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The measurement of ammonia (NH3) in ambient air is a sensitive and priority topic due to its impact on ecosystems. NH3 emissions have continuously increased over the last century in Europe because of intensive livestock practices and the enhanced use of nitrogen-based fertilizers. European air quality monitoring networks monitor atmospheric NH3 amount-of-substance fractions. However, the lack of stable reference gas mixtures (RGMs) of atmospheric amount-of-substance fractions of ammonia to calibrate NH3 analyzers is a common issue of the networks, which results in data that are not accurate, traceable, or, thus, geographically comparable. In order to cover this lack, LNE (Laboratoire National de Métrologie et d'Essais) developed, in close collaboration with the company 2M PROCESS, a gas reference generator to dynamically generate NH3 RGMs in air. The method is based on gas permeation and a further dynamic dilution to obtain an amount-of-substance fractions ranging between 1 and 400 nmol mol−1 (also well known as ppb or parts per billion; 1 ppb (NH3) to ≈ 0.7 µg m−3) to cover the amount-of-substance fractions of ammonia measured in ambient air (emissions) and the operating range of the NH3 analyzers used by the monitoring networks. The calibration of the elements of the generator against the LNE primary standards ensures the traceability of the RGMs to the international system of units. Furthermore, the highly accurate flow and oven temperature measurements of the reference generator, together with the associated calibration procedure defined by LNE, guarantee relative expanded uncertainties of the calibration of the NH3 analyzers that are lower than 2 % (coverage factor = 2). This result is very satisfactory, considering the low NH3 amount-of-substance fraction levels (1 to 400 nmol mol−1) and the phenomena of adsorption and desorption, especially in the presence of traces of water on contact surfaces. A bilateral comparison was organized between METAS (Swiss Federal Institute of Metrology) and LNE, which consisted of the calibration of a Picarro G2103 gas analyzer by both national metrology institutes (NMIs). The results highlighted the good agreement between the NH3 reference generators developed by the two institutes and allowed the validation of both LNE's reference generator and calibration procedure. Since the end of 2020, LNE has calibrated several NH3 analyzers from the French air quality monitoring networks (Associations Agréées de Surveillance de la Qualité de l'Air – AASQA) using the newly developed SI-traceable RGMs. The enhanced number of calibrations provided may increase the comparability, accuracy, and traceability of the NH3 measurements carried out on French territory.

The measurement of ammonia (NH3) in ambient air is a sensitive and priority topic due to its harmful effects on human health and ecosystems. NH3 emissions have continuously increased over the last century in Europe, because of intensive livestock practices and enhanced use of nitrogen-based fertilizers. European air quality monitoring networks monitor atmospheric NH3 amount fractions. However, the lack of stable reference gas mixtures (RGMs) at atmospheric amount fractions to calibrate NH3 analyzers is a common issue of the networks, which results in data that are not accurate, traceable and, thus, geographically comparable. In order to cover this lack, LNE developed, in close collaboration with the company 2M PROCESS, a gas reference generator to generate dynamically NH3 RGMs in air. The method is based on gas permeation and further dynamic dilution to obtain an amount fraction range between 1 and 400 nmol/mol. The calibration of the elements of the generator against LNE primary standards ensures the traceability of the RGMs to the international system of units. Furthermore, the highly accurate flow and oven temperature measurements of the reference generator, together with the associated calibration procedure defined by LNE, guarantee relative expanded uncertainties of the calibration of the NH3 analyzer calibrations lower than 2 % (coverage factor = 2). This result is very satisfactory considering the low NH3 amount fraction levels (1 to 400 nmol/mol) and the phenomena of adsorption and desorption, especially in the presence of traces of water on the surfaces in contact. A bilateral comparison was organized between METAS and LNE, consisting on the calibration of a PICARRO G2103 gas analyzer by both national metrology institutes (NMI). The results highlighted the good agreement between the NH3 reference generators developed by the two institutes and allowed to validate both LNE’s reference generator and calibration procedure. The development of the NH3 reference generator has already raised great interest within the French air quality monitoring networks (AASQA). Since the end of 2020, LNE calibrated several NH3 analyzers of the networks. These requests shows the interest of the AASQA in the development of this new gas reference generator to guarantee the traceability of measurements carried out on the French territory.

