Evidence for Increased Gaseous PCB Fluxes to Lake Michigan from Chicago

Urban-industrial areas exhibit atmospheric concentrations of organic contaminants that are often > 5−10× 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 ΣPCB 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 ΣPCB concentrations ranged from 48 to 302 pg/L with concentrations in winter ∼2.5× 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 ΣPCB in the southern quarter of Lake Michigan was −18 ug/m 2 -yr ( net absorption) in 1994, corresponding to 140 kg/yr net input.