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Polycyclic aromatic hydrocarbon (PAH) samples in the ambient air of rural, urban and trafficintersection sites have been collected by PS-1 samplers, NRI (Noll Rotary Impactor) and MOUDIs (Micro-orifice Uniform Deposit Impactors) from July, 1993 to January, 1995 in southern Taiwan. Twenty one individual PAHs were analyzed primarily by a gas chromatograph/mass spectrometer (GC/MS). The mean total-PAH concentrations (gas+particle phases) in the ambient air of trafficintersection was approximately 5.6 and 14.1 times higher than those mean values for the urban and rural atmosphere, respectively. It is reveals that the high density of vehicle exhaust raises the PAH concentrations in the urban ambient air. In the ambient air of the traffic-intersection, most of the G/R (ground/roof) ratios for individual PAHs concentration in gas phase were higher than 1.0, except BaA, BeP, PER and BghiP. This result shows that PAHs concentration in gas phase was related to the automobile exhaust. Upon entering the ambient air of the traffic-intersection, these PAHs was condensed, cooled and dispersed at higher elevation. In the traffic intersection, the PAHs are predominantly absorbed on particles with aerodynamic diameters less than 2.5 µm (the fine particles), a fact which strongly relates to the risk potential. The results also show that the total PAHs in the ambient air of a traffic intersection originated mainly from mobile exhaust and the phenomena of condensation process for the young aerosols. However, in the traffic-intersection, higher fraction of total-particle mass in the coarse particle mode is primarily the road dust which is due to traveling vehicles.

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