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Novel traceable analytical methods and reference gas standards were developed for the detection of trace-level ammonia in biogas and biomethane. This work focused on an ammonia amount fraction at an upper limit level of 10 mg m–3 (corresponding to approximately 14 μmol mol–1) specified in EN 16723-1:2016. The application of spectroscopic analytical methods, such as Fourier transform infrared spectroscopy, cavity ring-down spectroscopy, and optical feedback cavity-enhanced absorption spectroscopy, was investigated. These techniques all exhibited the necessary ammonia sensitivity at the required 14 μmol mol–1 amount fraction. A 29-month stability study of reference gas mixtures of 10 μmol mol–1 ammonia in methane and synthetic biogas is also reported.

This report describes work to evaluate the performance of different commercial and proprietary cylinder treatments in improving the stability of ammonia reference materials in high pressure cylinders. Gas mixtures of 100 µmol/mol and 10 µmol/mol ammonia in nitrogen were prepared gravimetrically at both NPL and VSL. Comparative measurements at each amount-of-substance fraction were used to assess which passivation technique minimised the loss of ammonia upon preparation. The results indicate little difference between the commercial treatments, except at lower amount-of-substance fractions (10 μmol/mol). The variation observed in performance might be explained by the different abilities of the various treatments to prevent the adsorption of ammonia molecules on the internal surfaces of the cylinder, although the role of residual water on the cylinder surface in reacting with ammonia is unclear.

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.

European Commission targets specify that 32% of the European energy consumption should come from renewable sources by 2030. One of the most promising options to reach this target is gas generation from biomass, especially biomethane, for injection into natural gas grid. EN 16723 presents specifications for VOCs, corrosive components and compressor oil in biomethane, impurities monitored because of integrity of gas infrastructure and for health and safety reasons. Currently, it proposes test methods that are neither harmonized nor validated, and usually not dedicated to biomethane. Launched in June 2017, the EMPIR project 16ENG05 Metrology for Biomethane is aimed for specific, robust and standardized analytical methods development, along with novel and improved reference standards. The present paper focusses on the developed methods for the monitoring of amines, terpenes and ammonia involving μGC-TCD, TD-GC-MS and OFCEAS.

We have developed a unique dynamic dilution system for generating high accuracy reference standards of reactive gases at concentrations which are unstable in high pressure cylinders. It uses state of the art ‘Molbloc’ flow elements and is capable of generating adjustable reference standards with an estimated relative expanded uncertainty lower than 1%. This is a significant development, improving the accuracy of primary reference gas mixtures used to provide and disseminate traceability for measurements of many key gaseous air pollutants.

The National Institute of Metrological Research (INRiM), in Italy, has among its duties the development, the maintenance and the dissemination of primary standards for establishing a correct traceability chain at national level. For this reason, INRiM has been developing research activities on reference materials, mainly in the chemical field, dealing both with the characterization and the certification of reference materials. The present paper focuses on the certified reference solutions for electrolytic conductivity, on the primary reference gas mixtures, and on INRiM contribution in the certification of various reference materials by determining trace element mass fraction by means of Instrumental Neutron Activation Analysis. The description of the main features of the produced reference materials, of the used procedures, and of the uncertainty evaluation are given.

Density measurements are frequently associated to specific requirements to evaluate the quality of a process or to determine mass and/or volume of the material. Certified reference liquids can be used to assure metrological traceability of density measurements to the SI with uncertainty lower than 0.005%. This paper presents the new approach of INRIM to set density standards. The procedure involved accurate density determinations of some reference liquids which were supported by gas-chromatography coupled with mass spectrometry (GC–MS) in order to assess their homogeneity and short-term stability. GC–MS analyses on tetrachloroethylene and trichloroethylene were carried out before and after density measurements. Samples that had undergone to variations in density value showed also different gas-chromatographic profiles. In the same time, samples that had not undergone to density variations kept similar gas-chromatographic profiles. The results support the approach of combining independent methods in order to set physico-chemical properties of reference materials.

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.

Metrologically traceable measurements are needed, in environmental monitoring, to provide meaningful information on the pollution level and the possibility to have suitable reference standards is crucial to this purpose to calibrate instruments. The Italian National Institute of Metrological Research (I.N.Ri.M.), as a primary metrological institute, realizes and maintains primary standards for the basic and derived units of the International System of Units (SI). In this framework and regarding gas analysis, in the last few years I.N.Ri.M. has started a research line on the preparation of primary reference mixtures (PRMs) by the gravimetric method that led to plan and build a facility for evacuating and filling cylinders and a device for high precision weighing. In the present work the developments in such field at I.N.Ri.M. are reported to underline the relevance, in the atmospheric pollutants monitoring, of performing accurate and reliable measurements and having reference standards fit for the calibration of the analytical instrumentation.

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.

The present work deals with the evaluation of measurement uncertainty in the determination of carbon dioxide (CO2) concentration in atmosphere, given the high relevance of this greenhouse gas that influences earth climate. In order to carry out CO2 measurements, non dispersive infrared (NDIR) analysers are usually employed as they are stable and scarcely affected by interferences from other air components or pollutants. Typical uncertainty sources are the resolution of the analyser, its time drift and the contributions due to instrument calibration, which is required in order to produce traceable measurement results. The calibration uncertainty takes into account the uncertainty of the composition of the calibration gas mixtures, the instrument repeatability and the possible or residual lack of fit of the adopted mathematical model.

Carbon dioxide monitoring is significant in the environmental field since this gas plays an important role in the greenhouse effect. In order to determine CO2 concentration and to develop simulation models, it is necessary to carry out measurements which are accurate and comparable in time and space, i.e. SI-traceable. Non-dispersive infrared (NDIR) analysers are employed for CO2 measurements, as they are precise and stable. In order to achieve traceability, such instruments have to be characterized and calibrated. At the Istituto di Metrologia "G. Colonnetti"--CNR, a procedure for calibrating NDIR analysers for CO2 at atmospheric level was developed, which enables to calculate a correction for the analyser output. In addition, a complete uncertainty analysis was carried out and a correct traceability chain was established. The goal of the present work is the study of the stability of a NDIR analyser by repeating calibrations during three years and comparing the correction curves obtained to identify a proper re-calibration interval for such analysers. The investigated instrument has good repeatability and reproducibility, hence satisfactory stability during time, as shown by the short-term and long-term compatibility of calibration curves.

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).