Main text This report presents the results of CCQM-K150, a key comparison between nine National Measurement Institutes (NMIs) which tested the capability of the NMIs to measure particle number concentration (in the range of 100 to 20 000 cm-3) using condensation particle counters (CPCs), and particle charge concentration (in the range of 0.15 to 3 fC cm-3) using aerosol electrometers (AEs). Measurements of aerosol particle number concentration are needed to demonstrate compliance to vehicle emission legislation and are becoming increasingly important in other areas such as ambient air and workplace monitoring. The measurements are typically carried out using condensation particle counters, which are calibrated using either reference CPCs or reference AEs. An analogous report is available for the CCQM-P189 comparison. CCQM-P189 was identical to and used the same experimental data as CCQM-K150 with one exception: data from TROPOS, which is not an NMI or Designated Institute (DI), were only included in CCQM-P189. CCQM-K150 was an amount-of-substance Track C comparison. 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 https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Main text This report presents the results of CCQM-P189, a pilot comparison between 10 laboratories which tested the participants’ capability to measure particle number concentration (in the range of 100 to 20 000 cm-3) using condensation particle counters (CPCs), and particle charge concentration (in the range of 0.15 to 3 fC cm-3) using aerosol electrometers (AEs). Measurements of aerosol particle number concentration are needed to demonstrate compliance to vehicle emission legislation and are becoming increasingly important in other areas such as ambient air and workplace monitoring. The measurements are typically carried out using condensation particle counters, which are calibrated using either reference CPCs or reference AEs. An analogous report is available for the CCQM-K150 comparison. CCQM-K150 was identical to, and used the same experimental data as CCQM-P189 with one exception: data from TROPOS, which is not a National Measurement Institute (NMI) or Designated Institute (DI), were only included in CCQM-P189. CCQM-P189 was an amount-of-substance Track C comparison. 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 https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Main text The CCQM-K10.2018 comparison aimed to evaluate the capabilities of national metrology institutes (NMIs) to prepare and/or value assign primary reference mixtures containing benzene, toluene, ethylbenzene, p-xylene, m-xylene and o-xylene (subsequently referred to as BTEX) in nitrogen. This key comparison was separated into two parallel studies. The first study, deemed the "gravimetric study", evaluated the level of compatibility of BTEX standards provided by NMIs. Seven participating laboratories each submitted one standard at nominal 5 nmol mol-1 BTEX in nitrogen. Comparison measurements were performed by the National Institute of Standards and Technology (NIST) from July to October 2018. The second study, deemed the "comparative study", compared the capabilities of NMIs to measure the amount fractions of BTEX in a mixture provided by NIST. NIST prepared one standard at nominal 5 nmol mol-1 BTEX in nitrogen, which was measured consecutively by three participating laboratories. The participants' measurements took place from August 2018 to March 2019. The comparison protocol adopted for CCQM-K10.2018 was more challenging than for the original comparison, CCQM-K10 in 2001, and the results provide an extended evaluation of the level of compatibility of BTEX in nitrogen standards. 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 https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

L’arrete du 19 avril 2017 relatif au dispositif national de surveillance de la qualite de l’air ambiant specifie que le LCSQA doit « garantir l’exactitude et la qualite des donnees d’evaluation de la qualite de l’air ».Pour repondre a cette exigence, le LCSQA a mis en place un dispositif permettant d’assurer la fiabilite et la comparabilite spatio-temporelle des donnees de l’observatoire sur le territoire national et europeen, ainsi que leur adequation avec les exigences europeennes et les besoins de surveillance.Ce dispositif repose sur les actions suivantes :raccordement des mesures de la qualite de l’air aux etalons de reference nationaux ;participation du LCSQA et des AASQA a des comparaisons interlaboratoires ;realisation d’audits techniques des AASQA par le LCSQA ;verification de la conformite technique des appareils de mesure par rapport aux exigences stipulees dans les normes europeennes.

