Simulations of vertical profiles of sulfur oxides and chlorosulfanes in Venus’ mesosphere

The primary sulfur species in Venus’ atmosphere, sulfur dioxide (SO₂) may be a precursor for the unidentified UV-blue absorber(s), which, along with CO₂ near the tops of the clouds, appears to be responsible for absorbing about half of the solar energy deposited in Venus’ atmosphere [1]. Published simulations using standard photochemistry [2,3] indicate the mixing ratio of SO₂ should decrease roughly monotonically with increasing altitude, although a small inversion is evident in one set of simulations [3]. Observations, however, despite disagreeing on the magnitude of the phenomenon, have consistently found an inversion layer in the upper mesosphere (above about 85 km altitude) where the mixing ratio of SO₂ increases with increasing altitude [4,5,6]. Simulations using H₂SO₄ as the medium for transporting sulfur from the lower mesosphere to the upper mesosphere that replicated the upper mesosphere SO₂ inversion layer [2] either required assumptions that stretch the boundaries of known laboratory data or had a calculated H₂SO₄ abundance that exceeds the observational upper limit on upper mesospheric gaseous H₂SO₄ [7]. A possible alternative is transport via a combination of sulfur-chlorine-oxides [8].

The Caltech/JPL photochemical model [9] was used for the numerical simulations. Preliminary results using a simplified model suggest the inclusion of both ClSO₂ and SO₂Cl₂ in the model and adjustment of selected reaction rate coefficients within their standard uncertainties can produce at least a factor of two upper mesosphere inversion for SO₂. The results from simulations using a more comprehensive photochemical model will be presented.

1. Titov D.V. et al. (2007), in Exploring Venus as a Terrestrial Planet, AGU, 121–138.

2. Zhang X. et al. (2012), Icarus, 217, 714–739.

3. Krasnopolsky V.A. (2012), Icarus, 218, 230–246.

4. Sandor B.J. et al. (2010), Icarus, 208, 49–60.

5. Belyaev D.A. et al. (2017), Icarus, 294, 58–71.

6. Vandaele A.C. et al. (2017), Icarus, 295, 16–33.

7. Sandor B.J. et al. (2012), Icarus, 217, 839–844.

8. Petrass. J.B. (2013), Physics Honours Thesis, Australian National University, 76 pp.

9. Allen M. et al. (1981), J. Geophys. Res., 86, 3617–3627.