In situ measurement of water vapor isotope ratios in air with a laser-based spectrometer

[Display omitted] •Simultaneous measurement of δ18O, δ17O, and δD in air with a single DFB laser.•Mixing ratios of four isotopes agreed well with the values from a hygrometer.•High measurement precision of isotope ratios with fast time response (1 s)•Measured δ values highly correlated with the water vapor mixing ratios.•Broad applications in atmospheric and hydrological research. Simultaneous measurement of H217O/H216O, H218O/H216O, and HDO/H216O in air with a compact spectrometer based on a mid-infrared distributed feedback (DFB) laser was described. The obtained mixing ratios of H216O, H217O, and H218O agreed reasonably well with those measured by a hygrometer. The precision and repeatability of the spectrometer were analyzed. Indoor air tests demonstrated that its 220-s precision was 0.08 ‰, 0.06 ‰, and 0.14 ‰ for δ18O, δ17O, and δ2H respectively. The measured values of δ18O, δ17O, and δ2H in indoor air were highly correlated with the water vapor mixing ratios. The compact spectrometer provides in situ measurements of water vapor isotopes with high precision and fast time response, which opens new possibilities for its application in atmospheric and hydrological research in the future.