High‐resolution Fourier transform measurement of the NO₂ visible and near‐infrared absorption cross sections: Temperature and pressure effects

High‐resolution NO 2 absorption cross sections have been obtained in the near‐IR (NIR) and visible regions using a Fourier transform spectrometer coupled to a multiple reflection cell. Spectra were recorded at 0.05 cm −1 in the NIR region (10,800–15,100 cm −1 ) and at 0.1 cm −1 in the visible region (13,800–26,000 cm −1 ), under various pressure conditions (pure NO 2 and NO 2 /air mixtures) and at three temperatures (220, 240, and 294 K). The effects of the temperature and the pressure on the NO 2 cross sections have been investigated. As expected, an increase of temperature results in a decrease of the absorption at the maxima of the absorption bands and an increase at the minima. From the measurements performed with pure NO 2 at different temperatures a linear regression of the cross section with temperature has been carried out. This enabled the cross sections to be reproduced within 2% at room temperature and 7% at the lower temperatures. The variation of the cross sections with the total pressure of NO 2 /air mixtures has also been investigated at high resolution.