A detailed analysis of CO2 4.3-μm limb radiances measured by the Stratospheric and Mesospheric Sounder on Nimbus 7 has been conducted using a non-local thermodynamic equilibrium (non-LTE) radiative transfer model. The data display diurnal, latitudinal, and seasonal variations which are shown, after the latitudinal variation of the instrument's response has been taken into account, to be caused by different conditions of solar illumination and variations in the kinetic temperature profile. A study of the sensitivity of the populations and limb radiances to spectral, atmospheric, and collisional interactions parameters has been undertaken, and a limited range of values for some of these quantities has been derived. Among other findings, we conclude that the rate at which energy is exchanged (as &ngr;3 quanta) between N2 and CO2 may be approximately twice the initial model value, which was inferred from laboratory data, and that the CO2 volume mixing ratio above 80 km may be significantly less than that predicted by photochemical models. ¿ American Geophysical Union 1989