Chemical composition of fine aerosol measured by AMS at Fukue Island, Japan during APEX period

The size distribution and chemical composition of ambient aerosols was analyzed using an Aerodyne aerosol mass spectrometer (AMS) at Fukue, Japan in the spring of 2003. The average concentration of ammonium, nitrate, sulfate, chloride and organics was 1.57, 0.56, 4.80, 0.07 and 5.03 μg m−3, respectively. The size distribution showed that the modes of ammonium, sulfate and organics were all about 400–700 nm throughout the entire observation period with the exception of a few cases, indicating that these species were internally mixed. The average equivalent ratio of ammonium to sulfate was 0.88, which means that the aerosol was slightly acidic. When air masses came from China and Korea with high aerosol concentration (25–27 March and 6–7 April), nitrate was found in fine particles with ammonium and sulfate. The average ratio of organics to sulfate was 1.05, indicating that the contribution of organics is not negligible in this region. Mass spectra showed that the largest signal in organic fragments was m/z=44, which shows that organic species are well-oxygenated.