The American Lung Association released its 27th annual "State of the Air" report.
Researchers say it shows more than 152 million people in the United States are living in areas with unhealthy levels of air pollution.
Valley cities are some of the most polluted locations in the nation.
Visalia ranked number 2, and the Fresno-Hanford-Corcoran area came in at number 5 for the worst for high ozone days out of 226 metropolitan areas.
Visalia ranked 5th, and Fresno-Hanford-Corcoran was higher at 4th for year-round particle pollution.