Influences of Traffic Emissions and Meteorological Conditions on Ambient PM10 and PM2.5 Levels at a Highway Toll Station

The PM10 and PM2.5 levels at a highway toll station were monitored from October to December 2008. Experimental results show that hourly average PM10 and PM2.5 levels at the highway toll station were 10.6-208.4 mu g/m(3) and 6.6-187.9. mu g/m(3), respectively. Additionally, the PM2.5-to-PM10 ratio at the highway toll station was 0.73, indicating that emissions from traffic sources are dominant in PM2.5 fraction. At the highway toll station, the time variations of the PM10 and PM2.5 levels were not strongly correlated with traffic volumes; however, traffic on the highway markedly elevated ambient PM10 and PM2.5 levels. The PM10 and PM2.5 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 PM10 and PM2.5 levels. Moreover, high wind speed also could have resulted in high PM10 and PM2.5 levels due to the re-suspension of particulate matter under well dispersed conditions. Measurements indicate that both traffic emissions and meteorological conditions drive PM10 and PM2.5 levels at the highway toll station.