Standards to underpin atmospheric monitoring

Following the CCQM, CCQM Working Group on Gas Analysis (GAWG) and CCQM Working Group on Isotope ratios (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.

Ongoing comparisons for CO₂

The BIPM has been establishing a central facility to act a stable reference in the future ongoing BIPM.QM−K2 comparison, to compare consistency of amount fraction values in CO₂ in air standard mixtures from the participants. This facility is based on the manometric method. It provides SI traceable values of CO₂ in air amount fractions by measuring the pressure and temperature of a sample of the standard mixture and of the CO₂ extracted from it by cryogeny, completed by the ratio between their volumes. The comparison start date is January 2024.

A second ongoing key comparison, BIPMQM-K5, will be launched soon, to underpin most stringent measurements of 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 is working with the CCQM-GAWG-TG-GHG to develop the protocol of this comparison. The aim is to demonstrate the maintenance or divergence of the relationship between scales based on different sets of primary CO₂ in air standards over decadal time periods.

See also

CCQM-GAWG Task Group on GHG Scale Comparisons (CCQM-GAWG-TG-GHG)

Publications

All publications