Greenbelt, Maryland
and
Georgia Institute of Technology
School of Electrical and Computer Engineering
Atlanta, Georgia 30332-0250
New abundance profiles of gaseous sulfuric acid (H2SO4) have been computed based on the measured absorptivity profiles of the Venus atmosphere obtained during the 1991-1992 Magellan radio occultation experiments (Jenkins et al.,Icarus 110, 79, 1994; Hinson and Jenkins, Bull. Am. Astron. Soc. 27, 1079, 1995) and the 1974 Mariner 10 radio occultation experiment (Lipa and Tyler, Icarus 39, 192, 1979). The Magellan abundance profiles are different than those previously reported by Jenkins et al. due to the completion of new laboratory measurements of the microwave opacity of gaseous H2SO4 in a CO2 environment. While these new experiments follow the same general procedure as Steffes (Icarus 64, 576, 1985; Astrophys. J. 310, 482, 1986), a more accurate determination of the H2SO4 to CO2 number mixing ratio is obtained by using resonators with gold as opposed to silver plating to eliminate unaccounted-for chemical reactions. In addition, a significant reduction in the uncertainty of the absorptivities is achieved due to our ability to account for changes in the dielectric properties of the resonators when a lossy gaseous mixture is introduced into them. New power law multiplicative expressions for the microwave opacity of gaseous H2SO4 in a CO2 environment are presented. The opacity expressions at S- and X-band are then applied to the Mariner 10 and Magellan absorptivity profiles, yielding sub-cloud gaseous H2SO4 abundances ranging from 10-14 ppm at the equator to 3-7 ppm at 67° latitude to 6-10 ppm at 88° latitude. The differences between profiles indicate both zonal and latitudinal variations in H2SO4 vapor abundance.