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, PM2.5 sulfate, PM2.5, 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 PM2.5 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 PM2.5 (35 μg m-3) reached 10.11% during four months campaign. The fraction of PM2.5 sulfate to PM2.5 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 PM2.5 is an obvious characteristic of the ambient PM2.5 in Fukuoka during the springtime. However, the average fraction of PM2.5 sulfate to PM2.5 in three rain events occurred during our intensive campaign fell right down to 15.53%. Unusually high PM2.5 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 PM0.5-0.3 was originally calculated and then compared to PM2.5 sulfate. A close resemblance between the diurnal variations of the theoretically calculated number concentration of (NH4)2SO4 in PM0.5-0.3 and PM2.5 sulfate concentration indicates that the secondary formed (NH4)2SO4 was the primary form of sulfate in PM2.5 during our monitoring period.