Seasonal variations in SO sub(2) plume transport over Japan: Observations at the summit of Mt. Fuji from winter to summer

• Published in: Atmospheric environment (1994) Vol. 40; no. 36; pp. 7018 - 7033
• Main Authors: Igarashi, Yasuhito, Sawa, Yosuke, Yoshioka, Katsuhiro, Takahashi, Hiroshi, Matsueda, Hidekazu, Dokiya, Yukiko
• Format: Journal Article
• Language: English
• Published: 01.11.2006
• Subjects: Japan; IN, North Pacific; INW, Japan; North Pacific
• ISSN: 1352-2310
• DOI: 10.1016/j.atmosenv.2006.06.017

We undertook continuous measurements of SO sub(2) concentrations at the summit of Mt. Fuji, Japan (3776 m above sea level), during the period January to July, 2004. These data include the first data set that fills the previous gap in SO sub(2) time series for the springtime middle troposphere over Japan. The time series shows trends in high-SO sub(2) long-range transport events from winter to spring. Elevated SO sub(2) concentrations are always accompanied by elevated CO and super(222)Rn concentrations, and backward trajectories for such events indicate a continental origin. These data display clear sporadic signatures of Asian outflow over Japan to the North Pacific. Such high-SO sub(2) events decline in strength and frequency during spring. The observed seasonal variation of SO sub(2) events may in fact have nothing to do with seasonality in SO sub(2) emissions from the Asian continent, as seasonal patterns in SO sub(2) events show a similar phase shift to that of the prevailing wind direction and relative humidity (RH) observed on-site. The changes in air mass indicated by daily backward trajectory analysis may also explain the observed temporal changes in SO sub(2) events. A major factor appears to be the removal of SO sub(2) from the continental pollution plume during long-range transport. The SO sub(2)-bearing polluted air is dry during the depths of winter; accordingly, little SO sub(2) is removed by cloud processes at this time of year. The nature of the air mass changes during spring when increasing humidity levels lead to the increased removal of SO sub(2) by cloud processes. RH data along the air mass travel path also support the importance of cloud processes in reducing SO sub(2) concentrations within the pollution plume.