To investigate the potential cancer risk resulting from biomass burning, polycyclic aromatic hydrocarbons (PAHs)
bound to fine particles (PM2.5) were assessed in nine administrative northern provinces (NNP) of Thailand, before
(N-I) and after (N-II) a haze episode. The average values of Σ3,4-ring PAHs and B[a]PEquivalent concentrations in
world urban cities were significantly (p b 0.05) much higher than those in samples collected from northern
provinces during both sampling periods. Application of diagnostic binary ratios of PAHs underlined the predominant
contribution of vehicular exhaust to PM2.5-bound PAH levels in NNP areas, even in the middle of the agricultural
waste burning period. The proximity of N-I and N-II values in three-dimensional (3D) principal component analysis
(PCA) plots also supports this conclusion. Although the excess cancer risk in NNP areas ismuch lower than those of
other urban area and industrialized cities, there are nevertheless some concerns relating to adverse health impacts
on preschool children due to non-dietary exposure to PAHs in home environments.