Infrared emission spectroscopy for trace gas retrievals in the Arctic

The solar absorption spectroscopy has been established as a powerful tool to monitor the trace gas composition of the atmosphere and is used in world wide networks such as TCCON (Total Carbon Column Observing Network) and NDACC (Network for Detection of Atmospheric Composition Change). The solar absorption measurements have the disadvantage that in Arctic regions there are no measurements possible during polar night leading to significant gaps in the data record. To fill those gaps we deploy a Bruker Vertex 80 spectrometer in emission geometry at the AWIPEV station in Ny-Ålesund, Svalbard. For highest possible resolution of 0.08 cm⁻¹, one-sided interferograms are recorded. Total power calibration procedures with two reference black bodies developed for double-sided interferograms (having lower resolution) are adjusted to obtain radiometrically calibrated zenith viewing emission spectra. The optimal estimation method is used to retrieve atmospheric water vapor and methane for cloud-free scenes. Results are compared to radiosondes and TCCON measurements. We investigate in detail the influence of black body emissivity and temperature uncertainty as quality check of our setup. The importance of spectral resolution is tested to prepare our retrieval to work with other instruments such as the 1 cm⁻¹ resolution E-AERI deployed during the MOSAiC campaign.