PM_2.5-bound PAHs in three indoor and one outdoor air in Beijing: Concentration, source and health risk assessment

Three indoor (residential home, dormitory, and office) and one outdoor concentrations of PM_2.5-bound Polycyclic aromatic hydrocarbons (PAHs) were analyzed in Beijing across four seasons. The highest and lowest concentration of total PAHs for outdoor appeared in winter and in summer with averages of 200.1 and 9.1 ng/m³ respectively. The seasonal variations of total PAHs in three indoor sites were the same as outdoor. The correlation analysis between the indoor and outdoor samples showed that the annual mean I/O ratios of total PAHs in the three sites were lower than 1. Source apportionment showed vehicle exhaust, coal combustion, and biomass burning were the major contributors of indoor and outdoor PM_2.5-bound PAHs. Indoor source, such as camphor pollution, was identified in the dormitory, while camphor pollution and cooking sources were identified in the residential home. The annual averages of Benzo[a]pyrene equivalent concentration (BaP_eq) were 7.6, 7.8, 7.7 and 12.7 ng/m³ for the dormitory, office, residential home and outdoor samples respectively, far higher than the annual limit of 1 ng/m³ regulated by European Commission. Life lung cancer risk (LLCR) in four sites across four seasons were over the acceptable cancer risk level, showing the cancer risk were at a high level in both indoor and outdoor sites in Beijing, and its level in indoor sites was much lower than in the outdoor site. The health risk assessment indicated the level of PAHs cancer risk on human for three indoor sites were similar. The results call for the development of more stringent control measures to reduce PAHs emissions.