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Abstract:
The need for a unifying scale anchor for isotopes of CO2 in air was brought to light at the 11th WMO/IAEA
Meeting of Experts on Carbon Dioxide in Tokyo 2001.
During discussions about persistent discrepancies in isotope
measurements between the worlds leading laboratories,
it was concluded that a unifying scale anchor for Vienna
Pee Dee Belemnite (VPDB) of CO2 in air was desperately
needed. Ten years later, at the 2011 Meeting of Experts on
Carbon Dioxide in Wellington, it was recommended that the
Jena Reference Air Set (JRAS) become the official scale anchor
for isotope measurements of CO2 in air (Brailsford,
2012).
The source of CO2 used for JRAS is two calcites. After releasing
CO2 by reaction with phosphoric acid, the gases are
mixed into CO2-free air. This procedure ensures both isotopic
stability and longevity of the CO2. That the reference
CO2 is generated from calcites and supplied as an air mixture
is unique to JRAS. This is made to ensure that any measurement
bias arising from the extraction procedure is eliminated.
As every laboratory has its own procedure for extracting the
CO2, this is of paramount importance if the local scales are
to be unified with a common anchor.
For a period of four years, JRAS has been evaluated
through the IMECC1 program, which made it possible to distribute
sets of JRAS gases to 13 laboratories worldwide. A
summary of data from the six laboratories that have reported the full set of results is given here along with a description of the production and maintenance of the JRAS scale anchors.
