Size distribution of particle‐bound PAH composition in the ambient air of bus station

Abstract

The particle‐bound composition of polycyclic aromatic hydrocarbons (PAHs) associated with size distribution were measured for the ambient air of a bus station, an urban and a rural site with two MOUDIs and a NRI from April to September 1996 in Ping Tung area of Southern Taiwan. Twenty one individual PAH were analyzed primarily by using a gas chromatograph/ mass spectrometer (GC/MS). In the ambient air of bus station, the particle size distribution of particle‐bound total‐PAH composition was dominant in the submicron particles. In general, a smaller size particle has a higher total‐PAH composition. This is due to the fact that a smaller size of particle has a higher specific area and may therefore contain a greater amount of organic carbon which allows more PAH adsorption. These results showed that the values of total‐PAH composition in the fine particle mode (Dp < 1.0 μm) for bus‐station atmosphere averaged 2.2 and 9.0 times of magnitude higher than those measured in the urban and rural atmospheres. In the particle size range between 0.056∼ 3.2 μm, both the U/B and R/B ratios of particle‐bound total‐PAH composition have the lowest values, with the U/B ratio ranging from 0.31 to 0.47 and averaging 0.42 and the R/B ratio ranging from 0.13 to 0.26 and averaging 0.19, respectively. This reveals that the PAH mass, from the vehicular sources to the urban or rural site, is shifted from the particle phase to the gas phase, or react and decay in the atmosphere during the transport process, which results in the depletion of particle‐bound PAH composition. In the ambient air of the bus station, the particle‐bound composition for higher molecular weight PAHs (MW > 252) — BbF, BkF, BeP, BaP, PER, IND, DBA, BbC, and BghiP — were much higher than those in the urban or rural atmosphere. Except Acp, Flu, Ant, FL and BaA, the particle‐bound compositions of remaining 16 PAHs had a unimodal‐like distribution in a stepwise shape, with the trend similar to the size distribution of particle‐bound total‐PAH composition, which decreases as particle size increases. The size distribution of particle‐bound individual‐PAH composition for bus‐station atmosphere showed that individual PAH had their highest peaks localized in the submicron (0.056∼0.32 μm) size range. The preponderance of the contribution of the fine particle (Dp < 1.0 μm) to the PAH composition is a strong potential factor that induces high rates of lung cancer near vehicular sources.