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| Titel |
SI-traceable standards for atmospheric monitoring of halogenated gases |
| VerfasserIn |
Myriam Guillevic, Simon A. Wyss, Céline Pascale, Martin K. Vollmer, Bernhard Niederhauser, Stefan Reimann |
| 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 |
250141516
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| Publikation (Nr.) |
 EGU/EGU2017-5037.pdf |
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| Zusammenfassung |
| To support atmospheric monitoring of greenhouse gases and in particular halogenated gases,
we have developed a method to produce reference gas mixtures at nmol/mol (ppb) to
pmol/mol levels (ppt). This method is dynamic and SI-traceable. This work is conducted in
the framework of the EMRP projects HIGHGAS and KEY-VOCs as well as METAS’
AtmoChemECV project.
The method has been already applied to HFC-125 (pentafluoroethane, widely used in air
conditioners), HFC-1234yf (2,3,3,3-tetrafluoropropene, a car air conditioner fluid of
growing importance) and SF6 (insulant in electric switch-gears). It is currently being
extended to HCFC-132b and CFC-13. It is particularly suitable for gas species and/or
concentration ranges that are not stable in cylinders and it can be applied to a large
variety of molecules related to air pollution and climate change (e.g., NO2, volatile
organic compounds such as BTEX, NH3, water vapour at ppm level, CFCs, HCFCs,
HFCs). The expanded uncertainty is less than 3 % (95 % confidence interval or
k=2).
The generation process is composed of four successive steps. In the first step the matrix
gas, nitrogen or synthetic air is purified. Then this matrix gas is spiked with the pure
substance, using a permeation device which contains a few grams of the pure substance (e.g.,
HFC-125) in the liquid form and loses it linearly over time by permeation through a
membrane. This mass loss is precisely calibrated in our lab in Bern, using a magnetic
suspension balance. In a third step the desired concentration is reached by dilution of the high
concentration mixture exiting the permeation chamber with a chosen flow of the matrix gas in
one or two subsequent dilution steps. All flows are piloted by mass flow controllers. All parts
in contact with the gas mixture – including the balance – are passivated using coated
surfaces, to reduce adsorption/desorption processes as much as possible. In the last
step the mixture can be i) directly used to calibrate an analyser, ii) sampled on
sorbent tubes or iii) pressurized into Silconert2000-coated stainless steel cylinders by
cryo-filling.
We focus here on standards made for the gases HFC-125 and HFC-1234yf. We present
here the method, the uncertainty budget as well as first results of intercomparisons to other
references. |
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