Carbonaceous species in PM2.5 in the coastal urban agglomeration in the Western Taiwan Strait Region, China

► Carbonaceous species in PM2.5 were studied at urban sites in Western Taiwan Strait Region, China. ► The highest levels of OC and EC in PM2.5 were found in January and lowest in August. ► High OC/EC ratios (5.8) indicated the formation of secondary organic carbon. ► OC and EC showed strong correlations with biomass-burning potassium in November. ► 42.1 ± 15.1% of the total carbon in November was attributed to biomass burning.