by Bryan Walsh
The World Health Organization has ranked cities around the world on their amount of particulate pollution in the air. Here's the dirtiest of the dirty in the U.S.
10 - 9. Pittsburgh/San Diego
7 to 4. Visalia-Porterville, Calif./Hilo, Hawaii/Modesto, Calif./Fairbanks, Alaska
3. Riverside/San Bernardino/Ontario, Calif.
2. Fresno, Calif.
1. Bakersfield, Calif.