Seasonal variation and source identification of ambient polychlorinated biphenyls in Xi'an city

To understand the concentrations, seasonal variation, and sources of polychlorinated biphenyls (PCBs) in the ambient air of Xi'an City, China, twenty-two air samples (in both gaseous and particulate phases) were collected for 24 hours per week using an active air sampler during summer and winter in 2012 in Xi'an City. The results showed that the concentrations of ∑₆₄PCBs ranged form 76.21 to 338.77 pg·m^-3 with a mean of 183.85 pg·m^-3, with much higher concentration for PCBs in gas-phase than that in particle-phase. Lower molecular weight PCB congeners were dominated, and the ratio of concentrations for tri-and tetra-CBs to the total PCBs concentrations ranged from 59.64% to 91.39%. For the gaseous phase, the average concentration of PCBs was 201.68 pg·m^-3 in summer, higher than 151.11 pg·m^-3 in winter. However, for the particular phase, the mean concentration in winter was 6.65 times higher than that in summer. Principal component analysis (PCA) was applied to identify the sources of PCBs in the air of Xi'an City. The first principal component (PC1), accounting for 36.06% of the total variance, was recognized as transformer oil produced in China. PC2 accounted for 20.29%, which might be originated from the use of painting.