Simultaneous High-Precision ¹³C Isotope Ratio Analysis of CO₂ and CH₄ Using an FDM-OA-CEAS Sensor.

Area of Science:

• Environmental Science and Analytical Chemistry
• Spectroscopy and Isotope Ratio Mass Spectrometry
• Atmospheric and Climate Science

Background:

• Accurate measurement of carbon dioxide (CO2) and methane (CH4) concentrations and their carbon isotope ratios (13C/12C) is essential for understanding the carbon cycle.
• Existing methods may lack the precision or simultaneous detection capabilities required for comprehensive source identification and dynamic tracking of these greenhouse gases.
• High-sensitivity isotope analysis is critical for distinguishing between natural and anthropogenic sources of CO2 and CH4.

Purpose of the Study:

• To develop a novel sensor system for high-precision, simultaneous measurement of 13C/12C isotope ratios in both CO2 and CH4.
• To enable direct determination of the stable carbon isotope composition (δ13C) for CO2 and CH4.
• To provide a practical analytical tool for environmental and isotopic studies requiring sensitive gas analysis.

Main Methods:

• Development of a frequency-division multiplexed off-axis cavity-enhanced absorption spectroscopy (FDM-OA-CEAS) sensor system.
• Concurrent detection of four isotopic species: 12CO2, 13CO2, 12CH4, and 13CH4.
• Utilized a kilometer-scale effective absorption path length and selected weak near-infrared absorption lines for enhanced sensitivity.

Main Results:

• Achieved detection limits as low as 0.025 ppb for 13CO2 and 0.008 ppb for 13CH4.
• Demonstrated high sensitivity for δ13C measurements: 0.0108‰ for CO2 and 0.086‰ for CH4.
• The system enables simultaneous acquisition of two pairs of CO2 and CH4 isotope absorption lines per laser scan, improving efficiency and reducing cost.

Conclusions:

• The developed FDM-OA-CEAS system offers unprecedented simultaneous, high-precision isotope analysis capabilities for CO2 and CH4.
• This technology represents a significant advancement for environmental monitoring and isotopic research.
• The sensor system holds strong potential as a practical tool for detailed carbon cycle investigations.