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 me asured gas-phase polychlorinated biphenyl (PCB) concentrations in the atmos phere 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 PC B concentrations near Lakes Superior, Michigan, and Erie and in Chicago. Co ncentrations of individual PCB congeners were well correlated to temperatur e 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, t he 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 b y short-range transport, but at the three remote sites, these concentration s are controlled by long-range transport. Gasphase PCBs also exhibited decr easing concentrations over the period 1991-1997 near Lakes Michigan and Eri e and in Chicago. Significant half-lives ranged from 0.5 to 7.5 years for i ndividual congeners and 2.8 to 3.3 years for total PCBs. Gas-phase PCBs nea r Lake Superior showed no general trend in gas-phase concentration over thi s same time period.