Calibration strategies for FTIR and other IRIS instruments for accurate 13C and 18O measurements of CO2 in air

Edgar Flores, BIPM (FR)

This talk will describe calibration strategies in laboratory conditions that can be applied to ensure accurate measurements of the isotopic composition of the CO2 in air, expressed as δ13C and δ18O on the VPDB scale, with either FTIR (in this case a Vertex 70V (Bruker)) or an Isotope Ratio Infrared Spectrometer (IRIS) (in this case a Delta Ray (Thermo Fisher Scientific)). In the case of FTIR a novel methodology using only two standards of CO2 in air with different mole fractions but identical isotopic composition was demonstrated to be highly accurate for measurements of δ13C and δ18O with standard uncertainties of  0.2 ‰ and 0.8 ‰ respectively, at a nominal CO2 mole fraction of 400 µmol mol-1 in air. In the case of the IRIS system, we demonstrate that the use of two additional standards of CO2 in air of known δ13C and δ18O isotopic composition allows standard uncertainties of 0.3 ‰ and 0.60 ‰, to be achieved for δ13C and δ18O measurements respectively. The calibration strategies were validated using a set of five traceable Primary Reference Gas Standards. The standards, produced with whole air or synthetic air, covered the mole fraction range of (378- 420) µmol mol-1 and were prepared and/or value assigned either by the National Institute of Standards and Technology (NIST) or the National Physical Laboratory (NPL). The standards were prepared using pure CO2 obtained from specific sources, namely: combustion; Northern Continental and Southern Oceanic Air and a gas well source, with δ13C values ranging between -35‰ and -1‰. The isotopic composition of all standards was value assigned at the Max Planck Institute for Biogeochemistry Jena (MPI-Jena).


Pen Profile

My most significant contribution during last years is the technical development and coordination of the international key comparisons of NO2/N2 (CCQM-K74), CH4/air (CCQM-K82) and CO2/air (CCQM-K120) involving the most active National Metrologies Institutes of the Gas Analysis Working Group (GAWG) of the Consultative Committee for Amount of Substance: Metrology in Chemistry and Biology (CCQM).

This has led to the development of a capacity and knowledge transfer programme in metrology for clean air at the BIPM, focused on knowledge transfer on the use of FTIR for gas standard analysis. The training programme started in June 2016 with CENAM (Mexico) and NIM (China) staff members joining the skills broadening secondment program on FTIR operation and analysis of FTIR spectra for gas analysis. In 2017 members of NPL (UK), LNE (France) and NPLI (India) are expected.

I hold a PhD degree in Atmospheric Physics from the National Autonomous University of Mexico, obtained in 2008 after a thesis on Characterization of aircrafts combustion products by Emission Fourier Transform Infrared Spectroscopy (FT-IR) and was a PhD in Post during the period 2004 to 2006 at the Institute of Meteorology and Climate Research Atmospheric Environmental Research (IMK-IFU), in Germany.

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