Single-site source apportionment modeling of PM2.5-bound PAHs in the Tehran metropolitan area, Iran: Implications for source-specific multi-pathway cancer risk assessment

This study was designed to assess the occurrence, relationships, sources, spatiotemporal variations, and source-specific multi-pathway cancer risk of PM2.5-bound PAHs at three urban environments in Tehran, Iran during a one-year campaign (2018-2019). The mean concentrations of PM2.5-bound n-ary sumation 16PAHs were 24.6, 26.7, and 38.9 ng m- 3 in HFT, AZD, and SHR sites, respectively. High molecular weight (HMW) PAHs were the main PAHs in the fine particle phase (76-83.4%) compare to low molecular weight (LMW) PAHs (16.6-24%). Redundancy analysis (RDA) showed that relative humidity (RH) and temperature (T) along with O3, NO2, and PM2.5 were critical driving factors affecting PAHs concentrations. Positive matrix factorization (PMF) extracted five PAHs emission sources: heavy-duty vehicles, light-duty vehicles, petrogenic, natural gas and coal/biomass combustion, industrial emissions, with different source contributions for each sampling site. The principal component analysis-multilinear regressions (PCA-MLR) and diagnostic ratios (DRs) methods indicated that the pyrogenic sources were the major sources of PM2.5-bound PAHs. The coefficient of divergence (COD) and Pearson correlation coefficient (R) of PAHs compounds and PMF derived source contributions (ng m-3) at paired sites indicated a relatively divergent spatiotemporal distribution. Based on incremental lifetime cancer risk (ILCR) levels of n-ary sumation PAHs source contributions, adults showed a more significant risk (1.33E-2.28E-05) than children (5.40E-9.22E-06). Source-specific-ILCR indicated that heavy-duty vehicles and natural gas-coal/biomass combustion emissions had the highest cancer risk contributions than the other apportioned sources.

Automated summary

This study assessed the occurrence, relationships, sources, spatiotemporal variations, and cancer risk of PM2.5-bound PAHs in Tehran, Iran. High molecular weight PAHs were the main PAHs in fine particles, while heavy-duty and light-duty vehicles were identified as major sources of PM2.5-bound PAHs. Adults showed a higher cancer risk from PAH exposure compared to children, with heavy-duty vehicles and natural gas-coal/biomass combustion emissions contributing the most to cancer risk.