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Raman Characterization of Ambient Airborne Soot and Associated Mineral Phases

Airborne particulate matter samples were collected in an urban and a rural–suburban monitoring stations of the city of Rome, Italy, and the particles were analyzed through the Raman microspectroscopy. A careful examination of the spectral bands, performed with a five-(Voigt) curve deconvolution model previously described by the literature and here adapted to the purpose, lead to the characterization of the graphitic and carbonaceous material plus the identification of the mineral particles associated with it. Statistical analysis of the full-width at half-maximum (FWHM) values of the bands, as well as of their intensity ratio, revealed the presence of two classes of soot particles that can be ascribed to a different degree of crystallinity. The population of soot collected at the urban site, where the vehicular emission component prevails, exhibits mostly crystalline characteristics (with a D1 FWHM of 150–155 cm−1), whereas the population collected at the rural–suburban site, particularly the coarse fraction, shows a prevailing amorphous nature (with a D1 FWHM of ∼175 cm−1). A similar aspect emerges for the pure black carbon particles, mainly crystalline, and the black carbon particles associated with minerals, generally disordered. These results add useful information and characterization of the soot, a relevant component of the ambient air, and its different features with respect to the urban or rural–suburban areas. Copyright 2014 American Association for Aerosol Research