VERTICAL-DISTRIBUTION OF WATER IN THE ATMOSPHERE OF VENUS - A SIMPLE THERMOCHEMICAL EXPLANATION

Several lines of evidence concerning the vertical abundance profile of water in the atmosphere of Venus lead to stikingly unusual distributions (the water vapor abundance decreases sharply in the immediate 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 sulfiric acid, requiring it to be a somewhat stronger absorber than water vapor in this 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.