KEY-VOCs: Metrology for VOC indicators in air pollution and climate change

At a glance

Project number	ENV56
Short name	KEY-VOCs
Programme	EMRP, 2013 call (Environment)
Duration	October 2014 – September 2017 (36 months)
Coordinator	Annarita Baldan, VSL (Netherlands)

Why it was needed

Volatile organic compounds (VOCs) are carbon compounds that evaporate readily at room temperature. They enter the air from fuel combustion, paints, glues and solvents, building materials and plants. Some, like benzene, are directly harmful to health; others contribute to ozone and secondary organic aerosol formation, affecting air quality and climate. Benzene is regulated by the EU Air Quality Directive (2008/50/EC), and VOC emissions from building materials by the Construction Products Regulation.

The World Meteorological Organization’s Global Atmosphere Watch (WMO GAW) network monitors long-term VOC trends at remote stations such as the Jungfraujoch, at concentrations from parts per billion (ppb) down to parts per trillion (ppt). Measuring at these levels is very difficult: most VOCs adsorb to or react with the surfaces of sampling lines, cylinders and pressure regulators, and even a few ppt of impurities in the “clean” nitrogen or air used for calibration cause significant errors. In the first WMO GAW VOC intercomparison in 2003, only 18 of 76 components were measured accurately by at least half of the laboratories. Traceable, stable gas standards for priority VOC classes were still lacking.

Objectives

1. Quantify adsorption and reaction effects of VOCs on material surfaces to identify the best materials and passivation techniques for trace-level measurements; develop traceable standards for VOC-free zero gas (nitrogen and air) and tools for uncertainty evaluation.
2. Prepare traceable, accurate and long-term stable gas standards of oxygenated VOCs (OVOCs), formaldehyde and monoterpenes for atmospheric monitoring, using static (gravimetric) and dynamic methods.
3. Develop reference gas standards of polar and semi-volatile VOCs, and constant-emitting polymer reference materials, for indoor air measurements.
4. Validate the new standards through partner comparisons, and evaluate commercially available low-cost VOC sensors, particularly for benzene, in the laboratory and in the field.

Results

Surface effects and zero gas

Methods were developed to quantify VOC losses on surfaces, and the suitability of specific novel coating technologies was demonstrated. The project produced first-in-the-world knowledge on passivation methods for preparing stable VOC standards at trace (ppb) levels and for measuring reactive compounds such as alcohols and aldehydes. A new in-situ gas cell was established at PTB to measure gas sorption on surfaces by total-reflection X-ray fluorescence. A certification protocol for determining ppt-level VOC impurities in zero gases served as input to the revision of ISO 19229.

Gas standards for atmospheric monitoring

• VSL prepared new OVOC gas mixtures of methanol, ethanol, acetone, MEK, MVK, methacrolein and acetaldehyde at 100 nmol/mol.
• NPL developed the first monoterpene reference gas standards in Europe at 2–4 nmol/mol.
• LNE and NPL gained experience in preparing formaldehyde standards at 1 µmol/mol by static and dynamic methods. In the formaldehyde comparison, results from NPL, LNE and TÜBİTAK agreed within their uncertainties. The work also showed that stability remains an issue for very reactive compounds such as formaldehyde.
• METAS (ReGaS2, based on permeation) and INRIM (based on diffusion) designed two portable dynamic gas generators, which were validated for field calibration.

Standards for indoor air

Polar VOCs (hexanal, n-butanol, cyclopentanone, 2-isopropoxyethanol, acetic acid) generated with INRIM’s dynamic diffusion system were loaded onto sorbent tubes to create transfer standards. Their analysis and stability testing were carried out at TÜBİTAK using the isotope dilution mass spectrometry (IDMS) method developed in the project; the tubes were stable for up to three months at –20 °C. VSL prepared dynamic gas mixtures of semi-volatile VOCs by continuous syringe injection. BAM developed a new reference material on thermoplastic polyurethane basis with characterised emission behaviour, mimicking a real construction product test specimen. In a comparison among BAM, TÜBİTAK and VSL, most semi-volatile VOCs were measured consistently with the reference values.

Low-cost sensors

Tests in JRC’s sensor exposure chamber and at a semi-rural monitoring station showed that most current sensor technology cannot measure benzene accurately and selectively at ambient levels. Only a miniaturised gas chromatograph met the 30% data quality objective, with an expanded uncertainty of 22% at 1.4 ppb. The validation protocol developed in the project fed into the CEN/TC264 technical specification for air quality sensors.

Impact

• One of the OVOC standards developed in the project was used in a round-robin among ACTRIS and WMO GAW laboratories, and zero-gas verification was included in the WMO guideline for non-methane hydrocarbons.
• The adsorption studies were used by the IAGOS-CARIBIC project, which measures the atmosphere from commercial passenger aircraft, to select the tubing material for a new inlet system.
• The portable calibrators were used at Swiss and Italian monitoring stations and for breath analysis in hospitals; ReGaS2 was set for commercialisation.
• The indoor-air reference material and transfer standards were prepared for proficiency testing of emission testing laboratories under EN 16516 and ISO 16000.
• The project produced 13 peer-reviewed publications and a PhD thesis, with 36 oral and 18 poster presentations.

Partners

• National metrology institutes: VSL (Netherlands, coordinator), BAM (Germany), CMI (Czech Republic), INRIM (Italy), LNE (France), METAS (Switzerland), NPL (United Kingdom), PTB (Germany), TÜBİTAK UME (Türkiye)
• Other partners: European Commission Joint Research Centre (JRC); researcher grants with the German Weather Service (DWD), Politecnico di Torino and Saarland University

Selected publications

• Spinelle, L. et al. (2017). Review of portable and low-cost sensors for the ambient air monitoring of benzene and other volatile organic compounds. Sensors, 17(7), 1520. doi:10.3390/s17071520
• Richter, M. et al. (2017). Reproducibly emitting reference material on thermoplastic polyurethane basis for quality assurance/quality control of emission test chamber measurements. Building and Environment. Article
• Pascale, C. et al. (2017). Two generators to produce SI-traceable reference gas mixtures for reactive compounds at atmospheric levels. Measurement Science and Technology. doi:10.1088/1361-6501/aa870c
• Demichelis, A. et al. (2018). Development of a primary diffusion source of organic vapors for gas analyzer calibration. Measurement Science and Technology, 29, 035802. doi:10.1088/1361-6501/aa9ef6
• Sauerwald, T. et al. (2018). Highly sensitive benzene detection with metal oxide semiconductor gas sensors – an inter-laboratory comparison. Journal of Sensors and Sensor Systems, 7, 235–243. doi:10.5194/jsss-7-235-2018
• Lecuna, M. et al. (2018). Compact devices for generation of reference trace VOC mixtures: a new concept in assuring quality at chemical and biochemical labs. Analytical and Bioanalytical Chemistry, 410. doi:10.1007/s00216-018-0935-8

Full list: EURAMET publications repository

Links

• EURAMET project page
• Project website