Standards to underpin atmospheric monitoring
Following the CCQM, CCQM Working Group on Gas Analysis (CCQM-GAWG) and CCQM Working Group on Isotope ratios (CCQM-IRWG) strategies, the BIPM Chemistry Department coordinates comparisons of National Metrology Institute (NMI) gas standard capabilities for the three major greenhouse gases – carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) – in air, as well as isotope ratios of CO2 relevant to source apportionment and the basis of international scales for carbon isotope. The BIPM maintains specialized facilities to run the comparisons, based on procedures using two different analytical techniques to ensure any method bias is detected, and methods operated at optimized minimum uncertainties.
Active comparisons
Active pilot studies
Completed comparisons
Completed pilot studies
Ongoing comparisons for CO2 in air standards
The BIPM maintains a central facility to act a stable reference for comparison with amount fraction values in CO2 in air standard mixtures assigned by participants, as part of the ongoing BIPM.QM-K2 comparison. This facility is based on manometry and provides SI traceable values of CO2 in air amount fractions by measuring the pressure, temperature and the volume ratio of a sample of the standard mixture and of the CO2 extracted from it cryogenically.
More details are available on the dedicated webpage.
A second ongoing key comparison, BIPM.QM-K5, will be launched soon, to underpin more stringent measurements of atmospheric background CO2 which require traceability to a common set of standards, referred to as a CO2 scale. The BIPM has been setting up its own scales and worked with the CCQM-GAWG Task Group on GHG Scale Comparisons (CCQM-GAWG-TG-GHG) to develop the protocol of this comparison. The aim is to demonstrate the relationship between scales based on different sets of primary CO2 in air standards over decadal time periods.
Publications