Development and Validation of an Isotopic Water Vapor Analyzer for Rapid Measurements of 18O/16O and D/H in Ambient Air

Routine measurements of stable oxygen and hydrogen isotopes are crucial to the advancement of hydrological and climate research at the local, regional and global scales. Water isotopes provide critical knowledge about the source, history and age of water supplies, degree of water mixing. Current technology involves collecting and condensing individual water samples, transporting them to a laboratory, and quantifying the isotope ratios via an Isotope Ratio Mass Spectrometer. In practice, this procedure has made long-term continuous monitoring of water supplies prohibitively time-consuming and labor intensive. We will report on the development, deployment and independent validation of a novel isotopic water vapor analyzer, based on cavity-enhanced laser absorption spectroscopy techniques (Off-Axis Integrated Cavity Output Spectroscopy), capable of accurately quantifying 18O/16O and D/H in 1-second time intervals. The analyzer provides continuous monitoring of ambient water vapor over a large range of mixing ratios from 500 ppmv to over 40000 ppmv. Independent validation of the instrument's capabilities at several different locations will be presented and results from recent field tests at the Mauna Loa Observatory will be discussed.