Recommendations and Protocols for the Use of the Isotope RatioInfrared Spectrometer (Delta Ray) to Measure StableIsotopes from CO2: An Application to Volcanic Emissions atMount Etna and Stromboli (Sicily, Italy)

Co-auteur étrangerInternational audienceAmong major volatiles released from the Earth’s interior, CO2 is an important target for the international community. The interestis keenly motivated by the contribution of CO2 in the Earth’s carbon budget and its role on past, current, and future climatedynamics. In particular, the isotopic signature of CO2 is fundamental to characterize the source of this gas and its evolution upto the atmosphere. The recent development of new laser-based techniques has marked an important milestone for the scientificcommunity by favoring both high-frequency and in situ stable isotope measurements. Among them, the Delta Ray IRIS(Thermo Scientific Inc., Waltham, USA) is one of the most promising instruments thanks to its high precision, its limitedinterferences with other gaseous species (such as H2S and/or SO2), and its internal calibration procedure. These characteristicsand the relative easiness to transport the Delta Ray IRIS have encouraged its use on the field to analyze volcanic CO2 emissionsin recent years but often with distinct customized protocols of measurements. In this study, various tests in the laboratory andon the field have been performed to study the dependence of CO2 isotope measurements on analytical, instrumental, andenvironmental conditions. We emphasize the exceptional ability of the Delta Ray IRIS to perform isotope measurements for alarge range of CO2 concentration (200 ppm–100%) thanks to a dilution system and to get a reliable estimation of the real CO2content from the diluted one. These tests lead to point out major recommendations on the use of Delta Ray IRIS and allow thedevelopment of adapted protocols to analyze CO2 emissions like in volcanic environments