June 3, 2003 CHICAGO, June 1 — Chicago has long been known as one of the nation's worst cities for asthma sufferers. Now scientists think they may know why. The culprit, they say, is the familiar lake breeze effect that moves commuter-generated air pollution back and forth between the city and Lake Michigan.
Researchers have long known about this daily atmospheric swapping of air masses, but only now have they been able to identify and measure the concentrations of individual pollutants at different times during the cycle. In doing so, they have confirmed that the initial pollutants react with each other in a kind of chemical reactor over Lake Michigan, generating more toxic compounds. As the air mass moves back toward the city, residents may be exposed to high concentrations of these hazardous substances before they have a chance to dissipate.
The research was presented at a Great Lakes Regional Meeting of the American Chemical Society, the world's largest scientific society, by Martina Schmeling, Ph.D., assistant professor of chemistry at Loyola University Chicago, and Paul Doskey, Ph.D., of Argonne National Laboratory's Environmental Research Division.
The researchers looked specifically at particulate and ozone air pollution. "Particulate air pollution contributes to many urban problems including low visibility, fog and cloud formation," Schmeling said. Particulates and ozone are also considered the most likely triggers of respiratory diseases like asthma. The group measured several different pollutants including ozone, sulfate, nickel and lead.
Measurements were taken from LUCAS, the Loyola University Chicago Air Monitoring Station. "High-powered instrumentation made it possible for the first time to identify pollutants before and during the lake breeze in Chicago and compare the differences," Schmeling explained.
The differences were surprising. The lake breeze effect interacts with particulate air pollution rising over Chicago from approximately 5-7 million commuters during the early morning rush hour. It then gets swept over the lake by offshore winds. "Above the lake [the pollutants] react with each other, initiated by the intense sun light... like in a giant reactor," Schmeling said. When the breezes blow this processed pollution back over the city and suburbs at night it is more reactive.
"More reactive particulates could be more health impacting," Schmeling said, suggesting that these findings could have a "broad impact on the community." Doskey agreed: "City residents may experience an acute, short-term exposure to high concentrations of pollutants as the leading edge of the lake breeze returns to land." Already Chicago and its suburbs lead the nation in number of asthma cases per capita per year.
Since the lake breeze effect is most pronounced during the early summer months, Schmeling, Doskey and their colleagues plan further testing in June. The researchers also plan to study data from Detroit, Toronto and other cities with similar meteorological patterns.
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