Microanalysis of ambient particles from Lexington, KY, by electron microscopy

Analytical transmission electron microscopy has been used for in-depth characterization of the individual submicron (physical size<1 μm) particulate matter (PM) from the urban atmosphere of Lexington, Kentucky, USA. Carbonaceous particles and sulfur-bearing particles dominate the PM samples on a particle count basis. Soot aggregates are the major form of carbonaceous particles. Organic-type and biogenic carbonaceous particles are also observed and exhibit quite different morphologies and microstructures compared with combustion-generated soot and char particles. Ammonium sulfate is the dominant chemical type of sulfur-bearing particles. Other types of sulfur-bearing particles include crystalline sodium, potassium and calcium sulfates. Silicon-bearing particles consist mainly of silicon oxides and aluminosilicates. Iron and titanium oxide particles are the major metal oxides found in this study. Considerable amounts of iron oxide with other transition metal elements (e.g. Mn and Zn) have been observed, typically in the form of spinel nanocrystals. Minor amounts of other species (e.g. phosphates, lead compounds, and carbonates) have also been observed. The combined use of these analytical techniques is capable of revealing much new information on the microcharacteristics of individual submicron particles; such information should be relevant to toxicological, epidemiological, and source apportionment studies.