Gas Metrology Landing Page

Gas Metrology

Supporting reliable measurements of our atmosphere and the air we breathe.

 

Atmospheric measurement standards

Confidence in the measurements that help us understand our atmosphere

Reliable measurements help scientists track changes in the atmosphere and support the monitoring of pollutants that affect human and environmental health. The BIPM Chemistry Department develops, maintains and operates specialized measurement facilities and uses them as stable references for international comparisons of gas standards.

 

The BIPM’s work in gas metrology

Measurements for our atmosphere and the air we breathe

Understanding changes in atmospheric composition and assessing the quality of the air around us depend on measurements that can be trusted and compared across countries. The BIPM provides common reference points for this work by comparing gas standards maintained by National Metrology Institutes (NMIs) and Designated Institutes (DIs), helping them demonstrate that their measurements are equivalent.

 

Atmospheric monitoring

Atmospheric composition

Tracking how the Earth’s atmosphere is changing depends on being able to detect small differences in gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), and on knowing that measurements made in different countries are comparable. The BIPM compares standards maintained by participating NMIs and DIs against stable reference facilities operated at the BIPM.

The programme uses spectroscopic, manometric and mass-spectrometric techniques, as appropriate, to compare standards and investigate potential measurement bias at low uncertainties. It covers CO2 and CH4  in air, as well as CO2 isotope-ratio measurements relevant to understanding atmospheric sources and maintaining international carbon-isotope scales. Standards compared in this way are used to calibrate atmospheric observations worldwide.

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Environmental and health monitoring

Air quality

Air-quality decisions depend on measurements that accurately show the levels of pollutants in the air people breathe. For surface ozone, which can be harmful to human health at ground level, the BIPM maintains Standard Reference Photometers that provide reference standards for its international comparison programme. The programme also includes comparisons for other important air-quality gases, including nitrogen dioxide (NO2).

The ongoing BIPM.QM-K1 key comparison allows participating National Metrology Institutes and Designated Institutes to compare their ozone standards with the BIPM reference and demonstrate measurement equivalence. This provides metrological traceability for surface-ozone measurements and supports consistent results across national, regional and global monitoring networks.

 

Comparison results and recognition

Gas comparisons and technical information

Explore BIPM gas-metrology comparisons and the internationally recognized Calibration and Measurement Capabilities (CMCs) published in the BIPM Key Comparison Database (KCDB).

Comparison results

Gas comparisons

Access active and completed comparisons and pilot studies, including the results used to assess the equivalence of participating institutes’ measurement standards.

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International recognition

BIPM Key Comparison Database (KCDB)

Explore internationally recognized Calibration and Measurement Capabilities (CMCs), together with key and supplementary comparison information supporting the Mutual Recognition Arrangement of the International Committee for Weights and Measures (CIPM MRA).

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Frequently asked questions

Find quick answers about how BIPM gas comparisons work, the measurements they support and how the results contribute to international confidence in measurement standards.

How does a BIPM gas comparison work?

The BIPM maintains and operates specialized reference facilities used to run international gas comparisons. Participating National Metrology Institutes and Designated Institutes send their standards to the BIPM to compare against these stable references, with the comparison results allowing them to assess and demonstrate the equivalence of their measurement capabilities.

Which atmospheric measurements are covered by the BIPM programme?

The programme includes comparisons for carbon dioxide (CO2), methane (CH4) and in air, together with CO2 isotope-ratio standards. In air quality, the programme includes surface ozone and other important gases such as nitrogen dioxide (NO2).

Why does accurate surface-ozone measurement matter?

Ground-level ozone is a pollutant that can affect human health and the environment, so monitoring networks need measurements that are accurate and comparable. The BIPM maintains Standard Reference Photometers and operates the ongoing BIPM.QM-K1 key comparison, providing a common metrological reference for participating institutes and supporting traceable surface-ozone measurements.

How are comparison results linked to internationally recognized measurement capabilities?

Key and supplementary comparisons provide evidence of measurement equivalence between participating institutes. Together with the review processes of the Mutual Recognition Arrangement of the International Committee for Weights and Measures (CIPM MRA), the results support internationally recognized Calibration and Measurement Capabilities (CMCs) published in the BIPM Key Comparison Database (KCDB).

What does metrological traceability mean for air-quality monitoring?

Metrological traceability connects a measurement result to recognized references through an unbroken chain of calibrations or comparisons, each with stated uncertainty. For air-quality monitoring, this helps ensure that results from different instruments, laboratories and monitoring networks can be meaningfully compared.

Explore the BIPM Chemistry Department

Learn more about the Chemistry Department’s programmes, international activities and measurement expertise.

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