he distribution of nano/micron dicarboxylic acids in size-segregated suburban aeroslo of southern Taiwan was studied for a PM episode and a non-episodic pollurtion period. Oxalic caid, accounting for 77.3% and 83.9%, respectively, of the total dicarboxylic acid, followed by succinic, malonic, maleic, malic and tartaric acid. The mass emdian aerodynamic diameter (MMAD) of oxalic acid was 0.77um with a bi-modal presence at 0.54um and 18nm during non-episodic pollution and a MMAD of 0.67 um with mono-modal presence at 0.54um in PM episode aerosol. The concomitant formation of oxalic and malonie acid bar tartaric acids were significant nuclei mode species. Nano and condensation mode malic and succinic acids were almost perfectly correlated (r>0.98), suggesting that malic acid accumulated in the atmosphere prior to decomposition into succinic acid.