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Under the World Meteorological Organization (WMO)/Global Atmosphere Watch (GAW) Programme, there are central facilities for quality control and quality assurance. Among them, World Calibration Centres organize inter-comparisons for scale traceability, a necessary step to meet the compatibility goal of ±0.02 ppt (extended goal: ±0.05 ppt) within the GAW network. Korea Meteorological Administration (KMA)/National Institute of Meteorological Sciences (NIMS) has been the World Calibration Centre for SF6 (WCC-SF6) from 2012 and has organized inter-comparison experiments using WCC’s travelling cylinders (with measurement uncertainty of 0.01~0.02 ppt). Here we present our system and analysis methods for those cylinders. The 1st SF6 inter-comparison experiment (SICE) was conducted from 2016 to 2017 with 11 labs from 7 countries. Laboratories that calibrated the circulated cylinders on the same scale with WCC-SF6 (WMO-X2014) meet the extended compatibility goal for the high or low levels cylinders, and 75% of laboratories among them meet the compatibility goal for both levels. When laboratories calibrated the cylinders with their own standard scales, differences between WCC-SF6 and laboratories increased to 2.3% depending on their scales. This suggested the importance all labs adopting a single standard scale for long-term measurements and in the same network. Through inter-comparison experiments conducted with the Central Calibration Laboratory (CCL) on the same scale, drift and non-linear instrument characteristic affected the analysis results. When instrument drift corrections were applied, the differences from the CCL decreased from [(-0.25) to 0.43 ppt] to [(-0.07) to 0.02 ppt]. Non-linear analyzers underestimate high level SF6, e.g., by 8% at 20 ppt (even after instrument drift correction), so that a calibration strategy with a minimum of two standards (bracketing the expected range of observations) is necessary for accurate measurements.
