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D.M. Hunten, A.L. Sprague (LPL), M.H. Wong (U. Michigan)
The Galileo Probe Mass Spectrometer observed many peaks in the mass region corresponding to C2 and C3 hydrocarbons. A feature of the published analysis was that the mixing ratios increased with depth, a behavior not expected for compounds being transported downwards from their source in the stratosphere. However, our current assessment is that this increase is not statistically significant. We explore the possibility that the origin is the evaporation and decomposition of the smog particles that also flow downward from the stratosphere. We have modeled this descent and evaporation, using the large eddy diffusion coefficients derived from a mixing-length analysis of convective heat transport at levels deeper than 1 -- 2 bars. Because this eddy transport is very rapid, the predicted number densities of both particles and compounds derived from them are small, orders of magnitude less than required to explain the observed signals. The mixing ratios of the compounds are predicted to be independent of depth. Perhaps the vertical eddy transport in the hot-spot region where the Probe descended is much slower than in normal regions, a hypothesis that might also help explain the remarkable deficiency of water vapor in hot spots. Or it may be that the observed molecules were generated inside the instrument as it was heated to much higher temperatures than it was designed to withstand.