[Pollution Characteristics and Source Identification of PAHs in Atmospheric PM_2.5 in Changzhou City]

A total of 55 ambient fine particle (PM_2.5) samples were collected in Changzhou City from January to August 2016. The concentrations of 17 PM_2.5-bound PAHs in the samples were analyzed by GC-MS. Results showed that seasonal average mass concentrations of PAHs in winter, spring, and summer were 140.24, 41.42, and 2.96 ng·m^-3, respectively, which indicating that the pollution of PAHs in winter appeared more serious than in the other two seasons, and 4-6-ring high molecular weight PAHs were predominant in all three seasons. The average daily level of BaP was 3.64 ng·m^-3 and the days it exceeded the permitted standard accounted for 41% of total days. PAH concentration had significant negative correlations with temperature (correlation coefficient: -0.643) and visibility (correlation coefficient: -0.466), whereas it had good positive correlations with atmospheric pressure (correlation coefficient: 0.544) and poor correlations with wind speed and relative humidity. PAH concentrations were higher at nighttime than at daytime, because of the influences of temperature difference, atmospheric stratification, as well as pollution sources. The results from the air backward trajectory model indicated that PM_2.5-bound PAHs in Changzhou were mainly affected by local emission sources and short-distance transportation, whereas the contribution of long-distance transmission was small (only 11%). Based on analysis of characteristic ratios, PAHs were mainly sourced from coal burning, vehicle emissions, and biomass burning. An incremental lifetime cancer risk (ILCR) model was used to evaluate the health impact of PAHs via breathing exposure pathways. Results revealed that the ILCR of adults was higher than that of children. The ILCRs of the group for winter and spring were slightly higher than the risk threshold, but a difference was not obvious for summer.