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The design and fabrication of innovative nanostructured materials that could display improved sensitivity, selectivity, and rapid response/recovery characteristics still present significant scientific challenges.

There are few studies that have assessed greenhouse gas (GHG) effluxes under dryland agriculture, especially in South Africa. Subsequently, limited data in the sub-Saharan region impedes the formulation of policies on GHG mitigation and adaptation. Therefore, the need to study effluxes of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) was salient. The objective of the study was to assess GHG effluxes across seasons in conventional tillage (CT) and no-till (NT) systems under nitrogen (N) fertilizer management. Gases were sampled using static PVC chambers and sampling was done by inserting a 25-mL polypropylene syringe into the chamber septa and slowly removing the gas. Samples were analysed for CO2, CH4 and N2O using gas chromatography. In winter, CH4 effluxes were higher under NT than CT for each application rate (p

Accurate measurements for the determination of hydrogen sulfide (H2S) are critical for the compliance with legislation in various industries, including natural gas and environmental sectors such as air pollution monitoring. H2S measurements at ambient level are challenging because H2S tends to adsorb on the internal surfaces of the sample collection devices such as gas cylinders and transfer lines. Prolonged exposure to H2S has known health implications to humans, such as irritation to the nose, throat and airways that results in coughing or inflammation, wheezing and shortness of breath around the chest. H2S is mainly monitored for occupational health and safety and indoor air quality monitoring. It is a highly reactive gas that can easily react with oxygen to form sulfur dioxide (SO2) and with water to form sulfuric acid (H2SO4). The traceability of H2S measurements is achieved through the preparation of reference gas mixtures. These gas mixtures are gravimetrically prepared in accordance with International Organization for Standardization (ISO 6142–1:2015). The H2S reference gas mixtures were produced with the highest metrological capability; thus, the molar mass, purity assessment, and the weighing gave an overall gravimetric relative uncertainty which is less than 0.10% (k = 1). One of the biggest challenges in producing a H2S reference gas mixture is the handling of a gas cylinder from the gravimetric preparation process until the verification stage. This work will detail the improved techniques and measurements used to produce the H2S reference gas mixtures. The internal consistency between the mixtures was verified using a non-dispersive ultraviolet (NDUV) spectroscopy analyzer, an ultraviolet fluorescence spectroscopy (UVFS) analyzer and gas chromatography coupled with a pulsed discharged helium ionization detector (GC-PDHID). Our measurement uncertainty results show that the gravimetric value, internal consistency, adsorption, homogeneity, and stability were within a relative uncertainty of 1.2% as compared to our previous uncertainty of 4.4%. This is a significant improvement for the measurements of H2S reference gas mixtures.

The dual-functionality sensor derived from semiconductor metal oxides operating at low temperature for low power consumption and robust stability toward humidity is a striking platform for economic...

