This report presents the development and validation of new Primary Reference Materials (PRMs) for impurities in carbon dioxide (CO2), addressing a critical gap in the metrological support required for carbon capture, utilisation, and storage (CCUS). As CO2 streams captured from industrial processes inevitably contain impurities such as water, sulfur oxides, nitrogen oxides, hydrogen and hydrocarbons, their accurate quantification is essential for safeguarding transport infrastructure, ensuring compliance with the project specifications, and enabling safe long-term storage. International and project-specific guidelines, including those from ISO TR 27921, Porthos, and Northern Lights define strict thresholds for impurities, highlighting the need for traceable gas standards that can be used to calibrate analytical instruments with high accuracy and comparability.
Within this framework, binary and multi-component PRMs were prepared by VSL, NPL, CMI, IPQ and SINTEF ER, following ISO 6142-1 gravimetric methods. The selected impurities covered sulfur dioxide, hydrogen sulfide, nitrogen dioxide, nitrous oxide, water, dimethyl sulfide, ethanol and non-condensable gases (N2, Ar, H2, O2, CH4 and CO) at amount fractions relevant to CCUS specifications. To address possible adsorption and degradation effects, mixtures were prepared in different cylinder materials and surface treatments, such as Aculife IV and polished aluminium. In parallel, dynamic preparation systems and a portable trace gas generator were validated to provide flexible alternatives for generating low-level mixtures of reactive species like ammonia.
The stability of the PRMs was systematically studied over two years. Results demonstrated that several
impurities, including sulfur dioxide, hydrogen sulfide, dimethyl sulfide, ethanol, and nitrous oxide, remained
stable within their expanded uncertainties. For multi-component mixtures, major components such as
methane, hydrogen, and nitrogen proved stable, while sulfur dioxide, nitrogen dioxide, and nitric oxide
displayed significant degradation, indicating strong reactivity and wall effects in both treated and untreated
cylinders. Dynamic dilution systems developed by VSL and NPL provided mixtures that agreed with static
PRMs within 1 to 5%, confirming the robustness of these approaches, while the portable trace gas generator further demonstrated accurate production of ammonia in CO₂ within a relative uncertainty of about
2%.
In conclusion, this work has established a solid metrological foundation for impurity analysis in CO₂ by
delivering new PRMs with proven stability for several key species. The PRMs developed in MetCCUS directly
support the industry by providing traceable calibration capabilities aligned with CO₂ quality specifications from ISO/TR 27913, Porthos, Northern Lights and other European initiatives. These materials enable operators to verify analytical performance, monitor impurity thresholds and ensure safe and reliable CO2 transport and storage across Europe.
