The emission and absorption spectra of N2-O2 plasmas under thermal and chemical equilibrium have been calculated taking into account molecular, atomic and ionic contributions for a temperature up to 20000K. All the contributing spectra of the electronic systems of the diatomic molecules have been calculated using a RKR method and up to date electronic moments and Dunham coefficients. The positions and strengths of the neutral and ionized atomic lines are taken from the NIST database. The Stark line broadening parameters have been calculated systematically from a semi-classical approach. The continuum radiation resulting from photoionization and photodetachment, photodissociation and Bremsstrahlung has been taken into account. The radiative transfer equation has then been solved for a planar geometry with specified temperature profiles in order to analyse with a high spectral resolution approach the contribution of each phenomenon to the radiative flux escaping from the medium. For small thicknesses of the coldest regions (a few millimeters), it is found that practically all the radiation emitted by the hot layers below 50000 cm−1 escapes from the medium while the predominant absorption mechanisms in the VUV are due to the Schumann-Runge O2 continuum, to N2 VUV systems, and to N2 photoionization.