CCQM-K120.a comparison involves preparing standards of carbon dioxide in air which are fit for purpose for the atmospheric monitoring community, with stringent requirements on matrix composition and measurement uncertainty of the CO2 mole fraction. This represents an analytical challenge and is therefore considered as a Track C comparison. The comparison will underpin CMC claims for CO2 in air for standards and calibrations services for the atmospheric monitoring community, matrix matched to real air, over the mole fraction range of 250 μmol/mol to 520 μmol/mol. CCQM-K120.b comparison tests core skills and competencies required in gravimetric preparation, analytical certification and purity analysis. It is considered as a Track A comparison. It will underpin CO2 in air and nitrogen claims in a mole fraction range starting at the smallest participant's reported expanded uncertainty and ending at 500 mmol/mol. Participants successful in this comparison may use their result in the flexible scheme and underpin claims for all core mixtures This study has involved a comparison at the BIPM of a suite of 44 gas standards prepared by each of the participating laboratories. Fourteen laboratories took part in both comparisons (CCQM-K120.a, CCQM-K120.b) and just one solely in the CCQM-K120.b comparison. The standards were sent to the BIPM where the comparison measurements were performed. Two measurement methods were used to compare the standards, to ensure no measurement method dependant bias: GC-FID and FTIR spectroscopic analysis corrected for isotopic variation in the CO2 gases, measured at the BIPM using absorption laser spectroscopy. Following the advice of the CCQM Gas Analysis Working Group, results from the FTIR method were used to calculate the key comparison reference values. KEY WORDS FOR SEARCH FTIR, CO2, GC-FID, Carbon dioxide at background level, Carbon dioxide at urban level, Delta Ray, CO2 gas standards 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 (CIPM MRA).

High purity nitrogen or air, often referred to as zero gas, is essential for calibrating instrumentation used in a wide variety of measurements, such as air quality monitoring. Providing traceable and accurate quantification of impurities of the target component in zero gas is a major challenge, as the detection limits of appropriate analytical techniques are often close to the amount fraction of the measurand and accurate reference standards to underpin these measurements are yet to be developed. Purity analysis of zero gas is a significant contributor to the uncertainty budget and is compromised by a dependence on a zero reference for its realisation. This work describes state-of-the-art methods currently used to certify zero gas standards. We distinguish between absolute and relative techniques and provide guidance on calibration of the latter at trace amount fractions. Measurements to assess the performance of a selection of zero air generators and purifiers are also presented here.

The CCQM-K90 comparison is designed to evaluate the level of comparability of national metrology institutes (NMI) or designated institutes (DI) measurement capabilities for formaldehyde in nitrogen at a nominal mole fraction of 2 μmol mol−1. The comparison was organised by the BIPM using a suite of gas mixtures prepared by a producer of specialty calibration gases. The BIPM assigned the formaldehyde mole fraction in the mixtures by comparison with primary mixtures generated dynamically by permeation coupled with continuous weighing in a magnetic suspension balance. The BIPM developed two dynamic sources of formaldehyde in nitrogen that provide two independent values of the formaldehyde mole fraction: the first one based on diffusion of trioxane followed by thermal conversion to formaldehyde, the second one based on permeation of formaldehyde from paraformaldehyde contained in a permeation tube. Two independent analytical methods, based on cavity ring down spectroscopy (CRDS) and Fourier transform infrared spectroscopy (FTIR) were used for the assignment procedure. Each participating institute was provided with one transfer standard and value assigned the formaldehyde mole fraction in the standard based on its own measurement capabilities. The stability of the formaldehyde mole fraction in transfer standards was deduced from repeated measurements performed at the BIPM before and after measurements performed at participating institutes. In addition, 5 control standards were kept at the BIPM for regular measurements during the course of the comparison. Temporal trends that approximately describe the linear decrease of the amount-of-substance fraction of formaldehyde in nitrogen in the transfer standards over time were estimated by two different mathematical treatments, the outcomes of which were proposed to participants. The two treatments also differed in the way measurement uncertainties arising from measurements performed at the BIPM were propagated to the uncertainty of the trend parameters, as well as how the dispersion of the dates when measurements were made by the participants was taken into account. Upon decision of the participants, the Key Comparison Reference Values were assigned by the BIPM using the largest uncertainty for measurements performed at the BIPM, linear regression without weight to calculate the trend parameters, and not taking into account the dispersion of dates for measurements made by the participant. Each transfer standard was assigned its own reference value and associated expanded uncertainty. An expression for the degree of equivalence between each participating institute and the KCRV was calculated from the comparison results and measurement uncertainties submitted by participating laboratories. Results of the alternative mathematical treatment are presented in annex of this report. 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 (CIPM MRA).

