Ecotech Spectronus Fourier Transform Infrared Spectrometer (FTIR)

The Ecotech Sprectonus utilises an FTIR interferometer (IRcube, Bruker Optics, Germany) to modulate a broadband light source coupled to a 3.5 L multi-pass metal cell with 24m optical path length (schematic Figure 1).

The cell is continually flushed with dried ambient air, or calibration gases, and the transmission is measured across the broadband spectrum (1800 – 5000 cm-1) (Figure 2). Separate spectral regions are fitted on the spectrum for CH₄ (3001 – 3150 cm-1), all isotopologues of CO₂ (3520-3775 cm-1) and 13CO₂, 12CO₂, CO and N₂O (2150-2320 cm-1).

The FTIR is routinely calibrated using calibration cylinders produced at the Integrated Carbon Observation Systems (ICOS) Flask and Calibration Laboratory. Five calibration cylinders, covering the ambient atmospheric range, are used to generate a response curve for CO₂ (WMO X2007), N₂O (WMO X2006A), CH₄ (WMO X2004A) and CO (WMO X2014A).

The δ¹³C-CO₂ and δ¹⁸O-CO₂ are calibrated by accurately determining the mole fractions of the three most abundant isotopologues of CO₂ (¹²C¹⁶O¹⁶O, ¹³C¹⁶O¹⁶O and ¹²C¹⁸O¹⁶O). An in depth description of how the δ¹³C-CO₂ and δ¹⁸O-CO₂ in the air sample can be determined using calibrations gases with known δ¹³C-CO₂ and δ¹⁸O-CO₂ values is described in detail in Griffith (2019).

Griffith, D. W. T. (2018). Calibration of isotopologue-specific optical trace gas analysers: A practical guide.

Data is displayed in near real-time on the Weybourne webpage

Archive Data

• Data is provided in NetCDF files following the AMOF data standard
• Instrument name is
  • ncas-ftir-1
• The data product(s) associated with this instrument:
  • ch4-n2o-co2-co-concentration
• Example data file
  • How to use example data
  • ncas-ftir-1_ral_29001225_ch4-n2o-co2-co-concentration_v0.1.nc