It looks at 277 metro areas in the U.S. Houston ranks seventh highest on the list when it comes to ozone. But it's 112th when it comes to 24-hour particle pollution.
Dallas-Fort Worth ranks eighth when it comes to ozone. The Beaumont-Port Arthur area ranks 20th.
As far as the most polluted city, that's Los Angeles. The cleanest is Ames, Iowa.
Click here to see the entire list and report.
Take ABC13 with you!
Download our free apps for iPhone, iPad, Android and Blackberry devices