Main text The CCQM-P172 comparison was designed to evaluate the level of compatibility of laboratories' spectroscopic methods for trace gas quantification using nitric acid (HNO3) as a model system. Because it is present in NO2 gas standards as an impurity, HNO3 was chosen as the analyte for study. As primary reference gas mixtures of HNO3/N2 are (generally) unavailable for calibration, traceability for spectroscopic measurements will rely on the use of referenced molecular parameters (such as tabulated in the HITRAN database, acronym for high-resolution transmission molecular absorption database). Laboratories that took part in this pilot study CCQM‐P172 were required to submit one secondary standard of NO2 in nitrogen at a nominal amount fraction of 10 μmol mol−1 with a requirement that the HNO3 amount fraction present in the mixture is between 100 nmol mol−1 and 1000 nmol mol−1. As the mixtures are similar to the ones compared in the Key Comparison CCQM-K74.2018, also coordinated by the BIPM during the same period, a similar linear decrease of the main component NO2 and a correlated linear increase of the major impurity HNO3 was initially foreseen. The CCQM-P172 protocol was designed to deal with standards that followed a well-behaved decay profile, allowing BIPM measurements to be compared to interpolated values for participants' standards. However, as with CCQM-K74.2018, the behavior of the standards deviated from this expectation, showing nonlinear variations of the components. The study was further complicated with deviations from the protocol which have been recorded and described in this report. The complications resulted in a reduced number of analyses by the coordinating laboratory for two of the five participants. The first version of this report distributed in May 2021 between participants described only the measurements performed by the BIPM and the results submitted by participants, without attempting to provide reference values. Nevertheless, a number of important observations and conclusions were drawn as reported below: 1) The BIPM operated two methods for FTIR quantification of HNO3, the first based on direct reference to HITRAN parameters, the second based on calibration with a permeation system. Whilst both methods demonstrate very good correlation and linearity with respect to each other, the HITRAN method provided measurement results 23% higher than for the permeation system calibrated FTIR method. 2) The fitting of HNO3 FTIR spectra was often complicated by the presence of other species, in particular the considerable NO2 absorption band for gas mixtures from cylinders, and the presence of considerable amounts of water in the case of the BIPM permeation calibration gas mixtures in the 1550 cm-1 to 1750 cm-1 spectral window. The effect of the spectral windows used for fitting deserves further consideration. 3) Stabilization of the FTIR signal in the BIPM system (45 m gas cell) with the flows of gas that are permissible from gas cylinders for HNO3 resulted in residual drift in signal that varied between standards submitted, and in the best cases was characterized by an additional uncertainty component with magnitude of 20 nmol mol−1 (standard uncertainty), and a compromise between increased signal sensitivity and its stability. 4) Due to the complications in the study, the set of results obtained, which had sufficiently complete sets of measurements to compare data, were for the cylinders received from NPL and VSL. In the case of the NPL standard, BIPM and NPL FTIR measurements were performed with similar HITRAN based methods, and agreement of results can be concluded if the rise in HNO3 levels can be considered to have stabilized in the standard at the time of measurement at the BIPM. The VSL method fits individual absorption lines within a different band from BIPM and NPL. For the VSL standards the absolute change in HNO3 amount fractions between their measurement periods is of the same order of magnitude as the uncertainties reported for the BIPM FTIR measurement methods. As a result both of the BIPM and the VSL results could be considered in agreement, without being able to readily differentiate for which of the BIPM results the agreement is better. During the GAWG meeting of June 2021, participants agreed to complete the study with the following actions: • reanalysis of participants' FTIR spectra when feasible: CENAM and NPL spectra were reanalysed using the submitted participants parameters, and the recalculated nitric acid mole fractions. Unfortunately, NMISA and KRISS could not provide enough information to reanalyse their spectra. VSL did not use FTIR for the analysis. The reanalysis confirmed good agreement with NPL and revealed differences with CENAM. • reanalysis using different regions: the impact of fitting HNO3 amount fractions in alternative regions, 1240 to 1400 cm-1 and 1240 to 1800 cm-1, was studied. The maximum difference in amount fractions calculated was dependant on the database used. • the Pacific Northwest National Laboratory (PNNL) database was used as alternative infrared database to retrieve HNO3 amount fractions of calibration mixtures produced by the permeation facility. A bias of 6.7 %, contrasting with 23 % identified using HITRAN, was found against HNO3 permeation-based values. Based on the measurements performed at the BIPM using FTIR calibrated with dynamic standards on one hand, and with molecular parameters found in the two databases HITRAN and PNNL, a strategy to further calibrate HNO3 values measured by FTIR in standards of NO2 in nitrogen is proposed. This is based on applying a correction to amount fraction values determined by the FTIR-HITRAN method, with the correction factor determined from the comparison with values from the Permeation system method, considered as the reference method. The corrected FTIR-HITRAN method, with traceability of values to the permeation method, can be applied reproducibly, provided that the FTIR gas cell's pathlength is regularly verified, and the spectral region fitted is defined. 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 CCQM-K3.2019 was a repeat of the key comparison CCQM-K3 on the composition of automotive exhaust gases. New in CCQM-K3.2019 was the addition of the amount fraction oxygen to the programme. The key comparison reference values were obtained independently, using static gravimetry and appropriate corrections from purity analysis. The key comparison results show equivalence between the measurement standards maintained by the participating national metrology institutes. The demonstrated equivalence can be used to underpin services related to automotive exhaust gases as well as generically through the flexible scheme ("track A"). 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).

