The CO2-broadened H2O continuum in the 100-1500 cm-1 region. Measurements, predictions and empirical model

TL;DR

This study measures and models the CO2-broadened H2O continuum absorption between 100 and 1500 cm-1, providing experimental data, validation of a quasistatic prediction model, and an empirical correction for atmospheric applications.

Contribution

It offers new experimental measurements, validates a historical line-shape model, and proposes an empirical correction for the H2O continuum in CO2-rich atmospheres.

Findings

Good agreement with previous experimental data at 1300 cm-1

Model predictions slightly overestimate the continuum, but are generally accurate

Empirical correction improves the continuum representation for climate models

Abstract

Transmission spectra of H$_2$O+CO$_2$ mixtures have been recorded, at 296, 325 and 366 K, for various pressures and mixture compositions using two experimental setups. Their analysis enables to retrieve values of the 'continuum' absorption by the CO$_2$-broadened H$_2$O line wings between 100 and 1500 cm$^{-1}$. The results are in good agreement with those, around 1300 cm$^{-1}$, of the single previous experimental study available. Comparisons are also made with direct predictions based on line-shape correction factors $\chi$ calculated, almost thirty years ago, using a quasistatic approach and an input H$_2$O-CO$_2$ intermolecular potential. They show that this model quite nicely predicts, with slightly overestimated values, the continuum over a spectral range where it varies by more than three orders of magnitude. An empirical correction is proposed, based on the experimental data, which should be useful for radiative transfer and climate studies in CO$_2$ rich planetary atmospheres.