Concentrations of homologous (C2--C11) dicarboxylic acids were measured in the atmosphere over Chichi-jima Island (27¿04'N, 142¿13'E), western North Pacific, from April 1990 to November 1993. The monthly averaged concentrations of straight-chain C2--C7 dicarboxylic acids, and some branched, keto-, and unsaturated dicarboxylic acids showed a maximum in winter to spring and a minimum in the summer season. In contrast, straight-chain C8--C11 dicarboxylic acids showed an opposite trend with a maximum in spring to summer. Principal component analysis revealed that there is a source characterized by a strong contribution of C2--C7 dicarboxylic acids, phthalic acid, some keto-dicarboxylic acids, and unsaturated-dicarboxylic acids, whereas there seems to be another source(s) for the C8--C11 dicarboxylic acids. A combined model of backward trajectories and emission inventories was used to better understand the sources and source regions of the dicarboxylic acids. The results show that concentrations of various C2--C7 dicarboxylic acids in the western North Pacific atmosphere are largely controlled by their emissions and/or their precursor emissions from anthropogenic sources in the Asian continent, followed by long-range atmospheric transport. On the other hand, longer-chain dicarboxylic acids cannot be explained by long-range atmospheric transport from a continental region, which implies emissions and/or formation from natural sources, possibly from the ocean.