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Hydroxide Salts in the Clouds of Venus: Their Effect on the Sulfur Cycle and Cloud Droplet pH

Published version
Peer-reviewed

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Article

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Authors

Jordan, Sean 
Constantinou, Tereza 
Woitke, Peter 

Abstract

Abstract: 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 entails a droplet pH of ∼1 at 50 km. Because sulfuric acid is constantly condensing out into the cloud droplets, there must be a continuous and pervasive flux of salts of ≈10−13 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.

Description

Keywords

500, Planetary Science

Journal Title

The Planetary Science Journal

Conference Name

Journal ISSN

2632-3338

Volume Title

2

Publisher

The American Astronomical Society
Sponsorship
Simons Foundation (SF) (599634)
EC ∣ H2020 ∣ H2020 Priority Excellent Science ∣ H2020 Marie Skłodowska-Curie Actions (MSCA) (860470)