Measuring VOCs under real driving emission conditions by means of PTR-MS – experiences and insights from vehicle campaigns

In this contribution, we present our experiences and insights on the online measurement of volatile organic compounds (VOCs) under real driving emission (RDE) conditions. The measurements were carried out in the framework of the EU and UKRI funded project AEROSOLS at ‘IFP Energies nouvelles’ in Paris, during two campaigns in summer and winter 2025. Among the numerous instruments used in these campaigns, we employed an advanced laminar-flow oxidation reactor (ILOx; IONICON Analytik) and two proton-transfer-reaction - time-of-flight - mass spectrometry (PTR-TOF-MS) instruments (IONICON Analytik) for online VOC and semi volatile organic compounds (SVOCs) measurements. One of the two PTR-TOF-MS instruments was equipped with a sensitivity enhancing RF+DC reaction chamber and a TOF analyzer with a mass resolution of 10,000 (full width at half maximum (FWHM) definition). The other PTR-TOF-MS instrument was a more compact, customized device that could be installed inside the boot of an SUV. This device was used for online VOC measurements both on the road and in a chassis dynamometer. It consists of two easily separable cubes that can be easily lifted and transported thanks to their robust construction. Two different types of reagent ions were utilized in the study, namely H₃O⁺ and NO⁺. H₃O⁺ is a well-known reagent ion and the cornerstone of PTR-MS technology. H₃O⁺ can be used to ionize and detect a wide range of VOCs in the atmosphere, while the main constituents of air remain unionized and thus do not interfere in the detection of trace gases. NO⁺, on the other hand, is known to be more sensitive to the ionization of alkanes, which is important for analysis of exhaust gases from combustion engines. The product ions produced via proton transfer reaction, hydride abstraction or adduct formation are then analysed by means of a time-of-flight mass spectrometer with a mass resolution of 3,000 (FWHM definition). In order to track rapid changes in VOC concentrations, average mass spectra were recorded at least once every second.

Two SUVs were examined as part of the summer and winter campaigns. One was equipped with a diesel engine, the other with a plug-in hybrid gasoline engine. VOC emissions were measured for both SUVs both on the road and in the chassis dynamometer. We provide an overview of the campaigns and report in detail on the challenges and difficulties of online VOC measurements under RDE conditions, as well as some of the results of these two campaigns.

Acknowledgement: This research was co-funded by the European Union’s Horizon Europe research and innovation programme within the AEROSOLS project under grant agreement No. 101096912 and UK Research and Innovation (UKRI) under the UK government’s Horizon Europe funding guarantee [grant numbers 10092043 and 10100997].