Analysis of High SO₂ Concentration in Nagasaki Prefecture

Abstract

High concentration phenomena of SO₂ in Nagasaki prefecture were analyzed using the surface air monitoring data and mountain top measurement at Unzen Nodake (1142m). Results showed good relationship between the high SO₂ concentration at Unzen Nodake and E-SW wind direction of 850 mb level at Kagoshima Meteorological observatory due to the long range transportation of volcanic plume from Mt. Sakurajima. On the other hand, the surface SO₂ concentration in Nagasaki prefecture did not necessarily agree with the high SO₂ concentration at Unzen Nodake. This analysis showed that the surface SO₂ episode were usually observed when Nagasaki prefecture was located just after the passage of moving high atmospheric pressure system. During these period, stable layer is formed aloft and decending wind is observed. Under these meteorological condition, the volcanic plume from Mt. Sakurajima is transported to the surface area.