Characteristics of Individual Particles at a Rural Site in the Eastern United States

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Abstract
To determine the nature of aerosol particles in a rural area of the eastern United States, aerosol samples were collected at Deep Creek Lake, Maryland, on various substrates and analyzed by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). SEM analysis of particles larger than 2.5 μm collected on Nuclepore filters revealed the following: clay minerals, quartz, gypsum, and calcite comprised 50 percent of the particles analyzed; spores, pollen, and plant debris comprised 25 percent; 9 percent were fly ash; 11 percent were sulfates; 5 percent were unidentified. Particles ranging from 0.3 to 2 μm were collected in a cascade impactor on grid-supported carbon films and analyzed by TEM for decomposition rate as well as for reaction with the barium chloride and nitron (C20H16N4) films that were applied after sampling. The TEM analyses indicated that as much as 95 percent of the particles in the 0.3- to 2-μm diameter range were pure ammonium sulfate or acidic ammonium sulfate; they contained essentially no insoluble or nonvolatile matter. About 5 percent of the particles were fly ash spheres. When replicas of particles collected on Nucleopore filters were analyzed by TEM, we observed agglomerates of particles smaller than 0.1 μm.