Atmospheric dispersion of polycyclic aromatic hydrocarbons from open burning of agricultural residues in Chiang Rai, Thailand

California Puff Mesoscale Dispersion Model (CALPUFF) was applied to simulate concentrations and the spatial distributions of polycyclic aromatic hydrocarbons (PAHs) emitted from open burning of maize residues in Chiang Rai, Thailand. The model was simulated during the burning season between January 1 and April 30, 2014. The 95th percentile values of 24-h average concentration of total PAHs at 117 specified ground level receptors were calculated. The spatial distribution of predicted concentration is also illustrated. The modeled results indicated that the open burning of maize residues contributed to high PAH concentration in particularly at the receptors located near the burned areas. The cancer risk of carcinogenic PAHs was evaluated using the calculation of benzo(a)pyrene equivalent (BaPeq). The results show that the calculated BaPeq values on daily basis ranged from 0.1 to 18.6 ng m(-3). These concentrations exceeded the Chinese's standard of 2.5 ng m(-3) at 26 among 117 receptors. It was estimated that about 20% of the population living in Chiang Rai was exposed to PAHs at this level. This finding suggests that the open burning of maize residues could significantly contribute to high cancer risk to local population. It is expected that the outcome of this study can support the setting up an appropriate mitigation strategy for reducing their emissions and health impacts on population in the affected areas.