Hydroxide salts in the clouds of Venus: their effect on the sulfur cycle and cloud droplet pH release_telqbykn75bjffnouimiod5hne

Abstract

The depletion of SO_2 and H_2O 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 SO_2 and H_2O depletion: (1) varying the below-cloud water vapor (H_2O), (2) varying the below-cloud sulfur dioxide (SO_2), and (3) the incorporation of chemical reactions inside the sulfuric acid cloud droplets. We find that increasing the below-cloud H_2O to explain the SO_2 depletion results in a cloud top that is 20 km too high, above-cloud O_2 three orders of magnitude greater than observational upper limits and no SO above 80 km. The SO_2 depletion can be explained by decreasing the below-cloud SO_2 to 20 ppm. The depletion of SO_2 in the clouds can also be explained by the SO_2 dissolving into the clouds, if the droplets contain hydroxide salts. These salts buffer the cloud pH. The amount of salts sufficient to explain the SO_2 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 ≈ 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 SO_2 below the clouds.
In text/plain format

Archived Files and Locations