Pollution characteristics, sources, and health risks of PM2.5-bound polycyclic aromatic hydrocarbons in outdoor air along the Xi’an metro lines, China

Environmental exposure in urban traffic microenvironments is a key pathway linking combustion emissions, fine particulate pollution and public health risks. PM 2.5 samples collected outside ten stations along Xi’an Metro Lines 1 and 2 during October–November 2017 were analyzed for 20 PAHs by GC–MS, combined with source apportionment, trajectory analysis and probabilistic risk assessment. Total PAH concentrations ranged from 13.87 to 134.44 ng m −3 , with a mean of 75.39 ± 56.76 ng m −3 ; higher levels occurred in central traffic-intensive areas, especially Zhonglou Station. Four-ring PAHs dominated the compositional profile, whereas 5–6 ring PAHs increased in November, indicating enhanced enrichment of high-molecular-weight combustion products during the early heating period. BaP averaged 6.21 ± 3.62 ng m −3 , highlighting the toxicological relevance of PM₂.₅-bound PAHs in these traffic-adjacent environments. Exploratory PMF attributed approximately 43%, 31%, 20%, and 6% to vehicle-related, biomass-burning, coal-combustion, and other/mixed factors, respectively. Trajectory analyses suggested that PAH pollution was mainly controlled by local accumulation within the Guanzhong Basin. Health risk assessment showed that total BaP-equivalent toxic concentration increased from 8.04 ng m −3 in October to 14.27 ng m −3 in November, mainly driven by BaP and DahA. Deterministic ILCR values ranged from 6.13 × 10 –7 to 7.37 × 10 –6 , and Monte Carlo simulation showed that high-exposure scenarios could reach the 10 –5 level. These findings characterize PAH pollution and associated health risks in traffic-adjacent metro environments in Xi’an during October–November 2017 and provide a historical baseline for evaluating subsequent changes in pollution levels and source profiles.