| Combustion of coal, petroleum-based fuels and biomass causes considerable amounts of particulate matter (PM) to be present in the ambient environment. In this research, a combination of electron microscopy techniques, including scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), computer-controlled scanning electron microscopy (CCSEM), conventional transmission electron microscopy (CTEM), electron diffraction, high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM), energy-filtered transmission electron microscopy (EFTEM), and electron energy-loss spectroscopy (EELS), has been employed for in-depth analysis of the individual particles generated from the combustion of coal, residual oil, diesel fuel, gasoline, jet fuel and wood. Ambient PM collected from the Lexington urban atmosphere has also been investigated. Various compositional and microstructural differences have been observed among different types of carbonaceous particles. Ultrafine soot aggregates with spherical primary particles having sizes less than 100 rim have been observed in all PM samples investigated in this study. Micron-sized coke and char particles are common for coal fly ash (CFA) and residual oil fly ash (ROFA) PM. Jet PM contains carbonaceous particles intermixed with metallic elements. Hard wood PM is distinguished by its content of potassium-containing tar ball particles. The inorganic PM in western/low rank CFA samples is dominated by Ca-aluminosilicates, while that of eastern/bituminous CFA samples exhibits significant amounts of Fe-aluminosilicates. The ultrafine inorganic particles in three CFA PM samples show quite different morphologies, compositions and microstructures from particles in coarser micron-sized particles from the same coals. Individual inorganic particles in two high-sulfur ROFA PM samples are compositionally complex. Sulfates, transition metal oxides, vanadates, phosphates, and sulfides have been identified. Ultrafine soot aggregates and various sulfates dominate the submicron fraction of the Lexington airborne PM samples. Other observed inorganic species include mainly silicon oxides, aluminosilicates, iron oxides, titanium oxides and phosphates. Information regarding the morphologies, sizes, compositions, microstructures and chemical phases of different types of individual particles may provide important clues to epidemiological and toxicological studies aimed at discovering the underlying mechanisms that cause adverse health effects. In addition, such information also can be used in source apportionment studies of ambient PM. |
