The origin and properties of the nitrogen and oxygen K excitations in solid NaNO2 were investigated combining high-resolution X-ray absorption and resonant photoemission spectroscopy. The absorption spectra obtained were treated on the basis of comparison between the spectra of solid NaNO2 and gas-phase NO2 and CH3NO2 molecules, as a result of which main absorption bands were assumed to be associated with the core electron transitions to unoccupied π and σ molecular orbitals of the planar NO2Na quasimolecule - the structural unit of the crystal. Examining series of the photoemission spectra taken at the N K and O K edges, it was found that the π and σ excitations decay in different ways: three decay channels (spectator, participator and normal Auger processes) were observed for the π excitations whereas only the normal and spectator Auger decay channels were seen for the σ excitations. This fact was qualitatively explained in terms of differences in the spatial localization and lifetime of the corresponding core excitations. The results of the resonant photoemission study give a direct evidence for the quasimolecular NO2- origin of the lowest unoccupied electronic states of the π type in solid NaNO2.