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Natural gas is an important energy vector. The determination of its composition is often used as the basis for the calculation of the calorific value. The calorific value in turn is one of the two key parameters used in natural gas trade. In the first series of key comparisons (CCQM-K1e-g), natural gas was already included with three different compositions. These mixtures contained carbon dioxide, nitrogen, ethane, propane and n-butane in methane (matrix) and were only to a limited extent representative of real natural gas. In the past years, national metrology institutes have broadened the range of components by including, e.g., i-butane, neo-pentane, n-pentane, i-pentane and n-hexane. Based on this extended components list, two new mixtures have been defined, one characteristic for a low calorific mixture (type IV) and the other for a high calorific mixture (type V). In the low calorific mixture, helium was also present. Due to presence of the butane and pentane isomers, the mixtures of type IV and V are more demanding with respect to the separation technique than the mixtures used in CCQM-K1e-g.The measurements in this key comparison took place in 2001. There were eight participants and two coordinating laboratories. The key comparison reference value (KCRV) was based on the gravimetric preparation for all components. Even for the heavier hydrocarbons (pentanes and n-hexane) the effects of, e.g., adsorption can be controlled to such an extent that this approach is still valid. The uncertainty evaluation of the KCRVs reflected also the extent to which the preparation data could be demonstrated to be valid. The validity of the preparation data was demonstrated by comparing the composition of the mixtures prepared for this comparison with measurement standards maintained by the coordinating laboratories.The key comparisons demonstrated that the results of the laboratories agreed within 1% relative to the reference value for most components. Even better agreement was obtained for nitrogen in the low calorific mixture (0.5%), carbon dioxide (0.5%), ethane (0,5%), propane (0.5%) and methane (0.1%). In some cases, larger differences were observed, which then also exceeded the associated expanded uncertaintyMain text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the Mutual Recognition Arrangement (MRA).

The measurement of greenhouse gases in the atmosphere is one of the activities to monitor changes in the global environment, as some of these gases are presumed to contribute to climate change. The CCQM Gas Analysis Working Group has organised a pilot comparison for carbon dioxide and methane at ambient levels to compare primarily the capabilities of national metrology institutes (NMIs) for measuring these species in air. The participation in this comparison was not limited to signatories of the MRA, as is usually the case. Laboratories from the World Meteorological Organisation (WMO) were invited as well, and two participated.The project has been split in two parts, a comparison of the (analytical) measurement capability, and a high-accuracy comparison of primary standard gas mixtures for greenhouse gases. In this first part, the measurement capability was compared between NMIs and WMO laboratories. The nominal amount-of-substance fraction levels are 365 µmol/mol for carbon dioxide and 1.8 µmol/mol for methane. The matrix was synthetic air, simulated by a mixture of nitrogen, oxygen (209 mmol/mol) and argon (9.3 mmol/mol). The measurements took place in the spring of 2003.The protocol used for this comparison was the same as used so far in the gas analysis area for key comparisons and studies of this type. The reference values were assigned to each gas mixture on the basis of the gravimetric preparation, taking into account the results from the purity verification. In particular for the value assignment of methane, traces of methane in the matrix gases (nitrogen, oxygen and argon) can influence the value assigned to the gas mixture appreciably.The results for methane agree within 4% relative, and for most participants even within 2% relative at an amount of substance fraction level of 1.8 µmol/mol. For carbon dioxide all results agree within 1% relative, and for most the agreement is even better: within 0.5% relative at an amount of substance fraction level of 365 µmol/mol. The methane data show a discrepancy of approximately 0.025 µmol/mol between the averages of the WMO laboratories and the NMIs, which confirms results of earlier comparisons. Measurement traceability is quite differently established in NMIs and WMO laboratories, and may account for this difference. Further work is needed to find out the causes of this difference.Main text. To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM.

The World Meteorological Organization (WMO) coordinates worldwide monitoring of greenhouse gases in the background atmosphere. Emissions of the key greenhouse gases such as carbon dioxide and methane are increasing as a result of human activities and are implicated in global climate change. In 1992, the United Nations Framework Convention on Climate Change was established, resulting in the proposal of legally binding limits (the 1997 Kyoto Protocol) aimed at reducing these emissions. The accuracy and traceability of greenhouse gas monitoring over the global space-scale and the decade-to-century time

During the protocol development phase of CCQM-K16, interest was shown by two more national metrology institutes (NMIs) in participating in the comparison, but rather as a study instead of a key comparison. Therefore it was decided to organize in parallel to CCQM-K16 a study, CCQM-K49, enabling NMIs that did not wish to participate in the key comparison to participate in a study with mixtures with the same nominal specifications. The natural gas mixtures type IV (low calorific mixture) and type V (high calorific mixture) have been prepared and checked in the same time frame as those for CCQM-K16.The protocol used for CCQM-P49 differed only in two aspects from that of CCQM-K16: (1) the results would be reported as results from a CCQM study, and (2) it was permitted that NMIs did not analyse all components present in the mixtures. The measurements in this comparison took place in 2001. There were two participants. The coordinating laboratories were the same as in CCQM-K16. The reference value for each component was based on the gravimetric preparation for all components.For most components, the results of the participating NMIs agreed within 1% relative of the reference value.Main text. To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the Mutual Recognition Arrangement (MRA).