[en] The effect of moisture on the adsorption of ammonia was systematically studied using different surface materials and humidity levels. The experimental water amount fractions varied between 6 and 18,000 µmol mol⁻¹, and the ammonia amount fraction was 400 nmol mol⁻¹. The investigated materials included plain 316L stainless steel and stainless steel cured with Dursan, SilcoNert 2000 and halocarbon wax coatings. Furthermore, Teflon (PTFE) and polyvinylidene difluoride (PVDF) polymer surfaces were studied. Dynamically diluted ammonia, test tubes prepared with the investigated materials, a commercial ammonia analyzer based on cavity ring-down spectroscopy, and a commercial dew-point transmitter were employed. The adsorption was assessed quantitatively using continuous flow conditions and real-time monitoring of the adsorption process. The ammonia adsorption was found to increase substantially in dry conditions for all the studied materials except PVDF. The increase was largest for plain stainless steel which was the most adsorbing material. The coatings applied on stainless steel decreased the adsorption significantly in dry conditions. Polymers PVDF and PTFE were the least-adsorbing materials. In water amount fractions between 1000 and 10,000 µmol mol⁻¹, the ammonia adsorption was at its lowest. The adsorption increased again above 1% humidity levels.

[en] 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. (paper)