Size distribution and estimated carcinogenic potential of particulate polycyclic aromatic hydrocarbons collected at a downtown site in Kumamoto, Japan, in spring

Atmospheric particles at a roadside site in the downtown area of Kumamoto, Japan, were collected in the spring of 2006. A cascade impactor was used to fractionate the particles into nine size ranges: > 11.0, 11.0-7.0, 7.0-4.7, 4.7-3.3, 3.3-2.1, 2.1-1.1, 1.1-0.65, 0.65-0.43, and < 0.43 mu m. Ten polycyclic aromatic hydrocarbons (PAHs) with 4, 5, and 6 rings [fluoranthene (Flu), pyrene (Pyr), benz(a)anthracene (BaA), chrysene (Chry), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(a)pyrene (BaP), benzo(ghi)perylene (BghiP), dibenz(a,h)anthracene (DahA), indeno(1,2,3-cd)pyrene (IcdP)] in the size ranges were expressed and investigated in terms of their total and individual concentrations and the equivalents of benzo(a)pyrene (BaPE) upon their relative carcinogenic potential. The correspondence of PAHs to particle size, PAHs tending to accumulate in small size ranges, was confirmed. The mass of PAHs in the size range < 2.1 mu m averaged 4-fold more than that in the range > 2.1 mu m. The PAHs with 5 and 6 rings predominated in the total mass of the 10 PAHs, exhibiting approximately monomodal distributions with the mode around or smaller than 0.5 mu m. The PAHs with 4 rings composed 28% of the total PAHs in mass and showed bimodal distributions with one mode in the range of < 0.5 mu m and another in the range of > 1.0 mu m. The estimate of BaPE using the 5- and 6-ring PAHs indicated that PAHs in particles < 2.1 mu m accounted for approximately 80% of the equivalents, suggesting that the carcinogenic potential of the PAHs was dominated by small particles. BaP together with BbF, DahA, and IcdP predominated in the equivalents, while the equivalents due to BaA and BkF were very small in all size ranges.