Size and Composition of Ambient Particulates in the Yueguangshan-Tunnel, Taiwan

The aim of this study is to investigate the characteristics of size distribution and chemical composition of ambient particulates inside a tunnel. Inside the tunnel, the average concentration of PM2.5 and PM2.5-10 was 479 and 444 mu g/m(3) respectively. The average mass-size distribution showed a trimodal distribution (25-30, 4.075.0, and <0.30 mu m) of ambient particulates inside the tunnel. It can be found from the cumulative mass curve that PM2.5, PM2.5-10, and PM>10 were 25%, 40%, and 35% of the total suspended particulates. Because of the poor air ventilation inside the tunnel, the particulates accumulate inside the tunnel. The dominated species of PM2.5 were EC (average concentration 122.91 mu g/m(3), 25.78%), OC (47.68 mu g/m(3), 10.53%), SO42- (37.42 mu g/m(3), 8.24%), and NO3- (35.01 mu g/m(3), 7.95%), and were EC (131.77 mu g/m(3), 29.87%), OC (53.74 mu g/m(3), 12.15%), SO42- (31.35 mu g/m(3), 7.11%), and NO3- (28.10 mu g/m(3), 6.42%) for PM2.5-10. Results from this study showed that the concentrations of coarse particulate matter and several metals are apparently dominated by re-suspended matter rather than emissions from vehicles, e.g., Al, Ca, and Fe. Therefore, ambient particulate matter is caused by not only vehicle exhaust emission but also dusty roads and traffic-generated dust.