We report on the propanol vapour (C3H8O) gas sensing characteristics of ZnO nanostructures prepared via hydrothermal assisted method. The ZnO-4h sensor showed a high response (i.e. resistance ratio), sensitivity and selectivity toward C3H8O gas at low operating temperature of 125 °C. A response and recovery times of approximately 190 and 200 s were recorded. The response of ZnO-4h based sensor to 40 ppm C3H8O was approximately 2 times higher than that of other sensing materials in dry air, while in the presence of 40% RH the response was 5 times higher. The exceptional C3H8O-sensing performance of ZnO-4h is related to more C3H8O adsorption sites provided by VO. The ZnO-04h based sensor showed a clear repeatability towards 40 ppm C3H8O for four successive cycles in the presence of various RH of 40 and 60% at 125 °C. The sensor response improved in the presence of RH humidity showing that the water vapour was not competing with the C3H8O for the pre-adsorbed oxygen ions, thus its interfering effect in the C3H8O sensing was considerably minimized. The ZnO-4h based sensor was further tested for long-term stability and the sensor was very stable after 45 days. The fundamental sensing mechanism towards C3H8O vapour is also discussed.

Nitrous oxide (N2O) is an important greenhouse gas and is the third-largest contributor to global warming with a global warming potential (GWP) higher than that of carbon dioxide. Ambient N2O is monitored globally and described at nanomole per mole (nmol mol−1) levels. Metrologically traceable and highly accurate N2O gas standards are required to understand the behaviour of the greenhouse gases in the atmosphere and GWP. A group of primary standard gas mixtures (PSGMs) in aluminium cylinder material has been prepared in synthetic air for the calibration of analytical instruments for measurement of N2O at an ambient level. An automatic weighing system with a mass comparator and a fully automated circular rotary plate, as well as a gas filling station, was used in the preparation of the gas mixtures. Analytical methods such as gas chromatography coupled with micro-electron capture detector and cavity ring-down spectroscopy were adopted in the verification process. Four PSGMs in the final preparation step were used to analyse unknown background and filtered air samples at the ambient level. An expanded uncertainty relative to the gravimetric amount fraction was found to be 0.02 %. Results show that the background air samples lie within the calibration range with 329 to 330 nmol mol−1 obtained and 135 nmol mol−1 obtained for filtered air sample.

p-xylene is a harmful volatile organic compound that needs to be tested for indoor air quality detection. We report on the sensing characteristics of CuO and Zn doped CuO nanoplatelets of various concentrations that were prepared by hydrothermal synthesis, against nine different gases. These CuO and Zn based nanoplatelets were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence emission and vibrating sample magnetometer measurements. CuO and 0.1 at. % Zn doped CuO samples were most sensitive and selective to p-xylene gas with relatively high responses (Ra/Rg ratio) of about 42 and 53 at an operating temperature of 150 °C, respectively. These responses were about six times higher compared to the other 8 tested interfering gases. All these samples further exhibited a paramagnetic behaviour at room temperature, due to small traces of point defects, such as oxygen vacancies. Both these sensor materials did not show green luminescence at room temperature that is normally associated with oxygen vacancies. However, temperature dependent photoluminescence (PL) measurements for the 0.1 at. % Zn doped CuO showed broad visible emission, including green luminescence, which increased with temperature up to 150 °C and coincided with the gas sensing temperature. The pure CuO, however, showed a rapid quenching in PL emission with an increase in the temperature up to 150 °C. Nevertheless, both pure CuO and 0.1 at. % Zn doped CuO based sensors were highly sensitive to the p-xylene gas. The mechanism associated to the xylene superior sensing was considered in terms of point defects and surface area as active sites for adsorption of gas molecules.

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).

