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7 U.S. cities with the worst air pollution

Aug. 4, 2010, 12:20 p.m.
Cincinnati skyline

Photo: rainbowbeth/Flickr

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Cincinnati

Cincinnati-Middletown, Ky.-Wilmington, Ind.,  ranked #9 for year-round particle pollution. This was one of the 16 metropolitan areas that reported the lowest levels ever.