Séminaire F. Villanueva - research gate profile
University of Castilla La Mancha, Institute for Combustion and Atmospheric Pollution,
Ciudad Real, Spain and Science and Technology Park of Castilla La Mancha, Albacete, Spain.
10 juillet 2018, 10:45, Amphithéâtre P. Glorieux, CERLA, Université de Lille
Heterogeneous reactivity of soot generated in the combustion of different fuels and accurate quantification of polycyclic aromatic compounds adsorbed on soot samples
Soot is composed of elemental carbon and numerous organic comopunds1-2 and is one of the products generated as pollutant in the incomplete combustion of fuels. Soot is the second largest contributor to global warming after CO23. Soot particles can adsorb complex mixtures usually containing thousands of organic compounds such as polycyclic aromatic hydrocarbons (PAHs) that can interact with NO2 to form nitrated PAH (NPAH). PAHs are carcinogenic and mutagenic after metabolic activation, whereas NPAHs are powerful direct-acting mutagens. Therefore, it is obviously of major interest to analyze PAHs and their nitrated derivatives. According to this, to know the chemical composition and atmospheric reactivity of soot is important in order to evaluate its impact on human health and climate change.
The heterogeneous reaction of NO2 and CF3COOH with soot produced by diesel and GTL (gas to liquid) fuels and also with Printex-U (used as reference) were investigated using a Knudsen flow reactor with mass spectrometry as a detection system for gas phase species4. The initial (g0) and the steady-state (gss) uptake coefficients were measured indicating that GTL soot reacts faster than diesel soot and Printex U for NO2 gas reactant while the initial uptake coefficients for the reactions with CF3COOH gas reactant are very similar. The number of reacted molecules have also been calculated for CF3COOH and NO2 reactions. More information of the surface composition has been obtained using Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTS) before and after the reaction of soot samples with gas reactants. As conclusion, the interface of diesel and GTL soot before reaction mainly consists of polycyclic aromatic hydrocarbons (PAHs), nitro-compounds as well as ether functionalities. After reaction with gas reactant, it was observed that PAHs and nitro-compounds remain on the soot surface and new spectral bands such as carbonyl groups (carboxylic acids, aldehydes, esters and ketones) are observed.
On the other hand, a methodology for the extraction and quantitative analysis of 28 polycyclic aromatic compounds, PACs (PAH, nitro-PAH and oxy-PAH) from soot particles have been developed using Printex-U and a standard reference material (SRM) NIST1650b. Four blends of solvents were tested in order to simultaneously extract all PACs using microwave assistant extraction (MAE). PACs were quantified with gas chromatography coupled with tandem mass spectrometry (GC-MS/MS) operating in Multiple Reaction Monitoring (MRM) mode. The results showed that the best solvent was acetone:toluene with regard to precision and accuracy. This method was applied to the diesel soot mentioned above. The results showed that SRM 1650b and diesel soot present differences regarding the adsorption of the heaviest PAH and nitro-PAH since the recoveries of internal standards (IS) were much higher for SRM than for diesel soot. However, when soxhlet extraction is used the recoveries of IS improve.
1 Poschl, U., 2005. Angew. Chem. Int. Ed. 44, 7520–7540.
2 Daly, H.M., Horn, A.B., 2009. Phys. Chem. Chem. Phys. 11, 1069–1076.
3IPCC, 2013. Climate Change 2013. Cambridge University Press.
4 Tapia, A., Salgado, S., Martín, P., Villanueva, F., García-Contreras, R., Cabañas, B. 2018. Atmos. Environ. 177, 214-221.