ATMOSPHERIC CONCENTRATIONS OF POLYCHLORINATED-BIPHENYLS AT BERMUDA

Air was collected at Bermuda from May 1992 to July 1993 and analyzed for polychlorinated biphenyls (PCBs). The concentrations of approximately 80 PCB congeners were determined in 34 samples. The average total PCB concentration was 0.38 ng/m(3) or 7.6 x 10(5) ems. PCB concentrations showed very little change in the past 20 years; statistical analysis of our data and of historical data in the literature indicates that the atmospheric half-life of PCBs is greater than 23 years. The atmospheric residence times for each congener and for each homologue class ranged from 40 to 75 days. Residence times were dependent on the level of chlorination; the more highly chlorinated PCBs had shorter residence times. The fluxes of PCBs from the atmosphere to the earth's surface were 13 mu g m(-2) year(-1). This is comparable to other fluxes found in the literature. Isentropic air trajectories were used to evaluate the importance of different source areas. Concentrations were significantly higher in the summer when the air parcels originate in Africa and the eastern Atlantic.