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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
14 Feb 2017
Review status
A revision of this discussion paper was accepted for the journal Atmospheric Measurement Techniques (AMT) and is expected to appear here in due course.
Abundances of isotopologues and calibration of CO2 greenhouse gas measurements
Pieter P. Tans1,3, Andrew M. Crotwell2,3, and Kirk W. Thoning1,3 1Global Monitoring Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, 80305, USA
2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, 80309, USA
3Central Calibration Laboratory, World Meteorological Organization Global Atmosphere Watch program (WMO/GAW)
Abstract. We have developed a method to calculate the fractional distribution of CO2 across all of its component isotopologues based on measured δ13C and δ18O values. The fractional distribution can be used with known total CO2 to calculate each component isotopologue individually, in units of mole fraction. The technique is applicable to any molecule where isotopologue-specific values are desired. We used it with a new CO2 calibration system to account for isotopic differences among the primary CO2 standards that define the WMO X2007 CO2 in air calibration scale and between the primary standards and standards in subsequent levels of the calibration hierarchy. The new calibration system uses multiple laser spectroscopic techniques to measure amount of substance fractions (in mole fraction units) of the three major CO2 isotopologues (16O12C16O, 16O13C16O, and 18O12C16O) individually. The three measured values are then combined into total CO2 (accounting for the rare unmeasured isotopologues), δ13C, and δ18O values. The new calibration system significantly improves our ability to transfer the WMO CO2 calibration scale with low uncertainty through our role as the World Meteorological Organization Global Atmosphere Watch Central Calibration Laboratory for CO2. Our current estimates for reproducibility of the new calibration system are ±0.01 μmol mol−1 CO2, ±0.2 ‰ δ13C, and ±0.2 ‰ δ18O, all at 68 % confidence interval (CI).

Citation: Tans, P. P., Crotwell, A. M., and Thoning, K. W.: Abundances of isotopologues and calibration of CO2 greenhouse gas measurements, Atmos. Meas. Tech. Discuss.,, in review, 2017.
Pieter P. Tans et al.
Pieter P. Tans et al.


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