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Despite its crucial role in the Earth's radiative balance, upper air water vapor (H2O) is still lacking accurate, in-situ, and continuous monitoring. Especially in the upper troposphere-lower stratosphere (UTLS), these measurements are notoriously difficult, and significant discrepancies were reported in the past between different measuring techniques. Here, we present a laboratory validation of a recently developed mid-IR quantum-cascade laser absorption spectrometer for balloon-borne measurements of H2O in the UTLS (ALBATROSS). The validation was performed using SI-traceable reference gas mixtures generated based on the permeation method and dynamic dilution. The accuracy and precision of ALBATROSS were evaluated at a wide range of pressures (30‒250 mbar) and H2O amount fractions (2.5‒35 ppm), representative of the atmospheric variability of H2O in the UTLS. Best agreement was achieved by implementing a quadratic Speed-Dependent Voigt Profile (qSDVP) line-shape model in the spectroscopic retrieval algorithm. The molecular parameters required by this parameterization were determined empirically using a multi-spectrum fitting approach over different pressure conditions. ALBATROSS achieves an accuracy better than ±1.5 % with respect to the SI-traceable reference at all investigated pressures and H2O amount fractions. The measurement precision was found to be better than 30 ppb (i.e., 0.1 % at 35 ppm H2O) at 1 s resolution for all conditions. This performance, unprecedented for a balloon-borne hygrometer, demonstrates the exceptional potential of mid-IR laser absorption spectroscopy as a new reference method for in-situ measurements of H2O in the UTLS.

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.

Environmental observations of essential climate variables (ECVs) and related quantities made by satellites and in situ observational networks are used for a wide range of societal applications. To identify a small climate trend from an observational record that is also sensitive to changes in weather, to seasonal effects and to geophysical processes, it is essential that observations have a stable basis that holds for multiple decades, whilst still allowing for changes in the observation instrumentation and operational procedures. To achieve this, all aspects of data collection and handling must be underpinned by robust quality assurance. The resultant data should also be linked to a common reference, with well-understood uncertainty analysis, so that observations are interoperable and coherent; in other words, measurements by different organisations, different instruments and different techniques should be able to be meaningfully combined and compared. Metrology, the science of measurement, can provide a critical role in enabling robust, interoperable and stable observational records and can aid users in judging the fitness-for-purpose of such records. In addition to Global Climate Observing System (GCOS) monitoring principles, metrology’s value, and the role of National Metrology Institutes (NMI) in observations, has been recognised in initiatives such as the Quality Assurance Framework for Earth Observation (QA4EO) established by the Committee on Earth Observation Satellites (CEOS) and in the implementation plans of the World Meteorological Organization’s (WMO’s), Global Atmosphere Watch and the European Ocean Observing System. The European Association for National Metrology Institutes (EURAMET) has recently created the “European Metrology Network (EMN) for Climate and Ocean Observation” to support further engagement of the expert communities with metrologists at national metrology insitutes and to encourage Europe’s metrologists to coordinate their research in response to community needs. The EMN has a scope that covers metrological support for in situ and remote sensing observations of atmosphere, land and ocean ECVs (and related parameters) for climate applications. It also covers the additional economic and ecological applications of ocean Essential Ocean Variable (EOV) observations. It is the European contribution to a global effort to further enhance metrological best practice into such observations through targeted research efforts. In late 2019 and early 2020 the EMN carried out a survey to identify the need for metrology within the observational communities and held a webinar workshop to prioritise the identified needs. Here we present the results of the survey and discuss the role that metrology can play in the climate observing system of the future.

A critical issue for the long-term monitoring of atmospheric trace gases is precision and accuracy of the measurement systems employed. Both measuring and preparing reference gas mixtures for trace gases are challenging due to, for example, adsorption and desorption of the substances of interest on surfaces; this is particularly critical at low amount fractions and/or for reactive gases. Therefore, to ensure the best preparation and measurement conditions for trace gases in very low amount fractions, usage of coated materials is in demand in gas metrology and atmospheric measurement communities. This study focuses on testing potential adsorption and desorption effects for different materials or coatings that are currently used or that may be relevant in the future for the measurements of greenhouse gases. For this study we used small volume chambers designed to be used for adsorption studies. Various materials with or without coatings were loaded into the small cylinder to test their adsorption and desorption behavior. We used the aluminum cylinder as the measurement chamber and glass, aluminum, copper, brass, steel and three different commercially available coatings as test materials. Inserting the test materials into the measurement chamber doubles the available geometric area for the surface processes. The presented experiments were designed to investigate the pressure dependency of adsorption up to 15 bar and its temperature dependency up to 80 ∘C for the test materials placed in the measurement chamber. Here, we focused on the species CO2, CH4, CO and H2O measured by a cavity ring-down spectroscopy analyzer. Our results show that the materials currently used in atmospheric measurements are well suited. The investigated coatings were not superior to untreated aluminum or to stainless steel at the tested pressure ranges, whereas under changing temperature aluminum showed better performance for CO2 ( µmol mol−1 change in measured amount fractions) than stainless steel (>0.1 µmol mol−1). To our knowledge, this study is one of the first attempts to investigate surface effects of different materials in such a setup for the abovementioned gases.

