High Time-resolution Characterization of PM2.5 Sulfate Measured in a Japanese Urban Site.

The high time-resolution monitoring data are essential to estimate rapid changes in chemical compositions, concentrations, formation mechanisms, and likely sources of atmospheric particulate matter (PM). In this study, PM_2.5 sulfate, PM_2.5, PM₁₀, and the number concentration of size-resolved PMs were monitored in Fukuoka, Japan by good time-resolved methods during the springtime. The highest monthly average PM_2.5 sulfate was found in May (8.85 µg m^-3), followed by April (8.36 µg m^-3), March (8.13 µg m^-3), and June (7.22 µg m^-3). The cases exceed the Japanese central government's safety standard for PM_2.5 (35 µg m^-3) reached 10.11% during four months campaign. The fraction of PM_2.5 sulfate to PM_2.5 varied from 12.05% to 68.11% with average value of 35.49% throughout the entire period of monitoring. This high proportion of sulfate in PM_2.5 is an obvious characteristic of the ambient PM_2.5 in Fukuoka during the springtime. However, the average fraction of PM_2.5 sulfate to PM_2.5 in three rain events occurred during our intensive campaign fell right down to 15.53%. Unusually high PM_2.5 sulfate (>30 µg m^-3) marked on three days were probably affected by the air parcels coming from the Chinese continent, the natural sulfur in the remote marine atmosphere, and a large number of ships sailing on the nearby sea. The theoretical number concentration of (NH₄)2SO₄ in PM_0.5-0.3 was originally calculated and then compared to PM_2.5 sulfate. A close resemblance between the diurnal variations of the theoretically calculated number concentration of (NH₄)2SO₄ in PM_0.5-0.3 and PM_2.5 sulfate concentration indicates that the secondary formed (NH₄)2SO₄ was the primary form of sulfate in PM_2.5 during our monitoring period. [ABSTRACT FROM AUTHOR]