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Vertical profile of H 2 SO 4 vapor at 70–110 km on Venus and some related problems

Icarus, ISSN: 0019-1035, Vol: 215, Issue: 1, Page: 197-203
2011
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Metrics Details

  • Citations
    15
    • Citation Indexes
      15
  • Captures
    23

Article Description

The vertical profile of H 2 SO 4 vapor is calculated using current atmospheric and thermodynamic data. The atmospheric data include the H 2 O profiles observed at 70–112 km by the SOIR solar occultations, the SPICAV-UV profiles of the haze extinction at 220 nm, the VeRa temperature profiles, and a typical profile of eddy diffusion. The thermodynamic data are the saturated vapor pressures of H 2 O and H 2 SO 4 and chemical potentials of these species in sulfuric acid solutions. The calculated concentration of sulfuric acid in the cloud droplets varies from 85% at 70 km to a minimum of 70% at 90 km and then gradually increasing to 90–100% at 110 km. The H 2 SO 4 vapor mixing ratio is ∼10 −12 at 70 and 110 km with a deep minimum of 3 × 10 −18 at 88 km. The H 2 O–H 2 SO 4 system matches the local thermodynamic equilibrium conditions up to 87 km. The column photolysis rate of H 2 SO 4 is 1.6 × 10 5 cm −2 s −1 at 70 km and 23 cm −2 s −1 at 90 km. The calculated abundance of H 2 SO 4 vapor at 90–110 km and its photolysis rate are smaller than those presented in the recent model by Zhang et al. (Zhang, X., Liang, M.C., Montmessin, F., Bertaux, J.L., Parkinson, C., Yung, Y.L. [2010]. Nat. Geosci. 3, 834–837) by factors of 10 6 and 10 9, respectively. Assumptions of 100% sulfuric acid, local thermodynamic equilibrium, too warm atmosphere, supersaturation of H 2 SO 4 (impossible for a source of SO X ), and cross sections for H 2 SO 4 ·H 2 O (impossible above the pure H 2 SO 4 ) are the main reasons of this huge difference. Significant differences and contradictions between the SPICAV-UV, SOIR, and ground-based submillimeter observations of SO X at 70–110 km are briefly discussed and some weaknesses are outlined. The possible source of high altitude SO X on Venus remains unclear and probably does not exist.

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