Raman characterization of ambient airborne soot and associated mineral phases

Airborneparticulatemattersampleswerecollectedinanurban andarural–suburbanmonitoringstationsofthecityofRome,Italy, and the particles were analyzed through the Raman microspectroscopy. A careful examination of the spectral bands, performed withafive-(Voigt)curvedeconvolutionmodelpreviouslydescribed bytheliteratureandhereadaptedtothepurpose,leadtothecharacterization 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,aswellasoftheirintensityratio,revealedthepresenceoftwo classesofsootparticlesthatcanbeascribedtoadifferentdegreeof 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, particularlythecoarsefraction,showsaprevailingamorphousnature (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.