Surface interactions in oxygenated VOC analysis

Stefan Persijn, VSL (NL)

The Global Atmosphere Watch (GAW) programme of the WMO has identified a core set of VOCs to be monitored. From this set, the monitoring of oxygenated VOCs (OVOCs) like methanol and ethanol poses in particular a challenge due to the strong interaction of these species with the material surface.  Within the KEY-VOCs EMRP research project (www.key-vocs.eu), the interaction of methanol and other OVOCs is being investigated at static and dynamic conditions with the aim to improve respectively the preparation of (long-term stability) gas standards in pressurised cylinders and to guarantee the integrity of the real air samples during sampling.

Firstly, a batch of gas mixtures containing methanol, ethanol and acetone at low amount fractions (100 nmol/mol) and a batch containing formaldehyde at 1 µmol/mol have been prepared using state-of-the-art gravimetric preparation methods (ISO 6142-1).  Gas cylinders were supplied by specialty gas producers. Losses occurring upon gas mixture preparation have been quantified and both short and mid-term stability of the mixtures were determined.

In the second part of the research, the interaction of OVOCs with surface materials has been studied in a more fundamental way. Surface analysis technique based on soft x-rays has been used to directly observe the adsorbed OVOCs on metal surfaces. Furthermore, the adsorption and desorption kinetics of trace levels methanol passing through polymer and metal (both coated and uncoated) sampling lines were investigated. Both laser spectroscopic and Flame Ionisation Detector methods were used for quantifying the effect in real time. Finally, the observed methanol adsorption/desorption kinetics were simulated using Computational Fluid Dynamics.
The presentation will provide the results of this comprehensive study and come up with recommendations for the sampling of OVOCs.


Pen Profile

At VSL he has designed and constructed sensitive mid-infrared-based and visible spectrometers for trace gas analysis. He has applied these instruments to adsorption studies and the analysis of pure gases, biogas, hydrogen purity and greenhouse gases. In addition, he developed a high power infrared source which was used for calibration of the TROPOMI satellite instrument (to be launched in 2017). He holds a PhD from the Radboud University of Nijmegen.


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