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America's 25 Most Ozone-Polluted Metropolitan Areas, 2013

Each year the American Lung Association issues their "State of the Air" report. They track year-round and short-term particle pollution as well as the ozone pollution listed here. Though ozone pollution isn't the obvious, sooty kind of pollution, it can still be harmful to your health. Studies have shown that ozone pollution can worsen conditions such as bronchitis, asthma, emphysema, and cardiovascular disease.

Rank: City
#1: Los Angeles-Long Beach-Riverside, CA
#2: Visalia-Porterville, CA
#3: Bakersfield-Delano, CA
#4: Fresno-Madera, CA
#5: Hanford-Corcoran, CA
#6: Sacramento--Arden-Arcade--Yuba City, CA-NV
#7: Houston-Baytown-Huntsville, TX
#8: Dallas-Fort Worth, TX
#9: Washington-Baltimore-Northern Virginia, DC-MD-VA-WV
#10: El Centro, CA
#11: Merced, CA
#11: San Diego-Carlsbad-San Marcos, CA
#13: Modesto, CA
#14: Birmingham-Hoover-Cullman, AL
#14: Cincinnati-Middletown-Wilmington, OH-KY-IN
#16: Las Vegas-Paradise-Pahrump, NV
#17: Louisville-Jefferson County-Elizabethtown-Scottsburg, KY-IN
#17: New York-Newark-Bridgeport, NY-NJ-CT-PA
#19: Charlotte-Gastonia-Salisbury, NC-SC
#20: Oklahoma City-Shawnee, OK
#20: Philadelphia-Camden-Vineland, PA-NJ-DE-MD
#20: Beaumont-Port Arthur, TX
#23: Phoenix-Mesa-Glendale, AZ
#24: Pittsburgh-New Castle, PA
#25: St. Louis-St. Charles-Farmington, MO-IL
Source: State of the Air: 2013, American Lung Association.