“…Black carbon (BC) aerosols are an important atmospheric component because of their potential deleterious impact on health and climate (Baumgardner et al, 2002), and dust, resulting from natural emissions, is involved in the biogeochemical cycling of iron, an essential micronutrient to marine phytoplankton (Arimoto, Balsam, & Schloesslin, 2002). Both BC (Bohren & Huffman, 1998;Lindberg, Douglass, & Garvey, 1993;Ackerman & Toon, 1981;Bodhaine, 1995) and dust (Gillespie & Lindberg, 1992, Caquineau, Gaudichet, Gomes, Magonthier, & Chatenet, 1998 particles absorb light at visible wavelengths, and therefore both, if present, contribute to measurements of aerosol absorption coefficient, aerosol ( , t) of the type reported here. It is therefore desirable to develop a method to estimate the contribution of each to such measurements.…”