Concentration effects on laser-based 18O and 2H measurements and implications for the calibration of vapour data with liquid standards
Abstract
Recently available laser instruments can directly measure the isotopic composition of water vapour (δ18O, δ2H) in air. Here, we evaluate the calibration of a wavelength-scanned cavity ring-down spectrometer (CRDS) with vapourised liquid standards. We also quantify the dependency of the measured isotope values on the water concentration for a range of isotopic compositions. In both liquid and vapour samples, we found an increase of δ18O and δ2H with water vapour concentration. For δ18O, the slope of this increase was similar for liquid and vapour, with a slight positive relationship with sample δ-value. For δ2H, we found diverging patterns for liquid and vapour samples, with no dependence on δ-value for vapour, but a decreasing slope for liquid samples. Direct vapour measurements with CRDS in a controlled experimental chamber agreed well with results obtained from vapour simultaneously collected in cold traps analysed by CRDS and IRMS. We conclude that vapour measurements can be calibrated reliably with liquid standards. We demonstrate how to take the concentration dependencies of the δ-values into account.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B23A0381S
- Keywords:
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- 0452 BIOGEOSCIENCES / Instruments and techniques;
- 0454 BIOGEOSCIENCES / Isotopic composition and chemistry