The societal inhalation cancer risk was obtained by multiplication of ICR values with million people (Jung et al., 2010). The 24-hrs average value of ICR in normal period based on WHO guideline were 230 cases/million people or 3.30 cases/year, while those based on CalEPA was 3 cases/million people or 0.04 cases/year. Comparing with a previous studies, the inhalation cancer risk of PM10 in ambient air of Chiang Mai, based on WHO was lower (2 cases/year (Pengchai et al., 2008) and 1.3 cases/year, (Wiriya et al., 2013)) than the values found in this study (3.3 cases/year). However, these results should be noted that the values are only a crude estimation of cancer risk from the PM2.5-bound PAHs inhalation.