Real-time detection of n-propanol vapour is important in human health protection. Thus, we report on the influence of large surface area and crystallinity of p-type NiO nanostructures on propanol sensing characteristics. Structural properties of p-type NiO were investigated by using an X-ray diffractometer and the morphology was analysed by scanning electron microscopy. A Brunauer-Emmett-Teller confirmed the surface area and porosity of the NiO nanostructures. The elemental composition and existences of potential defects were investigated by X-ray photoelectron spectroscopy and photoluminescence, respectively. A systematic comparison study was performed on the annealed nanostructures prepared by hexamethylenetetramine and urea precursors by subjecting all the sensors to volatile organic compounds like ethanol, propanol, toluene, and other reducing and oxidizing gases like methane and nitrogen dioxide using different controlled gas concentrations and operating temperatures. The NiO based sensor derived from the urea precursor and calcined at 400 °C, exhibited a significantly improved sensing response (Ra/Rg ratio of 1.59), higher sensitivity (0.02 ppm−1), ultra-low theoretical detection limit (20 ppb) and excellent selectivity towards 60 ppm propanol vapour Additionally, the fundamental sensing mechanism was elucidated. The high sensitivity and selectivity of NiO based sensors for the detection of propanol is promising.

Main text CCQM-K118 was an international key comparison on natural gas composition with two types of gases, i.e., a low calorific hydrogen-enriched natural gas and a high calorific LNG type of gas. There were 14 participating laboratories. The traveling standards (i.e., 14 mixtures each) were obtained from an external source and checked for homogeneity and stability before and after the participants' measurements at the two coordinating laboratories. The data evaluation was performed using a consensus value and a laboratory effect model. The results of the participants were benchmarked against a key comparison reference value computed from the largest consistent subset (LCS) of the submitted results, adjusted for the differences between the travelling standards. For the first time in a key comparison in gas analysis, the model included a term to account for excess variability in the LCS. Most of the participants reported one or a few (slightly) discrepant results. Partly this is due to the heterogeneity and heteroscedasticity of the datasets. In all, the results in this key comparison demonstrate the good comparability of the national measurement standards for natural gas composition maintained by the participating NMIs. 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). 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 Hazardous air pollutants (HAPs) are toxic air pollutants that are mainly emitted from man-made sources such as chemical processes, automobiles, power plants, and refineries, building materials, and cleaning solvents. Some HAPs are emitted from wildfires and chemical leak. HAPs are regulated and monitored to protect public health and the environment because they cause severe health effects such as cancer, damages to the immune system, reproductive and respiratory health problems. For this supplementary comparison, a multicomponent mixture of HAPs in nitrogen has been chosen at an amount-of-substance fraction level of 100 nmol mol-1 that is closer to their emission levels from their sources. The supplementary comparison is designed to underpin calibration capabilities using HAPs gas mixtures that are prepared gravimetrically as transfer 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 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).

ZnO nano-rods and flower-like structures have been successfully synthesized by the hydrothermal process. These nanostructures were annealed at various temperatures (210, 310, 510, and 710 °C) both in air and vacuum (~10−4 mbar) for 1h and subsequently allowed to cool down slowly or rapidly. These structures were subsequently characterised by various techniques for structure and morphology. Laser photoluminescence spectroscopy performed with a continuous He–Cd laser chopped at 120 Hz and spectra were collected three times to study the emission stability over time. The un-annealed ZnO exhibited a very broad-band of defect related emission due to oxygen vacancies with the exciton recombination completely suppressed. These defect emissions were unstable and degraded under ultraviolet laser excitation, reducing in intensity after each emission measurement. Interestingly, annealing these ZnO samples in air together with thermal quenching significantly improved both the exciton emission and these defect-related emissions, thereby improving the overall emission stability including the green luminescence. The liquefied petroleum gas (LPG) sensing performance has been examined. The ZnO nanostructure with stable green luminescence has been found to exhibit the highest sensing response of about 80 at 200 °C low operating temperature compared to the other nanostructures. This showed a clear link between the green luminescence stability and LPG sensing properties. Therefore, the main innovation of this work is to link the stability of oxygen vacancies to the LPG detection and response and mechanical properties of these ZnO nanostructures, contrary to previous studies which this part is sought. The ZnO sensor further showed an excellent reproducibility for long-term stability, linear dependence, low detection limit, and higher selectivity towards LPG as compared to other interference gases (i.e. NH3, C2H2, H2, and CO2). The response and recovery times were as 400s and 100s, respectively. The sensitivity and stability of the samples towards LPG were also tested. In addition, the mechanical-stress improved sensor proved to be resilient and reliable even after subjected to harsh humid environment of ultra-violet light irradiation of 8 h in air.

