Aerosol chemical composition and number size distributions were measured aboard the R/V Ronald H. Brown during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) from 14 March to 20 April 2001. This manuscript focuses on the prefrontal and postfrontal air masses sampled aboard the ship in the Sea of Japan between 6 and 15 April 2001 to illustrate the different chemical sources/mixtures off the coast of Asia resulting from the contrasting meteorological transport patterns. The prefrontal air masses had a dominant accumulation mode composed of pollution and volcanic aerosols. The aerosol was predominately ammonium sulfate and organic carbon. Minor amounts of dust were present in the marine boundary layer (MBL) as a result of subsidence from a pronounced Taklimakan dust aerosol layer aloft. The sea salt in both the submicron and supermicron modes was highly depleted in chloride from reaction with sulfuric and nitric acid vapors. The passage of a large low-pressure center, surrounded by a widespread distribution of airborne dust, on 10 April brought elevated concentrations of submicron and supermicron Gobi desert dust to the ship. The supermicron dust particles contained high concentrations of sulfate, nitrate, organic, and elemental carbon. The MBL aerosol properties and controlling processes described here provide data to evaluate and refine chemical transport models.