Preprints
https://doi.org/10.5194/amt-2022-6
https://doi.org/10.5194/amt-2022-6

  13 Jan 2022

13 Jan 2022

Review status: this preprint is currently under review for the journal AMT.

Air pollution monitoring: Development of ammonia (NH3) dynamic reference gas mixtures at nmol/mol levels for improving the lack of traceability of measurements

Tatiana Macé1, Maitane Iturrate-Garcia2, Céline Pascale2, Bernhard Niederhauser2, Sophie Vaslin-Reimann1, and Christophe Sutour1 Tatiana Macé et al.
  • 1Department of Gas Metrology, Laboratoire National de Métrologie et d'Essais LNE, Paris Cedex 15, 75724, France
  • 2Department of Chemical and Biological Metrology, Federal Institute of Metrology METAS, Bern-Wabern, CH-3003, Switzerland

Abstract. 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.

Tatiana Macé et al.

Status: open (until 18 Feb 2022)

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Tatiana Macé et al.

Tatiana Macé et al.

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Short summary
LNE developed, with the company 2M PROCESS, a gas reference generator to generate dynamically NH3 reference gas mixtures in air at very low amount fractions between 1 and 400 nmol/mol. The procedure defined by LNE for calibrating NH3 analyzers used for monitoring air quality guarantees relative expanded uncertainties lower than 2 % on this measurement range. The results of a comparison organized between METAS and LNE allowed to validate both LNE’s reference generator and calibration procedure.