Standard Reference Gases: About the ESRL CCL
What is a CCL?A World Meteorological Organization (WMO) Central Calibration Laboratory (CCL) is responsible for maintaining and distributing the WMO Mole Fraction scale for a specified gas in air. NOAA ESRL GMD is the WMO, Global Atmosphere Watch (GAW) CCL for CO2, CH4, N2O, SF6, and CO. In support of GAW, GMD offers calibration services for these gases for a fee.
- The CCL for N2O and SF6 is maintained by Dr. Brad Hall (ESRL GMD Halocarbons and other trace species (HATS) group)
- The CCL for CO2 is maintained by Dr. Pieter Tans (ESRL GMD Carbon Cycle Group)
- The CCL for CH4 is maintained by Dr. Ed Dlugokencky (ESRL GMD Carbon Cycle Group)
- The CCL for CO is maintained by Dr. Paul Novelli (ESRL GMD Carbon Cycle Group)
According to recommendations by the WMO/IAEA group of experts on carbon dioxide and related tracer measurement techniques (see reference below), a CCL will:
- maintain the WMO Mole Fraction Scale for the respective gas in air by carrying out regular determinations of this primary scale with an absolute method. The scale is embodied in an adequate set of gas mixtures-in-air in large high-pressure cylinders (called WMO Primary Standards).
- carry out comparisons with independent primary scales, established either through gravimetric, manometric, or other means.
- update its scale when warranted, as the gas mole fractions of the WMO Primary Standards may become better known over time through repeated absolute measurements and comparisons. Revisions of the WMO Scale by the CCL must be distinguished by name, such as WMO X2005, and the appropriate version number should be included in each standard calibration report. The CCL archives all earlier versions of the WMO scale.
- provide complete and prompt disclosure of all relevant data pertaining to the maintenance and transfer of the primary scale, such as manometric calibration procedures and results, and an estimate of the expected uncertainty introduced by the calibration transfer procedure to each individual standard.
- provide calibrated reference gas mixtures of gas mixtures-in-air (called ?transfer standards?) at the lowest possible cost.
- provide for a backup in case a catastrophic event occurs.
- Organize, in collaborations with designated WMO World Calibration Centres, comparisons of laboratory calibrations by distributing sets of high-pressure cylinders to be measured by participating laboratories (called Round Robin comparisons).
14th WMO/IAEA Meeting of Experts on Carbon Dioxide, Other Greenhouse Gases and Related Tracers Measurement Techniques WMO/TD - No. 1487 (Helsinki, Finland, 10-13 September 2007). GAW Report No. 186, 2009