Benzene, toluene, ethylbenzene, o-xylene, m-xylene, and styrene (subsequently referred to gas BTEX) are volatile organic compounds emitted from gasoline, fossil fuel combustion, paints, rubber products, and adhesives. Exposure to BTEX can make adverse health effects on humans. Therefore, BTEX in both ambient and indoor air is regulated and monitored to protect public health. For this supplementary comparison, a multicomponent mixture of BTEX in nitrogen has been chosen at an amount-of-substance fraction level of 100 nmol mol−1 that is more close to their emission levels from new buildings and construction materials. The supplementary comparison is designed to underpin calibration capabilities using BTEX gas mixtures that are prepared gravimetrically as transfer 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).

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 the production and transport of fossil fuels. Therefore, it is important for NMIs to demonstrate measurement equivalence for the standard gases of CH4. This is the third comparison on methane in nitrogen or air. The first comparison is the key comparison of CCQM-K82 (ambient level methane in air) and the second comparison is the supplementary comparison of APMP.QM-S7 (2000 μmol/mol methane in nitrogen). As a supplementary comparison, the purpose of this comparison is to study the comparability of CH4 standard gas mixtures at emission level (0.05 cmol/mol - 0.5 mol/mol in nitrogen or air). Furthermore, this comparison can provide a link to APMP.QM-S7 through KRISS who participated in both previous comparisons. In this comparison, KRISS prepared gas standards and sent to participants. Each participant measured the standard on their laboratory and reported their measurement results to KRISS according to the measurement protocol. This report describes the results of a supplementary comparison for methane in nitrogen at 2000 μmol/mol. 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).

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).

The gas metrology laboratory of the National Metrology Institute of South Africa has developed methodology for the gravimetric preparation of corrosive gas mixtures such as nitric oxide (NO) in nitrogen, as well as sulphur dioxide (SO2) in nitrogen or synthetic air. Fourier transform infrared (FTIR) spectroscopy has been used to analyse for trace and ultra trace levels of infrared active gaseous species, such as NO, nitrogen dioxide and SO2 that are difficult to analyse by other means. These corrosive gas mixtures are also analysed using gas chromatography with pulsed helium ionisation detection to complement the work done using FTIR with infrared active impurities. A comparison between the techniques of FTIR, gas chromatography and non-dispersive infrared spectroscopy for corrosive gas analysis is also presented.

The trace detection of carbon monoxide (CO), methane (CH4) and carbon dioxide (CO2) by gas chromatography with flame ionisation detection (GC-FID) can be enhanced by paying attention to several practical aspects of the measurement process. Choosing the appropriate column material, column conditioning, sample loop size, methaniser temperature, detector temperature, flow rate, back-pressure regulation and peak integration method can all affect the repeatability of peak areas of very small peaks. The relative effect of each of these variables is discussed in the context of achieving simultaneous detection of CO, CH4 and CO2 in nitrogen in the low nmol/mol range.

As part of the on-going key comparison BIPM.QM-K1, a comparison has been performed between the ozone national standard of South Africa maintained by the National Metrology Institute of South Africa (NMISA) and the common reference standard of the key comparison, maintained by the Bureau International des Poids et Mesures (BIPM), via a transfer standard maintained by the National Institute of Standards and Technology (NIST). The instruments have been compared over a nominal ozone amount-of-substance fraction range of 0 nmol/mol to 500 nmol/mol. 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).

Noble gases are one of the key elements used in the various processes of the bulbs industry, automotive industry, space industry, lasers industry, display industry as well as the semiconductor industry. Considering continuous growth, the provision of a reliable standard is required for those industries to improve their productivity. In this report, a result of the key comparison, CCQM-K113: noble gas mixture, is presented. Nominal amount-of-substance fractions of argon, neon, krypton, and xenon in helium are 20, 10, 2, and 1 cmol/mol, respectively. 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 capability of preparing Primary Standard gas Mixtures (PSMs), performing 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 subsequent key comparison is classified as a track B key comparison, which means that the results of this key comparison can be used to underpin calibration and measurement capabilities for propane under the default scheme. The artefact was a binary mixture 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 result of the participating laboratory is consistent with the key comparison reference value within the respective expanded uncertainties and deviates less than 0.1 %. 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 a track A key comparison, which means that the results of this key comparison can be used to underpin calibration and measurement capabilities using the flexible scheme, and for propane under the default scheme. 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 but one are within ± 0.2 % 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).

