Final report: international comparison APMP.QM-S7 methane in nitrogen at 2000 μmol/mol

Methane is one of the major greenhouse gases that affect climate change. To mitigate anthropogenic CH4 emissions effectively, it is necessary to measure and monitor CH4 emissions from fossil fuel combustion. Therefore, it is important for NMIs to have the capability of an accurate CH4 emissions measurement. The first key comparison on methane in nitrogen or air is the key comparison of CCQM-K82 (ambient level methane in air). As a supplementary comparison, the purpose of this comparison is to cover a concentration level that is not covered by previous key comparisons: this report describes the results of a supplementary comparison for methane in nitrogen at 2000 mu mol/mol. Results from all participants, except two, agree well within their associated uncertainties.