Particle size distribution of Polycyclic Aromatic Hydrocarbons in the ambient air of a traffic intersection

Atmospheric particle and PAH (Polycyclic Aromatic Hydrocarbons) mass size distributions in both a traffic intersection and a rural site were measured with two MOUDIs (Micro-orifice Uniform Deposit Impactors) and a NRI (Noll Rotary Impactor) from June 1994 to June 1995 in southern Taiwan. In the ambient air of the traffic intersection, both the total PAHs and total particle mass were found to be with unimodal size distributions, while at the rural site, they were found to be with bimodal size distributions. Twelve PAHs were found to have a significant bimodal-distribution: Nap, AcPy, Flu, PA, Ant, FL, CYC, BaA, BkF, DBA, BbC and BghiP. The remaining PAHs (Acp, Pyr, CHR, BbF, BeP, BaP, PER, IND, and COR) had a unimodal or unimodal-like distribution. In the ambient air of the traffic intersection, the cumulative fraction of total PAHs in the particle size range below 1, 2.5, 10 and 25 μm, in sequence, were 50.9%, 74.2%, 90.8% and 95.9%, respectively, while those values at the rural site, in sequence, were 38.3%, 56.4%, 85.7% and 94.0%, respectively. The Traffic/Rural ratio of BaP varied between 7.07 and 17.6 and averaged 11.2 in the fine particle mode; it varied between 5.32 and 16.9 and averaged 10.6 in the coarse particle mode. The high concentration of carcinogenic PAHs in the ambient air of the traffic intersection is a strong potential factor for inducing a high rate of lung cancer. The MMD_o of total PAHs and total particle mass in the ambient air of the traffic intersection were 0.943 and 3.59 μm, respectively. However, these two values at the rural site were 1.67 and 2.03 μm, respectively. These results revealed that there was a larger amount of smaller particulates in the ambient air of the traffic intersection. Smaller particulates have more specific area and therefore allow more PAH mass to be adsorbed on them.