2015 年 30 巻 2 号 p. 115-125
In order to investigate the processes of chemical transformations of aerosol transported from East Asia to Japan the concentrations of ionic species in size-segregated aerosols were measured in Cape Hedo, Okinawa, Japan. By use of a cascade impactor (Nano sampler) we collected aerosols at 5 stages. Throughout the observation periods, species originated from anthropogenic sources such as NH4＋ and nss-SO42- were dominant in fine mode particles (0.1–0.5 μm, 0.5–1 μm), whereas species originated from natural sources such as Na＋ and
Cl- were dominant in coarse mode particles (2.5–10μm, ＞10μm). The (Cl-＋NO3-)/Na＋ ratio in coarse mode, 1.14 in equivalent basis, was very close to Cl-/Na＋ of sea water (1.17), which indicated that NH4NO3 was decomposed to gaseous NH3 and HNO3 during the long-range transport, and HNO3 deposited on sea-salt particles. The concentrations of NH4＋, nss-SO42- and nss-K＋ in fine mode were higher during high pressure episodes; it suggests that the fine particles emitted from anthropogenic sources (e.g. biomass burning) were transported with a migratory anticyclone. Increase of nss-Ca2＋ and nss-SO42- in coarse mode during Asian dust episode implied that surface reactions with gaseous species on CaCO3 particles occurred during the transport.