Many authors reported how the use of high-resolution transmission electron microscopy (HRTEM) images can highlight the presence of graphitic or amorphous components (Adachi and Buseck Citation2008), and the different structural frame of graphitic layers in the BC, related to different combustion processes such as pyrolysis of coal or combustion of liquid fuels (Su et al. Differently, transmission electron microscopy (TEM) analyses are particularly suitable to characterize the properties of soot (Buseck et al. For this aim, the classical approach to the airborne PM analysis (gas chromatography-mass spectrometry for organics and scanning electron microscopy and energy dispersive spectrometry for minerals and trace metals) is not sufficient to obtain detailed information about soot properties and consequently the genetic processes. Therefore, the understanding of the properties of air-dispersed soot in the atmosphere is important for recognizing the sources and evaluating the different impact related to its properties. Citation2005).Ī different and important field of research concerns the role of soot in the regulation of climate and environmental processes (Andreae and Gelencsér 2006). Owing to the variability of these processes, soot composition is given by a mix of graphitic carbon (or elemental carbon-EC), amorphous carbon, graphenes, and other organic compounds, such as hydrocarbons, aromatics, alkanes, fullerenes, and polyenes (Sadezky et al. Citation2004)-is usually defined as the product of incomplete combustion of organic matter (e.g., vehicular traffic, heating systems, industries, fossil-fueled power plants, incinerators), although it can also be generated by combustion of biomasses or woods and, in domestic ambients, by cooking. Soot-sometimes referred to as “black carbon” (BC) because of its optical properties (Mertes et al. Citation2003), that are responsible of oxidative stress on biological systems (Sørensen et al. Citation2006), and organic compounds (Sakurai et al. Besides, the observed effects on the health are also correlated to the soot properties and composition, in particular to the presence of trace metals (Lee et al. Therefore, due to its high content in the fine fraction and the ability to penetrate deeper in the lungs, soot particles are likely one of the most toxic components of ambient aerosol (Zerbi et al. Citation2005 Englert Citation2005), and similar results are also shown by toxicological studies (Gualtieri et al. Several authors have pointed out that the inhalation of particulate matter (PM) can cause acute and chronic toxicological effects, such as respiratory inflammations or lung disease on exposed people (Brunekreef and Forseberg Citation2005 Davidson et al. Soot is widely regarded as one of the most important air pollutants because of its occurrence in all urban areas and its impact on the environment, climate, and human health. 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.Ĭopyright 2014 American Association for Aerosol Research A similar aspect emerges for the pure black carbon particles, mainly crystalline, and the black carbon particles associated with minerals, generally disordered. 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). 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. 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. 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.
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