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| Titel |
What metrology can do to improve the quality of your atmospheric ammonia
measurements |
| VerfasserIn |
Daiana Leuenberger, Nicholas A. Martin, Céline Pascale, Myriam Guillevic, Andreas Ackermann, Valerio Ferracci, Nathan Cassidy, Josh Hook, Ross M. Battersby, Yuk S. Tang, Amy C. M. Stevens, Matthew R. Jones, Christine F. Braban, Linda Gates, Markus Hangartner, Paolo Sacco, Diego Pagani, John A. Hoffnagle, Bernhard Niederhauser |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250151746
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| Publikation (Nr.) |
 EGU/EGU2017-16502.pdf |
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| Zusammenfassung |
| Measuring ammonia in ambient air is a sensitive and priority issue due to its harmful
effects on human health and ecosystems. 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 to
ensure reliable ammonia measurements, namely in applicable analytical technology,
maximum allowed uncertainty, quality assurance and quality control (QC/QA)
procedures, as well as in the infrastructure to attain metrological traceability, i.e. that the
results of measurements are traceable to SI-units through an unbroken chain of
calibrations.
In the framework of the European Metrology Research Programme (EMRP)
project on the topic “Metrology for Ammonia in Ambient Air” (MetNH3), European
national metrology institutes (NMI’s) have joined to tackle the issue of generating
SI-traceable reference material, i.e. generate reference gas mixtures containing
known amount fractions of NH3.This requires special infrastructure and analytical
techniques:
Measurements of ambient ammonia are commonly carried out with diffusive samplers or
by active sampling with denuders, but such techniques have not yet been extensively
validated. Improvements in the metrological traceability may be achieved through the
determination of NH3 diffusive sampling rates using ammonia Primary Standard Gas
Mixtures (PSMs), developed by gravimetry at the National Physical Laboratory NPL and a
controlled atmosphere test facility in combination with on-line monitoring with a cavity
ring-down spectrometer.
The Federal Institute of Metrology METAS has developed an infrastructure to generate
SI-traceable NH3 reference gas mixtures dynamically in the amount fraction range
0.5-500 nmol/mol (atmospheric concentrations) and with uncertainties UNH3 <3%. The
infrastructure consists of a stationary as well as a mobile device for full flexibility for
calibrations in the laboratory and in the field. Both devices apply the method of temperature
and pressure dependant permeation of a pure substance through a membrane into a stream of
pre-purified matrix gas and subsequent dilution to required amount fractions. All relevant
parameters are fully traceable to SI-units. Extractive optical analysers can be connected
directly to both, stationary and mobile systems for calibration. Moreover, the resulting gas
mixture can also be pressurised into coated cylinders by cryo-filling. The mobile system as
well as these cylinders can be applied for calibrations of optical instruments in
other laboratories and in the field. In addition, an SI-traceable dilution system based
on a cascade of critical orifices has been established to dilute NH3 mixtures in
the order of μmol/mol stored in cylinders. It is planned to apply this system to
calibrate and re-sample gas mixtures in cylinders due to its very economical gas
use.
Here we present insights into the development of said infrastructure and results
performance tests. Moreover, we include results of the study on adsorption/desorption effects
in dry as well as humidified matrix gas into the discussion on the generation of reference gas
mixtures.
Acknowledgement: This work was supported by the European Metrology Research
Programme (EMRP). The EMRP is jointly funded by the EMRP participating countries
within EURAMET and the European Union. |
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