PAH characteristics in the ambient air of traffic-source

Abstract

Twenty-seven PAH (polycyclic aromatic hydrocarbon) samples in the ambient air of a traffic-source were investigated for their concentration, particle-bound PAH composition, phase distribution, time variation, and distance variation. In addition, 18 and 12 PAH samples in the ambient air of an urban site and a rural site, respectively, were determined and compared with those of the traffic-source. The total-PAH concentrations (gas + particle phases) in the ambient air of the traffic-source averaged approximately 5.3 and 8.3 times higher than mean values in the urban and rural atmosphere, respectively. The particle phase distribution of total-PAHs averaged 46.1, 18.7, and 20.6% measured at the traffic-source, urban site, and rural site, respectively. The condensation process prevailed in the ambient air of the traffic-source. Even though the TSP concentration near the traffic-source averaged only two times higher than the mean value measured on the urban or rural site, the particle-bound composition of 12 potentially carcinogenic PAHs, namely CYC, BaA, Chr, BbF, BkF, BeP, BaP, PER, IND, DBA, BbC, and BghiP, in the ambient air at the traffic-source averaged approximately 7.8 and 16.5 times higher than those measured at the urban and rural site, respectively. High concentrations of carcinogenic PAHs in the air near traffic sources is a strong factor in inducing a high rate of lung cancer in Taiwan. The results of both time-variation and distance-variation investigations show that traffic sources have a very significant impact on urban air quality. The results of PAH analyses of five commercial vehicle fuels showed that diesel had the highest total-PAH concentration (7341 mg/l). Lower molecular weight PAHs such as Nap, AcPy, and Acp were dominant in all vehicle fuels (concentration > 100 mg/l). Comparison of individual-PAH patterns in the vehicle fuels with those in the ambient air of traffic-source showed that a significant fraction of PAHs was formed during incomplete combustion with thermal synthesis.