The results of the first pilot study designed to evaluate the level of comparability of measurements of nitrogen dioxide (NO2) mole fractions in nitrogen based on measurement procedures that rely on FT-IR spectroscopy as an absolute method of quantification with the traceability of measurement results to line strength data are reported. Participants were required to report measurement results using FT-IR for the gas standard (nominal mole fraction of 10??mol/mol NO2 in nitrogen) received from the BIPM as part of the CCQM-K74 exercise. In addition, they were required to provide infrared spectra and instrument parameter information to enable a recalculation of their results by the BIPM's, using only its own synthetic spectra calibration procedure with values traceable to the line parameters contained in HITRAN 2004. The relative standard uncertainties based on FT-IR measurements reported by participating laboratories ranged from 0.6% to 4.3%. The relative standard uncertainty of the reference value for each gas standard was 0.4%, as determined during the CCQM-K74 exercise. Of the ten results submitted, only five agreed with the reference value within their expanded uncertainties. Furthermore, major contributions to the uncertainty of FT-IR measurements arose from the optical path length measurements and the uncertainty that could be attributed to line strength data from the HITRAN molecular database. The inclusion of these uncertainty contributions was estimated by the BIPM to result in achievable relative standard uncertainties of 3.4% for its FT-IR measurements using synthetic spectra calibration procedures. Finally the recalculation of the participants' results by the BIPM using the laboratories' submitted experimental characteristics and infrared spectra showed good agreement with the submitted results, indicating that the calculation algorithms were not in themselves a major reason for the spread of results. 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.

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).

This pilot study compares the performance of participants in analyzing gas mixtures of nitrogen dioxide in nitrogen by comparison with in-house gravimetric standards using Fourier transformed infrared spectroscopy (FT-IR). In this study the same gas mixtures were used as in the key comparison CCQM-K74, which was designed to evaluate the level of comparability of National Metrology Institutes' measurement capabilities for nitrogen dioxide (NO2) at a nominal mole fraction of 10 µmol/mol. In the comparison CCQM-K74 most of the participants used chemiluminescence, with a small number using UV absorption or FT-IR spectroscopy, and thus it is of interest to improve understanding of the comparative performance of these techniques because they do not exhibit any cross-sensitivity to nitric acid (HNO3), which was known to be present in the mixtures used for the comparison. The results of this pilot study indicate good consistency and a level of agreement similar to that reported in the comparison CCQM-K74, demonstrating that FT-IR can be operated as a comparison method when calibrated with appropriate gas standards and can achieve similar measurement uncertainties to chemiluminescence and UV absorption techniques. An additional pilot study, CCQM-P110-B2, was conducted on the same gas mixtures in parallel with this pilot study. The second study addressed FT-IR spectroscopy when used to measure the gas mixtures with respect to reference spectra. The results of this second study will be reported elsewhere. 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.

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).

This key comparison was performed to demonstrate the capability of NMIs to analyse the purity of methane for use as a source gas in the preparation of standard gas mixtures. This capability is an essential requirement for the preparation of accurate standards of natural gas and some other fuels. Since it is difficult to carry out a comparison with individual samples of pure gas, the sample for this comparison was a synthetic mixture of high purity methane with selected added impurities of nitrogen, argon, carbon dioxide and ethane. These mixtures were prepared by a gas company as a batch of 10 cylinders and their homogeneity and stability were evaluated by NMIJ. The KCRVs for the four different analytes in this key comparison are based on a consensus of values reported by participants. The uncertainties in the degrees of equivalence were calculated by combining the reported uncertainties with the homogeneity of the samples and the uncertainty of the KCRV. The results submitted are generally consistent with the KCRV within the estimated uncertainties. Finally, this comparison demonstrates that the analysis of nitrogen, argon, carbon dioxide and ethane in methane at amount fractions of 1 µmol/mol to 5 µmol/mol is generally possible with an uncertainty of 5% to 10%. 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).