Advancing traceability in atmospheric ammonia measurements
Accurate monitoring of atmospheric ammonia (NH₃) remains a significant challenge in air quality assessment due to the limited availability of stable and SI-traceable reference gas mixtures at environmentally relevant concentration levels. This scientific publication presents the development and validation of a dynamic reference gas generator capable of producing ammonia reference mixtures in the nanomole-per-mole range, enabling reliable calibration of analytical instruments used in ambient air monitoring networks. The study, carried out through collaboration between European National Metrology Institutes, including LNE (France) and METAS (Switzerland), addresses critical metrological challenges related to adsorption effects, instability at low concentrations, and the lack of measurement comparability across monitoring infrastructures.
A metrological approach based on permeation technology
The developed system combines permeation tube technology with controlled dynamic dilution stages, allowing the generation of stable NH₃ reference gas mixtures covering concentration ranges from 1 to 400 nmol/mol. Temperature-controlled permeation sources, high-precision mass flow controllers, and SI-traceable calibration procedures ensure accurate determination of emission rates and associated uncertainty budgets. The methodology enables the production of reference mixtures with expanded uncertainties typically between 1% and 2%, representing a substantial improvement for atmospheric measurements at trace concentration levels. Long-term stability investigations confirmed consistent permeation behaviour over extended operational periods, demonstrating the suitability of permeation-based reference sources for routine calibration activities within national air quality monitoring networks. The study further highlights the importance of emission stability, thermal control, and reproducibility of permeation devices as key parameters for achieving metrological performance compatible with modern environmental monitoring requirements.
Validation and impact on air quality monitoring
The calibration methodology was validated through bilateral comparison experiments between LNE and METAS using advanced spectroscopic ammonia analyzers. The results demonstrated strong agreement between independently generated reference mixtures, confirming improved measurement traceability and comparability. By enabling reliable calibration of NH₃ analyzers, the developed approach contributes to more accurate assessment of atmospheric emissions and supports harmonized environmental monitoring practices across Europe. This work represents an important advancement in metrological infrastructure for air quality monitoring, strengthening confidence in ammonia measurements used for environmental regulation, emission control strategies, and climate-related studies.
Technological relevance
The results confirm the central role of high-stability permeation technologies and dynamic reference gas generation in ensuring SI traceability at very low concentration levels. Such developments underline the growing importance of collaboration between national metrology institutes and industrial technology providers in advancing next-generation calibration solutions for atmospheric monitoring applications.
