Facilitating the development of a global measurement infrastructure for the measurement of stable isotope ratios for greenhouse gases source apportionment

Recent progress in the field of laser spectroscopy has transformed the measurement of major greenhouse gases in the atmosphere, enabling real-time, in-situ field measurements of carbon dioxide (CO₂) and methane (CH₄) stable isotope ratios. These advancements provide critical insights into sources and sinks at local, regional, and global scales. These new measurement capabilities have generated an urgent demand for commutable isotopic gas reference materials for CO₂ and CH₄ at ambient amount fractions in air. Achieving the level of uncertainty required for such reference materials to effectively support climate mitigation efforts remains challenging. Furthermore, the reliance on individual calibration procedures by end-users has resulted in inconsistent data and hindered comparability across datasets. Addressing these challenges requires the development of new reference materials, improved validation protocols, and standardised calibration guidelines. This effort is essential to ensure traceability for field-deployable spectroscopic methods and traditional offline flask sampling techniques using mass spectrometry. The Metrology for Climate Action workshop, co-hosted by BIPM and WMO in 2022, underscored the critical need for an improved metrological support infrastructure to advance global comparability of greenhouse gas stable isotope ratio measurements. National Metrology Institutes (NMIs), Designated Institutes (DIs), and the WMO's Central Calibration Laboratory (CCL) were identified as key contributors in expanding the global network of certified reference material suppliers. This collaboration is crucial for providing the atmospheric measurement community with access to traceable isotopic greenhouse gas reference materials, thereby supporting the verification of emissions measurements. To address these demands, a new CCQM GAWG/IRWG joint Isotope Ratio Task Group was established in April 2023. This task group coordinates efforts among NMIs, DIs, and intergovernmental organisations to facilitate the development of a robust metrological support infrastructure for the accurate measurement of stable isotope ratios for atmospheric greenhouse gases and related applications. As part of its foundational activities, the task group recently submitted a comprehensive paper entitled “Developing Calibration and Measurement Capabilities for Atmospheric Methane Stable Isotope Ratios at NMIs/DIs: Metrology for Global Comparability.” This collaborative effort brought together experts from NMIs, DIs, academia, and intergovernmental organizations to provide key recommendations for advancing the measurement of CH₄ stable isotope ratios. The paper also reviews the various elements that make up Calibration and Measurement Capabilities (CMC) to aid NMIs and DIs in developing their capabilities to support the atmospheric community's need for reliable stable isotope ratio measurements of CH₄. This presentation will summarise the task group’s objectives, progress, and key recommendations. Additionally, it will provide a preliminary result from a global survey that is conducted in the first quarter of 2025, mapping the global capabilities for the measurement stable isotope ratio of CH₄. Through fostering collaboration among diverse stakeholders, the task group aims to enhance global greenhouse gas data comparability and support effective climate action. We invite experts and organisations with a shared interest in this field to join us in this critical endeavour.