Tremoy G., Vimeux Françoise, Cattani O., Mayaki S., Souley I., Favreau Guillaume. (2011). Measurements of water vapor isotope ratios with wavelength-scanned cavity ring-down spectroscopy technology : new insights and important caveats for deuterium excess measurements in tropical areas in comparison with isotope-ratio mass spectrometry. Rapid Communications in Mass Spectrometry, 25 (23), p. 3469-3480. ISSN 0951-4198.
Titre du document
Measurements of water vapor isotope ratios with wavelength-scanned cavity ring-down spectroscopy technology : new insights and important caveats for deuterium excess measurements in tropical areas in comparison with isotope-ratio mass spectrometry
Rapid Communications in Mass Spectrometry, 2011,
25 (23), p. 3469-3480 ISSN 0951-4198
The new infrared laser spectroscopic techniques enable us to measure the isotopic composition (delta O-18 and delta H-2) of atmospheric water vapor. With the objective of monitoring the isotopic composition of tropical water vapor (West Africa, South America), and to discuss deuterium excess variability (d = delta H-2 - 8 delta O-18) with an accuracy similar to measurements arising from isotope-ratio mass spectrometry (IRMS), we have conducted a number of tests and calibrations using a wavelength-scanned cavity ring-down spectroscopy (WS-CRDS) technique. We focus in this paper on four main aspects regarding (1) the tubing material, (2) the humidity calibration of the instrument, (3) the water vapor concentration effects on delta, and (4) the isotopic calibration of the instrument. First, we show that Synflex tubing strongly affects delta H-2 measurements and thus leads to unusable d values. Second, we show that the mixing ratio as measured by WS-CRDS has to be calibrated versus atmospheric mixing ratio measurements and we also suggest possible non-linear effects over the whole mixing ratio range (similar to 2 to 20 g/kg). Third, we show that significant non-linear effects are induced by water vapor concentration variations on delta measurements, especially for mixing ratios lower than similar to 5 g/kg. This effect induces a 5 to 10% error in deuterium excess and is instrument-dependent. Finally, we show that an isotopic calibration (comparison between measured and true values of isotopic water standards) is needed to avoid errors on deuterium excess that can attain similar to 10%.
Plan de classement
Sciences fondamentales / Techniques d'analyse et de recherche [020]
;
Hydrologie [062]
