AtmoChemECV: Standards for Atmospheric, Chemical Essential Climate Variables

• Forschungsstelle: METAS
• Projektnummer: F-5232.30051
• Projekttitel Englisch: AtmoChemECV: Standards for Atmospheric, Chemical Essential Climate Variables

Schlüsselwörter (Englisch)

Dynamic generation; gas standards; adsorption, desorption, surface coatings, climate variables, F-gases; VOC, water

Kurzbeschreibung (Englisch)

50 so-called Essential Climate Variables (ECV) are monitored worldwide in support of the work of the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC). The Global Climate Observing System (GCOS) covers atmospheric, oceanic and terrestrial variables. The present project deals with the chemical composition of the atmosphere including water vapour only.
The under ECV subsumed chemical quantities comprise amount of substance fractions of carbon dioxide, methane, other long-lived greenhouse gases, ozone, ozone-precursors and water. For important stable compounds like carbon dioxide, methane and nitrous oxide National Metrology Institutes (NMI) provide gas standards in cylinders. Often these gas standards have to be subsequently diluted down to ambient concentrations. For very low concentrations, reactive gaseous compounds and recently focused-on compounds corresponding gas standards are missing. There is a clear demand to provide these standards applying new techniques. It can be foreseen that despite improvements in coating and passivation gas standards will not be provided in cylinders only.
With its core competencies and the existing infrastructure for the dynamic generation of gas mixtures the gas analysis laboratory of METAS has the potential to contribute substantially. It is actually not a new area for the laboratory, rather an extension of today’s activities and cos-tumers. So far the focus was on the national needs for gas standards of regulated air pollutants. The goal to build up new measurement and calibration capabilities of very low amount of substance fractions of atmospheric chemical ECVs, which, due to their reactivity cannot be provided in gas cylinders, is a logical and valuable extension.
Methods to provide gas standards in situ and/or canisters will be developed in close collaboration with MeteoSuisse, the EMPA and the Oeschger Centre for climate research of the University of Berne. Appropriate material and coating choices will minimise adsorption and desorption on walls and thus increase the live time of provided gas standards. This ensures a comparison of the developed SI-traceable measurement and calibration capabilities to existing scales and their implementation in the GCOS monitoring network. With this METAS resp. Switzerland will contribute to long-term stable and comparable climate date and models.

 

A part of this Project is carried out in the Framework of the European Metrology Research Programme (EMRP, http://www.euramet.org/index.php?id=emrp); it is partly funded by the European Union on the basis of Decision No 912/2009/EC.

Projektziele (Englisch)

The goal is to build up new measurement and calibration capabilities of very low amount of substance fractions of atmospheric chemical ECVs, which, due to their reactivity or adsorption phenomena cannot be provide in gas cylinders. Of interest are NMHC (Non Methane Hydrocarbons): F-Gases (Fluorinated gases), OVOC (Oxygenated Volatile Organic Com-pounds), terpenes and water. The specified demands of the WMO-GAW (World Meteorological Organisation – Global Atmosphere Watch) for NMHC are stable and traceable standards with amount of substance fractions < 1 nmol/mol for F-Gases and < 100 pmol/mol for OVOC and terpenes in air. The aimed for uncertainties are less than 10 % relative. For water in air stable and traceable standards with amount of substance fractions between 1 µmol/mol – 20 µmol/mol (corresponds to dew points between – 81 °C to – 60 °C) will be realised. The targeted uncertainties lie below 3 % relative.
Parallel to the built-up of measurement and calibration capabilities, methods to provide dynamically produced gas standards on-site and/or in canisters will be developed in close collaboration with EMPA and the Oeschger Center for Climate research of the University of Berne. With appropriate materials respectively coatings the adsorption and desorption phe-nomena will be minimised and sufficient long-term stabilities of dynamically (> 3 months) and statically (> 5 years) prepared gas standards achieved.
Maximal impact of the newly developed competencies will be ensured by their international acceptance: first by comparison with today’s established scales of the meteorologists and secondly by successful participation in the relevant key comparisons organised by CCQM (“Consultative Committee for Amount of Substance – Metrology for Chemistry and Biology“). Subsequently the internationally accepted measurement and calibration capabilities (CMC) need to be adopted by the WMO-GAW network. This adoption depends on how climate research will develop and how other national metrology institutes will further develop their capabilities. The adoption will not be achieved within the project frame, as it does not only de-end on METAS. For specific national needs of the networks of FOEN and MeteoSuisse METAS shall define the standards.

Abstract (Englisch)

Extension of the primary infrastructure:
A new magnetic suspension balance "MSW3" made of steel for the production of primary reference gas mixtures has been successfully put into operation. Therewith the operation under pressure is possible. This allows the generation of very low, atmospheric concentrations. It is fully coated to prevent the adsorption of reactive gas components. This primary standard was used for water, ammonia and halogenated gas components. The expanded measurement uncertainty of these reference gas mixtures prepared for the first time is generally <2%.

