Water vapor δsup2/supH and δsup18/supO measurements using off-axis integrated cavity output spectroscopy

摘要

We present a detailed assessment of a commercially available water vaporisotope analyzer (WVIA, Los Gatos Research, Inc.) for simultaneous in-situmeasurements of δ2H and δ18O in water vapor. This method, based on off-axisintegrated cavity output spectroscopy, is an alternative to the conventionalwater trap/isotope ratio mass spectrometry (IRMS) techniques. We evaluate theanalyzer in terms of precision, memory effects, concentration dependence,temperature sensitivity and long-term stability. A calibration system basedon a droplet generator is used to characterize the performance and tocalibrate the analyzer. Our results show that the precision at an averagingtime of 15 s is 0.16‰ for δ2H and 0.08‰ for δ18O. The isotoperatios are strongly dependent on the water mixing ratio of the air. Takinginto account this concentration dependence as well as the temperaturesensitivity of the instrument we obtained a long-term stability of the waterisotope measurements of 0.38‰ for δ2H and 0.25‰ for δ18O. Theaccuracy of the WVIA was further assessed by comparative measurements usingIRMS and a dew point generator indicating a linear response in isotopiccomposition and H₂O concentrations. The WVIA combined with a calibrationsystem provides accurate high resolution water vapor isotope measurements andopens new possibilities for hydrological and ecological applications.