A dedicated robust instrument for water vapor generation at low humidity for use with a laser water isotope analyzer in cold and dry polar regions
Abstract. Obtaining precise continuous measurements of water vapor isotopic
composition in dry places (polar or high-altitude regions) is an important
challenge. The current limitation is the strong influence of humidity on the
measured water isotopic composition by laser spectroscopy instruments for
low humidity levels (below 3000 ppmv). This problem is addressed by
determining the relationships between humidity and measured
 δ18O and δD of known water standards. Here, we present the
development of a robust field instrument able to generate water vapor, down
to 70 ppmv, at very stable humidity levels (average 1 σ lower than 10 ppmv). This instrument, operated by a Raspberry interface, can be coupled to
a commercial laser spectroscopy instrument. We checked the stability of the
system as well as its accuracy when expressing the measured isotopic
composition of water vapor on the VSMOW–SLAP (Vienna Standard Mean Ocean Water – Standard Light Antarctic Precipitation) scale. It proved to be highly
stable during autonomous operation over more than 1 year at the East
Antarctic Concordia and Dumont d'Urville stations.