Characterization of the major chemical species in PM2.5 in the Kaohsiung City, Taiwan

The concentrations and characteristics of the major components in ambient fine particles in the urban city of Kaohsiung, Taiwan were measured and evaluated. PM2.5 samples were collected using a dichotomous sampler from November 1998 to April 1999 and analyzed for water-soluble ion species using ion chromatography and for carbonaceous species using an elemental analyzer. It was found that SO42−, NO3−, and NH4+ dominated the identifiable components, and occupied 42.2% and 90.0% of PM2.5 mass and total dissolved ionic concentrations. Carbonaceous species (organic and elemental carbon) accounted for 20.8% of PM2.5. The secondary aerosol formed through the NO2/SO2 gas-to-particle conversion was estimated based on the sulfur/nitrogen oxidation ratio (SOR/NOR), i.e., sulfate sulfur/nitrate nitrogen to total sulfur/total nitrogen. The average SOR and NOR values were 0.25 and 0.07 for PM2.5. The high SOR and NOR values obtained in this study suggested that there existed a secondary formation of SO42− from SO2 along with NO3− from NO2 in the atmosphere. The secondary organic carbon formed through the volatile organic compound gas-to-particle conversion was estimated from the minimum ratio between organic and elemental carbon obtained in this study, and was found to constitute 40.0% of the total organic carbon for PM2.5 (6.6% of the particle mass). The results obtained in this study suggest that the formation of secondary aerosols due to conversion from gaseous precursors is significant and important in urban locations.