SICE (SF₆ Inter-comparison Expriment)
The SF₆ Inter-Comparison Experiment (SICE) was conducted to evaluate and improve the consistency of sulfur hexafluoride (SF₆) measurements among global atmospheric monitoring laboratories. Conducted from 2016 to 2017, this inter-comparison study involved leading research institutions and atmospheric monitoring stations across Europe and the Asia-Pacific region.
How the Experiment Worked
Two SF₆ reference cylinders were circulated among 13 participating laboratories in two circuits:
| Circuit 1: Europe (9 laboratories)  Participants and experiment schedule of 1st circuit |
| Circuit 2: Asia-Pacific (4 laboratories)  Participants and experiment schedule of 2nd circuit |
Each laboratory measured SF₆ concentrations in the cylinders using their own analytical setups and calibration methods. The results were then compared to the WCC-SF₆ reference values, ensuring alignment with the WMO standard.
| Table 1. The results of inte-comparison experiment of 1st circuit | ||||||||
| Order | Laboratory | Result (pmol/mol) | Repeatability (%) | Lab-WCC diff. (pmol/mol) | Scale | |||
| Low | High | Low | High | Low | High | |||
| 1 | WCC-SF₆ | 7.89 | 9.21 | 0.23 | 0.22 | - | - | WMO-X2014 |
| 2 | UEA | 7.85 (7.86) | 9.16 (9.17) | 0.51 (0.51) | 0.45 (0.44) | -0.04 (-0.03) | -0.05 (-0.04) | WMO-X2006 (WMO-X2014) |
| 3 | LSCE | 7.88 | 9.1.9 | 0.88 | 0.65 | -0.01 | -0.02 | WMO-X2014 |
| 4 | Schauinsland | 7.96 | 9.20 | 0.03 | 0.03 | 0.07 | -0.01 | WMO-X2006 |
| 5 | Heidelberg | 8.02 | 9.42 | 0.26 | 0.36 | 0.13 | 0.21 | Heidelberg scale |
| 6 | Zugspitze | 8.00 | 9.24 | 1.00 | 0.80 | 0.11 | 0.03 | WMO-X2014 |
| 7 | METAS | 7.95 | 9.30 | 0.46 | 0.22 | 0.06 | 0.09 | METAS-2016 |
| 8 | ICOS | 7.92 | 9.18 | 0.23 | 0.27 | 0.03 | -0.03 | WMO-X2014 |
| 9 | MPI-BGC | 7.89 | 9.21 | 0.48 | 0.42 | 0.00 | 0.00 | WMO-X2014 |
| 10 | NOAA | 7.89 | 9.21 | 0.12 | 0.12 | 0.00 | 0.00 | WMO-X2014 |
| Table 2. The results of inte-comparison experiment of 2nd circuit | ||||||||
| Order | Laboratory | Result (pmol/mol) | Repeatability (%) | Lab-WCC diff. (pmol/mol) | Scale | |||
| Low | High | Low | High | Low | High | |||
| 1 | WCC-SF₆ | 7.88 | 9.20 | 0.11 | 0.18 | - | - | WMO-X2014 |
| 2 | NIWA | 7.88 | 9.12 | 1.13 | 0.47 | 0.00 | -0.08 | WMO-X2014 |
| 3 | NOAA | 7.89 | 9.21 | 0.16 | 0.15 | 0.01 | 0.01 | WMO-X2014 |
| 8 | KRISS | 7.91 | 9.16 | 0.25 | 0.22 | 0.03 | -0.04 | WMO-X2014 KRISS primary |
| 9 | AMY | 7.87 | 9.20 | 0.62 | 0.59 | -0.01 | 0.00 | WMO-X2014 |
Key Findings
- The experiment revealed high consistency among most laboratories, with many achieving results within the WMO/GAW compatibility goal.
- Some deviations were identified, helping laboratories refine their calibration methods and improve measurement accuracy.
- The study reinforced the importance of ongoing inter-comparisons to maintain global data integrity for atmospheric monitoring.
Further information
The report of the result on SF₆ Inter-Comparison Experiment, 2016-2017 [View] [Download]
Biennial inter-comparison with CCL
Since 2013, WCC-SF₆ has conducted biennial inter-comparison experiments with the Central Calibration Laboratory (CCL, NOAA/GML) under the WMO/GAW program. These inter-comparisons are essential for confirming the traceability and compatibility of laboratory and transfer standards maintained by WCC-SF₆ against primary and secondary standards.
Consistency and Key Findings
Between 2013 and 2019, four inter-comparison experiments were conducted (2013, 2015, 2017, and 2019) using the same calibration scale (WMO X2014). The results demonstrated strong consistency, with WCC-SF₆ measurements remaining within the compatibility goal of ±0.05 pmol/mol, except for the 2015 experiment, which was certified using a one-point calibration method.
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The most recent inter-comparison in 2023 showed a higher level of uncertainty compared to previous years. However, this was primarily due to the introduction of a new measurement instrument, which is currently undergoing a stabilization phase. Despite this temporary increase in uncertainty, the results remain within the 1σ range, ensuring continued reliability and traceability of WCC-SF₆ standards.
By maintaining regular inter-comparisons with CCL, WCC-SF₆ continues to ensure high-quality, traceable, and globally compatible SF₆ measurements, reinforcing its role in the WMO/GAW quality assurance framework.
