Simulations of Vertical Profiles of SO and SO2 in Venus Mesosphere

The primary reservoir for SO2 on Venus lies in the troposphere, but a pronounced SO2 inversion layer has been consistently observed my multiple instruments since modern observations began in 2004. The Caltech/JPL photochemical model with simplified standard chemistry was used to calculate steady-state vertical profiles for SO2 as a function of solar zenith angle at 58110 km altitude. Assuming photochemistry ceases at each altitude at the solar zenith angle where the photochemical lifetime equals the zonal transport lifetime, an estimate of the actual non-steady-state vertical profile at the evening terminator has been constructed for the equatorial region. The resultant profile has a factor of two increase in the SO2 mixing ratio from 70 to 80 km altitude. This agrees qualitatively but not quantitatively with the observations, which suggests the interaction of photochemistry and dynamics may be important for creating the observed mesospheric SO2 inversion layer.