Hourly measurements of elemental carbon (EC) and organic carbon (OC) weremade at Mong Kok, a roadside air quality monitoring station in Hong Kong, fora year, from May 2011 to April 2012. The monthly average EC concentrationswere 3.8–4.9 μg C m?3, accounting for 9.2–17.7% of thePM2.5 mass (21.5–49.7 μg m?3). The EC concentrations showedlittle seasonal variation and peaked twice daily, coinciding with the trafficrush hours of a day. Strong correlations were found between EC and NOxconcentrations, especially during the rush hours in the morning, confirmingvehicular emissions as the dominant source of EC at this site. The analysisby means of the minimum OC / EC ratio approach to determine the OC / EC ratio representativeof primary vehicular emissions yields a value of 0.5 for(OC / EC)vehicle. By applying the derived (OC / EC)vehicle ratio tothe data set, the monthly average vehicle-related OC was estimated to accountfor 17–64% of the measured OC throughout the year. Vehicle-related OCwas also estimated using receptor modeling of a combined data set of hourlyNOx, OC, EC and volatile organic compounds characteristic of differenttypes of vehicular emissions. The OCvehicle estimations by the twodifferent approaches were in good agreement. When both EC andvehicle-derived organic matter (OM) (assuming an OM-to-OC ratio of 1.4) areconsidered, vehicular carbonaceous aerosols contributed ~ 7.3 μg m?3 to PM2.5, accounting for ~ 20% ofPM2.5 mass (38.3 μg m?3) during winter, when Hong Kong receivedsignificant influence of air pollutants transported from outside, and~ 30% of PM2.5 mass (28.2 μg m?3) duringsummertime, when local emission sources were dominant. A reduction of 3.8 μg m?3 in vehicular carbonaceous aerosols was estimated during07:00–11:00 (i.e., rush hours on weekdays) on Sundays and public holidays.This could mainly be attributed to less on-road public transportation (e.g.,diesel-powered buses) in comparison with non-holidays. These multiple linesof evidence confirm local vehicular emissions as an important source ofPM2.5 in an urban roadside environment and suggest the importance ofvehicular emission control in reducing exposure to PM2.5 in busyroadside environments.
展开▼
