What gases do humans emit? Yes, I know about H2O and CO2 and methane, I want to know what else is in the mix.
Suppose you made a bare room with nothing but a metal chair in it; sealed so that you control what gas goes in and you control where the gas goes afterwards. Douse the place with 30% peroxide, bake the whole thing for a few hours--make sure anything that could outgas already has. Use an airlock to get in and out.
The gas that goes in is as pure a mix of O2 and N2 as you can manage. Chill the gas down until nearly liquefied to fractionate all impurities, and then warm up what’s left so you don’t freeze the volunteers; adding a little pure H2O so they don’t dry out. Gas flowing out of the room is also chilled to nearly the boiling point, except that you try to capture all the stuff that condenses out.
Put a man in there for a few hours. What will turn up in the pool of condensate? Whatever it is (aside from the obvious), there won’t be much and so studying it will be tricky.
Cleaning up after a volunteer wouldn’t be trivial--we shed skin, which will presumably continue to outgas long after we’ve left the area. (Who knows what the mites will do.) That’s why I suggested making the chamber a bake-able facility.
I could tell pretty easily on Monday when Richard had made himself a garlic pizza on Saturday. If I use a volume of air 2mx2mx2m, and the garlic smell chemical was 1ppm, then there’s about .03% of a mole of the stuff. If the molecular weight is O(100g/mole), and the density of the liquid is about 1g/cm^3, then I expect about .03cc of the goo to condense on the chilling system. That’s going to be hard to scrape together, but I don’t think it would be impossible.
Things that show up at the ppb level or smaller (still sometimes detectable by dogs, I’m told) are obviously going to require heroic collection measures. (I'm thinking of a cyclonic gas flow inside a super-chilled pipe--have to worry about lubricant contamination too.)
Do people outgas differently when sick or when well? Does a woman have a different chemical mix at different points in her period? Is a baby’s scent the same as an adults?
What comes out through the breath, what through the skin? And how much of it depends on the bacteria on the skin?