Getting the measure of ammonia The EU has passed regulations limiting ammonia emissions in Member States, yet it remains difficult to reliably measure levels of the gas in the atmosphere. We spoke to Daiana Leuenberger, Ph.D. and Bernhard Niederhauser about the MetNH3 project’s work goal of improving the metrological infrastructure for ammonia at ambient air amount fractions A gas compound
that plays an important role in atmospheric chemistry, ammonia (NH 3) can have harmful effects on both human health and the environment. With emissions steadily increasing, accurately measuring atmospheric ammonia amount fractions is an important issue in environmental science, yet it is a major challenge. “Ammonia is very difficult to measure, as it reacts easily with other molecules, for example with water. In addition, it readily adsorbs on material surfaces,” says Daiana Leuenberger. Based at the Swiss Federal Institute for Metrology (METAS), Leuenberger is acting coordinator and one of the research scientists working on the MetNH3 project, an initiative that brought together 10 partners from national metrology institutes (NMIs) and other research institutions across Europe to address a diverse range of issues around ammonia metrology in a 3-year project that ended in May 2017. A key goal of MetNH3 was to develop SI-traceable reference material, either in the form of reference gas mixtures or as instrumental transfer standards. “It is only via traceability to a common reference, in our case to the International System of Units (SI), that measurements from one place can be made comparable to other measurements elsewhere,” says Bernhard Niederhauser, the coordinator of the project.
The project itself was organised in three technical workpackages, encompassing work in several different areas. Some partners focussed on the traceability of laser based measurement instruments, while others investigated the generation of SI-traceable reference gas mixtures (RGM) at known amount fractions of NH 3 used for the calibration of laser based spectroscopic instruments “A third focus was on the application and validation of the developed reference gas mixtures and laser based optical instruments and their
It is only via traceability to a common reference, in our case to the International System of Units (SI), that measurements from one place can be made comparable to other measurements elsewhere comparison to instruments of collaborators and stakeholders,” continues Leuenberger. “This has been realised in laboratory and field studies and allowed the assessment of difficulties associated with ammonia measurements, while we have also been able to lower their uncertainty.”
Ammonia emissions This work has been prompted in part by regulatory changes. European Directive 2016/2284/EU sets individual emission ceilings for each Member State to be met by 2020, based on the revised Gothenburg
Provisional results of the NH3 intercomparison study held in South East Scotland.
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Protocol and sets even more ambitious reduction commitments for 2030 so as to cut the health impacts of air pollution by half compared with 2005. Previous directives led to the incorporation of ammonia measurements into national air monitoring networks and considerable funds have been invested in compliance measures, with the agricultural sector a major area of interest. “The main source of ammonia emissions is the agricultural sector, due to fertilizer application and livestock production,” outlines Leuenberger.
Reducing agricultural emissions requires substantial governmental subsidies, making the assessment of their effectiveness all the more important, over both the short-term and the longer-term and with a consistent geographical resolution. The choice of site for measurements is highly important, as the majority of NH 3 is deposited close to the source. “The development in the emissions is very slow. The detection of small trends requires measurements realised with high precision and low measurement uncertainty,” continues Leuenberger. “Moreover, the datasets have to be coherent over long time periods and consistent in space in order to be comparable. Regular calibration of the instruments with SI-traceable reference gas mixtures, or by comparison to an
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