PM_1.0and PM_2.5characteristics in the roadside environment of Hong Kong

Daily mass concentrations of PM1.0(particles less than 1.0 μm in diameter), PM2.5(particles less than 2.5 μm in diameter), organic carbon (OC), and elemental carbon (EC) were measured from January through May 2004 at a heavily trafficked sampling site in Hong Kong (PU). The average concentrations for PM1.0and PM2.5were 35.9 ± 12.4 μg cm-3and 52.3 ± 18.3 μg cm-3. Carbonaceous aerosols were the dominant species in fine particles, accounting for ∼45.7% of PM1.0and ∼44.4% of PM2.5. During the study period, seven fine-particle episodes occurred, due to the influence of long-range transport of air masses from mainland China. PM1.0and PM2.5responded in similar ways; i.e., with elevated mass and OC concentrations in those episode days. During the sampling period, PM1.0OC and EC generally behaved similarly to the carbonaceous aerosols in PM2.5, regardless of seasonal variations and influence by regional pollutions. The low and relatively constant OC/EC ratios in PM1.0and PM2.5indicated that vehicular emissions were major sources of carbonaceous aerosols. PM1.0and PM2.5had the same dominant sources of vehicular emissions in winter, while in spring PM2.5was more influenced by PM1-2.5(particles 1-2.5 μm in diameter) that did not form from vehicle exhausts. Therefore, PM1.0was a better indicator for vehicular emissions at the Roadside Station.