America's most polluted cities

This time of year, many Americans are concerned with sunburns. In some areas, they should pay more attention to smog.

The reason? Though it's often invisible, air pollution is a threat to 186 million Americans, according to a new report released by the American Lung Association.

The annual report--State of the Air 2009--found that six in 10 Americans live in counties where ozone or particle pollution has reached dangerous levels. Both types of pollution can be deadly and have been linked to worsening respiratory conditions like asthma, emphysema and bronchitis, and there is evidence that particle pollution increases risk of heart attacks and strokes.

How does your city rank, for particulant pollution and ozone? All the details in Forbe's in-depth article can be found here.