Spectral line profiles of the D1 and D2 sodium line emission from the twilight and the nightglow have been obtained by means of a 150 mm aperture Fabry-Perot interferometer. The observed doppler broadening of the twilight profiles yields a temperature for the emitting atoms of (210¿15) K, in good agreement with the expected temperature of the sodium layer at ~90 km. By way of contrast, the nightglow line profiles are found to be much broader, their width yielding an apparent temperature of (600¿50) K. It is shown that chemiexcitation is the most likely process which imparts kinetic energies in excess of ambient thermal values to the emitting atoms.