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

Date Established: April 2023

Status: Active

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.