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).

Monoterpenes play an important role in atmospheric chemistry due to their large anthropogenic and biogenic emission sources and high chemical reactivity. As a consequence, measurements are required to assess how changes in emissions of monoterpenes impact air quality. Accurate and comparable measurements of monoterpenes in indoor and outdoor environments require gaseous primary reference materials (PRMs) that are traceable to the international system of units (SI). PRMs of monoterpenes are challenging to produce due to the high chemical reactivity and low vapour pressures of monoterpenes and also their propensity to convert into other compounds, including other terpenes. In this paper, the long-term stability of gravimetrically prepared static monoterpene PRMs produced in differently passivated cylinders, including sampling canisters, was assessed. We demonstrate that static PRMs of multiple monoterpenes can be prepared and used as a suitable long-term standard. For the first time the effect of cylinder pressure and decanting from one cylinder to another on the chemical composition and amount fraction of monoterpenes was also studied. Gravimetrically prepared PRMs of limonene in high pressure cylinders were compared to a novel portable dynamic reference gas generator based on dilution of pure limonene vapour emitted from a permeation tube.

Volatile organic compounds (VOCs) in gas mixtures at trace level (nmol/mol) are routinely measured by chemical and biochemical laboratories as climate indicators, indoor air quality pollutants from building materials emissions, contaminants in food and beverages, and biomarkers in body fluids (blood, urine, breath) of occupational exposure or human diseases. Current analytical instruments used for measurements are gas chromatographs equipped with various injector and detector configurations. The assurance of measurement quality is done by using a huge amount of certified liquid VOC standard solutions (or gaseous VOC standard cylinders) with multiple dilutions to reach the required trace level. This causes high standard uncertainty in instrument calibrations, high cost, and high consumption of analysis and laboratory personal time. In this paper, we present the implementation of portable generators producing VOC gas standards at trace level for automatic and direct calibration of VOC detectors employed in various contexts, removing the need for preparation of matrix calibration standards in cylinders. Two compact devices in-house developed by two national metrology institutes-the Istituto Nazionale di Ricerca Metrologica (INRIM) and the Federal Institute of Metrology (METAS)-are here used to dynamically generate reference gas mixtures in an SI traceable way. The two devices are based on different technologies: diffusion and permeation, for INRIM and METAS, respectively. A metrological characterization is given and the practical implementation at chemical and biochemical laboratories is discussed. Graphical abstract Onsite calibration with transportable generation system with similar performances to primary laboratory devices.

EURAMET, the association responsible for coordinating the integrated metrology community in Europe, has recently established European Metrology Networks (EMNs) to support its aim to bring high-quality scientific research and coordinated metrological services to meet the rapidly advancing needs of different stakeholders for metrology. The EMN for Climate and Ocean Observation is one of the initial six EMNs and has been set up as a European coordination body to support the global effort to bring rigorous metrological discipline into the observations that underpin our understanding of the climate and the oceans. This paper describes the network, its activity so far, and its plans.

Main text At the highest metrological level, ammonia gas standards are commonly prepared gravimetrically as Primary Standard Mixtures or using a dynamic standard. This international key comparison addressed the measurement of the amount fraction ammonia in nitrogen, to support calibration and measurement services for mainly environmental applications. The nominal amount fraction was 14 μmol mol-1. The results in this Track C key comparison on the composition of biogas are generally good. 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).

Monoterpenes play an important role in atmospheric chemistry due to their large anthropogenic and biogenic emission sources and high chemical reactivity. As a consequence, measurements are required to assess how changes in emissions of monoterpenes impact air quality. Accurate and comparable measurements of monoterpenes in indoor and outdoor environments require gaseous primary reference materials (PRMs) that are traceable to the international system of units (SI). PRMs of monoterpenes are challenging to produce due to the high chemical reactivity and low vapour pressures of monoterpenes and also their propensity to convert into other compounds, including other terpenes. In this paper, the long-term stability of gravimetrically prepared static monoterpene PRMs produced in differently passivated cylinders, including sampling canisters, was assessed. We demonstrate that static PRMs of multiple monoterpenes can be prepared and used as a suitable long-term standard. For the first time the effect of cylinder pressure and decanting from one cylinder to another on the chemical composition and amount fraction of monoterpenes was also studied. Gravimetrically prepared PRMs of limonene in high pressure cylinders were compared to a novel portable dynamic reference gas generator based on dilution of pure limonene vapour emitted from a permeation tube.

