Chemical pathway analysis of the Martian atmosphere: CO2-formation pathways

• Published in: Icarus (New York, N.Y. 1962) Vol. 219; no. 1; pp. 13 - 24
• Main Authors: Stock, Joachim W., Boxe, Christopher S., Lehmann, Ralph, Grenfell, J. Lee, Patzer, A. Beate C., Rauer, Heike, Yung, Yuk L.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.05.2012; Elsevier
• Subjects: Astronomy; Atmospheres, Chemistry; Atmospheres, Composition; Earth, ocean, space; Exact sciences and technology; Mars; Mars, Atmosphere; Photochemistry; Solar system; Atmospheres, Chemistry; Mars; Atmospheres, Composition; Mars, Atmosphere; Photochemistry; Planetary atmospheres; Trace compound; Abundance; Chemical reactions; Reaction rates; Photodissociation; Atmospheric stability; Algorithms; Atmospheric composition; Chemical composition; Transport processes; Solar system; Rate constant; Atmospheric structure
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2012.02.010

► The first automated quantified chemical pathway analysis of the martian atmosphere with respect to CO2 is presented. ► All dominant pathways related to CO2-production have been quantified as a function of altitude. ► Their contributions to the atmospheric CO2 abundance of individual pathways vary considerably with altitude. ► Results endorse the importance of transport processes in governing the stability of CO2 in the martian atmosphere. ► An unknown chemical pathway contributing approximately 8% to global CO2-production has been identified. 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 CO2. 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 CO2-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 CO2-production have been quantified as a function of height up to 86km. We quantitatively show that CO2-production is dominated by chemical pathways involving HOx and Ox. In addition, we find that NOx in combination with HOx and Ox exhibits a non-negligible contribution to CO2-production, especially in Mars’ lower atmosphere. This study reveals that only a small number of chemical pathways contribute significantly to the atmospheric abundance of CO2 on Mars; their contributions to CO2-production vary considerably with altitude. This analysis also endorses the importance of transport processes in governing CO2-stability in the Martian atmosphere. Lastly, we identify a previously unknown chemical pathway involving HOx, Ox, and HO2-photodissociation, contributing 8% towards global CO2-production by chemical pathways using recommended up-to-date values for reaction rate coefficients.