The daily mean concentrations of PM2.5 mass ionic species carbonaceous species and HNO3, HCl, and NH3 were analyzed at three background sites in Korea : Kangwha, Kosan, and Dongbaik during two intensive field studies between December 1996 and January 1997, Four-day backward trajectory analysis was also carried out. The mean concentrations of anthropogenic species were higher at Kangwha and Dongbaik than Kosan. At these two sites themean concentrations of nitrate and ammonium/ammonia were higher than those of Kosan. It was suggested that these two sites be considered as the background sites of the Seoul Metropolitan Area and Pusan respectively. Major chemical components in fine particles were sulfate organic carbon nitrate and ammonium for all the sites. More than 90% of sulfate were non-sea-salt(nss) sulfates and most of the nss sulfate in PM2.5 might be present as ammonium sulfates at all sites. Most of air parcels arriving a Kangwha and Dongbaik were from the northern China. At Kosan during the measurement period half of air parcels were from the northern China and the other half from the southern China. At Kosan the concentrations of anthropogenic air pollutants originated from the southern China were higher than those typically observed from the northern China.