Abstract: We examined the characteristics, sources, and distribution of PM2.5 and carbonaceous species in particulate samples collected from June 2009 to May 2010 in Incheon, Korea. The average PM2.5 concentration (41.9 ± 9.0 μg m−3) exceeded the annual level set by the United States'' National Ambient Air Quality Standards (15 μg m−3). The major fraction of PM2.5 consisted of ionic species (accounting for 38.9 ± 8.8%), such as NO3 −, SO4 2−, and NH4 +, as well as organic carbon (OC) (accounting for 18.9 ± 5.1%). We also analyzed the seasonal variation in PM2.5 and secondary aerosols such as NO3 − and SO4 2− in PM2.5. While SO4 2− concentrations were higher in spring and summer, the concentration of PM2.5 and NO3 − were the highest in winter. SO4 2− concentrations were higher during the spring and summer, but PM2.5 and NO3 − were highest during the winter. As an important aerosol indicator, water-soluble organic carbon (WSOC) (mean 4.7 ± 0.8 μg m−3, 58.9 ± 10.7% of total OC) showed a strong relationship with NO3 −, SO4 2−, and SOC (R 2 = 0.56, 0.67, and 0.65, respectively), which was indicative of favorable conditions for SOC formation during the sampling period. Among the individual organic aerosols measured, n-alkanes, n-alkanoic acids, levoglucosan, and phthalates were major components, whereas PAHs (polycyclic aromatic hydrocarbons), oxy-PAHs, hopanes, and cholestanes were minor components. The concentration of organic compounds during smoggy periods was higher than during non-event periods. The n-alkane and n-alkanoic acid species during the smoggy periods were 10–14 times higher than during the normal period. Using principal component analysis coupled with multiple linear regression analysis, we identified the primary sources of PM2.5 to be motor vehicle/sea salt, secondary organic aerosols, combustion, biogenic/meat cooking, and soil sources. [Copyright &y& Elsevier]