PM_1.0 and PM_2.5 Characteristics in the Roadside Environment of Hong Kong

Daily mass concentrations of PM _1.0 (particles less than 1.0 μm in diameter), PM _2.5 (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 PM _1.0 and PM _2.5 were 35.9 ± 12.4 μ g cm ^{− 3} and 52.3 ± 18.3 μ g cm ^{− 3} . Carbonaceous aerosols were the dominant species in fine particles, accounting for ∼ 45.7% of PM _1.0 and ∼ 44.4% of PM _2.5 . During the study period, seven fine-particle episodes occurred, due to the influence of long-range transport of air masses from mainland China. PM _1.0 and PM _2.5 responded in similar ways; i.e., with elevated mass and OC concentrations in those episode days. During the sampling period, PM _1.0 OC and EC generally behaved similarly to the carbonaceous aerosols in PM _2.5 , regardless of seasonal variations and influence by regional pollutions. The low and relatively constant OC/EC ratios in PM _1.0 and PM _2.5 indicated that vehicular emissions were major sources of carbonaceous aerosols. PM _1.0 and PM _2.5 had the same dominant sources of vehicular emissions in winter, while in spring PM _2.5 was more influenced by PM _{1 − 2.5} (particles 1–2.5 μ m in diameter) that did not form from vehicle exhausts. Therefore, PM _1.0 was a better indicator for vehicular emissions at the Roadside Station.

Acknowledgments

Received 16 March 2005; accepted 28 November 2005. This project is supported by the Research Grants Council of Hong Kong (PolyU5145/03E), G-T 216, and Area of Strategic Development on Atmospheric and Urban Air Pollution (A516) funded by the Hong Kong Polytechnic University. The authors are grateful to Hong Kong Environmental Protection Department (HKEPD) for provision of the data sets and permission for publication. The content of this paper does not necessarily reflect the views and policies of the HKSAR Government, nor does mention of trade names or commercial products constitute endorsement or recommendation of use.

Notes

^a 1–2 m away from the major road

^b more than 30 m away from the major road.

^a The sample might be contaminated.