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&ndash;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&ndash;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&ndash;11:00 (63.4&nbsp;&mu;g/m3) and 17:00&ndash;18:00 (65.0&nbsp;&mu;g/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&nbsp;h&minus;1, respectively. BC is emitted mainly by diesel-fueled vehicles and this showed the highest concentration (31.2&nbsp;&mu;g/m3) during the midday period (10:00&ndash;11:00 LT) on workdays. A poor correlation was found between PM2.5 concentration and wind speed (R&nbsp;=&nbsp;0.51, P-value&nbsp;&gt;&nbsp;0.001). In contrast, the concentration of PM10&ndash;2.5 was found to depend upon wind speed and it increased with obvious statistical significance as wind speed increased (R&nbsp;=&nbsp;0.98, P-value&nbsp;&lt;&nbsp;0.0001).</p