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https://doi.org/10.5194/egusphere-2026-4770
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2026-4770
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
Preprints
08 Sep 2026
 | 08 Sep 2026
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Recent changes in the O3 and CO trends in the troposphere as observed by IAGOS

Thibaut Lebourgeois, Valérie Thouret, Hannah Clark, Yasmine Bennouna, Romain Blot, Damien Boulanger, Florian Brunet, Simon Cleris, Jean-Marc Cousin, Philippe Nedelec, Julie Patuel, Pawel Wolff, and Bastien Sauvage

Abstract. IAGOS has been measuring Ozone (O3) and Carbon Monoxide (CO) since 1994 and 2002 respectively. This dataset allows us to calculate O3 and CO trends in the upper troposphere across nine regions of the Northern Hemisphere. Trends are computed over multiple time periods to highlight recent changes.

O3 growth in the upper troposphere (UT) of the Northern Hemisphere was more pronounced between 1994 and 2013 (e.g 0.34 ± 0.09 ppb/y in East US and 0.32 ± 0.07 ppb/y in Europe). These trends are significantly higher than those calculated from 1994 to 2023 (0.17 ± 0.07 ppb/y in East US and 0.16 ± 0.05 ppb/y in Europe). This difference in trend of O3 appears to be associated with high positive anomalies of O3 in the early 2010s, as well as significantly lower O3 levels after 2020, at least partially linked to the COVID-19 crisis.

For CO, we observe a gradual reduction in its rate of decline over the years, until a point where trends are no longer detected or are associated with low positive values since the 2010s at mid-latitudes in the Northern Hemisphere.

Further studies will be necessary to constrain the causes of recent O3 and CO variations. Continued IAGOS monitoring over the coming years will be essential, to further update this analysis and to determine whether the recent change in the observed trends are temporary or represent a sustained change in the upper tropospheric air composition.

How to cite. Lebourgeois, T., Thouret, V., Clark, H., Bennouna, Y., Blot, R., Boulanger, D., Brunet, F., Cleris, S., Cousin, J.-M., Nedelec, P., Patuel, J., Wolff, P., and Sauvage, B.: Recent changes in the O3 and CO trends in the troposphere as observed by IAGOS, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2026-4770, 2026.
Received: 14 Aug 2026 – Discussion started: 08 Sep 2026
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Thibaut Lebourgeois, Valérie Thouret, Hannah Clark, Yasmine Bennouna, Romain Blot, Damien Boulanger, Florian Brunet, Simon Cleris, Jean-Marc Cousin, Philippe Nedelec, Julie Patuel, Pawel Wolff, and Bastien Sauvage

Status: open (until 20 Oct 2026)

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Thibaut Lebourgeois, Valérie Thouret, Hannah Clark, Yasmine Bennouna, Romain Blot, Damien Boulanger, Florian Brunet, Simon Cleris, Jean-Marc Cousin, Philippe Nedelec, Julie Patuel, Pawel Wolff, and Bastien Sauvage
Thibaut Lebourgeois, Valérie Thouret, Hannah Clark, Yasmine Bennouna, Romain Blot, Damien Boulanger, Florian Brunet, Simon Cleris, Jean-Marc Cousin, Philippe Nedelec, Julie Patuel, Pawel Wolff, and Bastien Sauvage
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Latest update: 08 Sep 2026
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Short summary
IAGOS has been measuring Ozone (O3) and Carbon Monoxide (CO) since 1994 and 2002 respectively with commercial aircraft. O3 concentrations increased significantly from 1994 to 2013 in the Northern Hemisphere. The following decade shows a more uncertain trend, with some regions even exhibiting decreases in O3 concentrations, potentially reflecting the impact of the COVID-19 pandemic. CO shows a reduction in its rate of decline over the years, until a point where changes are no longer detected.
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