Metrology for ammonia in ambient air

Intensive livestock farming and widespread fertilizer usage have increased ammonia pollution levels in Europe, reducing biodiversity and generating secondary particles hazardous to human health. An EU Directive on reducing atmospheric pollutants will, from 2020, impose strict limits on ammonia emissions, obliging member states to introduce reduction strategies. National monitoring networks are being set-up to collect ammonia data, by air sampling using low-cost trapping methods, requiring chemical analysis. Automated continuous analysers are also used for real-time measurements. Both require improved calibration methods with robust links to SI units and new ways to assess performance in-thefield. Additionally, optimisation of materials based on inertness to ammonia – a reactive gas – could help reduce measurement losses before gas analysis.

This project developed ammonia reference gas standards for use in calibrations and in-the-field device performance assessments, and commissioned, then used, a facility for evaluating material/ammonia interactions to help inform user selection decisions.

The project:

• Developed ammonia gas cylinder standards and point-of-use generation methods to improve calibrations and in-the-field performance assessments of measuring devices
• Used these reference gas standards to calibrate laser-based cavity ring-down spectroscopy and quantum cascade laser technologies showing potential for use as SI transfer standards
• Upgraded a lab-based Controlled Atmosphere Test Facility (CATFAC) for use with ammonia, and used it to assess the performance of ammonia sampler trapping media
• Investigated interactions between ammonia and the materials used in measurement devices to optimise the selection of inert materials throughout the measurement chain.

The upgraded CATFAC facility was used for a comparison of 16 ammonia measuring devices in the lab followed by a pioneering field study. The project’s new reference gas standards enabled the assessment of their performance and the generation of an improved understanding of ammonia trapping efficiencies which when implemented by manufacturers has increased measurement accuracy. Studies performed using the CATFAC facility, have supported laser-based spectrometry instrument manufacturers by identifying inert materials and determining ways to correct for water vapour interferences that hamper ammonia detection. These developments have been taken up by Picarro Inc, a manufacturer of cavity ring-down spectrometers and Mirico, a developer of laser-based spectrometry technologies. Another early adopter of the project’s developments has been the Swiss national air pollution monitoring network who have invested in the project’s point-of-use generation method for field tests of ammonia sampling devices.

Closer agreement between ammonia measurement devices and new tools to determine the efficiency of samplers will enable European air quality monitoring networks to produce validated data of suitable accuracy for identifying successful ammonia emission reduction strategies. This will be vital for achieving compliance with the EU’s National Emission Ceilings Directive on reducing atmospheric pollutants.