Metrology in Gas Analysis at the Federal Office of Metrology METAS

Gas analysis as a metrological discipline has a history of about 25 years in Switzerland. Starting with the requirement of reliable reference gas mixtures for legal applications the Swiss Federal Office of Metrology (METAS) had to increasingly find also calibration solutions for the ambient air level. Thereby the metrological principles of traceability, uncertainty evaluation and verification as well as the use of unambiguous terminology for quantities and units were in the focus of the activities. Using three examples different ways of implementing these principles are explained. For the emission range, traceability is mainly achieved by gravimetrically prepared certified gas mixtures in pressurised cylinders using high purity gases and a highly reproducible comparison method. The reactivity and limited stability of the important analytes in the ambient range ask for dynamic methods to secure traceability to the international system of units (SI). The dynamic methods requiring additionally high accuracy gas flow measurement techniques and trace gas analysis will be the focus for further developments at METAS.