About 1 million Iowans live in counties that topped federal small-particle or ozone limits at least once over the past three years, a Des Moines Register investigation into emissions across the state shows.

Environmentalists say fears about health risks associated with Iowa's air are warranted. While it's difficult to prove any one plant's emissions directly caused a particular person's illness, national studies at numerous universities have found the types of compounds emitted by many of Iowa's facilities cause or worsen health problems such as asthma, decreased lung function and bronchitis, and can even kill.

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