Seasonal variation of water-soluble ion species in the atmospheric aerosols at the summit of Mt. Fuji

Aerosol samples were collected at the summit of Mt. Fuji (3776 m a.s.l., at 35.21N, 138.43E) from July 2001 to August 2002, using a high volume air sampler (ca. 700 L/min) with quartz filters. The concentrations of major ionic species were determined using ion chromatography. The concentrations of Ca2+, Na+, Mg2+, Cl− and NO3− were comparable to those reported for the free troposphere and are considered to be close to the background concentrations of the species. The concentrations of Ca2+, Na+, Mg2+, Cl− and NO3− at the summit were higher in spring, than that of SO42− in spring and summer, and that of NH4+ in summer than those in the rest of the respective seasons. The equivalent concentrations of SO42− and NH4+ showed a good 1:1 correlation and their stoichiometry indicates the occurrence of (NH4)2SO4 in summer, autumn and winter. The sources of SO42− and NH4+ are mainly China, but also the Kanto area especially in summer. However, the 1:1 correlation was not seen in spring. It is inferred that NO3− and SO42− ions have replaced carbonate in CaCO3 in Kosa particles, are then transported from the Asian continent. The present study demonstrated the importance of continuous monitoring of the atmosphere at a high elevation in Japan, especially using consistent protocols, and that the summit of Mt. Fuji is one of the best locations for the monitoring of the atmosphere over the Asian continent as well as the western Pacific Ocean.