This key comparison aims to assess the core capabilities of the participants in gas analysis. Such competences include, among others, the capabilities to prepare Primary Standard gas Mixtures (PSMs), perform the necessary purity analysis on the materials used in the gas mixture preparation, the verification of the composition of newly prepared PSMs against existing ones, and the capability of calibrating the composition of a gas mixture. According to the Strategy for Key Comparisons of the Gas Analysis Working Group, this key comparison is classified as an RMO track A key comparison. The artefacts were binary mixtures of propane in nitrogen at a nominal amount-of-substance fraction level of 1000 μmol/mol. The values and uncertainties from the gravimetric gas mixture preparation were used as key comparison reference values (KCRVs). Each transfer standard had its own KCRV. The results are generally good. All results are within ± 1 % of the KCRV. 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 (CIPM MRA).

This key comparison aims to assess the capabilities of the participants to determine the amount-of-substance fraction oxygen in nitrogen. The GAWG has classified this as a track B comparison, due to the unexpected 50 μmol/mol argon mole fraction content of the transfer standards, which effects the achievable performance of some measurement techniques such a GC-TCD. The separation of oxygen and argon is challenging, and not all systems in use are equally well designed for it. As this analytical challenge due to a substantial fraction of argon in the transfer standards became a reality, the Gas Analysis Working Group (GAWG) decided to qualify this key comparison as a regular key comparison and not as a core comparison, which may be used to support calibration and measurement capabilities (CMCs) for oxygen in nitrogen, or for oxygen in nitrogen mixtures containing argon only (see also the section on support to CMCs). 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 (CIPM MRA).

This supplementary comparison (EURAMET.QM-S8) concerns the purity analysis of nitrogen as used in reference gas mixture preparation. This project was carried out without adding impurities to the gas used for this comparison, and is therefore more representative to evaluate the analysis of carbon monoxide, carbon dioxide, methane, oxygen, argon and water impurities in high-purity nitrogen. The analysis of the amount-of-substance fraction water was optional. Two 50 litre high purity nitrogen cylinders were purchased from a well-qualified supplier of specialty gases. The listed components were expected to be present in the pure nitrogen at the target levels as a result of the purification of the nitrogen. From the start of this comparison it was clear that the comparison may not lead to reference values for the constituents analysed. The results indicate that analyses of high purity gases are often limited by the limits of detection of analytical equipment used. The reports of the participating laboratories also indicate that there is no agreed method of determination of the uncertainty on a detection limit value. The results provide useful information on the performance of participants. For all analysed components there is reasonable agreement in results for LNE, VSL, METAS and NPL. For BAM only the argon result is in agreement. 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 EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

This report presents the results of CCQM-K93, a key comparison between 13 National Measurement Institutes (NMIs), which tested the capability of the NMIs to prepare standard gas mixtures of ethanol at a nominal amount fraction of 120 µmol/mol in nitrogen. This composition is typical of the levels used to calibrate evidential breath analysers in many countries. Such standards fulfill the agreed requirements of the International Organization of Legal Metrology (OIML) for the calibration of evidential breath-alcohol analysers. 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 (CIPM MRA).

There is a high international priority attached to activities which reduce NOx in the atmosphere. The current level of permitted emissions is typically between 50 µmol/mol and 100 µmol/mol, but lower values are expected in the future. Currently, ambient air quality monitoring regulations also require the measurement of NOx mole fractions as low as 0.2 µmol/mol. The production of accurate standards at these levels of mole fractions requires either dilution of a stable higher concentration gas standard or production by a dynamic technique, for example one based on permeation tubes. The CCQM-K74 key comparison was designed to evaluate the level of comparability of National Metrology Institutes' measurement capabilities and standards for nitrogen dioxide (NO2) at a nominal mole fraction of 10 µmol/mol. The measurements of this key comparison took place from June 2009 to May 2010. Seventeen laboratories took part in this comparison coordinated by the BIPM and VSL. The key comparison reference value was based on BIPM measurement results, and the standard measurement uncertainty of the reference value was 0.042 µmol/mol. This key comparison demonstrated that the results of the majority of the participants agreed within limits of ±3% relative to the reference value. The results of only one laboratory lay significantly outside these limits. Likewise this comparison made clear that a full interpretation of the results of the comparison needed to take into account the presence of nitric acid (in the range 100 nmol/mol to 350 nmol/mol) in the cylinders circulated as part of the comparison, as well as the possible presence of nitric acid in the primary standards used by participating laboratories. 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).

