Abstract
Continuous sampling of dioxins in ambient air was carried out using a low-volume air sampler at the southeast site in Tokyo during a period of FY 2000 to FY 2004. The temporal trend of toxic equivalency quantity (TEQ) was evaluated the relation with Tokyo's inventory which was estimated to be almost completely emitted from combustion sources. The annual average of TEQ was observed to have a more similar tendency to a variation in the inventory than that of regular monitoring with a short term sampling. However, the reduction rate of TEQ for 5 years was less than that of the inventory. Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) increased from late autumn to winter, whereas those of coplanar polychlorinated biphenyls (Co-PCBs) elevated in summer and the seasonal variation seemed to be dependent on temperature. As PCB products and combustion were known to be the major sources of Co-PCBs, we have attempted to estimate the source contribution rates using the method of Bayesian chemical mass balance. Though Co-PCBs derived from PCB products were extrapolated a significant contributor at total concentration base, Co-PCBs emitted from combustion seemed to constitute over 90 % based on TEQ as consequence of higher toxic equivalency factor of their isomers.
