Oxygenated Volatile Organic Compounds (OVOCs), present in air at trace levels, are measured by the World Meteorological Organization Global Atmosphere Watch (WMO-GAW) VOC network because they are relevant oxidation products from anthropogenic and biogenic origin. The measured data support the studies in atmospheric chemistry to assess trends and ultimately to understand climate changes.
A priority list of VOCs, prepared by the WMO-GAW and revised in 2014, included OVOCs such as methanol, ethanol, acetone, methacrolein, acetaldehyde, methyl ethyl ketone and methyl vinyl ketone. For these components there are no traceable gas standards with the composition, uncertainty and long-term stability that can fulfill the Data Quality Objectives set by this network.
In order to fill this gap, a set of OVOC gas standards in nitrogen, ranging from 5 µmol/mol to 100 nmol/mol, were prepared at VSL by gravimetric method in high-pressure gas cylinders (ISO 6142-1). The preparation involved a special procedure to minimize interaction of these reactive components with material surfaces. This set was compared to dynamically prepared standard gas mixtures using continuous injection and diffusion methods (ISO 6145- part 4 and 8, respectively). An on-line Thermal Desorption-GC-FID was applied to compare the measurement results from the two preparation methods. In order to develop accurate gas standards, different cylinder types were tested, specifically aluminum and coated stainless steel gas cylinders from 3 to 10 L volume, part of them provided by specialty gas manufacturers. Finally, stability studies of the set of OVOC gas mixtures have been carried out to evaluate the suitability of these gas mixtures for the long-term monitoring of OVOCs in the atmosphere.
The presented work is performed in the framework of the KEY-VOCs EMRP research project (www.key-vocs.eu).
Annarita Baldan works at VSL (Dutch Metrology Institute) for more than 15 years as a scientist first and currently as a consultant. Her main research work is devoted to gas analysis and specifically to the development of the metrological infrastructure in air quality and atmospheric monitoring. Her research activities include the development of primary reference gas mixtures containing volatile organic compounds (VOCs) at trace concentration levels, by use of gravimetric and dynamic primary preparation techniques. Further she participates in international projects as consultant on QA/QC activities in air quality and she is active member of several standardisation bodies including CEN/TC264 “Air Quality” and ISO/TC158 “Gas Analysis”.
Annarita has been coordinator of the successful EMRP MACPoll research project (Metrology for air chemical pollutants) and she is now managing the KEY-VOCs project (Metrology for VOC indicators for air pollution and climate change) and the EMPIR Support for Impact Zero Gas project.