PM2.5 and PM10 particle size fractions were measured every Wednesday and Sunday for an 18-month period from 1 January 2001 at three key ACE-Asia sites: Hong Kong, Cheju Island in southern Korea, and Sado Island in Japan. Median 24 hour PM2.5 mass loadings of 29, 16, and 9.1 ¿g/m3 and coarse mass loadings of 33, 14, and 11 ¿g/m3 were measured at Hong Kong, Cheju, and Sado Island sites, respectively, during the study period. The corresponding maximum PM2.5 and coarse mass values for the three sites were 109, 81, and 78 ¿g/m3 and 101, 162, and 253 ¿g/m3, respectively. Accelerator-based ion beam analysis (IBA) techniques were used to quantify major components as well as significant trace elements. These included total hydrogen, black carbon, F, Na, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, and Pb, with detection limits close to or below 1 ng/m3. The average PM2.5 percentage composition by weight across the three sites was estimated to be around (8.4 ¿ 4)% black carbon, (7.7 ¿ 7)% soil, (43 ¿ 14)% ammonium sulfate, (11 ¿ 16)% organic matter, (10 ¿ 12)% salinity, and (0.6 ¿ 0.3)% trace elements. Soil fingerprints for the east Asian region were generated using oxides of measured Al, Si, K, Ca, Ti, Mn, and Fe concentrations. The coarse fraction was dominated by wind blown soil (23%) and sea salts (48%). 10/PM2.5> mass ratios were typically (2.1 ¿ 0.4) averaged across all sites for the whole year. 10/PM2.5> mass ratios for the 21 IBA elements analyzed were also provided. This quantitative data providing both masses and dates over an 18-month period provide useful input for aerosol transport modeling for the east Asia region.