Seasonal and spatial distributions of atmospheric polychlorinated naphthalenes in Shanghai, China.

Air samples were collected in Shanghai during summer and winter 2013, and the gas and particulate concentrations of polychlorinated naphthalenes (PCNs) were measured. All 75 congeners were quantified and the corresponding toxic equivalents (TEQs) were calculated. PCN concentrations were higher in summer than winter, at 8.22-102 pg/m(3) (average of 61.3 pg/m(3)) in summer and 16.5-61.1 pg/m(3) (average of 37.7 pg/m(3)) in winter. Their seasonal TEQ values were in contrast, at 1.35-7.31 fg/m(3) (average of 3.84 fg/m(3)) in summer and 4.08-23.3 fg/m(3) (average of 8.80 fg/m(3)) in winter, because of the seasonal change in congener profiles. Tri-CNs were the predominant homologs in both the summer and winter samples. However, the major congeners in summer were PCNs containing less chlorine, but these decreased over winter. Air mass back trajectories suggested that wind direction over various sites was similar in the summer and winter seasons, yet there were clear seasonal variations in atmospheric PCN concentrations. Ratios of several characteristic congeners were calculated and the results indicated that the ratios varied only to a limited extent with PCN emissions profile from industrial thermal sources, but varied strongly with profiles of technical PCN and PCN contaminants in polychlorinated biphenyl mixtures. The results of principal component analysis suggest that local industrial thermal emissions (thermal processes containing waste incineration and secondary metal smelting processes) still play a considerable role in influencing the atmospheric PCNs in Shanghai.