Size distributions of C2--C4 dicarboxylic acids in aerosols were studied in the marine boundary layer (MBL) of the central to western North Pacific as well as off the coasts of East Asia. C2--C4 Diacids were mostly present in submicron particles over the coastal ocean, but they were relatively abundant in supermicron particles over the remote ocean. We found that the peak diameters for the concentration of C2--C4 diacids in supermicron particles over the remote ocean were similar to that for the surface-area distribution of sea salts, suggesting a deposition of gaseous diacids on sea-salt particles and/or their heterogeneous formation during long-range transport. The present results, together with the solubility product of calcium oxalate, suggest that oxalic acid in sea salts may partly form insoluble calcium salt, which potentially enhances the uptake of gaseous oxalic acid by the aerosol particles.