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Polycyclic aromatic hydrocarbons (PAHs) have been of health concern due to its carcinogenesis and mutagenesis. In this study, we aimed to assess the variations, sources, and lifetime excessive cancer risk (ECR) attributable to PAHs bound to ambient particulate matters with aerodynamic diameter less than 2.5 μm (PM_2.5) in metropolitan Beijing, China. We collected 24-hour integrated PM_2.5 samples on daily basis between November 2014 and June 2015 across both central heating (cold months) and non-heating (warm months) seasons, and further analyzed the PAH components in these daily PM_2.5 samples. Our results showed that total concentrations of PM_2.5-bound PAHs varied between (88.6 ± 75.4) ng/m³ in the cold months and (11.0 ± 5.9) ng/m³ in the warm months. Benzo[a]pyrene (BaP), the carcinogenic marker of PAHs, averaged at 5.7 and 0.4 ng/m³ in the cold and warm months, respectively …