Revision of the World Meteorological Organization Global Atmosphere Watch (WMO/GAW) CO 2 calibration scale

Hall, Bradley D.; Crotwell, Andrew M.; Kitzis, Duane R.; Mefford, Thomas; Miller, Benjamin R.; Schibig, Michael F.; Tans, Pieter P.

The NOAA Global Monitoring Laboratory serves as the World Meteorological Organization Global Atmosphere Watch (WMO/GAW) Central Calibration Laboratory (CCL) for COinline-formula2 and is responsible for maintaining the WMO/GAW mole fraction scale used as a reference within the WMO/GAW program. The current WMO-COinline-formula2-X2007 scale is embodied by 15 aluminum cylinders containing modified natural air, with COinline-formula2 mole fractions determined using the NOAA manometer from 1995 to 2006. We have made two minor corrections to historical manometric records: fixing an error in the applied second virial coefficient of COinline-formula2 and accounting for loss of a small amount of COinline-formula2 to materials in the manometer during the measurement process. By incorporating these corrections, extending the measurement records of the original 15 primary standards through 2015, and adding four new primary standards to the suite, we define a new scale, identified as WMO-COinline-formula2-X2019. The new scale is 0.18 inline-formulaµmol molinline-formula−1 (ppm) greater than the previous scale at 400 ppm COinline-formula2. While this difference is small in relative terms (0.045 %), it is significant in terms of atmospheric monitoring. All measurements of tertiary-level standards will be reprocessed to WMO-COinline-formula2-X2019. The new scale is more internally consistent than WMO-COinline-formula2-X2007 owing to revisions in propagation and should result in an overall improvement in atmospheric data records traceable to the CCL.



Hall, Bradley D. / Crotwell, Andrew M. / Kitzis, Duane R. / et al: Revision of the World Meteorological Organization Global Atmosphere Watch (WMO/GAW) CO2 calibration scale. 2021. Copernicus Publications.


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