Impact of Molecular Spectroscopy on Carbon Monoxide Abundances from TROPOMI

Abstract

The impact of SEOM–IAS (Scientific Exploitation of Operational Missions–Improved Atmospheric Spectroscopy) spectroscopic information on CO columns from TROPOMI (Tropospheric Monitoring Instrument) shortwave infrared (SWIR) observations was examined. HITRAN 2016 (High Resolution Transmission) and GEISA 2015 (Gestion et Etude des Informations Spectroscopiques Atmosphériques 2015) were used as a reference upon which the spectral fitting residuals, retrieval errors and inferred quantities were assessed. It was found that SEOM–IAS significantly improves the quality of the CO retrieval by reducing the residuals to TROPOMI observations. The magnitude of the impact is dependent on the climatological region and spectroscopic reference used. The difference in the CO columns was found to be rather small, although discrepancies reveal, for selected scenes, in particular, for observations with elevated molecular concentrations. A brief comparison to Total Column Carbon Observing Network (TCCON) and Network for the Detection of Atmospheric Composition Change (NDACC) also demonstrated that both spectroscopies cause similar columns; however, the smaller retrieval errors in the SEOM with Speed-Dependent Rautian and line-Mixing (SDRM) inferred CO turned out to be beneficial in the comparison of post-processed mole fractions with ground-based references.

Computational aspects of speed-dependent Voigt and Rautian profiles

“…the Greenhouse Gases Observing Satellite [GOSAT,10], the Orbiting Carbon Observatory [OCO-2, 11] and the Sentinel-5p TROPOspheric Monitoring Instrument [TROPOMI,12]) have also highlighted the need for improved molecular spectroscopy in the short-wave IR [e.g. [13][14][15][16][17][18][19]. Improved Atmospheric Spectroscopy databases (IAS) have been the objective of a study funded by ESA in the context of the Scientific Exploitation of Operational Missions (SEOM) initiative: SEOM-IAS provides data for CO, CH 4 and H 2 O in the TROPOMI 2.3 µm region [20].…”