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7 U.S. cities with the worst air pollution

By: chief on Aug. 4, 2010, 12:20 p.m.
Highway traffic

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According to the report, busy highways are high risk zones. Pollution from highway traffic contributes to higher risk for heart attack, allergies, premature births and the death of infants near the time they are born. New studies looking at the impact of traffic pollution — even in cities with generally “cleaner” air — show increased negative health effects from chronic exposure to exhaust from heavy traffic.