Seasonal and spatial variations in atmospheric PM2.5-bound PAHs in Karaj city, Iran: Sources, distributions, and health risks

Potential sources, temporal and spatial distribution, and health risks of 16 US EPA priority PAHs bound to PM2.5 in Karaj city have been monitored in order to assess the effect abatement and cleanup strategies. A total of 130 PM2.5 samples were collected in three different sites located in the southeast, northwest, and central parts of Karaj city in 2018 and 2019 and the average annual PAHs concentrations were 22.55 +/- 13.74, 16.16 +/- 10.62, and 16.67 +/- 9.21 ng/m3, respectively. Atmospheric PM2.5-bound PAHs levels at all sites were lower in warm seasons than cold seasons, dominated by low molecular weight PAHs in the spring and high molecular weight PAHs in other seasons. The positive matrix factorization modeling (PMF) showed that diesel and gasoline engine emissions were dominant contributors to PAHs which accounted for 37.4 % and 31.1 %, respectively, followed by natural gas and biomass burning (14.8 %), industrial emissions (10.1 %), and petrogenic sources (6.6 %). The conditional bivariate probability function plots (CBPF) for PMF-resolved factor contributions were consistent with the predominant wind directions from northwest and southeast and known local emission sources. Benzo(a) pyrene (BaP) carcinogenic equivalent (BaPPEQ), BaP mutagenic equivalents (BaPMEQ) and the incremental lifetime lung cancer risk (LLCR) methodologies were calculated to evaluate human exposure to carcinogenic PAHs. The health risk related to PAHs was higher in cold seasons. Based on LLCR model, the total cancer risk related to PAHs exceeded the "safe limit" recommended by the USEPA (10-6) at all sites, indicating serious health risks for population of Karaj city mostly due to gasoline engine emissions.