Evaluating the Role of Polysulfur in the Atmosphere of Venus
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Date
2023-05
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The Ohio State University
Abstract
Polysulfur, Sx where (2 ≤ x ≤ 8), is a speculative species in the atmosphere of Venus. Sx absorbs in the UV region and has been proposed as the identity of the unknown UV absorber in the cloud tops in the middle atmosphere of Venus, where a significant amount of solar flux is absorbed. The middle atmosphere contains the sulfur species SO2, SO, OCS, and H2SO4 and the region is dominated by photochemistry, which should produce Sx, from these species, though polysulfur has never be definitively detected in the atmosphere. Large uncertainties in the reaction rates for reactions of polysulfur create large uncertainties in the concentration of Sx in models of the atmosphere. For the first part of this thesis, to determine which reactions should be prioritized for laboratory study, a sensitivity analysis was performed on a model of the atmosphere of Venus. The results identified six reactions that should be prioritized for study, where M is an inert third body: 2S2+M = S4+M, S3+S4 = S2+S5, Cl+S4 = S2+ClS2, SO+OCS = S2+CO2, 2S2O = S3+SO2, and O+S4 = SO+S3. The second part of this thesis investigates the beginning of the polysulfur production chain, 2S+M = S2+M, using a macro flow through photoreactor. The reaction rate determined from experimental study for the low pressure limit was k0 = 9.77 ×10-26 e206./T. In the third part of this thesis, the model of the atmosphere was updated with the new reaction rate, though no change was observed in any species concentration. A previous version of the model was very sensitive to the reaction rate when the low-pressure limit was changed by just one order of magnitude, so the improved reaction rate may have a large impact on the polysulfur concentration as the conditions of the model are refined over time.
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Keywords
Venus, Atmospheric Chemistry, Allotropes of Sulfur, Elemental Sulfur, Planetary Science