Urban Contamination of the Chicago/Coastal Lake Michigan Atmosphere by PCBs and PAHs during AEOLOS

Abstract

Air concentrations of PCBs and PAHs were measured in the urban/industrial complex of Chicago, IL, over southern Lake Michigan, and in a non-urban area as part of the AEOLOS (Atmospheric Exchange Over Lakes and Oceans) Project. Air samples were collected simultaneously in intensive experiments during May and July 1994 and January 1995 in order to determine the influence of contaminated air masses from the Chicago urban/industrial complex on the southern Lake Michigan atmosphere. Gas phase ∑PAH concentrations over the lake ∼10−20 km offshore ranged from 0.8 to 70 ng/m3 while urban air concentrations were 27−430 ng/m3. Photooxidation of gas phase PAHs during the day resulted in daytime over-lake concentrations that were ∼75% less than corresponding nighttime concentrations. Gas phase ∑PCB concentrations ranged from 0.14 to 1.1 ng/m3 over the lake and from 0.27 to 14 ng/m3 in the urban area. ∑PCB concentrations varied seasonally as a result of higher volatilization during the summer. The highest concentrations occurred when the air flow was from the urban/industrial area encompassing Evanston, IL, to Gary, IN, toward the lake, and concentrations were near regional background when the wind was from any other direction. The urban air emissions increased the average coastal atmospheric concentrations above the continental background signal by factors of 12 and 4 for ∑PAHs and ∑PCBs, respectively. Because of photooxidation of gas phase PAHs during the day, the average daytime concentration was increased by only a factor of 5 while the average nighttime concentration was increased by a factor of 18.