Advances in the production of traceable amount fraction and isotope ratio gas reference materials to underpin climate monitoring

The National Physical Laboratory (NPL) in the United Kingdom provides traceable gas reference materials for calibration of atmospheric gas analysers where low uncertainty measurements of the amount fraction and/or stable isotope ratio of atmospheric components are required. Primary gas Reference Materials (PRMs) are available for amount fraction traceable to the SI and, for CO 2 amount fractions between 380 and 800 μmol mol -1 , can be linked to the WMO-CO 2 -X2019 scale via the BIPM.QM-P5 comparison. Traceable stable isotope ratio PRMs for the most potent anthropogenic greenhouse gases and climate relevant species including carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O) and carbon monoxide (CO) are available and are traceable to current globally recognised isotope reference scales including VPDB for δ 13 C-CO 2 , δ 18 O-CO 2 and δ 13 C-CH 4 , VSMOW/SLAP for δ 2 H-CH 4 and δ 18 O-N 2 O and Air N 2 for δ 15 N-N 2 O. This paper details recent advances in the production of PRMs at NPL and outlines the PRMs and services currently being developed.