CO2 is pretty dominant and has a large Rayleigh scattering cross-section (see below). The thing I'm wondering is with all that Rayleigh scattering, how any of the light makes it to the surface instead of being bounced. Here is a good summary.http://link.springer.com/referenceworkentry/10.1007/978-3-642-27833-4_1349-2#page-1
We can assume for now that 30% of the light makes it through the clouds (if no gas is present). If there were no clouds, the optical thickness of the CO2 (and N2) would be about 20. This should reflect 90% of the light and transmit 10%. I suppose the net effect of clouds + gas would be to transmit 3%. It's unclear to me where the absorption (about 27%) of the light happens, since 70% is the albedo of Venus. Perhaps Venus reflects more light when the sun is overhead rather than lower where somewhat more can be absorbed by the clouds.https://books.google.com/books?id=lL57o9YB0mAC&pg ... us rayleigh scattering&f=false
Yes, Huygens recorded lots of relevant data from upward and downward spectral radiometers (link earlier posted). I think asymmetry parameters were derived with single scattering albedo. This is where I'm endeavoring to derive phase functions for single scattering and what I call an effective phase function for multiple scattering. We can see Titan also has an N2 gas optical depth of 1.45.