Characterization of the Bermuda tropospheric aerosol by combined individual-particle and bulk-aerosol analysis

Marine boundary layer aerosol samples collected from Bermuda were examined by combined individual-particle analysis using an electron microprobe and bulk-sample analysis using INAA. Within the fine-fraction samples (< 2 μm) 65 particle types, including frequently occurring aggregates, are identified. Principal components analysis (PCA) indicates the presence of eight assemblages of particle types. A group of silicate and other crustal particle types are associated with bulk-sample Al, I, Mg, V, Co, Cs, Eu, Fe, Hf, Sc, and Th; this is most abundant when transport was across the ocean from North Africa. Three assemblages of S-rich particle types were generally most abundant when transport was from North America. One of these S-rich assemblages is associated with bulk-sample Zn and Se; another is associated with Cr. Also identified by PCA is a component with superfine silica, probably produced by reduction-vaporization during coal combustion. Na and Cl in bulk samples do not significantly correlate with fine-fraction Na-CI particle types, demonstrating the statistical independence of sea-salt particles in the fine fraction from sea-salt particles in the coarse fraction. A variety of individual-particle parameters are shown to be dependent upon transport direction; examples include relative concentrations of silicate types within the crustal particle assemblage, the degree of coating or agglomeration of silicates with S-bearing species, and the relative sizes of different particle types within the crustal assemblage.