Evidence for increased gaseous PCB fluxes to Lake Michigan from Chicago

Urban-industrial areas exhibit atmospheric concentrations of organic contaminants that are often, >5-10x regional background. Increased emissions of PCBs into the urban-industrial atmosphere leads to enhanced depositional fluxes to proximate waters. In this study, the increased air-water exchange inputs of PCB congeners into southern Lake Michigan driven by elevated atmospheric concentrations emanating from the Chicago, IL/Gary, IN air plume was studied. Intensive experiments were conducted in May and July 1994 and January 1995. The gaseous Sigma PCB concentrations at the overlake site 15-km from Chicago ranged from 132 to 1120 pg/m(3) with higher concentrations occurring in warm periods and when winds were from southerly and westerly quadrants. Dissolved phase Sigma PCB concentrations ranged from 48 to 302 pg/L with concentrations in winter similar to 2.5 x higher than summer concentrations. Instantaneous net air-water exchange fluxes ranged from -32 (absorption) to + 59 ng/m(2)-d with absorptive flux highest in summer when winds were from the urban area and gas-phase concentrations were highest. Air and surface water temperatures and wind direction were the dominant factors influencing the magnitude and direction of air-water exchange fluxes. The modeled net air-water exchange flux of Sigma PCB in the southern quarter of Lake Michigan was -18 ug/m(2)-yr (net absorption) in 1994, corresponding to 140 kg/yr net input.