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| Titel |
State of the art stationary and mobile infrastructure for the dynamic
generation and dilution of traceable reference gas mixtures of Ammonia at
ambient air amount fractions |
| VerfasserIn |
Daiana Leuenberger, Céline Pascale, Myriam Guillevic, Andreas Ackermann, 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 |
250147639
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| Publikation (Nr.) |
 EGU/EGU2017-11830.pdf |
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| Zusammenfassung |
| Ammonia (NH3) in the atmosphere is the major precursor for neutralising atmospheric acids
and is thus affecting not only the long-range transport of sulphur dioxide and nitrogen oxides
but also stabilises secondary particulate matter. These aerosols have negative impacts on air
quality and human health. Moreover, they negatively affect terrestrial ecosystems after
deposition.
NH3 has been included in the air quality monitoring networks and emission
reduction directives of European nations. Atmospheric concentrations are in the
order of 0.5-500 nmol/mol. However, the lowest substance amount fraction of
available certified reference material (CRM) is 10 μmol/mol. This due to the fact that
adsorption on the walls of aluminium cylinders and desorption as pressure in the
cylinder decreases cause substantial instabilities in the amount fractions of the gas
mixtures.
Moreover, analytical techniques to be calibrated are very diverse and cause challenges for
the production and application of CRM.
The Federal Institute of Metrology METAS has developed, partially in the framework of
EMRP JRP ENV55 MetNH3, an infrastructure to meet with the different requirements
in order to generate SI-traceable NH3 reference gas mixtures dynamically in the
amount fraction range 0.5-500 nmol/mol and with uncertainties UNH3 <3%. The
infrastructure consists of a stationary as well as a mobile device for full flexibility in the
application:
In the stationary system, a magnetic suspension balance monitors the specific temperature
and pressure dependent mass loss over time of the pure substance in a permeation tube (here
NH3) by permeation through a membrane into a constant flow of carrier gas. Subsequently,
this mixture is diluted with a system of thermal mass flow controllers in one or two
consecutive steps to desired amount fractions.
The permeation tube with calibrated permeation rate (mass loss over time previously
determined in the magnetic suspension balance) can be transferred into the
temperature-regulated permeation chamber of a newly developed mobile reference gas
generator (ReGaS1). In addition to the permeation chamber it consists of the same dilution
system as afore mentioned, stationary system. All components are fully traceable to SI
standards.
Considerable effort has been made to minimise adsorption on the gas-wetted stainless
steel surfaces and thus to reduce stabilisation times by applying the SilcoNert2000® coating
substance.
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 in
other laboratories and in the field.
In addition, an SI traceable system based on a cascade of critical orifices has been
established to dilute NH3 mixtures in the order of μmol/mol stored in cylinders for the
participation in the international key-comparison CCQM K117. It is planned to establish this
system to calibrate and re-sample gas cylinders due to its very economical gas
use.
Here we present insights into the development of said infrastructure and results of the first
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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