New measurements of the NO₂ absorption cross section in the 440‐ to 460‐nm region and estimates of the NO₂‐N₂O₄ equilibrium constant

Absolute determinations of the NO 2 absorption cross section in the 440‐ to 460‐nm region at different temperatures are reported. This region is of special interest for remote sensing applications. The interpretation of the results is rendered complex by the coexistence of NO 2 and its dimer. In the experiment both NO 2 and N 2 O 4 absorption features are observed. Different approaches are utilized to obtain the partial pressure of NO 2 ; a new estimate of the NO 2 ‐N 2 O 4 equilibrium constant from spectroscopic measurements is also obtained. Within experimental errors the overall shape of the spectrum does not show a dependence on temperature, but some features are affected; in particular, a slight increase of a few maxima and a decrease of the other maxima and of the minima when the temperature is lowered have been observed.