New analyser for fluorinated gas components:
An advanced pre-concentration mass spectrometer (APRECON) was put into operation at the METAS and validated.
The reproducibility of the measurements in the pmol/mol range is extremely good (<0.5% rel.). This system also includes the ability to adapt to additional compounds (especially VOCs). This adaptation is already realised in a similar device on the Jungfraujoch.
Out of plan, a "cryofilling" method for the filling of gas cylinders by fluorinated gases has been developed.

New measurement capabilities and their validation

Analyte	Range	Matrix	Comparison
H2O	ppm	N2	CCQM-K116
H2O	ppm	Synth. Luft	Bilateral with MBW Calibration (DI)
SF6	ppt	Synth. Luft	WMO-SICE 2016
HFC-125, HFO-1234yf, CFC13	ppt	Synth. Luft	Bilateral with Empa (SIO/NOAA References)
EtOH	ppb	N2	EMRP comparison with VSL,NPL

The following new measurement capabilities were validated by participation in comparisons:

• CCQM-K116 for water in nitrogen in the μmol/mol range
• WMO-SICE 2016-2017 for SF₆ in pmol/mol range.
• Bilateral H₂O measurement comparison in air in μmol/mol range with MBW Calibration (DI for water)
• Comparison of mixtures with fluorinated components against currently used AGAGE references (via measurements at Empa for SF6, HFC-125, HFO-1234yf and CFC-13) in the pmol/mol range.
• Additionally, ethanol was generated and compared against the static references of VSL and NPL as part of the EMRP Key-VOCs project.

For all measurement comparisons with other SI standards, the results are in accordance with the measurement uncertainty. When comparing with references with unclear traceability, however, significant differences have occurred.

Umsetzung und Anwendungen (Englisch)

With the developed cryofilling method, 11 cylinders with 5 fluorinated gas components (SF6, HFC-125, HFO-1234yf, HCFC-132b, CFC-13) each in the ppt range were filled for Empa. All had slightly different concentrations in order to cover environmental concentrations. The reproducibility of the filled amount fractions is better than 1% and the relative expanded uncertainty of the individual components is < 2%.
Incidentally, CFC-13 in these reference cylinders has been implemented as the official reference for the AGAGE network.

The portable generator ReGaS2 was used at the ETH to generate gas mixtures of VOCs. The aim was to calibrate a clinical diagnostic breath analyser and check its linearity
The ReGaS2 will also be used by the DWD (German Weather Service, mandated for VOC measurements). It will generate a reference gas mixture of 5 reactive VOCs that are not stable at atmospheric concentrations in cylinders under pressure.
Rental interest in the portable gas generators ReGaS has also been expressed by other private or public authorities (NPL, Philip Morris, UBA Austria).
The generators are also used for services and measurement comparisons at METAS.

Publikationen / Ergebnisse (Englisch)

Pascale, C., Guillevic, M., Ackermann, A., Leuenberger, D., and Niederhauser, B.:  Two generators to produce SI-traceable reference gas mixtures for reactive compounds at at-mospheric level, Meas. Sci. Technol., 28, 12402, https://doi.org/10.1088/1361-6501/aa870c , 2017

Vollmer, M. K., Young, D., Trudinger, C. M., Mühle, J., Henne, S., Rigby, M., Park, S., Li, S., Guillevic, M., Mitrevski, B., Harth, C. M., Miller, B. R., Reimann, S., Yao, B., Steele, L. P., Wyss, S. A., Lunder, C. R., Arduini, J., McCulloch, A., Wu, S., Rhee, T. S., Wang, R. H. J., Salameh, P. K., Hermansen, O., Hill, M., Langenfelds, R. L., Ivy, D., O'Doherty, S., Krummel, P. B., Maione, M., Etheridge, D. M., Zhou, L., Fraser, P. J., Prinn, R. G., Weiss, R. F., and Simmonds, P. G.: Atmospheric histories and emissions of chlorofluorocarbons CFC-13 (CClF3), ΣCFC-114 (C2Cl2F4), and CFC-115 (C2ClF5), Atmos. Chem. Phys., in review

Demichelis, A., Pascale, C., Lecuna, M., Niederhauser, B., Sassi, G., and Sassi, M.P.: Compact devices for generation of reference trace VOC mixtures: a new concept in assuring quality at chemical and biochemical labs, Analytical and bioanalytical chemistry, in prep.

Guillevic, M., Vollmer, M. K., Wyss, S. A., Leuenberger, D., Ackermann, A., Pascale, C., Niederhauser, B., and Reimann, S.: Dynamic-gravimetric preparation of metrologically traceable primary calibration standards for halogenated greenhouse gases, in prep.