Semi-Continuous Measurements of Sulfate in Fine Particles in Central Japan: On High Concentration Events and Comparison with Measurement Concentrations by a Commercial Sulfate Monitor

At a site on the Sea of Japan side of central Japan, the concentrations of ionic components in PM_2.5 were measured semi-continuously for about 15 months using filter collection and ion chromatography (filter method). Continuous measurements of sulfate particles were simultaneously performed in summer and autumn using a commercial sulfate monitor (Sulfate Particle Analyzer, SPA). High concentrations of sulfate ion (SO₄²⁻) were sometimes observed from spring to summer, and the high SO₄²⁻ was thought to be due not only to trans-boundary pollution from the Asian continent but also the influence of volcanic plumes. A comparison between the SPA and the filter method showed that the sulfate concentrations measured by the SPA method tended to be about 20% lower than those by the filter method. High concentrations of sulfate particles were observed not only from volcanoes from the Kyushu District such as Sakurajima, but also from volcanic smoke derived from Nishinoshima in the Ogasawara Islands. In recent times, sulfate particles from volcanos may be important contributors to PM_2.5 in Japan.