19ENV06 MetClimVOC: Metrology for climate relevant volatile organic compounds

• Forschungsstelle: METAS
• Projektnummer: F-5232.30136

Schlüsselwörter (Englisch)

volatile organic compounds (VOCs), reference gas mixture, permeation, reference gas generation, SI-traceable gas mixture, oxy-VOCs, terpenes, halogenated VOCs

Kurzbeschreibung (Englisch)

Climate change poses high risks to society. Long-term, accurate, worldwide measurements of volatile organic compounds (VOCs) are pivotal to understanding changes in the Earth’s climate and to addressing the effects of climate change. VOCs are indirect greenhouse gases as they can influence the oxidising capacity of the atmosphere and hence the lifetime of methane. Furthermore, they are precursors of ozone and aerosols, which both contribute to the radiative forcing. As the abundance of atmospheric VOCs is low (parts-per-trillion (pmol/mol) to parts-per-billion (nmol/mol)) with some components being very reactive, there are challenges in sampling, analysis and calibration. The availability of high-quality reference materials and well-defined methods is essential to reach the necessary accuracy, as expressed in the WMO data quality objectives. This project will improve the quality of reference gas mixtures and it will ensure the correct dissemination of references to the field via adequate working standards and recommendations, along with well-characterised sampling and analytical methods. Finally, it will provide SI-traceable spectral parameters for spectrum-based measurement techniques.

Projektziele (Englisch)

The EURAMET-EMPIR project finished on the due date (31.05.2023). The main objectives of the project were:

1. preparation of new accurate, SI-traceable and stable reference gas mixtures of VOCs, which are considered priority by stakeholders (WMO-GAW, AGAGE, ACTRIS, EMEP), at atmospheric amount fraction levels.
2. optimization of sampling and analytical methods used in monitoring stations.
3. development and assessment of fit-for-purpose traceable working standards.

Abstract (Englisch)

Priority VOCs were selected based on their importance in climate research and the lack of stable and SI-traceable reference gas mixtures (RGMs) and included the required amount-of-substance fraction range, uncertainty, and temporal stability. The priority that were considered were:

• Oxy-VOCs: ethanol, methanol, acetone, acetaldehyde, methyl vinyl ketone (MVK), methacrolein;
• Terpenes: alpha-pinene, beta-pinene, myrcene, terpinolene, beta-caryophyllene;
• Halogenated VOCs: 1,2-dichloroethane, HFO-1336mmzz-Z, HFC-134, HFC-124, desflurane

METAS generated RGMs of oxy-VOCs at different amount-of-substance fractions (5 – 100 nm/mol), RGMs of terpenes at low amount-of-substance fractions (2 – 25 nmol/mol), and RGMs for 6 selected halogenated VOCs in synthetic air at near-ambient amount-of-substance fractions (low pmol/mol levels), using the dynamic method based on permeation (ISO 6145-10:2002). The generation by MSB showed that it is possible to generate oxy-VOC RGMs at 10-50 nmol/mol in nitrogen with expanded uncertainties between 0.7 – 3% (k = 2). However, the permeation method is not yet suitable for the generation of terpene RGMs at very low amount-of-substance fractions (< 50 nmol/mol) and target uncertainties (< 5%, k = 2).  The RGM for the 6 halogenated gases amount-of-substance fractions were <1 nmol/mol with expanded relative uncertainty for all compounds better than the target 3% (k = 2).

The calibration standards developed at METAS were compared with those form other laboratories in order to asses the working standard protocols. The results suggest that the new SI-traceable working standard protocols based on permeation seem to be suitable for acetone monitoring, but not for MVK, MEK, methanol, alpha- or beta-pinene. SI-working standards based on diluted reference gas mixtures seems to be the most suitable for acetaldehyde.  

Umsetzung und Anwendungen (Englisch)

The cryo filling system optimised during the project by METAS was shown to be suitable for the preparation of halogenated VOC RGMs, and will be offered as a calibration service as part METAS's role as the Central Calibration Laboratory for halogenated VOCs. Results from the inter-comparison study of the generation of RGMs will enable METAS to become a reference for acetone calibration services at low amount fractions (<100 nmol/mol). 

Publikationen / Ergebnisse (Englisch)

The METAS contribution to MedGU2023, in collaboration with LNE and VSL, will be published in the conference proceedings (in Advances in Science, Technology and Innovation (Springer)). A short manuscript on this contribution is currently being revised for publication in a special issue of Earth System and Environment (Springer).
The following manuscripts, written by METAS, will be submitted in the months following the end of the project:

1. Manuscript on the new scale produced by METAS as reference material for halogenated VOCs.
2. Manuscript on the transfer of SI traceability from the laboratory to the field for oxygenated VOC standards within the framework of TOAR-II.