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.
Highlights
Both sulfur dioxide (SO2) and water vapor (H2O) are known to be depleted in the cloud layer of Venus and to vary in abundance above the cloud top by an order of magnitude or more both spatially (Jessup et al 2015; Encrenaz et al 2019; Marcq et al 2020) and temporally in years-long cycles (Marcq et al 2013; Vandaele et al 2017b)
The results agree with observations as closely as when we consider cloud droplet chemistry below with one possible exception of sulfur monoxide (SO), which is below 1 ppb between 80 and 100 km
This may be brought into better agreement by including a mesospheric source of sulfur acid vapor or by adjusting the below-cloud concentrations of SO2 because we have found that the above-cloud SO2 is vpalresoroyfilpesreewndshiicettinsveHfSO2to2c»othn1ec5ebnpetprlaomtwi.o-Tncshloeouf1d5∼Sp1Op0m2ppabnmedloawtbh-oecvloeEud7dd0ySkOmd2i.fmfuosidoenl
Summary
Both sulfur dioxide (SO2) and water vapor (H2O) are known to be depleted in the cloud layer of Venus (see, e.g., Vandaele et al 2017a; Bierson & Zhang 2020) and to vary in abundance above the cloud top by an order of magnitude or more both spatially (Jessup et al 2015; Encrenaz et al 2019; Marcq et al 2020) and temporally in years-long cycles (Marcq et al 2013; Vandaele et al 2017b) Both of these species participate in Venus’s atmospheric sulfur cycle (Yung & Demore 1982; Krasnopolsky 1982, 2007, 2010a, 2012; Mills et al 2007; Zhang et al 2012; Bierson & Zhang 2020).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
