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24-h PM_2.5 samples were simultaneously collected at six sites in a subtropical city of South China during November–December, 2009. Particle-phase concentrations of polycyclic aromatic hydrocarbons (PAHs) and organic tracers such as hopanes for vehicular emissions (VE), levoglucosan for biomass burning (BB) and picene for coal combustion (CC) were determined. Meanwhile, their gas-phase concentrations were calculated from gas/particle (G/P) partitioning theory using the particle-phase concentrations. The 4 ring PAHs (fluoranthene to chrysene) had lower particle-phase fractions (10%–79%) than other species. Estimated BaP_eq and lifetime cancer risk for particle-only (P-only) vs gas + particle (G + P) data sets showed similar values, indicating PAHs with 5–7 rings dominated the carcinogenicity of PAHs. Positive Matrix Factorization (PMF) was applied on both P-only and G + P data sets to estimate the …