Investigation of the microcharacteristics of PM2.5 in residual oil fly ash by analytical transmission electron microscopy.
Atmospheric emissions from combustion of residual oils often consist of carbonaceous material and metal compounds, both of which are of concern for health and environmental issues. In this study, particulate matter fractions with aerodynamic diameters nominally less than 2.5 microm (PM2.5) in two residual oil fly ash (ROFA) samples generated from combustion experiments were investigated by analytical transmission electron microscopy (TEM) techniques, including energy-dispersive X-ray spectroscopy, selected area electron diffraction (SAED), high-resolution TEM, and electron energy loss spectroscopy (EELS). Carbonaceous particles, which dominate both samples, exist in two distinctive forms: as soot aggregates with spherical primary particles of size 10-80 nm that exhibit a concentric arrangement of graphitic layers around the particle center and as larger spherical or irregular-shaped porous residual char particles of size 1-20 microm that usually have anisotropic microtextures and contain organic sulfur species. Such carbon-rich particles were often observed to be coated with inorganic species, notably transition metals (V, Ni, Fe, Zn) in the form of sulfates, oxides, vanadates, and phosphates. In this respect, they therefore differ from similar carbonaceous particles generated in combustion of diesel fuels that lack significant inorganic species. Crystalline phases of vanadium, nickel, and iron oxides and multi-element oxides were identified by the SAED technique. The valence state of V in some V-rich oxide particles probed by EELS was found to vary from +2 to +5. Individual transition metal sulfate, oxide, and phosphate particles are typically compositionally complex, containing multiple metallic elements. These microcharacteristics of individual PM2.5 particles revealed by electron microscopy techniques should be important parameters to include in future toxicological investigations of ROFA PM.
Chen
Yuanzhi
Y
University of Kentucky, 533 South Limestone Street, Lexington, Kentucky 40508-4005, USA.
Shah
Naresh
N
Huggins
Frank E
FE
Huffman
Gerald P
GP
D000393:Air Pollutants / Q000032:analysis*; D002244:Carbon / Q000737:chemistry*; D003031:Coal; D060729:Coal Ash; D004784:Environmental Monitoring; D017745:Incineration; D007220:Industrial Waste; D046529:Microscopy, Electron, Transmission; D010316:Particle Size; D052638:Particulate Matter
D000393:Air Pollutants; D003031:Coal; D060729:Coal Ash; D007220:Industrial Waste; D052638:Particulate Matter; D002244:Carbon