LOW-TEMPERATURE HIGH PRECISION MEASUREMENTS OF LINE MIXING and COLLISIONAL INDUCED ABSORPTION IN THE OXYGEN A-BAND

Because of the constant mixing ratio of molecular oxygen (\chem{O_2}) within the Earth’s atmosphere, the \chem{O_2} A-band is commonly used in satellite and remote sensing measurements as a measure of the airmass. A recent collaborative effort has produced a self-consistent integrated spectroscopic model for the \chem{O_2} A-Band that simultaneously accounts for high-order line-shapes, line mixing (LM), and collisional induced absorption (CIA).\footnote{B. J. Drouin, D. C. Benner, L. R. Brown, et al., Multispectrum analysis of the oxygen A-band, J. Quant. Spectrosc. Radiat. Transfer, 2017, 186: p. 118-138.} This model has improved OCO-2 mission retrievals of dry air \chem{CO_2}, however, limitations in existing spectroscopic models still lead to airmass dependent biases. Currently, model development is limited by a lack of high resolution experimental data at low temperatures and in the R-branch. To address this, measurements of the entire \chem{O_2} A-band were recently made with a variable-temperature cavity ring-down spectrometer (CRDS) over a range of temperatures, pressures, and molar fractions. Because of the limited dynamic range of the CRDS system, at high molar fractions of \chem{O_2} saturation can occur at the line cores of strong transitions. Therefore, a range of molar fraction \chem{O_2} samples were employed. Low mole fraction data, which was unaffected by saturation provided information on the temperature dependence of high-order line-shape parameters. Conversely, high molar fraction data provided information on LM and CIA effects that dominate absorption in the troughs between saturated transitions. By combining this high-resolution experimental data, that covers both the entire \chem{O_2} A-Band as well as a range of temperatures, with existing datasets, these results aim to improve on LM and CIA models for the next iteration of the global \chem{O_2} A-Band model