The PM 10 and PM 2.5 levels at a highway toll station were monitored from October to December 2008. Experimental results show that hourly average PM 10 and PM 2.5 levels at the highway toll station were 10.6-208.4 μg/m 3 and 6.6-187.9μg/m 3 , respectively. Additionally, the PM 2.5 -to-PM 10 ratio at the highway toll station was 0.73, indicating that emissions from traffic sources are dominant in PM 2.5 fraction. At the highway toll station, the time variations of the PM 10 and PM 2.5 levels were not strongly correlated with traffic volumes; however, traffic on the highway markedly elevated ambient PM 10 and PM 2.5 levels. The PM 10 and PM 2.5 levels at the highway toll station are higher than those at monitoring stations in the vicinity to the toll station by factors of 1.3-1.4 and 1.4-1.8 times, respectively. The low wind speeds and low mixing-layer heights lead to relatively high PM 10 and PM 2.5 levels. Moreover, high wind speed also could have resulted in high PM 10 and PM 2.5 levels due to the re-suspension of particulate matter under well dispersed conditions. Measurements indicate that both traffic emissions and meteorological conditions drive PM 10 and PM 2.5 levels at the highway toll station.

No abstract