The key comparison CCQM-K76 was designed to test the capabilities of the participants to measure and certify sulfur dioxide in nitrogen, and to provide supporting evidence for the CMCs of these institutes for sulfur dioxide. Also, as sulfur dioxide is designated a core compound, and the 100 ?mol/mol concentration is within the designated core compound concentration range, this comparison was also designed to demonstrate core capabilities of institutes which qualify under the rules of the Gas Analysis Working Group. The results of all 16 participants in this key comparison, except for three, are consistent with their key comparisons reference values. The three participants which are outside the KCRV interval are NIM, SMU and NPLI. This comparison may be used to demonstrate core analytical capabilities in accordance with the rules and procedures of the CCQM Gas Analysis Working group. 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).

The first key comparison on carbon monoxide (CO) in nitrogen dates back to 1992 (CCQM-K1a). It was one of the first types of gas mixtures that were used in an international key comparison. 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 mixtures. Furthermore, in the April 2005 meeting of the CCQM (Consultative Committee for Amount of Substance) Gas Analysis Working Group, a policy was proposed to repeat key comparisons for stable mixtures every 10 years. This comparison was performed in line with the policy proposal and provided an opportunity for NMIs that could not participate in the previous comparison. NMISA from South Africa acted as the pilot laboratory. Of the 25 participating laboratories, 19 (76%) showed satisfactory degrees of equivalence to the gravimetric reference value. The results show that the CO concentration is not influenced by the measurement method used, and from this it may be concluded that the pure CO, used to prepare the gas mixtures, was not 13C-isotope depleted. This was confirmed by the isotope ratio analysis carried out by KRISS on a 1% mixture of CO in nitrogen, obtained from the NMISA. There is no indication of positive or negative bias in the gravimetric reference value, as the results from the different laboratories are evenly distributed on both sides of the key comparison reference value., JRC.H.2-Air and Climate

The pilot study evaluated the level of comparability of laboratories' preparative capabilities for gravimetric nitrogen monoxide/nitrogen primary reference mixtures in the range (30?70) ?mol/mol. The comparison was designed so that measurements would be performed at a central laboratory (the BIPM) and measurement results compared to values assigned by each national metrology institute (NMI) based on gravimetry using regression analysis. The advantages and complications in organizing a comparison with measurements performed at a central laboratory have been clearly demonstrated, notably: analytical measurement uncertainties can be reduced; a degree of equivalence parameter and its uncertainty can be calculated; regression analysis and therefore reference values for the comparison are highly dependent on the data set chosen for regression analysis and the uncertainty ascribed to the analytical measurement system within the central laboratory. Participating laboratories reported standard uncertainties for gravimetric preparation which ranged from 0.01% to 0.22% relative to the nitrogen monoxide mole fraction value. Following FTIR analysis, the standards of three laboratories (six gas standards in total) were omitted from the regression analysis data set, as a significant difference between reported and measured values of impurity contents was observed. An additional standard was removed from the regression analysis set as its deviation from the regression line was of the same order of magnitude as the standards already omitted. A regression line consistent with the remaining calibration data (15 gas standards) could be obtained by increasing estimates of the coordinating laboratory's measurement uncertainty by approximately a factor of three, resulting in analytical standard uncertainties of 0.12% (at 70 ?mol/mol) and 0.27% (at 30 ?mol/mol), and predicted standard uncertainties of the nitrogen monoxide mole fractions of 0.09 ?mol/mol. Reported standard uncertainties related to gravimetric preparation ranged from 0.004 ?mol/mol to 0.11 ?mol/mol with a median of 0.03 ?mol/mol. Nevertheless, comparison of the results of CCQM-P73 to previous key comparisons for nitrogen monoxide in nitrogen at 100 ?mol/mol (CCQM-K1.c and EUROMET.QM-K1.c) illustrates the reductions in uncertainties that can be achieved through a comparison with measurements performed at a central facility. 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-GAWG.

