A one-year monitoring of spatiotemporal variations of PM2.5-bound PAHs in Tehran, Iran: Source apportionment, local and regional sources origins and source-specific cancer risk assessment

PM₂.₅-bound PAHs were analyzed in a total of 135 daily samples collected during four seasons from 2018 to 2019, at three urban sites in Tehran, Iran. This study aims to investigate spatio-temporal variations, source apportionment, potential local and regional sources contributions and lung cancer risks associated with the 16 US EPA priority PAHs. PM₂.₅ concentrations ranged from 43.8 to 80.3 μg m⁻³ with the highest concentrations observed in summer. Total PAHs (TPAHs) concentrations ranged between 24.6 and 38.9 ng m⁻³. Autumn period exhibited the highest average concentration (48.3 ng m⁻³) followed by winter (29.5 ng m⁻³), spring (25.9 ng m⁻³) and summer (16.1 ng m⁻³). Five PAHs sources were identified by positive matrix factorization (PMF) analysis: diesel exhaust, unburned petroleum-petrogenic, industrial, gasoline exhaust and coal/biomass combustion-natural gas emissions, accounting for 22.3%, 15.6%, 7.5%, 30.9%, and 23.6% of TPAHs, respectively. Site-specific bivariate polar (BP) and conditional bivariate probability function (CBPF) plots were computed to assess PM₂.₅ and TPAHs local source locations. CBPF pointed out that TPHAs sources are likely of local origin, showing the highest probability close to the sampling sites associated with low wind speed (<5 m s⁻¹). The potential source contribution function (PSCF) and the concentration weighted trajectory (CWT) models were applied to investigate the long-range transport of PM₂.₅ and TPAHs. In addition to local sources contributions, Eastern areas were highly related to long-distance transport of PM₂.₅ and the Western areas showed the highest contribution of the total, medium molecular weight (MMW) (4 rings) and high molecular weight (HMW) (5–6 rings) PAHs. The upper bound of incremental lifetime cancer risk (ILCR) via inhalation exposure to PM₂.₅-bound PAHs was at a moderate risk level (3.14 × 10⁻⁴ to 6.17 × 10⁻⁴).