First infrared measurement of atmospheric NO 2 from the ground

High resolution Fourier transform spectra of the atmosphere in the 2850 ‐ 2950 cm −1 region have been recorded from the ground using the sun as a source. For the first time, many NO 2 absorption peaks belonging to the ν 1 + ν 3 band and its associated hot band ν 1 + ν 2 + ν 3 − ν 2 have been located. Among them, 13 well isolated features have been used to determine NO 2 vertical column densities. Indeed, from the analysis of 4 spectra recorded at air masses of 10.7, 5.4, 3.1 and 10.8, that is for the 3 first ones just after sunrise and in the early morning and for the last one just before sunset, vertical column densities of 1.84 ± 0.34, 1.80 ± 0.28, 1.74 ± 0.44 and 3.24 ± 0.46 10 15 molecule.cm −2 have been obtained. The good absolute accuracy of these results is due to the use of several lines having a wide enough range of intensities and of lower state energy levels.