Temperature dependence and temporal trends of polychlorinated biphenyl congeners in the Great Lakes atmosphere

As part of the Integrated Atmospheric Deposition Network (IADN), we have measured gas-phase polychlorinated biphenyl (PCB) concentrations in the atmosphere around the Great Lakes since November of 1990. In this paper, we use these data to explore the temperature and time dependencies of gas-phase PCB concentrations near Lakes Superior, Michigan, and Erie and in Chicago. Concentrations of individual PCB congeners were well correlated to temperature for the three remote sites using the Clausius-Clapeyron equation, but the calculated heats of surface-air exchange did not correlate (on a congener basis) with laboratory-measured heats of vaporization. On the other hand, the heats of surface-air exchange for PCB congeners measured in Chicago are well correlated with laboratory-measured heats of vaporization. We conclude that the gas-phase PCB concentrations measured at Chicago are controlled by short-range transport, but at the three remote sites, these concentrations are controlled by long-range transport. Gasphase PCBs also exhibited decreasing concentrations over the period 1991-1997 near Lakes Michigan and Erie and in Chicago. Significant half-lives ranged from 0.5 to 7.5 years for individual congeners and 2.8 to 3.3 years for total PCBs. Gas-phase PCBs near Lake Superior showed no general trend in gas-phase concentration over this same time period.