10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Towards Monitoring Automobile Ultra-fine Particle Emissions: Size-dependent Chemical Composition
CRISTIAN FOCSA, Dumitru Duca, Jennifer Noble, Yvain Carpentier, Marin Vojkovic, Andreas Manz, Matthias Lyska, Roman Grzeszik, Torsten Tritscher, Juergen Spielvogel, Marcus Rieker, Université de Lille
Abstract Number: 1294 Working Group: Combustion
Abstract On-road motor vehicles are important sources of ultra-fine particulate matter (PM) emissions, which present acknowledged health and environmental risks. There is currently a critical lack of certified measurement procedures for the smallest particles (< 23 nm) under real driving conditions. The development of such measurement procedures would represent an important contribution towards future particle emission regulations. The aim of the European H2020 PEMs4Nano project (www.pems4nano.eu) is to develop a portable emission monitoring system for particles below 23 nm, to be used in real driving conditions. The development of a reliable measurement procedure first requires a thorough understanding of the emitted particle characteristics (morphology, structure, chemical composition, volatility, reactivity), and their size dependence. This work presents an investigation of the chemical composition of size-selected particles emitted by a gasoline direct injection engine.
Particulate matter probed in this study was produced by a generic single-cylinder test engine (Bosch) which can be operated in various working regimes. Particles were sampled using a cascade impactor (NanoMoudi-II, MSP/TSI) which allows size-separation into 13 different size bins. Since the main interest of this work is in small particles, only the five size bins covering the range 180 to 10 nm were analysed.
Chemical characterisation of the collected particles is performed using a home-made two-step laser mass spectrometer (L2MS, Faccinetto et al., 2015). Combining gentle (low-fluence) laser desorption and various ionisation wavelengths, our instrument is able to provide detailed (nonfragmented) molecular analysis on chemical classes of critical interest, such as organosulphates, oxygenated hydrocarbons, nitrogenated hydrocarbons, and polycyclic aromatic hydrocarbons (PAHs), as well as very effective detection of heavy metals. Additional high-resolution chemical mapping is performed using a commercial Secondary Ion Mass Spectrometer (IONTOF).
The very rich mass spectra of size-selected particles require powerful statistical treatment to unveil subtle differences in chemical composition. This is done using principal component analysis (PCA) and hierarchical clustering analysis (HCA). Chemical species responsible for these variations can thus be definitively identified and the size-selected particles can be discriminated and classified according to their origin. Moreover, the influence of various experimental parameters (engine regime, fuel additives, lubricating oil, mechanical wear, etc.) can be easily identified.
The combination of mass spectrometric studies with statistical procedures reveals indisputable evidence of a size-dependence in the chemical composition of PM. This information represents critical physico-chemical data necessary for the development of a reliable portable device for the measurement of ultra-fine particles emitted by automobile engines.
This work has received funding from the European Union’s Horizon2020 Programme for research, technological development and demonstration under Grant Agreement no. 724145 (H2020-GV-2016).
Faccinetto, A. et al. (2015), Environmental Science and Technology, 49, pp. 10510-10520. DOI:10.1021/acs.est.5b02703.