Working Group Members

CCQM-IRWG/GAWG Task Group on Carbon Dioxide and Methane Stable Isotope Ratio Measurements (CCQM-GAWG-IRWG-TG-ISOTOP)


Dr Abneesh Srivastava

National Institute of Standards and Technology

United States of America


Dr Christoph Nehrbass-Ahles

National Physical Laboratory

United Kingdom


Date Established: April 2023

Status: Active

List of meetings


Terms of Reference

The task group is to undertake specific actions to facilitate the development of a robust measurement infrastructure for the accurate, real-time measurement of stable isotope ratios for atmospheric greenhouse gases and related applications. The group will require collaboration between NMIs and expert laboratories, the GGMT community and measurement networks as well as engagement with instrument manufacturers.

The focus of the task group will be on measurements of: δ(13C/12C) in CO2 and CH4, δ(18O/16O) and δ(17O/16O) in CO2, δ(2H/2H) in CH4 and the isotope ratios R(13C/12C), R(2H/2H), R(17O/16O) and R(18O/16O) in CH4 and CO2.

Specific Goals of the Task Group:

  • Engage with stakeholders, including instrument manufacturers, to develop best practice guidelines for calibration of optical instruments. These shall focus on the measurement of isotope ratios in CO2 and CH4 at ambient amount fractions to meet the WMO network compatibility goals.
  • Review current calibration hierarchies for measurements of δ(13C/12C) in CO2 and CH4, δ(18O/16O) in CO2, δ(2H/2H) in CH4 and develop recommendations on actions that are required for the harmonization of these as well as recommendations related to international standards that are the basis of traceability of Calibration and Measurement Capabilities (CMCs) NMIs and DIs are seeking to publish in the BIPM KCDB.
  • Support coordinating laboratories to develop comparison protocols for the comparison of measurement capabilities of δ(13C/12C) and δ(2H/2H) in pure methane and methane in air reference materials, to be implemented in the CCQM GAWG/IRWG.
  • Provide advice to CCQM GAWG/IRWG and BIPM Headquarter laboratories on further development of comparisons and protocols for δ(13C/12C), δ(18O/16O) and δ(17O/16O) in pure CO2, CO2 in air reference materials, and carbonate materials, including follow on actions from the results reported for CCQM-P204.
  • Review potential alternative/ additional traceability schemes for δ(13C/12C) in CO2 and CH4, δ(18O/16O) in CO2, δ(2H/2H) in CH4 in air measurements including to the SI, and develop a roadmap for achieving these including performance criteria to be met and technical challenges to be overcome.

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