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Volume 10, issue 7 | Copyright
Atmos. Meas. Tech., 10, 2669-2685, 2017
https://doi.org/10.5194/amt-10-2669-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 26 Jul 2017

Research article | 26 Jul 2017

Abundances of isotopologues and calibration of CO2 greenhouse gas measurements

Pieter P. Tans1,3, Andrew M. Crotwell2,3, and Kirk W. Thoning1,3 Pieter P. Tans et al.
  • 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), Boulder, Colorado 80305, USA

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 the amount of substance fraction (mole fraction) of each component isotopologue in air individually. 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 mole fractions of the three major CO2 isotopologues (16O12C16O, 16O13C16O, and 16O12C18O) 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 ±0.01µmolmol−1CO2, ±0.2δ13C, and ±0.2δ18O, all at 68% confidence interval (CI).

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We describe a new CO2 calibration system for the Central Calibration Laboratory of the World Meteorological Organization Global Atmosphere Watch program. The system uses two laser spectroscopic instruments to measure the three major CO2 isotopologues individually. We account for isotopic differences between standards in the calibration hierarchy when assigning CO2 mole fraction, eliminating bias due to variations in the isotopic composition.
We describe a new CO2 calibration system for the Central Calibration Laboratory of the World...
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