Articles | Volume 9, issue 2
Research article
22 Feb 2016
Research article |  | 22 Feb 2016

Retrieval of xCO2 from ground-based mid-infrared (NDACC) solar absorption spectra and comparison to TCCON

Matthias Buschmann, Nicholas M. Deutscher, Vanessa Sherlock, Mathias Palm, Thorsten Warneke, and Justus Notholt

Abstract. High-resolution solar absorption spectra, taken within the Network for the Detection of Atmospheric Composition Change Infrared Working Group (NDACC-IRWG) in the mid-infrared spectral region, are used to infer partial or total column abundances of many gases. In this paper we present the retrieval of a column-averaged mole fraction of carbon dioxide from NDACC-IRWG spectra taken with a Fourier transform infrared (FTIR) spectrometer at the site in Ny-Ålesund, Spitsbergen. The retrieved time series is compared to colocated standard TCCON (Total Carbon Column Observing Network) measurements of column-averaged dry-air mole fractions of CO2 (denoted by xCO2). Comparing the NDACC and TCCON retrievals, we find that the sensitivity of the NDACC retrieval is lower in the troposphere (by a factor of 2) and higher in the stratosphere, compared to TCCON. Thus, the NDACC retrieval is less sensitive to tropospheric changes (e.g., the seasonal cycle) in the column average.

Short summary
The column-averaged dry-air mole fraction of CO2 has been retrieved from high-resolution solar absorption spectra from two different measurement networks. We investigate the differences between these retrievals and find that their sensitivity differs greatly. As a result the direct comparison of the two retrievals remains challenging.