Vertical Distribution of Water in the Atmosphere of Venus: A Simple Thermochemical Explanation
John S. Lewis 1 and
David H. Grinspoon 1
1 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721
Several lines of evidence concerning the vertical abundance profile of water in the atmosphere of Venus lead to strikingly unusual distributions (the water vapor abundance decreases sharply in the immediately vicinity of the surface) or to serious conflicts in the profiles (different infrared bands suggest water abundances that are discrepant by a factor of 2.5 to 10). These data sets can be reconciled if (i) water molecules associate with carbon dioxide and sulfur trioxide to make gaseous carbonic acid and sulfuric acid in the lower atmosphere, and (ii) the discrepant 0.94-micrometer water measurements are due to gaseous sulfuric acid, requiring it to be a somewhat stronger absorber than water vapor inthis wavelength region. A mean total water abundance of 50 ± 20 parts per million and a near-surface free water vapor abundance of 10 ± 4 parts per million are derived.
