The traceable and accurate measurement of biogas impurities is essential in order to robustly assess compliance with the specifications for biomethane being developed by CEN/TC408. An essential part of any procedure aiming to determinate the content of impurities is the sampling and the transfer of the sample to the laboratory. Key issues are the suitability of the sample container and minimising the losses of impurities during the sampling and analysis process. In this paper, we review the state-of-the-art in biogas sampling with the focus on trace impurities. Most of the vessel suitability studies reviewed focused on raw biogas. Many parameters need to be studied when assessing the suitability of vessels for sampling and storage, among them, permeation through the walls, leaks through the valves or physical leaks, sorption losses and adsorption effects to the vessel walls, chemical reactions and the expected initial concentration level. The majority of these studies looked at siloxanes, for which sampling bags, canisters, impingers and sorbents have been reported to be fit-for-purpose in most cases, albeit with some limitations. We conclude that the optimum method requires a combination of different vessels to cover the wide range of impurities commonly found in biogas, which have a wide range of boiling points, polarities, water solubilities, and reactivities. The effects from all the parts of the sampling line must be considered and precautions must be undertaken to minimize these effects. More practical suitability tests, preferably using traceable reference gas mixtures, are needed to understand the influence of the containers and the sampling line on sample properties and to reduce the uncertainty of the measurement.

The first reference gas mixtures of sulfur-free natural gas odorants that are traceable to the International System of Units (SI) have been produced and their compositions validated. These mixtures, which contain methyl acrylate and ethyl acrylate at amount fractions between 1.1 and 2.1 μmol mol-1, can be used to underpin measurements of sulfur-free odorants, which are increasingly being used to odorize natural gas in transmission networks as they have less harmful properties than traditional sulfur-containing odorants. The reference gas mixtures produced have been shown to be stable in passivated aluminum cylinders for at least 8 months and have been validated (to within 6% or less) by interlaboratory measurements at three National Measurement Institutes. The stability of methyl acrylate and ethyl acrylate in gas sampling bags has been investigated, and the challenges of analyzing 2-ethyl-3- methylpyrazine, which is used as a stabilizer in sulfur-free odorants, are also briefly discussed.

In the framework of the ongoing EMRP Joint Research Project (JRP) ENG 60 “Metrology for LNG” (2014-2017), co-funded by the European Union, a number of metrological challenges associated with custody transfer and transport of LNG will be faced. The project consists of four technical work packages (WP), whereby the main objective is to reduce the measurement uncertainty of LNG custody transfer by a factor two. The focus in WP1 is the design and development of a traceable mid-scale calibration standard for LNG mass and volume flow. The goal is to provide traceable mass and volume flow calibrations up to 400 m3/h (180000 kg/h). In WP2, the emphasis is on the development and validation of a LNG sampling and composition measurement reference standard, consisting of sampler, vaporizer, gas standards, and gas chromatography (GC), which will be used to  test and calibrate commercially available LNG sampling and composition measurement systems. The priority in WP3 is given to the development and validation of a method for the determination of the methane number, including correlations based on the LNG composition and corrections for traces of nitrogen and higher hydrocarbons. Since physical properties and quantities play an important role in LNG custody transfer, WP4 comprises reference quality density measurements of LNG to validate and improve models for LNG density predictions, the uncertainty evaluation of enthalpy and calorific value calculations and the development of a novel cryogenic sensor for the simultaneous measurement of speed-of-sound and density. The present paper gives an overview of recently achieved objectives within the project and provides an outlook to future activities.

Current anthropogenic carbon dioxide emissions generate besides global warming unprecedented acidification rates of the oceans. Recent evidence indicates the possibility that ocean acidification and low oceanic pH may be a major reason for several mass extinctions in the past. However, a major bottleneck for research on ocean acidification is long-term monitoring and the collection of consistent high-resolution pH measurements. This study presents a low-power (<1 W) small sample volume (25 μL) semiconductor based fluorescence method for real-time ship-board pH measurements at high temporal and spatial resolution (approximately 15. s and 100. m between samples). A 405. nm light emitting diode and the blue and green channels from a digital camera was used for swift detection of fluorescence from the pH sensitive dye 6,8-Dihydroxypyrene-1,3-disulfonic acid in real-time. Main principles were demonstrated by automated continuous measurements of pH in the surface water across the Baltic Sea and the Kattegat region with a large range in salinity (~3-30) and temperature (~0-25 °C). Ship-board precision of salinity and temperature adjusted pH measurements were estimated as low as 0.0001 pH units.

