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The European Metrology Network (EMN) for Climate and Ocean Observation has defined in its Strategic Research Agenda (SRA) several roadmaps intended to answer the metrological needs of the climate and ocean monitoring communities EMN Strategy.

In this post, we look more closely at the roadmaps for atmospheric stakeholder needs, particularly for standards and calibration procedures for gases and how a European metrological project contributed to this roadmap by addressing challenges faced by operators of atmospheric stations monitoring volatile organic compounds (VOCs).

Challenges for measuring volatile organic compounds (VOCs)

The roadmap on standards and calibration procedures for gases – based on the EMN Stakeholder Needs Report – identified the following main challenges faced by measuring networks:

1. fit-for-purpose working standards at appropriate amount-of-substance fractions and traceable to the International System of Units (SI)
2. certified reference material for newly emitted halogenated compounds lacking standards, and
3. metrological support for field calibrations and measurements.

Improved comparability of VOC monitoring

The EMPIR project Metrology for climate relevant volatile organic compounds (19ENV06, MetClimVOC, 2020-2023) was initiated to improve the comparability of monitoring VOC data and help air monitoring networks to reliably assess VOC trends.

For that purpose, among others, SI-traceable reference gas mixtures (RGMs) and working standards at atmospheric amount-of-substance fractions of VOCs relevant for climate were developed and measurement methods improved.

Returning to our roadmap, how does the MetClimVOC project contribute to the EMN SRA?

As described in the MetClimVOC project blog, the World Meteorological Organization (WMO) – Global Atmosphere Watch Programme (GAW) Report No. 171 (2006), formed the basis of the GAW strategy of supporting Global Long-Term Measurements of VOCs. This report included a list of VOCs to be monitored as key indicators of specific natural or anthropogenic sources.

In the project, several SI-traceable RGMs of priority oxygenated VOCs in nitrogen were prepared. These RGMs were designed to achieve the data quality objectives of monitoring networks such as ACTRIS and WMO-GAW, with the target amount-of-substance fractions and with expanded uncertainties (k= 2) of ca. 100 nm/mol and an uncertainty associated with the preparation of <5%.

Temporal stability after 18 months was good for most of these compounds and the results are promising for introducing calibration services and reference material of priority oxygenated VOCs, for which stable and SI-traceable RGMs were previously lacking. Furthermore, RGMs of priority halogenated VOCs in synthetic air were also prepared at target values (< 1 nmol/mol and relative expanded uncertainty (k = 2) < 3 %) thanks to a combination of permeation, dilution and cryo- filling.

This method, shown to be suitable for preparing certified reference material, will be used at the newly designated Central Calibration Laboratory for halogenated VOCs of the WMO-GAW programme.

These RGMs, together with other project outputs, such as the optimisation of in-situ and remote sensing measurement techniques and the development of guidelines and an online user-friendly tool for calculating measurement uncertainties at monitoring stations (TUCAVOC), advanced the state-of-the-art of VOC observations, in line with the EMN SRA outlook.