aircraft observations since the 1990s reveal increases of tropospheric ozone at multiple locations across the Northern Hemisphere

    Audrey Gaudel, Owen R. Cooper, Kai-Lan Chang, Ilann Bourgeois, Jerry R. Ziemke, Sarah A. Strode, Luke D. Oman, Pasquale Sellitto, Philippe Nédélec, Romain Blot, Valérie Thouret, Claire Granier

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