Carbon monoxide (CO) is the main product of CO2 photolysis in the Martian atmosphere. Production of CO is balanced by its loss reaction with OH, which recycles CO into CO2. CO is therefore a sensitive tracer of the OH-catalysed chemistry that contributes to the stability of CO2 in the atmosphere of Mars. To date, CO has been measured only in terms of vertically integrated column abundances, and the upper atmosphere, where CO is produced, is largely unconstrained by observations. Here we report vertical profiles of CO from 10 to 120 km, and from a broad range of latitudes, inferred from the Atmospheric Chemistry Suite on board the ExoMars Trace Gas Orbiter. At solar longitudes 164–190°, we observe an equatorial CO mixing ratio of ~1,000 ppmv (10–80 km), increasing towards the polar regions to more than 3,000 ppmv under the influence of downward transport of CO from the upper atmosphere, providing a view of the Hadley cell circulation at Mars’s equinox. Observations also cover the 2018 global dust storm, during which we observe a prominent depletion in the CO mixing ratio up to 100 km. This is indicative of increased CO oxidation in a context of unusually large high-altitude water vapour, boosting OH abundance.
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The datasets generated by the ExoMars Trace Gas Orbiter instruments, including ACS, and analysed during the current study are being made available in the ESA Planetary Science Archive (PSA) repository, https://archives.esac.esa.int/psa, following a six months prior access period, following the ESA Rules on Information, Data, and Intellectual Property. Data used herein can be found by searching for the ‘ExoMars 2016’ mission and then selecting the ACS and MIR instruments. Derived products (CO VMR vertical profiles) have been deposited in the Oxford University Research Archive at https://doi.org/10.5287/bodleian:wxxq2m6jo.
The GGG software suite is maintained by NASA’s Jet Propulsion Laboratory (JPL) and the California Institute of Technology. GGG is available at https://tccon-wiki.caltech.edu and distributed under a non-commercial software license. The LMD GCM is maintained at LMD. It can be obtained using the Subversion version control system following the instructions made available here: https://www.lmd.jussieu.fr/~lmdz/planets/mars/user_manual.pdf.
McElroy, M. B. & Donahue, T. M. Stability of the Martian atmosphere. Science 177, 986–988 (1972).
Parkinson, T. D. & Hunten, D. M. Spectroscopy and acronomy of O2 on Mars. J. Atmos. Sci. 29, 1380–1390 (1972).
Nair, H., Allen, M., Anbar, A. D., Yung, Y. L. & Clancy, R. T. A photochemical model of the Martian atmosphere. Icarus 111, 124–150 (1994).
Yung, Y. L. & DeMore, W. B. Photochemistry of Planetary Atmospheres (Oxford Univ. Press, 1999).
Lefèvre, F. & Krasnopolsky, V. in The Atmosphere and Climate of Mars (eds Haberle, R. M. et al.) 405–432 (Cambridge Univ. Press, 2017).
Krasnopolsky, V. A. Long-term spectroscopic observations of Mars using IRTF/CSHELL: mapping of O2 dayglow, CO, and search for CH4. Icarus 190, 93–102 (2007).
Encrenaz, T. et al. Seasonal variations of the Martian CO over Hellas as observed by OMEGA/Mars Express. Astron. Astrophys. 459, 265–270 (2006).
Smith, M. D., Wolff, M. J., Clancy, R. T. & Murchie, S. L. Compact Reconnaissance Imaging Spectrometer observations of water vapor and carbon monoxide. J. Geophys. Res. 114, E00D03 (2009).
Sindoni, G., Formisano, V. & Geminale, A. Observations of water vapour and carbon monoxide in the Martian atmosphere with the SWC of PFS/MEX. Planet. Space Sci. 59, 149–162 (2011).
Smith, M. D., Daerden, F., Neary, L. & Khayat, A. The climatology of carbon monoxide and water vapor on Mars as observed by CRISM and modeled by the GEM-Mars general circulation model. Icarus 301, 117–131 (2018).
