Chemical pathway analysis of the Martian atmosphere: CO 2-formation pathways

Joachim W. Stock, Christopher S. Boxe, Ralph Lehmann, J. Lee Grenfell, Beate A.C. Patzer, Heike Rauer, Yuk L. Yung

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


The chemical composition of a planetary atmosphere plays an important role for atmospheric structure, stability, and evolution. Potentially complex interactions between chemical species do not often allow for an easy understanding of the underlying chemical mechanisms governing the atmospheric composition. In particular, trace species can affect the abundance of major species by acting in catalytic cycles. On Mars, such cycles even control the abundance of its main atmospheric constituent CO 2. The identification of catalytic cycles (or more generally chemical pathways) by hand is quite demanding. Hence, the application of computer algorithms is beneficial in order to analyze complex chemical reaction networks. Here, we have performed the first automated quantified chemical pathways analysis of the Martian atmosphere with respect to CO 2-production in a given reaction system. For this, we applied the Pathway Analysis Program (PAP) to output data from the Caltech/JPL photochemical Mars model. All dominant chemical pathways directly related to the global CO 2-production have been quantified as a function of height up to 86km. We quantitatively show that CO 2-production is dominated by chemical pathways involving HO x and O x. In addition, we find that NO x in combination with HO x and O x exhibits a non-negligible contribution to CO 2-production, especially in Mars' lower atmosphere. This study reveals that only a small number of chemical pathways contribute significantly to the atmospheric abundance of CO 2 on Mars; their contributions to CO 2-production vary considerably with altitude. This analysis also endorses the importance of transport processes in governing CO 2-stability in the Martian atmosphere. Lastly, we identify a previously unknown chemical pathway involving HO x, O x, and HO 2-photodissociation, contributing 8% towards global CO 2-production by chemical pathways using recommended up-to-date values for reaction rate coefficients.

Original languageEnglish (US)
Pages (from-to)13-24
Number of pages12
Issue number1
StatePublished - May 2012

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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