Characteristics Of Particulate Matter Near A Major Road In Macau

Inhalable particulate matter is the primary air pollutant in the urban area in China.The environmental and healthy effects of particulate pollution have been of greatconcern in the past decades. With the rapid growth of vehicle counts, particle emissionfrom traffic activities has been one of the most important sources for particulate matterin roadside microenvironment. In particular, PM_2.5has been the focus in researches onthe correlation between.roadside particle level and traffic flow.PM_2.5and PM10samples were collected near a major road （Rua do Campo Road）and a background site （Tai Tam Mountain） in Macau in January and May2010. Theconcentrations of particulate matter, OC, EC and polycyclic aromatic hydrocarbonspollution were measured. Moreover, the temporal and spatial variations of theircharacteristics were analyzed.During the monitoring period, the average concentrations of the PM10and PM_2.5near Rua do Campo Road were25.59μg/m³and21.98μg/m³, respectively, which weresignificantly higher than those measured at Tai Tam Mountain.In addition, seasonal variation of PM_2.5concentration was observed at thebackground site （summer <winter）; however, there was no statistical difference betweensummer and winter PM_2.5level at the roadside site. Considering of the climatecharacteristics in Macau, the seasonal variation of PM_2.5concentrations at thebackground site should be attributed to the long-range transport of pollutants fromChinese mainland. While at the roadside site, the effects of long-range transport wasweakened by the strong local emissions from traffic activities. The study also found thatthere was a close relationship between diurnal variation of PM concentrations andtraffic flow.Results of carbon analysis suggested that the average concentrations of the OC andOC%near Rua do Campo Road were higher than Tai Tam Mountain, which representedthe contribution of vehicle emission in the roadside microenvironment of Rua doCampo Road. The OC%and EC%near Rua do Campo Road have no seasonal variationsince the PM_2.5emission from traffic was almost stable among different seasons. For thesize distribution, OC near Rua do Campo Road OC mainly enriched in the particle size<0.2μm，while EC mainly distributed in the particle size0.2⁰.5μm. The Ratios ofOC/EC near Rua do Campo Road showed that the carbon components in the roadside environment were affected by traffic flow.During the monitoring period, the average concentration of the total PAHSnearRua do Campo Road was3.61ng/m³; while lower concentrations were observed at TaiTam Mountain （1.69ng/m³）. Clear seasonal variation with low concentration insummer was identified at the background site, which was also closely related tolong-range transport of particles. The reduction in PAH concentration from winter tosummer near Rua do Campo Road was much lower compared to Tai Tam Mountain. Itwas also found that the concentrations of4-ring and5-ringPAHSwere higher in thedaytime than in the nighttime near Rua do Campo Road, which was primarily attributedto the vehicle emissions. Molecular diagnostic ratio method indicated that PM_2.5-boundPAHs in the roadside environment was mainly derived from vehicle emissions.