Temporal variation of water-soluble ions of free tropospheric aerosol particles over central Japan

Abstract

Free tropospheric aerosol particles were collected at Mt. Norikura (36.1°N, 137.5°E, 2770 m a.s.l.) in Japan during May.October in 2001 and 2002. An automated sequential daily nighttime (00-06 a.m.) sampler collected free tropospheric aerosols. Average, median, SD, minimum and maximum concentrations of total ionic weight of the 114 samples were, respectively, 3.9, 2.8, 3.7, 0.2 and 23.2 μg m-3 Transport conditions were analysed using backward air trajectory with precipitation amounts along the trajectory. Results suggest that low aerosol mass concentration causes are (1) descending trajectories and (2) precipitation scavenging during transport without contacting boundary layer atmosphere until arrival. It is suggested that, without precipitation scavenging after entrainment into the free troposphere, aerosol transport from active emissions at the surface enhances mass concentration at Mt. Norikura.Average concentrations of NO3 -, non-sea-salt (nss)K+ and C2O4 2- are high in March.June and low in winter. The highest average nssSO4 2-. concentration occurs in summer; it is high from spring through fall. Seasonal variation of NH4 + concentrations resembles that of nss SO4 2-, but the concentrations molar ratio (NH4 +/nssSO4 2-) is high (ca. 2) in spring and decreases to 1 in winter. Seasonal variation of NH4 + + NH3 concentration agrees with that of NH3 emissions in China.