I've been trying to find super GHGs that could warm Callisto enough to be habitable. Nitrogen trifluoride would be great for the initial stages because of its low boiling point compared to the other super GHGs, but the final concentration of it required would be too toxic (55 ppm, OSHA max. is 10 ppm). CFCs would work, as they aren't toxic, but you'll need at least a little ozone and those would destroy any forming in the upper atmosphere. So I started looking at the fluorinated ethers, specifically HFE-125, as the IPCC report says it has a carbon dioxide equivalent of more than 13,000. The problem is, I couldn't find any toxicity data for this particular substance. If my heat transfer calculations are correct (they're a bit rough), about 70 ppm would be required - could you breathe that 24/7 and be OK? If not, what's the maximum?
For a similar purpose (CO2 equivalent 12,000) how bad an effect does HFC-23 have on ozone and/or people? Could a planet hold an ozone layer with 80-90 ppm of that? (It wouldn't have to be much of an ozone layer, because the greater distance from the Sun reduces the incoming radiation by 97%, and our ozone cuts out 97% to 99% of incoming high-energy UV, so you're almost where you need to be already.)
