In the agency's state of the air report, Bakersfield is listed as the most polluted city because of its high pollution and ozone levels.
Hanford is number two on the list, in the year-round particle pollution category.
Visalia took the fourth spot, while Fresno was ranked fifth. Los Angeles was also included in the list.
The good news is, the report shows the US has made significant progress in cleaning the air. Ozone levels dropped 13 percent and particle pollution decreased between 2001 and 2010.