Decadal Shifts in PAH Sources and Health Risks in China under Clean Air Actions

Long-term monitoring of atmospheric polycyclic aromatic hydrocarbons (PAHs) is critical for understanding pollution dynamics and the associated health risks, yet their source-specific trends remain inadequately quantified due to the misclassification between biomass burning and fossil combustion. Here, we integrated radiocarbon (¹⁴C) analysis of coemitted black carbon with positive matrix factorization (PMF) to unambiguously resolve PAH sources across 2008, 2013, 2017, and 2020. This novel approach revealed distinct impacts of air quality actions: Phase I (2013-2017) drove a sharp decline (notably in northern China, -49.4%), primarily attributed to coal-combustion reductions with the end-of-pipe control measures targeting the power and industrial sectors. However, Phase II (2018-2020) witnessed a moderate improvement, characterized by relatively stable PAH emissions from biomass burning, while transportation emerged as the significant and rising contributor. These observations underscore the persistent challenges in enhancing the energy structure and curbing traffic source emissions. Crucially, this transition occurred concurrently with a counterintuitive increase in PAH toxicity (BaP_eq) and an elevation in health risks specifically during Phase II, which is directly linked to the growing relative contribution of traffic exhaust. Our findings underscore the urgency of energy transformation and accelerating vehicle electrification in China's next-stage clean air policies to mitigate the PAH public health burden.