The environmental impacts of ammonia (NH3) in ambient air have become more evident in the recent decades, leading to intensifying research in this field. A number of novel analytical techniques and monitoring instruments have been developed, and the quality and availability of reference gas mixtures used for the calibration of measuring instruments has also increased significantly. However, recent inter-comparison measurements show significant discrepancies, indicating that the majority of the newly developed devices and reference materials require further thorough validation. There is a clear need for more intensive metrological research focusing on quality assurance, intercomparability and validations. MetNH3 (Metrology for ammonia in ambient air) is a three-year project within the framework of the European Metrology Research Programme (EMRP), which aims to bring metrological traceability to ambient ammonia measurements in the 0.5-500 nmol mol-1 amount fraction range. This is addressed by working in three areas: (1) improving accuracy and stability of static and dynamic reference gas mixtures, (2) developing an optical transfer standard and (3) establishing the link between high-accuracy metrological standards and field measurements. In this article we describe the concept, aims and first results of the project.

The measurement of trace amounts of water in process gases is of paramount importance to a number of manufacturing processes. Water is considered to be one of the most difficult impurities to remove from gas supply systems and there is strong evidence that the presence of water contamination in semiconductor gases has a measurable impact on the quality and performance of devices. Consequently, semiconductor manufacturers are constantly reducing target levels of water in purge and process gases. As the purity of gases improves, the problem of quantifying contamination and ensuring that the gases are within specification at the point of use becomes more challenging. There are several established techniques for detecting trace water vapour in process gases. These include instruments based on the chilled mirror principle which measures the dew-point of the gas and the quartz crystal adsorption principle which measures the adsorption of water vapour into a crystal with a hygroscopic coating. Most recently, spectroscopic instruments such as those employing cavity ring-down spectroscopy (CRDS) have become available. The calibration of such instruments is a difficult exercise because of the very limited availability of accurate water vapour standards. This CCQM key comparison aims to assess the analytical capabilities of laboratories for measuring the composition of 10 μmol mol-1 water vapour in nitrogen. KEY WORDS FOR SEARCH Metrology, traceability, water vapour, process gas, advance manufacturing 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).

Dans le cadre du Programme de Recherche Europeen en Metrologie (EMRP), un projet de trois ans a debute en juin 2014 avec l’objectif d’ameliorer la comprehension et la tracabilite metrologique des mesures d’ammoniac (NH3) ambient, dans le domaine 0.5 - 500 nmol/mol. Les trois tâches principales de ce projet sont 1) d’ameliorer l’exactitude et la stabilite de melanges de gaz de reference statiques et dynamiques, 2) de developper un etalon de transfert optique et 3) d’etablir un lien entre les standards metrologiques de haute precision et les mesures de terrain. Les resultats attendus de ce projet vont ameliorer l’exactitude et la fiabilite des estimations d’emissions et ainsi aider a l’evaluation de l’efficacite des mesures de reduction d’emission prescrites par les reglementations internationales. Dans cette publication nous decrivons le concept, les objectifs et les premiers resultats du projet.

The evaluation results of the metrological performance of a dilution and a permeation standard for generating SI-traceable calibration gas mixtures of NO, SO2 and NO2 for ambient air measurements are presented. The composition of the in situ produced reference gas mixtures is calculated from the instantaneous values of the input quantities of the generating standards. In a measurement comparison, the calibration and measurement capabilities of five laboratories were evaluated for the three analytes at limiting amount of substance fractions in ambient air between 20 and 150 nmol mol−1. For the upper generated reference values the target relative uncertainties of ≤2% (for NO and SO2) and ≤3% (for NO2) for evaluating the laboratory results were fulfilled in 12 out of 13 cases. For the analytical results seven out of nine laboratories met the criteria for the upper values for NO and NO2, for SO2 it was one out of four. From the negative degrees of equivalence of all NO2 comparison results it was supposed that the permeation rate of NO2 through the FEP polymer membrane of the permeator was different in air and N2. Subsequent precision permeation measurements with various carrier gases revealed that the permeation rate of NO2 was ≈0.8% lower in synthetic air compared to N2. With the corrected NO2 reference values for air the degrees of equivalence of the laboratory results were improved and closer to be symmetrically distributed.

The European Directive (2008/50/EC) sets up, among other things, the limit values i.e. the maximum allowed concentrations at given time average in the air, for specified pollutants. Calibration of the measurement instruments needs to be performed at regular time intervals. In the framework of an European Joint Research Programme (JRP) named Metrology for Chemical Pollutants in Air (MACPoll) one task aims to provide harmonized dilution methods for air pollutant gases at low concentration for calibration and quality control purposes. The study focuses on the reactive gases nitrogen dioxide and sulphur dioxide at concentration levels corresponding to the limit values given in the European Directive (2008/50/EC). Nitrogen oxide (NO) is studied as well as NO2 because both of them are measured simultaneously for NOx. This work consists in improving the dilution methods for generating calibration standards for SO2 , NO, NO2 at limit values and to validate them by an interlaboratory comparison.