Seasonal variation of atmospheric polychlorinated biphenyls and polychlorinated naphthalenes in Japan

•Different seasonality trends of atmospheric PCBs and PCNs were confirmed in Japan.•The PCBs peaked in summer as expected of normal POPs behavior.•But the PCNs showed relatively elevated concentrations in winter.•Seasonality of the PCNs was marked by changes in emission origins of the tri-CNs.

This study investigated the seasonality of atmospheric polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs) in Japan. Polyurethane foam (PUF) disk passive air samplers (PAS) were deployed simultaneously at 55 sites in spring 2008, summer 2008 and winter 2008/09. Sampler deployment spanned 8 continuous weeks in each season. The non-outlier ranges of the two pollutants (ng/sample) were as follows; ∑190PCBs: 6.5-38.6 (spring), 43.5-220.5 (summer) and 25.9-136 (winter); and ∑63PCNs: 0.4-3.9 (spring), 0.7-7.1 (summer) and 1.1-9.2 (winter). The corresponding values in air were ∑190PCBs (pg m−3): 33-197 (spring), 222-1125 (summer) and 132-694 (winter); and ∑63PCNs (pg m−3): 2.2-20 (spring), 3.5-36 (summer) and 5.7-47 (winter), when sampling rate of 3.5 m3 day−1 was assumed. Thus, the PCBs peaked in summer, while the PCNs mostly peaked in winter; there was an apparent contrast in their seasonality in Japan. For the PCNs, seasonal variability was significant at rural than urban sites. Normally, POPs would show relatively increased air content in summer due to vaporization effect. The PCNs appeared to deviate from such a trend because of overriding input of tri-CNs presumably transported from long range by northwesterly winds in the winter season. The dioxin-like fractions of either pollutant were reduced in winter by about 30-50%.