Most Smog?
This gets a big WTF? Why would Knoxville be so high? (since I am moving there)

1. Los Angeles, California
2. Visalia-Porterville, California
3. Bakersfield, California
4. Fresno, California
5. Houston, Texas
6. Merced, California
7. Sacramento, California
8. Hanford, California
9. Knoxville, Tennessee
10. Dallas-Fort Worth, Texas

Here is the best explanation I could find: "Ragsdale noted that while pollution in Miami blows out to sea, the Great Smoky Mountains trap ozone in East Tennessee and western North Carolina, making the EPA air standards unreasonable for the region." I figured the mountains had something to do with it, which I think is similar to LA's problem.