In message , Sleepalot
writes

I was thinking about the greenhouse effect, and this question
occured to me: in the space around me, what's more common,
atoms or photons?


In the universe as a whole the photon to baryon ratio is 10^9. So the
question that now needs to be answered is by how much is the baryon
density (and photon density) enhanced in the space around you, and what
is the average number of baryons per atom in that region. The answer to
this depends on how big a space you're thinking of.
--
Stewart Robert Hinsley