The water vapor foreign continuum in the 810 0-850 0 cm-1 spectral range

In the Earth's atmosphere, the foreign absorption continuum of water vapor is due to the interaction of water molecules with other atmospheric gases (mostly N 2 and O 2 ). Following our study of the selfcontinuum in the high energy edge of the 1.25 mu m transparency window (Korovela et al, J. Quant. Spectrosc. Radiat. Transfer 286 (2022) 108206), we report here the first room temperature measurements of water vapor foreign continuum in the same spectral region. Foreign continuum cross-sections, C F , are derived at several selected spectral points between 8120 and 8500 cm -1 for humidified nitrogen, humidified oxygen and humidified air (10 0 0 0 ppm of H 2 O). The absorption signal is measured by cavity ring-down spectroscopy (CRDS) using pressure ramps up to 750 Torr. While the measured total continuum absorption follows nicely the expected quadratic dependence versus the total pressure, the uncertainty on the retrieved weak foreign continuum is strongly affected by other contributions which have to be subtracted from the measured absorption (far wings of the resonance lines, O 2 collision induced absorption, selfcontinuum, Rayleigh scattering). The obtained H 2 O-air and H 2 O-N 2 C F cross-section values are found to be comparable while the H 2 O-O 2 C F values appear to be significantly smaller. Overall, the retrieved C F values for H 2 O-air mixture validate the MT_CKD model in the considered region.(c) 2022 Elsevier Ltd. All rights reserved.