Concentrations and gas/particle partitioning of PCBs in Chicago

Thirty seven air samples were collected in Chicago, IL from June to October 1995 and analyzed for gas and particle concentrations of polychlorinated biphenyls (PCBs). Lower molecular weight (MW) PCBs dominated the samples and on average 95% of the Sigma50PCB concentration (gas+particulate) was in the vapor phase. Sigma50PCB concentrations were classified based on prevailing winds (lake and land). The Sigma50PCB concentration varied between 0.42 and 5.21 ng/m3 (1.80+/-1.70 ng/m3) for lake and 0.53 and 8.31 ng/m3 (2.41+/-2.15 ng/m3) for land wind directions. Back trajectory analyses suggested that SW of Chicago can be an important local or regional source sector for PCBs. Partitioning between gas and particulate phases was modeled using the Junge-Pankow model. The measured particle phase concentrations for low MW PCBs were lower than those predicted by the model while the opposite was observed for high MW PCBs. Plots of gas/particle partition coefficient (log Kp) vs. subcooled liquid vapor pressure (log pL(0)) had reasonable correlations for individual samples but the slope varied among the samples. Samples that originated from over the lake had higher slopes than samples that originated from over the land.