Characterization of Nanostructure Phenomena in Airborne Particulate Aggregates and Their Potential for Respiratory Health Effects
Airborne aggregates of nanoparticulates were collected on carbon/form-coated, 100-mesh Ni TEM grids in a thermal precipitator and observed in an analytical TEM utilizing a BF-SAED-DF-EDS characterization protocol to identify the nanocrystalline or nanoparticulate components, especially their degree of crystallinity, size, structural/morphologic features, and chemistries. Reference aggregates of TiO2 rutile and anatase as well as Si3N4 nanoparticles were used to establish these characterization protocols, which were applied to several hundred individual particulates: homogeneous aggregates of carbonaceous/diesel particulate matter, complex mixtures of carbonaceous matter, including carbon nanocrystals, and inorganic nanocrystals; and heterogeneous, nanocrystal/nanoparticulate aggregates. Most airborne particulates were aggregates ranging in aerodynamic diameters from a few nanometers to a few microns; containing as few as 2 nanocrystals to several thousand nanocrystals or nanoparticulates such as carbonaceous spherules arranged in complex branched homogeneous aggregates composing diesel exhaust, with spherule diameters ranging from 10 to 30 nm. The potential for ultrafine airborne aggregates to fragment into hundreds or thousands of nanoparticulate components in human airways and act as toxic agents in deep lung tissue is demonstrated.