ATMOSPHERIC CONCENTRATIONS OF POLYCHLORINATED-BIPHENYLS AT BERMUDA

Air was collected at Bermuda from May 1992 to July 1993 and analyzed f or polychlorinated biphenyls (PCBs). The concentrations of approximate ly 80 PCB congeners were determined in 34 samples. The average total P CB concentration was 0.38 ng/m(3) or 7.6 x 10(5) ems. PCB concentratio ns showed very little change in the past 20 years; statistical analysi s of our data and of historical data in the literature indicates that the atmospheric half-life of PCBs is greater than 23 years. The atmosp heric residence times for each congener and for each homologue class r anged from 40 to 75 days. Residence times were dependent on the level of chlorination; the more highly chlorinated PCBs had shorter residenc e 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 signific antly higher in the summer when the air parcels originate in Africa an d the eastern Atlantic.