A one-year monitoring of spatiotemporal variations of PM_2.5-bound PAHs in Tehran, Iran: Source apportionment, local and regional sources origins and source-specific cancer risk assessment

PM_2.5-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. PM_2.5 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 PM_2.5 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 PM_2.5 and TPAHs. In addition to local sources contributions, Eastern areas were highly related to long-distance transport of PM_2.5 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 PM_2.5-bound PAHs was at a moderate risk level (3.14 × 10^-4 to 6.17 × 10^-4).