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Polycyclic aromatic hydrocarbons (PAHs) in ambient particulate matter contribute considerably to human health risk. Simultaneous sampling of ambient PM 2.5 /PM 10 was done to analyze the Ʃ16PAH across the four seasons of 2017 in Islamabad, Pakistan. The average Ʃ16PAH concentrations in PM 2.5 and PM 10 were 25.69 and 40.69 ng m -3 , respectively. For both PM 2.5 and PM 10 , the highest PAHs concentration was in winter (45.14, 67.10 ng m -3 ), while the lowest was in summer (16.40, 28.18 ng m -3 ). Source appointment indicated that vehicular exhaust, i.e., diesel, gasoline and alternatively fuel liquid natural gas (LNG), and compressed natural gas (CNG) combustion was the primary PAHs contributor, whereas biomass burning and fuel combustion (coal, biomass, wood, CNG) from stationary sources were another important sources. Health risk assessment showed that the lifetime cancer risk (LCR) values of PAHs were higher than the acceptable level in all four seasons. LCR values were the highest in winter (9.23 × 10 -4 for PAHs in PM 2.5 and 13.98 × 10 -4 for PAHs in PM 10 ) which were 9 and 13 times higher than tolerable cancer risk level respectively, and they were 2-3 times higher than the acceptable values in other seasons., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)