Accurate, Stable, and SI-Traceable Reference Gas Mixtures of VOCs Relevant for Climate at Atmospheric Levels

Volatile organic compounds (VOCs) have effects on the oxidative capacity of the lower atmosphere, air quality and radiative forcing, and are thereby contributing to climate change. To identify atmospheric trends in VOC abundance and composition, comparable datasets of atmospheric measurements at different spatial and temporal scales are needed. Traceability to the international system of units (SI) is key to achieve comparability. However, in many cases, this is hardly accomplished due to the lack of SI-traceable reference gas mixtures (RGMs) to calibrate the measuring instruments. Within the framework of the EMPIR project “Metrology for Climate Relevant Volatile Organic Compounds”, new SI-traceable RGMs of selected VOCs were prepared. The RGMs were produced at atmospheric amount-of-substance fractions (<100 nmol/mol) following different dynamic and static methods. For most of the selected compounds (halogenated VOCs and oxygenated VOCs, such as methanol, ethanol, and acetone), relative expanded uncertainties (U) lower than 5% were achieved fulfilling stakeholders’ needs. This was not the case for specific oxygenated VOCs (acetaldehyde; U < 10%) and terpenes (α-pinene, β-pinene, myrcene, and β-caryophyllene, U = 7–13%) because of surface reactions (e.g., adsorption) and impurities. Further development of passivation treatments, as well as closer collaboration among manufacturers, metrologists and atmospheric researchers are needed to facilitate the production of accurate, stable, and SI-traceable RGMs and to enhance, in turn, data comparability and climate trend identification.