Three Different Ways to Explain the Sulfur Depletion in the Clouds of Venus


The depletion of SO2 and H2O in and above the clouds of Venus (45 -- 65 km) cannot be explained by known gas-phase chemistry and the observed composition of the atmosphere.

We apply a full-atmosphere model of Venus to investigate three potential explanations for the SO2 and H2O depletion: (1) varying the below-cloud water vapor (H2O), (2) varying the below-cloud sulfur dioxide (SO2), and (3) the incorporation of chemical reactions inside the sulfuric acid cloud droplets. We find that increasing the below-cloud H2O to explain the SO2 depletion results in a cloud top that is 20 km too high, above-cloud O2 three orders of magnitude greater than observational upper limits and no SO above 80 km. The SO2 depletion can be explained by decreasing the below-cloud SO2 to 20 ppm.

The depletion of SO2 in the clouds can also be explained by the SO2 dissolving into the clouds, if the droplets contain hydroxide salts. These salts buffer the cloud pH. The amount of salts sufficient to explain the SO2 depletion entail a droplet pH of ∼1 at 50 km. Since sulfuric acid is constantly condensing out into the cloud droplets, there must be a continuous and pervasive flux of salts of ~1e-13 mol cm−2 s−1 driving the cloud droplet chemistry. An atmospheric probe can test both of these explanations by measuring the pH of the cloud droplets and the concentrations of gas-phase SO2 below the clouds.

Paul B. Rimmer, Sean Jordan, Tereza Constantinou, Peter Woitke, Oliver Shorttle, Richard Hobbs, Alessia Paschodimas

Comments: Submitted to The Planetary Science Journal. We kindly ask the planetary science community for feedback and comments. (64 pages, 7 Figures, 5 Tables, Full Model Output Data: this https URL)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2101.08582 [astro-ph.EP] (or arXiv:2101.08582v1 [astro-ph.EP] for this version)
Submission history
From: Paul B. Rimmer
[v1] Thu, 21 Jan 2021 12:51:46 UTC (9,428 KB)

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