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A new calibration system of methane (CH 4) standard gases by using a wavelength-scanned cavity ring-down spectroscopy (WS-CRDS) analyzer was developed at the Japan Meteorological Agency (JMA) in collaboration with the Meteorological Research Institute. We used two sets of CH 4 primary standard gases with mole fractions assigned based on the World Meteorological Organization (WMO) CH 4 mole fraction scale maintained by the National Oceanic and Atmospheric Administration to test the performance of the new WS-CRDS calibration system. Our results showed high repeatability (0.06 nmol mol −1) and reproducibility (0.07 nmol mol −1) of measurements and good linearity against the WMO CH 4 mole fraction scale. The CH 4 calibration results for the new system agree well with those of the previous JMA calibration system, which employed a gas chromatograph with a flame ionization detector (GC/FID). These tests indicate that the new WS-CRDS CH 4 calibration system at JMA will provide results that are consistent with those of the previous GC/FID system but with precision that is one order of magnitude higher. We also evaluated the stability and consistency of the JMA calibrations over the past 10 years by examining data from the World Calibration Centre (WCC) Round Robin comparison experiments in Asia and the regions in the southwest Pacific. The results of our study clearly demonstrate that the new calibration system will provide more precise CH 4 measurements and improved traceability to the WMO scale of atmospheric CH 4 measurements for the JMA/WCC comparisons.

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