Cavity ring-down spectroscopy for the certification of the isotopic composition of CO2 in air CRMs

Carbon dioxide (CO2) is the most important long-lived anthropogenic greenhouse gas. Studying the ratio 13C/12C of the CO2 isotopic composition (δ13C-CO2) in the atmosphere gives useful information for assessing and quantifying the anthropogenic contribution to the continuously growing atmospheric CO2. INRiM, the Italian National Metrology Institute, is deeply involved in supporting the efforts of the metrological community to achieve the comparability of results and to assure accuracy and metrological traceability to CO2 stable isotope measurement results. In this framework, the realization of gaseous reference materials of CO2 in air at ambient level and known δ13C-CO2 represents a fundamental and promising activity. This work describes the preparation of the gas mixtures with δ13C-CO2 values in the range from +1.3 ‰ to -42 ‰ and the analytical procedure for the value assignment based on Cavity Ring-Down Spectroscopy. Preliminary stability studies are also shown.