Cavity ring-down spectroscopy of CO2 near λ = 2.06 μm: Accurate transition...

Fleurbaey, H., H. Yi, E. M. Adkins, A. J. Fleisher, and J. T. Hodges (2020), Cavity ring-down spectroscopy of CO2 near λ = 2.06 μm: Accurate transition intensities for the Orbiting Carbon Observatory-2 (OCO-2) “strong band”, J. Quant. Spectrosc. Radiat. Transfer, 252, 107104, doi:10.1016/j.jqsrt.2020.107104.

The λ = 2.06 μm absorption band of CO2 is widely used for the remote sensing of atmospheric carbon dioxide, making it relevant to many important top-down measurements of carbon flux. The forward models used in the retrieval algorithms employed in these measurements require increasingly accurate line intensity and line shape data from which absorption cross-sections can be computed. To overcome accuracy limitations of existing line lists, we used frequency-stabilized cavity ring-down spectroscopy to measure 39 transitions in the 12 C16 O2 absorption band. The line intensities were measured with an estimated relative combined standard uncertainty of ur = 0.08 %. We predicted the J-dependence of the measured intensities using two theoretical models: a one-dimensional spectroscopic model with HermanWallis rotation-vibration corrections, and a line-by-line ab initio dipole moment surface model [Zak et al. JQSRT 2016;177:31-42]. For the second approach, we fit only a single factor to rescale the theoretical integrated band intensity to be consistent with the measured intensities. We find that the latter approach yields an equally adequate representation of the fitted J-dependent intensity data and provides the most physically general representation of the results. Our recommended value for the integrated band intensity equal to 7.183 × 10−21 cm molecule−1 ± 6 × 10−24 cm molecule−1 is based on the rescaled ab initio model and corresponds to a fitted scale factor of 1.0069 ± 0.0 0 02. Comparisons of literature intensity values to our results reveal systematic deviations ranging from −1.16 % to +0.33 %.

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Orbiting Carbon Observatory-2 (OCO-2)