The atmospheric environment inside and outside historical organs in several European regions is reported. In each region, comparisons were made between an instrument suffering organ pipe corrosion and an organ without reported corrosion problems. Concentrations of acetic acid (ethanoic acid), formic acid (methanoic acid), acetaldehyde (ethanal), formaldehyde (methanal) and other volatile organic compounds in the organ environment were determined using active sampling. Temperature and relative humidity were recorded. In addition, polished metal samples that mimic the material used in the historical organ pipes have been exposed in the organ wind systemsfor up to 22 months. High concentrations of acetic acid andformic acid vapours are present in the wind system of the corroded organs. Acetaldehyde and formaldehyde are also present in smaller amounts. The main source of acetic acid is the wood from which the wind system is built. In contrast, formic acid is generated in the church environment outside the wind system. The results show that the two organic acids play an important role in the atmospheric corrosion of organ pipes. It is suggested that the corrosion of lead pipes in historical organs can be effectively reduced by removing the sources of gaseous acetic acid and formic acid in the wind system and in the church environment.

Compression and upgrading of biogas to vehicle fuel generates process water, which to varying degrees contains volatile organic compounds (VOCs) originating from the biogas. The compostion of this process water has not yet been studied and scientifically published and there is currently an uncertainty regarding content of VOCs and how the process water should be managed to minimise the impact on health and the environment. The aim of the study was to give an overview about general levels of VOCs in the process water. Characterisation of process water from amine and water scrubbers at plants digesting waste, sewage sludge or agricultural residues showed that both the average concentration and composition of particular VOCs varied depending on the substrate used at the biogas plant, but the divergence was high and the differences for total concentrations from the different substrate groups were only significant for samples from plants using waste compared to residues from agriculture. The characterisation also showed that the content of VOCs varied greatly between different sampling points for same main substrate and between sampling occasions at the same sampling point, indicating that site-specific conditions are important for the results which also indicates that a number of analyses at different times are required in order to make an more exact characterisation with low uncertainty.Inhibition of VOCs in the anaerobic digestion (AD) process was studied in biomethane potential tests, but no inhibition was observed during addition of synthetic process water at concentrations of 11.6 mg and 238 mg VOC/L.

Field sensor measurements are becoming more common for environmental monitoring. Solutions for enhancing reliability, i.e. knowledge of the measurement uncertainty of field measurements, are urgently needed. Real-time estimations of measurement uncertainty for field measurement have not previously been published, and in this paper, a novel approach to the automated turbidity measuring system with an application for “real-time” uncertainty estimation is outlined based on the Nordtest handbook’s measurement uncertainty estimation principles. The term real-time is written in quotation marks, since the calculation of the uncertainty is carried out using a set of past measurement results. There are two main requirements for the estimation of real-time measurement uncertainty of online field measurement described in this paper: (1) setting up an automated measuring system that can be (preferably remotely) controlled which measures the samples (water to be investigated as well as synthetic control samples) the way the user has programmed it and stores the results in a database, (2) setting up automated data processing (software) where the measurement uncertainty is calculated from the data produced by the automated measuring system. When control samples with a known value or concentration are measured regularly, any instrumental drift can be detected. An additional benefit is that small drift can be taken into account (in real-time) as a bias value in the measurement uncertainty calculation, and if the drift is high, the measurement results of the control samples can be used for real-time recalibration of the measuring device. The procedure described in this paper is not restricted to turbidity measurements, but it will enable measurement uncertainty estimation for any kind of automated measuring system that performs sequential measurements of routine samples and control samples/reference materials in a similar way as described in this paper.

The risk of misclassifying infected individuals as healthy constitutes a crucial challenge when screening blood donors by means of immunoassays. This risk is especially challenging when the numerical results are close to the clinical decision level, i.e. in the ‘grey zone’. The concept of using measurement uncertainty for evaluating the ‘grey zone’ has previously not been systematically applied in this context. This article explains methods, models and empirical (top-down) approaches for the calculation of measurement uncertainty using results from a blood bank according to the internationally accepted GUM principles, focusing on uncertainty sources in the analytical phase. Of the different approaches available, the intralaboratory empirical approaches are emphasised since modelling (bottom-up) approaches are impracticable due to the lack of reliable model equations for immunoassays. Different methods are applied to estimate the measurement uncertainty for the Abbott Prism® HCV immunoassay. The expanded uncertainty obtained at the clinical decision level from the intralaboratory empirical approach was 36 %. The estimated uncertainty was used to set acceptance and rejection zones following the procedure set in the Eurachem guideline, emphasising the need to minimise the occurrence of false negatives.

The increased use of biogas and biomethane urgently requires that these non-conventional energy gases can be transmitted through natural gas grids and refuelling stations. The European Standardization Organisation CEN is developing specifications for green gas which supplement the specifications for natural gas. The specifications for green gas address a range of parameters not commonly covered in natural gas, such as the contents of impurities (e.g., siloxanes, ammonia, halogenated hydrocarbons, and hydrogen chloride), dust content and particles. In a collaboration between 12 European metrology institutes and 3 university groups, robust and reliable methods are developed to support these draft specifications and to enable conformity assessment. The project also deals with issues related to density, calorific value, moisture content, and the sampling of biogas. This paper gives an overview of the state-ofthe-art in green gas testing, as well as an outlook what methods need be developed.