FILE - EPA officials set to announce new standards on Friday; above, smog covers downtown Los Angeles, Calif., April 2009.
FILE - EPA officials set to announce new standards on Friday; above, smog covers downtown Los Angeles, Calif., April 2009.
California is home to most polluted cities in the United States.
Based data from the U.S. Environmental Protection Agency, the American Lung Association (ALA) lists six California cities among the ten worst-polluted metropolitan areas in the country. 

The ALA rankings are included in its 2014 “State of the Air” report, released Wednesday.  The list is based on ozone and particle pollution for the years 2010-2012. 

Fresno, in north central California and home to 1.1 million residents, is the most polluted area, according to the report. Exhaust from agricultural operations, the area’s topography and smog from nearby San Francisco and Sacramento all contribute to Fresno’s problem.

Fresno citizens suffer from the worst particle pollution in the country.  It is so bad that school and city officials raise red flags when the air outside is dangerous to breath, according to the Los Angeles Times.

Los Angeles has the worst ozone pollution in the country. Ozone, according to scientists, is the most widespread pollutant in the United States, as well as one of the most dangerous.  Harmful to breathe, ozone aggressively attacks lung tissue by reacting chemically with it, according to the ALA.

The ALA report goes on to warn that nearly half of all Americans – more than 147 – live in metropolitan areas where pollution has become unhealthy to breathe.

Twenty-two of the 25 most ozone-polluted cities in the 2014 report – including Los Angeles, New York City, and Chicago – had more high ozone days on average when compared to the 2013 report.

According to the ALA report, these are the most polluted metropolitan areas in the United States:
  1. Fresno, California
  2. Visalia, California
  3. Bakersfield, California
  4. Los Angeles, California
  5. Modesto, California
  6. Pittsburgh, Pennsylvania
  7. El Centro, California
  8. El Paso, Texas
  9. Phoenix, Arizona
  10. St. Louis, Missouri
On the opposite end of the spectrum, four metropolitan areas were named by the ALA as the “cleanest cities” for having no days with unhealthy levels of ozone or particle pollution and for being among the 25 cities with the lowest year-round particle levels. These cities include:

-Bangor, Maine
-Bismarck, North Dakota
-Cape Coral-Fort Myers, Florida
-Salinas, California