Color-related differences in the chemical composition of aerosol-laden filters

We examined color-related differences in the chemical composition of 6000 aerosol filters collected from 1989 to 1997 at three sampling sites in the North Atlantic Ocean (Barbados, Bermuda, and Izaña) operated for the Atmosphere/Ocean Chemistry Experiment (AEROCE). The concentrations of the trace elements (Al, Br, Ca, Cl, Fe, Na, Sb, Sc, Se, V) and two ions, NO3− and SO42−; the activities of 210Pb and 7Be; and the mixing ratios of ozone were compared and contrasted for groups of samples and data matched to the three basic colors of aerosol filters (brown, gray or white). Chemical composition is related to filter color, that is, the brown and gray samples correspond to mineral dust and absorbing aerosol from various pollution sources, respectively, although these substances often are mixed in varying proportions. The white filters are best regarded as indicating the absence or low concentrations of dust or other absorbing aerosols, and they are often indicative of clean marine air. Relationships among atmospheric substances differ significantly in the color-stratified data subsets, and grouping the samples by color provides unique insight into the relationships among mineral dust, pollution aerosol, and other substances over the North Atlantic.