Abstract

PM_2.5-bound polycyclic aromatic hydrocarbons (PAHs) with adverse effect on human and ecosystem health is of concern worldwide. In this study, they were measured in summer and winter at an urban site in Chongqing, a megacity of southwest China to investigate their potential sources, to evaluate the inhalation cancer risks and to identify the dominant source responsible for health risk. The mean concentration of total PAHs was 9.67 ± 2.53 ng/m³ in summer, much lower than that in winter (49.6 ± 16.5 ng/m³). The source apportionment method of Positive Matrix Factorization combined with diagnostic ratios was successfully applied in this study and identified coal combustion and vehicle emission (contributing to 56% of the total PAHs mass), biomass burning (21%) and volatilization (23%) as the potential sources of PM_2.5-bound PAHs in Chongqing. Regional transport from southern and southeastern regions have contributed to the elevated PM_2.5-bound PAHs in summer while local and nearby areas acted as main source regions in winter mainly due to the specific topographic and meteorological conditions in Chongqing. Daily Benzo[a]pyrene equivalent (BaPeq) concentrations (2.47–17.9 ng/m³) during 97% of the winter campaign exceeded the National Ambient Air Quality Standard (2.5 ng/m³). Furthermore, the lifetime cancer risk (LCR) values denoted a high potential cancer risk in winter, especially during aerosol pollution period. The contribution from the mixed source of coal combustion and vehicle emission (64%) to LCR was higher than that to the mass concentration while that of biomass burning (13%) was lower, which may result from the emission of higher toxic compounds from the mixed source. Elevated contribution from the mixed source was observed in winter especially during pollution days, indicating the significance of controlling the sources with high health risks. The results in this study call for the attention to the source apportionment from a health risk perspective.