Water vapor isotopic composition analyzer
Project in collaboration with LSCE- closed (2013-2016)
This instrument measures simultaneously and continuously d18O and d2H of the atmospheric water vapor based on photo-absorption by the different isotopic forms of water molecules (1H1H16O, 1H2H16O, and 1H1H18O) in the infrared region of the spectrum, between 7193.5 and 7184 cm−1 (∼ 1.39µm)
The Picarro instrument makes use of Wavelength-Scanned Cavity Ring Down Spectroscopy (WS-CRDS) for the detection. By selecting spectral absorption features, which are highly specific for single isotopologues, stable isotope ratios are measured and compared with those of the respective standards. The instrument installed at Chacaltaya is calibrated once a week using two different water standards that are vaporized into the cavity carried by dry air (<100 ppm H2O). The calibration set-up combines the Picarro injection system with custom-made modifications. Data is then corrected offline following the procedure described by Tremoy et al. (2011, RCM).
In complement to water vapor measurements, precipitation samples are taken for every precipitation event and their composition is compared to the on-line water vapor isotopic composition.
This set of measurements aims at unveiling the climatic controls of the isotopic composition of precipitation (d) in the tropics, where not only the amount effect (the anti-correlation between local precipitation and d) but also a variety of factors exerts and influence on d.