10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Particulate and Gas Phase Separation in Simultaneous Sampling of Combustion Byproducts: New Insights into Chemical Composition by Mass Spectrometric Analysis
Jennifer Noble, Linhdan Ngo, Dumitru Duca, MARIN VOJKOVIC, Abd Raouf Ikhenazene, Cornelia Irimiea, Guillaume Lefevre, Alessandro Faccinetto, Claire Pirim, Yvain Carpentier, Bertrand Chazallon, Nicholas Nuns, Jerome Yon, Eric Therssen, Cristian Focsa, Université de Lille
Abstract Number: 1373 Working Group: Carbonaceous Aerosol
Abstract Combustion is the largest anthropogenic source of aerosol particles, accompanied by significant gas phase byproducts. Combustion soot particles can have a direct or indirect effect on climate that gives rise to important consequences for both atmospheric radiative forcing and cloud formation and lifetime. Although many studies have been conducted to characterise soot particles (e.g. Parent et al. 2016), more extensive investigation of their composition and molecular structure is required in order to better understand the role of particulate and gas phase combustion byproducts in atmospheric physicochemical processes.
In this study, a new simultaneous sampling method was developed for combustion byproducts in the particulate and gas phases. The experimental protocol was verified using a Combustion Aerosol Standard (CAST) burner supplied with various propane-air mixtures. Combustion byproducts were collected on two quartz microfibre filters in series. Firstly, a “front filter” was used to collect particulate matter and, secondly, a “back filter” covered with carbon black adsorbed gases that passed through the front filter, following the principle of Faccinetto et al. (2011).
An analytical approach combining micro-Raman and micro-Fourier Transform Infrared spectroscopies with Secondary Ion Time-of-Flight Mass Spectrometry (ToF-SIMS) and Two-step Laser Mass Spectrometry (L2MS) was adopted, in order to characterise the structural and chemical properties of the sampled particulate and gas phases. The custom built L2MS setup allows a detailed chemical analysis of trace amounts of deposited particles at the molecular level, revealing the presence of chemical classes such as aliphatics, aromatics, nitrogenated- /oxygenated-hydrocarbons, organosulfates and metals. For combustion soot, the degree of aromaticity, determined by the relative abundance of polycyclic aromatic hydrocarbons (PAHs), is decisive in determining its physicochemical properties. The L2MS technique is especially well adapted for PAH detection. ToF-SIMS has high sensitivity for both inorganic and organic species, notably the Cn- ion series, a proxy for elemental carbon. Vibrational spectroscopies provide complementary information about the chemical composition and structure of soot by probing the vibrational modes of its composite molecules (Ess et al. 2016).
Our combined mass spectrometry and vibrational spectroscopy studies suggest that the gas and particulate phases of combustion byproducts are sampled effectively using the chosen methodology, and confirm that they have significantly different chemistry. In the samples used to validate the method, the mass distribution of PAHs is found to vary significantly, not only with operation point of the CAST burner but also between the gas and particulate phases. Principal component analysis allowed discrimination between different working points of the burner, in both the particulate and gas phases. The gas phase of all sampled working points contains lower mass PAHs than the particulate phase and, perhaps surprisingly, the mass distribution of gas phase PAHs varies with the richness of the fuel-air mixture.
Following successful validation of the sampling and analysis protocol, combustion byproducts were sampled with the same double-filter method in a kerosene flame (with direct interest for the aeronautical domain). We present a comparison between CAST and flame byproducts in the particulate and gas phases.
This work was supported by the French National Research Agency (ANR) through the PIA (Programme d'Investissement d'Avenir) under contract ANR-10-LABX-005 (CaPPA – Chemical and Physical Properties of the Atmosphere), the European Commission Horizon 2020 project PEMs4Nano, and the CLIMIBIO project via the Contrat de Plan Etat-Région of the Haut-de-France region.
[1] Ess, M. N., Ferry, D., Kireeva, E. D., et al. (2016) Carbon 105, 572-585. [2] Faccinetto, A., Desgroux, P., Ziskind, M., et al. (2011) Combust. Flame 158, 227-239. [3] Parent., P., Laffon, C., Marhaba, I., et al. (2016) Carbon 101, 86-100.