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).

Twenty-two standards of synthetic natural gas standards were submitted from ten different NMIs for a comparison using the harmonization method developed by NPL. All standards had seven components. This method can remove the correlated variation in calibration data for multi-component mixtures and makes a significant improvement in fitting individual points to calibration curves. After removing the non-random variation from the data all the standards showed very good agreement with only a few outliers. The typical deviation from the calibration curves was around 0.05% (relative) for the main components and less than 0.2% for the butanes. 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 GAWG.

Accurate measurements of sulphur dioxide at the concentrations found in ambient air have become essential to support monitoring and legislation concerned with air quality. In general, the primary element of quality assurance for field instruments is regular calibration using certified gas mixtures. The concentration range chosen for this Key Comparison (240 nmol/mol to 320 nmol/mol) is defined by appropriate European standards and is typical of similar levels used around the world. The travelling standards used for the comparison were prepared commercially by a supplier with a proven track record of preparing stable mixtures of the relevant gases. The coordinating laboratory (NPL) carried out stability checks on the mixtures and determined the amount fraction using a primary gravimetric permeation facility. These data were used to determine the drift rate (and uncertainty) of each standard. The results for the 11 participants in CCQM-K26.b and the one participant in CCQM-P50.b are presented in this report. Degrees of equivalence have been calculated based on a reference value (corresponding to the KCRV) derived from the primary gravimetric facility used by the coordinating laboratory. 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).

At the highest metrological level, natural gas standards are commonly prepared gravimetrically as PSMs (primary standard mixtures). This international key comparison is a repeat of CCQM-K1e-g. The mixtures concerned contain nitrogen, carbon dioxide and the alkanes up to butane. The only difference with CCQM-K1e-g is the addition of iso-butane to the list. The results usually agree within 1% (or better) with the key comparison reference value. For ethane, nitrogen and carbon dioxide, the agreement is within 0.5% (or better), and for methane within 0.1% (or better) of the KCRV. 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).

We report a pilot study organized within the Consultative Committee for Amount of Substance (CCQM), in which the ozone reference standards of 23 institutes have been compared to one common reference, the BIPM ozone reference standard, in a series of bilateral comparisons carried out between July 2003 and February 2005. The BIPM, which maintains as its reference standard a standard reference photometer (SRP) developed by the National Institute of Standards and Technology (NIST, United States), served as pilot laboratory. A total of 25 instruments were compared to the common reference standard, either directly (16 comparisons) or via a transfer standard (9 comparisons). The comparisons were made over the ozone mole fraction range 0 nmol/mol to 500 nmol/mol. Two reference methods for measuring ozone mole fractions in synthetic air were compared, thanks to the participation of two institutes maintaining a gas-phase titration system with traceability of measurements to primary gas standards of NO and NO2, while the 23 other instruments were based on UV absorption. In the first instance, each comparison was characterized by the two parameters of a linear equation, as well as their related uncertainties, computed with generalized least-squares regression software. Analysis of these results using the Birge ratio indicated an underestimation of the uncertainties associated with the measurement results of some of the ozone standards, particularly the NIST SRPs. As a final result of the pilot study, the difference from the reference value (BIPM-SRP27 measurement result) and its related uncertainty were calculated for each ozone standard at the two nominal ozone mole fractions of 80 nmol/mol and 420 nmol/mol. 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.

This key comparison involved primary standards of ethanol in air maintained at eight laboratories. The nominal amount fraction of the standards used for the comparison was 120 µmol/mol, which is typical of the levels used to calibrate evidential breath analysers in many countries. Such standards fulfil the agreed requirements of the International Organization of Legal Metrology (OIML) for the calibration of evidential breath-alcohol analysers and can provide a more accurate calibration at field level than ethanol/water solution-based simulators, which have a high sensitivity to variations in the temperature of the solution. EUROMET.QM-K4 results are linked to CCQM-K4 results.