Seasonal PAH exposure and health risks at central European rural background sites driven by combustion sources and transport pathways

Particle-bound polycyclic aromatic hydrocarbons (PAHs) pose considerable health risks, including cancer, upon inhalation, yet source-specific contributions and transport pathways remain poorly constrained at rural background sites in Central Europe. This study combines parallel PM 2 . 5 filter sampling at three rural stations (Melpitz (MEL), Germany; Košetice (NAOK), and Frýdlant (FRY), Czech Republic) with quantitative measurements of PAHs, n-alkanes, and saccharide tracers, multivariate statistical analysis, and toxicological risk assessment. Principal component analysis (PCA) followed by k-means clustering identified three winter source-related factors: W1 (biomass burning dominated), W2 (coal and mixed combustion dominated), and W3 (background/biogenic dominated), and two in summer: S1 (biogenic/background dominated) and S2 (anthropogenic dominated). Summer PAH levels and associated excess cancer risk (ECR) were approximately two orders of magnitude lower than in winter. Winter campaign-based ECR based on benzo[a]pyrene equivalent concentrations ranged from 3.7 × 10 -5 at MEL to 6.1 × 10 -5 at FRY, exceeding the annual World Health Organization (WHO) reference level when used as a contextual benchmark and approaching values reported for some European urban background sites. Despite representing only 15%, 12%, and 15% of winter samples at MEL, FRY, and NAOK, respectively, W2 contributed 65%, 52%, and 48% of the corresponding winter campaign ECR. However, the transport dependence of this risk differed among sites. At MEL and FRY, winter ECR was dominated by infrequent easterly continental trajectories crossing industrial and coal-burning regions, whereas at NAOK it was more evenly distributed across trajectory clusters with a comparatively stronger local/regional residential-heating and biomass-burning influence. The combined source-related factors and trajectory framework provides a transferable approach for evaluating PAH-related health risks in regions influenced by both local emissions and long-range transport.