The seasonal variation in chemical composition of aerosols measured at Cheju Island, Korea, is presented and discussed. Daily tape filters have been obtained for the three year period analyzed, March 1992 through February 1995. The annual average non-sea-salt sulfate and nitrate mass concentrations of aerosols measured at Cheju, are 7.2 μg/m3 and 1.2 μg/m3, respectively; while calcium and potassium are present in nearly equal amounts of ~0.5 μg/m3, and ammonium averages 1.3 μg/m3. The annual mean mass ratios are SO42-/NO3-=6.2, NH4+/SO42-=0.2, Ca2+/Na+=0.3, and NH4+/NO3-=1.1. Each species is found to follow a seasonal cycle, with sulfate, nitrate, ammonium, potassium, and calcium all showing higher values in the spring. In contrast, chlorine concentrations are 10% lower in the spring. Aerosol enrichment factors relative to the composition of seawater and crustal material from the dust-source regions in central China reveal that the aerosol measured at Cheju is enriched in sulfate, nitrate, and ammonium, but is deficient in chlorine (relative to seawater). The data from the daily tape filters are also compared with those from weekly Hi-Vol filters located at the same site and other measurements in the region.¿ 1997 American Geophysical Union