Three campaigns of observations performed at the «Observatoire du Pic du Midi » are analysed from the point of view of nitric acid and chlorofluorocarbon 11. The spectra, obtained in the 10 window, in both absorption and emission, permit to determine that most of the nitric acid absorbs above the tropopause while on the contrary, CFC13 emits and absorbs in the troposphere. The trend of CFC13 is observed between 1980 and 1982 ; an increase rate equal to the one measured between 1972 and 1980 is determined.