The Japan Meteorological Agency (JMA) serves as the World Calibration Centre (WCC) for methane (CH4) and the Quality Assurance/Science Activity Centre (QA/SAC) in Asia and the South-West Pacific within the framework of the Global Atmosphere Watch (GAW) Programme of the World Meteorological Organization (WMO).

The GAW Implementation Plan notes the importance of observational network compatibility and homogeneity in quality management.

Reference gas intercomparison is one of the most important activities of WCC towards this goal by ascertaining to what extent the current practice of calibration is working at each station, to find out problems, if any, in the calibration scheme, and eventually to ensure that the measurements are intercomparable. A similar activity has been organized once in several years for carbon dioxide (CO2) by the NOAA Earth System Research Laboratories in Boulder, Colorado, USA, and many laboratories involved in CO2 measurement have participated.

Intercomparison has been carried out to compare CH4 measurements in GAW and other stations monitoring atmospheric CH4 mole fractions, particularly in Asia and the South-West Pacific. In the project, two cylinders containing air of known CH4 mole fractions are circulated.

Examples of the cylinders and their attachments are given in Annex 1.

Before and after the circulation, the cylinders are measured at the JMA CH4 calibration facility in Tokyo to check for any concentration changes. Participants measure the CH4 mole fractions in the circulated cylinders and submit the results to the WCC Secretariat (JMA). The Secretariat compiles the results from each partisipant and report their intercomparison results to all the partisipants after the circulation.

The results of the past intercomparisons are shown in Annex 2.