Thermodynamic Constraints on the Lower Atmosphere of Venus

The lower Venusian atmosphere is the region from the surface to the cloud deck or about 0–50 km. Early modeling studies of the atmosphere were primarily based on thermodynamics; more recent modeling studies are based on kinetics of the elementary reactions. In this paper, we take the accepted nominal composition of near-surface gases at ∼42 km and show some of the constituents are indeed at thermodynamic equilibrium. We impose a small oxygen gradient and use a thermodynamic free energy minimization code to describe the vertical gradients of mixing ratios for the primary gases in the lower atmosphere. The oxygen gradient is within the measurement errors on oxygen and thus maintains mass conservation. Reasonable agreement is found between our calculations and the vertical profiles of H2O, H2SO4, OCS, H2S, and Sn (n = 1–8). We then did a kinetic analysis of kinetic expressions for the formation of these species. Consistent with other investigators, we find that very few if any reactions should be at equilibr...