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Abstract:
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The roadside PM2.5 and BTEX pollutions were monitored in relation to traffic volume at a typical urban street in Ho Chi Minh City (HCMC), Vietnam. The 24-h PM2.5 concentration was 53 – 129 µg/m3 while 8-h PM2.5 concentration was 50 – 170 µg/m3. The hourly levels of benzene, toluene, ethylbenzene, m,p-xylenes and o-xylene vary between 6 – 53, 14 – 170, 3 – 24, 5 – 59, and 2 - 21 µg/m3, respectively, within a day. During the daytime higher concentrations were observed on weekdays than weekend but the opposite was observed at the nighttime and early morning when weekend had higher concentrations. This corresponds to the variations in traffic volume between weekdays and weekend. Pollution levels measured within 30 m from the traffic lane were found to reduce with increasing downwind distance. Principal component analysis (PCA) was applied to the set of air pollution concentration and traffic volume data which revealed that diesel fueled vehicles (truck and bus) were associated with PM2.5 while gasoline fueled vehicles (motorcycle, car, and delivery tricycle) were linked to BTEX. Vans were associated with both PM2.5 and BTEX as they use both diesel and gasoline fuels.Inverse CALINE4 modeling produced the average emission factors of PM2.5, benzene, toluene, ethylbenzene, m,p-xylenes, and o-xylene for the whole street fleet of 38 ± 3.9; 23 ± 4.3; 74 ± 14.8; 8 ± 1.3; 28 ± 9.5; and 9 ± 2.5 mg/vehicle.km which correspond to hourly fleet emission ranges during a day of 141 – 388; 18 – 435; 52 – 1493; 6 – 131; 18 – 655; and 6 - 194 g/km.hour, respectively. Solving the multilinear equation system constructed based on the hourly fleet emission and fleet composition was revealed that the gasoline fueled vehicles had lower PM2.5 emission factor but higher benzene, toluene, ethylbenzene, m,p-xylenes, and o-xylene emission factors than the diesel fueled vehicles. The corresponding emission factors for gasoline fueled vehicles were 25 ± 2.4; 22 ± 0.1; 68 ± 0.3; 8 ± 0.1; 22 ± 0.1; and 8 ± 0.1 mg/vehicle.km, respectively, while for diesel fueled vehicles the emission factors were 388 ± 164.0; 17 ± 5.3; 61 ± 22.2; 4 ± 3.3; 20 ± 5.5; and 5 ± 2.9 mg/vehicle.km, respectively. |