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We report the determination of ammonia (NH3) diffusive sampling rates for six different designs of commercial diffusive samplers (CEH ALPHA sampler, Gradko diffusion tube, Gradko DIFRAM-400, Passam ammonia sampler, and ICS Maugeri Radiello radial sampler (blue and white turbulence barriers)), together with the validation test results for a pumped sampler (CEH DELTA denuder). The devices were all exposed in the UK's National Physical Laboratory's (NPL) controlled atmosphere test facility (CATFAC). For each of the seven diffusive sampler exposure tests there were traceable concentrations of ammonia (in the range 3–25 μg m−3) generated under well-defined conditions of temperature, relative humidity and wind speed, which are applicable to a variety of ambient monitoring environments. The sampler exposure time at each concentration was 28 days, except for the radial devices, which were exposed for 14 days. The work relied on the dilution of newly developed stable Primary Standard Gas Mixtures (PSMs) prepared by gravimetry in passivated gas cylinders as a method of improving the metrological traceability of ammonia measurements. The exposed diffusive samplers were sent blind to the participants for analysis and the reported NH3 concentrations were then compared against the known reference concentration. From the results for each sampler type a diffusive sampling rate was calculated and compared against the rate used routinely by the participants. Some measurement results were in good agreement with the known traceable reference concentration (particularly for one diffusive sampler design (ALPHA)), while other devices exhibited over-reading and under-reading (each with a clear bias). The new diffusive sampling rates determined in the laboratory study were then applied to measurements in a field comparison campaign, and this was found to deliver an improvement in agreement between the different devices deployed.

Metrology in chemistry has its own features, which distinguish it from classical metrology: due to the lack of primary methods applicable in routine measurements, metrological traceability of measurement results can be achieved by using in a proper way suitable certified reference materials (CRMs), which can assure a direct relation to a reference. This article deals with the activity of the Italian National Institute of Metrological Research (Istituto Nazionale di Ricerca Metrologica—I.N.Ri.M.) on the analysis of various polychlorinated biphenyls congeners in organic solution by means of gas-chromatography coupled with mass spectrometry. The metrological traceability approach in the quantification step is pursued via calibration solutions prepared by gravimetrically diluting a CRM. The uncertainty for the calibration solutions was evaluated taking into account all the relevant contributions.

We have developed a dynamic reference standard of gaseous formaldehyde based on diffusion of the sublimate of trioxane and thermal conversion to formaldehyde in the gas phase. We have also produced a gravimetric standard for formaldehyde in a nitrogen matrix, also by thermal conversion of the sublimate of trioxane. Analysis of the gravimetric standard with respect to the dynamic standard has confirmed the comparability of the static and dynamic gravimetric values.

Automotive gas mixtures of carbon monoxide, carbon dioxide, oxygen and propane in nitrogen are used for the calibration of measurement equipment for automotive exhaust gases. This comparison involved four laboratories. Two have used their own gravimetric primary standards, one of them used standards prepared by an accredited laboratory and the other used their own gravimetric primary standards together with gravimetric primary standards prepared by other national laboratories. CEM operated as the coordinating laboratory in this comparison. The selected primary gas mixtures for this comparison were individually prepared gravimetrically and thoroughly studied for their chemical composition and stability. Main 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 EUROMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

The first key comparison on carbon dioxide in nitrogen dates from 1993–1994 (CCQM-K1.b). Since then, numerous national metrology institutes (NMIs) have been setting up facilities for gas analysis, and have developed claims for their Calibration and Measurement Capabilities (CMCs) for these type mixtures. In the April 2005 meeting of the CCQM Gas Analysis Working Group, a policy was proposed to repeat key comparisons for stable mixtures every 10 years. Consequently in 2007 the key comparison CCQM-K52 'Carbon dioxide in synthetic air' was carried out. This comparison is consistent with the proposed policy and enables NMIs that could not participate in the previous comparison to take part. This report describes the results of a key comparison for carbon dioxide in synthetic air. The amount-of-substance fraction level of carbon dioxide chosen for this key comparison (360 µmol/mol) represents the ambient level of this component in air. In total 18 NMIs and one WMO laboratory participated in the comparison. The agreement of the results in this key comparison is very good. With a few exceptions, the results agree within 0.3% (or better) with the key comparison reference value. Most of the participants that did not participate in CCQM-K1.b do very well. In some cases, the uncertainties claimed are quite large in comparison with the NMIs for which this comparison is a true 'repeat', but the observed differences with the KCRV usually reflect that these claims are realistic. All participants in CCQM-K1.b that participated in this key comparison show improved results. Main 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 CIPM Mutual Recognition Arrangement (MRA).