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Using a laser-based CO2 carbon isotope analyser to investigate gas transfer in geological media

Abstract : CO 2 stable carbon isotopes are very attractive in environmental research to investigate both natural and an-thropogenic carbon sources. Laser-based CO 2 carbon isotope analysis provides continuous measurement at high temporal resolution and is a promising alternative to isotope ratio mass spectrometry (IRMS). We performed a thorough assessment of a commercially available CO 2 Carbon Isotope Analyser (CCIA DLT-100, Los Gatos Research) that allows in situ measurement of δ 13 C in CO 2. Using a set of reference gases of known CO 2 concentration and carbon isotopic composition, we evaluated the precision, long-term stability , temperature sensitivity and concentration dependence of the analyser. Despite good precision calculated from Allan variance (5.0 ppm for CO 2 concentration, and 0.05 h for δ 13 C at 60 s averaging), real performances are altered by two main sources of error: temperature sensitivity and dependence of δ 13 C on CO 2 concentration. Data processing is required to correct for these errors. Following application of these corrections, we achieve an accuracy of 8.7 ppm for CO 2 concentration and 1.3 h for δ 13 C, which is worse compared to mass spectrometry performance, but still allowing field applications. With this portable analyser we measured CO 2 flux degassed from rock in an underground tunnel. The obtained carbon isotopic composition agrees with IRMS measurement, and can be used to identify the carbon source. S. Guillon () · E. Pili CEA, DAM,
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Sophie Guillon, · Pili, · Agrinier. Using a laser-based CO2 carbon isotope analyser to investigate gas transfer in geological media. Applied Physics B - Laser and Optics, Springer Verlag, 2012, 73, pp.450 - 457. ⟨10.1007/s00340-012-4942-8⟩. ⟨hal-01483369⟩

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