06 Nov 2023
 | 06 Nov 2023
Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

New infrared spectroscopy instrument for reliable low humidity water vapour isotopic composition measurements

Mathieu Casado, Amaelle Landais, Tim Stoltmann, Justin Chaillot, Mathieu Daëron, Frédéric Prié, Baptiste Bordet, and Samir Kassi

Abstract. In situ measurements of water vapour isotopic composition in Polar Regions has provided needed constrains of post-deposition processes involved in the archiving of the climatic signal in ice core records. During polar winter, the temperatures are so low that current commercial techniques are not able to measure the vapour isotopic composition with enough precision. Here, we make use of new developments in infrared spectroscopy and combine an optical feedback frequency stabilised laser source (OFFS technique) using a V-shaped optical cavity (VCOF) and a high-finesse cavity ring down cavity (CRDS) which yield sufficient precision to measure isotopic composition at water mixing ratios down to 1 ppmv. Indeed, thanks to the stabilisation of the laser by the VCOF, the instrument suffers extremely low drift and very high signal to noise ratio. Using new constrains on the fitting technique, the instrument is additionally not hindered by a large isotope-humidity response which at low humidity can create extensive biases on commercial instruments.

Mathieu Casado et al.

Status: open (until 30 Dec 2023)

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Mathieu Casado et al.

Mathieu Casado et al.


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Short summary
Measuring water isotopic composition in Antarctica is difficult because of the extremely cold temperature in winter. Here, we designed a new infrared spectrometer able to measure the vapour isotopic composition more than 95 % of the year in the coldest locations of Antarctica, while current commercial instruments are only able to measure during the warm summer months in the interior.