Sprague, A. L. et al. Mars’ south polar Ar enhancement: a tracer for south polar seasonal meridional mixing. Science 306, 1364–1367 (2004).
Sprague, A. L. et al. Interannual similarity and variation in seasonal circulation of Mars’ atmospheric Ar as seen by the Gamma Ray Spectrometer on Mars Odyssey. J. Geophys. Res. 117, E04005 (2012).
Smith, M. D. THEMIS observations of Mars aerosol optical depth from 2002–2008. Icarus 202, 444–452 (2009).
Mahaffy, P. R. et al. Structure and composition of the neutral upper atmosphere of Mars from the MAVEN NGIMS investigation. Geophys. Res. Lett. 42, 8951–8957 (2015).
Stevens, M. H. et al. Detection of the nitric oxide dayglow on Mars by MAVEN/IUVS. J. Geophys. Res. 124, 1226–1237 (2019).
Vandaele, A. C. et al. Martian dust storm impact on atmospheric H2O and D/H observed by ExoMars Trace Gas Orbiter. Nature 568, 521–525 (2019).
Fedorova, A. A. et al. Stormy water on Mars: the distribution and saturation of atmospheric water during the dusty season. Science 367, 297–300 (2020).
Forget, F. et al. Improved general circulation models of the Martian atmosphere from the surface to above 80 km. J. Geophys. Res. 104, 24155–24176 (1999).
Lefèvre, F., Lebonnois, S., Montmessin, F. & Forget, F. Three-dimensional modeling of ozone on Mars. J. Geophys. Res. 109, E07004 (2004).
Montabone, L. et al. Martian year 34 column dust climatology from mars climate sounder observations: reconstructed maps and model simulations. J. Geophys. Res. 125, e06111 (2020).
Krasnopolsky, V. A. Variations of carbon monoxide in the Martian lower atmosphere. Icarus 253, 149–155 (2015).
Holmes, J. A., Lewis, S. R., Patel, M. R. & Smith, M. D. Global analysis and forecasts of carbon monoxide on Mars. Icarus 328, 232–245 (2019).
Kass, D. M. et al. Mars Climate Sounder observation of Mars’ 2018 global dust storm. Geophys. Res. Lett. 46, e2019GL083931 (2019).
Smith, M. D. THEMIS observations of the 2018 Mars global dust storm. J. Geophys. Res. 124, 2929–2944 (2019).
Aoki, S. et al. Water vapor vertical profiles on Mars in dust storms observed by TGO/NOMAD. J. Geophys. Res. 124, 3482–3497 (2019).
Neary, L. et al. Explanation for the increase in high-altitude water on Mars observed by NOMAD during the 2018 global dust storm. Geophys. Res. Lett. 47, e84354 (2020).
The ExoMars mission is a joint mission of the European Space Agency (ESA) and Roscosmos. The ACS experiment is led by the Space Research Institute (IKI) in Moscow, assisted by LATMOS in France. This work was funded by Roscosmos, the National Centre for Space Studies of France (CNES), the Agence Nationale pour la Recherche (ANR)-MCUBE project, the Ministry of Science and Education of Russia, the Natural Sciences and Engineering Research Council of Canada (NSERC) (PDF – 516895 – 2018) and the UK Space Agency (ST/T002069/1, ST/R001502/1 and ST/P001572/1). Science operations are funded by Roscosmos and ESA.
The authors declare no competing interests.
Peer review information Nature Geoscience thanks Jun Cui and Daniel Viudez-Moreiras for their contribution to the peer review of this work. Primary Handling Editors: Tamara Goldin; Stefan Lachowycz.
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Olsen, K.S., Lefèvre, F., Montmessin, F. et al. The vertical structure of CO in the Martian atmosphere from the ExoMars Trace Gas Orbiter. Nat. Geosci. 14, 67–71 (2021). https://doi.org/10.1038/s41561-020-00678-w
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