Applications of cavity ring-down spectroscopy to high precision isotope ratio measurement of ¹³C/¹²C in carbon dioxide

Abstract

Recent measurements of carbon isotopes in carbon dioxide using near-infrared, diode-laser-based cavity ring-down spectroscopy (CRDS) are presented. The CRDS system achieved good precision, often better than 0.2‰, for 4% CO₂ concentrations, and also achieved 0.15–0.25‰ precision in a 78 min measurement time with cryotrap-based pre-concentration of ambient CO₂ concentrations (360 ppmv). These results were obtained with a CRDS system possessing a data rate of 40 ring-downs per second and a loss measurement of 4.0 × 10⁻¹¹ cm⁻¹ Hz^−1/2. Subsequently, the measurement time has been reduced to under 10 min. This standard of performance would enable a variety of high concentration (3–10%) isotopic measurements, such as medical human breath analysis or animal breath experiments. The extension of this ring-down to the 2 μm region would enable isotopic analysis at ambient concentrations, which, combined with the small size, robust design, and potential for frequent measurements at a remote site, make CRDS technology attractive for remote atmospheric measurement applications.

Keywords:

• Atmosphere
• Carbon dioxide
• Carbon-12
• Carbon-13
• Cavity ring-down spectroscopy
• Infrared diode laser

Acknowledgements

The authors at Picarro would like to thank the Department of Energy (DOE), which has made this work possible through their SBIR grant program (Grant no. DE-FG03-01ER83250). This support does not constitute an endorsement by the DOE of the views expressed in this article. The authors would also like to thank Richard Zare and Marc Levenson for their support and guidance over the past 2 years.