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Published March 26, 2009 | Published
Journal Article Open

Evidence for carbonyl sulfide (OCS) conversion to CO in the lower atmosphere of Venus


The chemical regimes in the atmosphere of Venus vary from photochemistry in the middle atmosphere to thermal equilibrium chemistry in the lower atmosphere and the surface. Many chemical cycles have been proposed, but few details about these cycles are fully verified by comparison between observations and modeling. Recent high-quality data of carbonyl sulfide (OCS) and CO from ground-based and Venus Express observations provide a unique opportunity to test our understanding of chemistry and transport in the lower atmosphere of Venus. The spatial distributions of OCS and CO in the atmosphere reflect a sensitive balance between chemistry and transport. On the basis of our updated photochemical model and winds from Lee et al.'s (2007) general circulation model, we study the chemistry and transport in a simplified two-dimensional chemistry-transport model. OCS is produced by heterogeneous reactions on the surface; the middle atmosphere is a net sink for OCS. The combination of data and modeling provides strong evidence for the loss of OCS by conversion to CO. The detailed chemical mechanism is currently unknown, although a number of speculations have been proposed. The sensitivity of the distributions of OCS and CO to model parameters is reported.

Additional Information

© 2009 American Geophysical Union. Received 31 January 2008; revised 30 December 2008; accepted 9 January 2009; published 26 March 2009. We thank K. Baines, P. Drossart, J. Moses, C. Parkinson, V. Natraj, and X. Zhang for helpful discussions, D. Crisp for providing UV absorber profiles, and K. F. Li, D. Yang, and X. Zhang for assistance in preparing the manuscript. Special thanks are due to W. B. DeMore for a critical discussion of sulfur chemistry and S. Lebonnois and three anonymous referees for raising fundamental issues the resolution of which led to a much better paper. This research was supported by NASA grant NNX07AI63G to the California Institute of Technology. M. Liang was supported by NSC 97-2628-M-001-001 grant to Academia Sinica.

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