Real-time measurements of PM2.5, PM10–2.5, and BC in an urban streetcanyon

A continuous dichotomous beta gauge monitor was used to characterize the hourly content of PM2.5, PM10–2.5, and Black Carbon (BC) over a 12-month period in an urban street canyon of Hong Kong. Hourly vehicle counts for nine vehicle classes and meteorological data were also recorded. The average weekly cycles of PM2.5, PM10–2.5, and BC suggested that all species are related to traffic, with high concentrations on workdays and low concentrations over the weekends. PM2.5 exhibited two comparable concentrations at 10:00–11:00 (63.4 μg/m3) and 17:00–18:00 (65.0 μg/m3) local time (LT) during workdays, corresponding to the hours when the numbers of diesel-fueled and gasoline-fueled vehicles were at their maximum levels: 3179 and 2907 h−1, respectively. BC is emitted mainly by diesel-fueled vehicles and this showed the highest concentration (31.2 μg/m3) during the midday period (10:00–11:00 LT) on workdays. A poor correlation was found between PM2.5 concentration and wind speed (R = 0.51, P-value > 0.001). In contrast, the concentration of PM10–2.5 was found to depend upon wind speed and it increased with obvious statistical significance as wind speed increased (R = 0.98, P-value < 0.0001)