Something that has bothered me is that CO2 appears to have a much greater role after dark than in the daytime. I was wondering if this is because of a CO2 population inversion during the sunlight hours. I am thinking that Sunlight and daytime blue sky, excite atmospheric nitrogen, The nitrogen vibration ally passes the energy to CO2, which spontaneously decays back to ground state. In a CO2 laser, helium is added to speed up the decay of the .2 eV back to ground. In the atmosphere, there is insufficient helium for this task, and so the CO2 energy cycle would slow down. The evidence of something like this happening would be 9.6 and 10.6 um emission spectra, present during sunlight hours, but not after dark. Does anyone have a source for daytime vs nighttime infrared sky spectra?