Towards a Consistent Metrological Infrastructure for Ammonia Measurements in Ambient Air: EMRP JRP MetNH3

Bernhard Niederhauser, METAS

Measuring ammonia in ambient air is a sensitive and priority issue due to its harmful effects on human health and ecosystems. In addition to its acidifying effect on natural waters and soils and to the additional nitrogen input to ecosystems, ammonia is an important precursor for secondary aerosol formation in the atmosphere. 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 certified reference material (CRM), applicable analytical methods, measurement uncertainty, quality assurance and quality control (QC/QA) procedures as well as in the infrastructure to attain metrological traceability.
As shown in a key comparison carried out in 2007, there are even discrepancies between reference materials provided by European National Metrology Institutes (NMIs) at amount fraction levels up to three orders of magnitude higher than ambient air levels.
MetNH3 (Metrology for ammonia in ambient air), a three-year project (June 2014-17) in the framework of the European Metrology Research Programme (EMRP) aimed to reduce the gap between requirements set by the European emission regulations and state-of-the-art of analytical methods and reference materials.
The overarching objective of the JRP was to achieve metrological traceability for ammonia measurements in ambient air from primary certified reference material CRM and instrumental standards to the field level. This required the successful completion of the three main goals, were assigned to three technical work packages:
1. To develop improved reference gas mixtures by static and dynamic gravimetric generation methods
Preparation and characterisation of traceable calibration standards (in pressurised cylinders as well as mobile generators) of ammonia amount fractions similar to those found in ambient air based on existing methods for other reactive analytes. The aimed uncertainty was < 1 % for static mixtures at the 10 to 100 µmol/mol level, and < 3 % for portable dynamic generators in the 0 to 500 nmol/mol amount fraction range. Special emphasis was on the minimisation of adsorption losses.
2. To develop and characterise laser based optical spectrometric standards
Evaluation and characterisation of the applicability of a newly developed open-path, as well as existing extractive measurement techniques to be employed as optical metrological transfer standards.
3. To establish the transfer from high-accuracy standards to field applicable methods
Employment of characterised exposure chambers as well as field sites for validation and comparison experiments to test and evaluate the performance of different instruments and measurement methods at ammonia amount fractions that are relevant to monitoring ambient air quality.

Pen Profile

Master in Chemistry at University of Berne, Switzerland in 1990. Different activities in the field of metrology for gas analysis for almost 25 years at METAS.
Since 2004 head of Gas Analytical Laboratory.
Expertise in high accuracy low inert gas volume flows, the dynamic preparation of traceable low concentration reactive gas mixtures as well as primary ozone measurements. Therefore participation in various key comparisons in the framework of CCQM (Consultative Committee of Amount of Substance) in the field and member of the Gas Working Group (GAWG) of CCQM.
Active participation in several projects of the European Metrology Research Program (EMRP). Responsible for the coordination of the Project ‘Metrology for Ammonia in ambient Air’ (MetNH3, www.metnh3.eu ) and active in developing traceable portable permeation and dilution generators for ambient ammonia concentrations in air.

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