The gas-particle partitioning, source, and lung cancer risk of atmospheric polycyclic aromatic hydrocarbons (PAHs) in different seasons were investigated in a megacity of China with coal dominating the energy structure over one year period. The total concentrations of 16 U.S. EPA priority PAHs (Σ₁₆PAHs) were highest in winter (gaseous: 36.6 ± 1.89 ng m⁻³; PM phase: 16.9 ± 10.2 ng m⁻³) and lowest in summer (gaseous: 4.78 ± 1.48; PM phase: 2.28 ± 1.26), and followed the sequence of urban site > tourist site > rural site. In addition, rural site had higher particulate PAH concentrations in summer, autumn, and winter than other sites, primarily due to the extensive biomass burning. Low molecular weight (LMW) PAHs (2- and 3-ring PAHs) were the dominating compounds in gaseous phase, which was quite different from the high molecular weight (HMW) PAHs (4- to 6-ring PAHs) predominating in the particulate phase. The fractions of LMW PAHs showed a declining trend with the decrease of particle size for all seasons. The gas-particle partitioning of PAHs was controlled by organic carbon absorption and primarily influenced by the particle sizes. Petrogenic, traffic emission, biomass burning, and coal combustion were the main sources of atmospheric PAHs, which contributed to 33%, 35%, 32%, and 32% in spring, summer, autumn, and winter, respectively. The overall population attributable fraction (PAF) for lung cancer due to inhalation exposure to PAHs was 0.78‰ (interquartile range (IR) = 0.17–2.4‰), corresponding to the excess annual lung cancer incidence rates of 6.6 × 10⁻⁸, 1.2 × 10⁻⁸, and 2.0 × 10⁻⁷ for children, adolescents, and adults, respectively.