Electron Microscope Comparisons of Fine and Ultra-Fine Carbonaceous and Non-Carbonaceous, Airborne Particulates
Particulate matter (PM) from a number of specific sources has been collected on carbon/formvar-coated 100-mesh nickel or copper grids for transmission electron microscopy (TEM) using a thermal precipitator. These sources included diesel truck exhaust, graphitic PM from brake-shop environments, jet engine exhaust streams, and a wide range of general airborne PM for comparison. Individual PM TEM images were compared with corresponding selected-area electron diffraction patterns and energy-dispersive (X-ray) spectra. Diesel PM was characterized by aggregate branching of carbonaceous spherules while graphitic PM consisted of layered carbon, crystalline carbon nanotubes and fullerene-related nanocrystals, and prominent mixtures of inorganic microcrystals. Essentially, all airborne PM collected was characterized by variations of cluster or aggregate morphologies and non-carbonaceous PM was mostly micro- or nanocrystalline. Mixtures of carbonaceous and nanocrystalline PM were also observed. Although tedious, individual PM analysis and comparison appears to be a necessary strategy to elucidate the apparent toxic effects increasingly identified with ultra-fine and nanoparticulates in the air.