EMRP-ENV55: Metrology for ammonia in ambient air (MetNH3)

• Forschungsstelle: METAS
• Projektnummer: F-5232.30041
• Projekttitel Englisch: EMRP-ENV55: Metrology for ammonia in ambient air (MetNH3)

Schlüsselwörter (Englisch)

Ammonia, agricultural emissions, traceability, calibration standards, biodiversity measures, instrumentation, environmental control, air quality measurements

Kurzbeschreibung (Englisch)

The measurement of ammonia in air is a sensitive and priority issue due to its harmful effects on human health and ecosystems. The European Directive 2001/81/EC on national emission ceilings for certain atmospheric pollutants (NEC) regulates ammonia emissions in the Member States; however, there is a lack of regulation regarding the analytical techniques to use, the maximum allowed uncertainty, the quality assurance and quality control (QC/QA) procedures and the metrological traceability infrastructure to underpin ammonia measurements. Discrepancies among European NMIs for primary ammonia reference gas standards and measurement techniques far above ambient air levels (30 to 50 μmol/mol) jeopardise not only the credibility of instrumental performance due to poor calibration but also the scientific value of extensive ambient air monitoring by national networks and the international exchange of scientific data.
This joint reserach project aims to develop the metrological traceability for the measurement of ammonia in air from the level of primary gas mixtures and instrumental standards to the field level.

This project is part of the European Metrology Research Programme (EMRP, http://www.euramet.org/index.php?id=emrp); it is partly funded by the European Union on the basis of Decision No 912/2009/EC.

A more detailed description of the project may be found in the encloed publishable summary.

Zugehörige Dokumente

• ENV55_Publishable_JRP_Summary.pdf [PDF] 201 kB

Projektziele (Englisch)

The JRP addresses the following scientific and technical objectives:

• WP1: To develop traceable preparative calibration standards (including portable) at ambient levels based on existing methods. This includes solving the problem of existing discrepancies between gas standards (e.g. CCQM-K46). The production/purification of a high purity matrix gas with validated levels of ammonia is a prerequisite for the preparation of static and dynamic reference standard mixtures. In addition, to produce guidance for the proper use of certified reference materials and sampling in field measurements.
• WP2: To develop a transportable optical transfer standard calibration device for calibration and validation of instruments currently used in field measurements of ammonia. In addition, to evaluate the applicability of open path measurement techniques as optical transfer standards. Finally, to characterise metrological performance of extractive and open-path laser spectrometric systems.
• WP3: To validate a controlled test chamber facility and an installation for proficiency tests to perform comparisons of different instruments and measurement methods for ammonia. In addition, to evaluate existing measuring instruments for traceable measurement of ammonia at ambient molar fractions (0.5 to 500 nmol/mol) under real air and artificial conditions, and to evaluate and compare results produced with field measuring methods, to develop suitable sampling methods in order to promote long-term efficiency monitoring of ammonia reduction measures. Finally, to provide validated measurement tools to enable EU SMEs developing new monitoring technologies to deliver improved instrumentation to the market.

METAS coordinates the project and is involved in WP1 and WP3.

Abstract (Englisch)

Adsorption/desorption experiments:
Tests of the effects of adsorption and desorption were carried out on different surfaces of materials widely used for the preparation of reference gas mixtures (e.g. PFA, PTFE, stain-less steel). In a second step, the influence of humidity on the adsorption of NH3 in the preparation of reference gas mixtures was assessed. It was concluded that adsorption on stainless steel surfaces in contact with NH3 can be minimised by up to 90 % when a silica-based coating (SilcoNert2000®, SilcoTek Inc.) is applied on gas-wetted surfaces. The results were implemented in the construction of the mobile reference gas generator ReGaS1 and in the dynamic generation of reference gas mixtures. Thus, SilcoNert2000® has been applied to all stainless steel surfaces in contact with NH3 as adsorption on coated surfaces are reduced by 90 % compared to uncoated stainless steel surfaces. The comparison of polymer (PFA, PTFE) to uncoated stainless steel surfaces yields similar results.

Adsorption of NH3 is reduced with increasing levels of humidity yet, at ambient levels of humidity, NH3 is dissolved in water H2O. Therefore, it is advised to use dried air or nitrogen N2 for the generation of reference gas mixtures, despite the fact that for spectroscopic applications, humid matrix gas is preferred.

Development and construction of a mobile reference gas generator ReGaS1:
A mobile instrument for the dynamic generation of SI-traceable NH3 reference gas mixtures has been planned and realised (ReGaS1). ReGaS1 is a development beyond the state of the art as it allows for the on-site permeation and dynamic dilution over two dilution steps and thus for the dynamic generation of NH3 at ambient amount fractions (0.5 – 500 nmol mol-1) with UNH3 ≤ 3 % (k = 2). Validation test have been conducted and the characterisation results are very promising.

Stability of temperature and pressure yield a constant mass loss of the permeation unit (UqmC ≤ 1 %, (k = 2). Mass flow rates are modifiable within seconds and thus allow for readily changing the generated amount of substance fractions over two dilution steps covering the entire range of atmospheric amount fractions (0.5 – 500 nmol/mol) with UNH3 ≤ 3 % (k = 2). The stabilisation time required to measure stable values is primarily depending on the adsorption on the surfaces of the comparator to be calibrated.

The prerequisites for ReGaS1 in terms of amount of substance fractions as well as uncertainty (0.5 – 500 nmol/mol at UNH3 ≤ 3 %, (k = 2)) could be met. The user feedbacks were positive throughout with particular emphasis on the user friendliness and the vast flexibility in the generated amount fractions.

Good Practice Guide:
The document is going to be compiled and made available to end-users with a delay of 4-5 months in the course of summer 2017.

Umsetzung und Anwendungen (Englisch)

The findings from adsorption experiments and from developing and constructing ReGaS1 could be applied in the construction of another two reference gas generators (ReGaS2 und ReGaS3), particularly regarding the software functionality.

An exact copy of ReGaS1 has been commissioned by the FOEN for Empa’s air quality department where the device is to be applied for calibrating the air quality instruments of NABEL, e.g. for nitrogen dioxide NO2.

The infrastructure developed by METAS in the framework of MetNH3 is to be applied for calibrations and intercomparisons as well as in the EMPIR project MetNO2. The first calibration campaign is planned for autumn 2017, CCQM K-117 (NH3 in N2) and CCQM K74:2018 (NO2 in N2) are planned for 2018.

Publikationen / Ergebnisse (Englisch)

Andrea Pogány et al.: A metrological approach to improve accuracy and reliability of ammo-nia measurements in ambient air. Meas. Sci. Technol. (2016) 27 115012.

Marsailidh M. Twigg et al.: An assessment of the applicability of ambient NH3 instrumenta-tion under field conditions. Proceedings of the 7th International Nitrogen Initiative Conference (2016).

Andrea Pogány et al.: Metrology for ammonia in ambient air – concept and first results of the EMRP project MetNH3. Procedings of the 17 International Congress of Metrology (2015).

Daiana Leuenberger, Bernhard Niederhauser: Start des Projektes für rückführbare Ammoni-akmessungen. MetInfo 2/2014.