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It is challenging to estimate the health risks posed by exposure to particulate pollutants due to limited information for chemicals bound to particles in toxicity databases. This study predicted the cancer risks posed by the vapor-phase and fine particulate matter (PM2.5)-bound polycyclic aromatic hydrocarbon (PAH) emissions during diesel combustion in an industrialized city in southern Taiwan by using two different approaches. In the first approach, the cancer risks were estimated based on the vapor-phase and PM2.5-bound PAH concentrations in the exhausts, while the observations of the vapor-phase and PM2.5-bound samples in the in vitro cell toxicity tests, including Ames test, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and tumor necrosis factor-alpha (TNF-alpha) detection were employed to modify the risks posed by the PM2.5-bound emission in the second approach. The results show that the vapor-phase concentrations of total PAH (30,944-118,565 ng/m3) and benzo(a)pyrene toxic equivalence quotient (BaP-TEQ; 8.2–69.1 ng/m3) were significantly higher than the PM2.5-bound concentrations (the total concentration and BaP-TEQ were 11.9–45.0 and 0.27–12.94 ng/m3, respectively), resulting in the dominance of the vapor-phase risk (71–98%) over the total risk (8.92 × 10−9–1.03 × 10−7). With the modification of the cell test results, the total risks were increased to 1.62 × 10−8–1.33 × 10−7. The ratios of the PM2.5-bound risk to the total risk in different conditions have been increased by 2–26 times (from 2–29% to 45–61%), suggesting the mixture effect of PM-bound pollutants on health risk assessment. [ABSTRACT FROM AUTHOR]