Key Points:

• Benzo[a]pyrene is a small contributor to human cancer risk of PAHs worldwide (11 %)

• Using benzo[a]pyrene as a surrogate compound leads to erroneous conclusions about high-risk populations and the importance of uncertain chemical processes
• Science and policy could be improved by considering a wider group of both emitted PAHs as well as their degradation products

Summary: Nearly 90% of global human lung cancer risk from polycyclic aromatic hydrocarbons (PAHs) comes from compounds omitted by prior analyses and not regulated directly. PAHs in the atmosphere are a complex mixture, but regulators and researchers often represent them using a single compound, namely benzo(a)pyrene. We show that benzo(a)pyrene is a poor indicator of global PAH cancer risk; its use as a proxy leads to erroneous conclusions about high-risk populations and atmospheric chemical processes. We find that approximately 17% of risk comes from PAHs that are produced in atmospheric reactions and are not regulated or routinely monitored. Regulators and researchers should focus on the entire mixture of PAHs in the atmosphere, and we recommend that benzo(a)pyrene not be used as a sole reference compound.