Improved Line Positions and Intensities of the CO2 Molecule for the HITRAN2020 Database

The quality of the reference spectroscopic parameters for the spectral lines of carbon dioxide (CO₂) is of paramount importance for monitoring concentrations of this gas in the terrestrial atmosphere using ground- and satellite-based spectrometers. Naturally the HITRAN database provides substantial updates in every new edition of the database.

The most recent edition of the database (HITRAN2016 [1]) overall presents a substantial improvement of the spectral parameters of CO₂ with respect to previous versions. However, a number of issues have been identified in new laboratory and atmospheric spectra below 8000 cm^-1 (mainly from the Kitt Peak National Observatory, MkIV balloon and CRDS spectra, Total Carbon Column Observing Network (TCCON)). In this work, we concentrate on the issues associated with deficient line positions and intensities. A general review of the bands affected by these issues in HITRAN2016 was performed. Alternative sources of data for each problematic band were considered. The comparison to the CDSD-296 [2], ab initio UCL [3] and Ames [4] databases and to available experimental works below 8000 cm^-1 is presented. Updated line positions and intensities for the CO₂ molecule result in significant improvements towards the HITRAN2020 edition and will have an important impact on current and future remote-sensing missions that monitor CO₂ concentrations.