More than four in 10 Americans – nearly 138.5 million people – live in counties where ozone or particle pollution levels make the air unhealthy to breathe, according to the American Lung Association’s “State of the Air 2015” report released today. The 16th annual national report card shows that improvement in the nation’s air quality was mixed, with many cities experiencing strong improvements, while others suffered increased episodes of unhealthy air, and a few even marked their worst number of unhealthy days.

Public domain image/National Atlas of the United States
Public domain image/National Atlas of the United States

Overall, the best progress came in the continued reduction of year-round particle pollution in the eastern half of the nation, thanks to cleaner power plants and cleaner diesel fleets. Covering air pollution data collected in 2011 to 2013, this year’s report also provides evidence that a changing climate will make it harder to protect human health from the dangers of air pollution. The impact of climate change is particularly apparent in the western United States, where heat and drought create situations ripe for episodes of high particle pollution, a pollutant recently found to cause lung cancer.

“Everyone has the right to breathe healthy air. We must meet our air pollution challenges head-on to protect the health of millions of Americans living with asthma and chronic obstructive pulmonary disease,” said Harold P. Wimmer, National President and CEO of the American Lung Association.

“One challenge is that many more people are actually at risk than even our estimates show. We use the current ozone standard as the basis of much of our assessment, but that standard is weak, and out of date and does not reflect what we know harms children and people with lung disease,” Wimmer said. “We urge the U.S. Environmental Protection Agency to update the ozone standard to reflect current science and give parents accurate information about the air pollution risks in their community. A standard set at 60 parts per billion would provide much more accurate information and better health protection.”

Key “State of the Air 2015” findings include:

  • More than four in 10 people (nearly 44 percent) in the United States live in counties that have unhealthful levels of either ozone or particle pollution.
  • Nearly 17.8 million people (5.6 percent) in the United States live in 12 counties with unhealthful levels of all three measures: ozone, short-term particle pollution and year-round particle pollution.
  • Overall, the best progress came in the continued reduction of year-round particle pollution in the eastern half of the nation, thanks to cleaner diesel fleets and cleaner power plants.
  • Six cities had a record number of days with dangerous levels of particle pollution, while many others had more than in the 2014 report, which covered 2010 to 2012.
  • Ozone was mixed, with many cities—particularly in California—doing better than in the 2014 report, but many having more unhealthy ozone days.

Los Angeles remains the metropolitan area with the worst ozone pollution, as it has for all but one of the 16 reports, although the city reported its lowest average year-round particles and fewest high ozone days in the report’s history. Fresno-Madera, Calif., remained at the top of both lists for most polluted area for particle pollution, as it was in the 2014 report. Six cities earned distinction as the “cleanest cities”: Bismarck, N.D.; Cape Coral-Fort Myers-Naples, Fla.; Elmira-Corning, N.Y.; Fargo-Wahpeton, N.D.-Minn.; Rapid City-Spearfish, S.D.; and Salinas, Calif. These cities had no days with unhealthy levels of ozone or particle pollution and ranked among the 25 cities with the lowest year-round particle levels.

Progress Continues in Reducing Year-round Particle Pollution

Reducing particle pollution is crucial to supporting health and reducing the risk of premature death, asthma attacks and lung cancer. Lower annual particle pollution levels result directly from the transition to cleaner diesel engines and steps taken to clean up power plants, especially in the eastern United States. Thirteen of the 25 metro areas with the worst year-round levels of particle pollution had their cleanest years yet, including Birmingham, Ala., Houston and Indianapolis.

However, dangerous short-term spikes in particle pollution increased in many cities, particularly in the western United States. Six cities had a record number of days with elevated particle pollution: Visalia, Calif.; greater San Francisco (including San Joaquin County); Fairbanks, Alaska; Phoenix; Yakima, Wash.; and Reno, Nev. Continuing drought and heat may have increased particles from dust, grass fires and wildfires, while burning wood as a heat source appears to contribute to the problem in many smaller cities.

Particle pollution data from all of Illinois, most of Tennessee and many counties in Georgia were missing because of problems with data processing in laboratories and other data issues. Without accurate information about the levels of particle pollution in these communities, several cities are not included in the report. Among the cities missing from the particle pollution rankings are Chicago, St. Louis and Atlanta; all were on the list for most polluted cities last year. Absent the data, they cannot be ranked, but, historically, these communities have had unhealthy air.

Ozone Pollution Improvement Mixed

One of the most common air pollutants in this country, ground-level ozone triggers asthma attacks, increases the risk of hospital admissions and emergency room visits and even increases the risk of premature death.

Of the 25 metro areas most polluted by ozone, 13 had fewer high ozone days on average compared to last year’s report, and five cities had their fewest unhealthy days ever in the 16 years of this report: Los Angeles; Visalia, Calif.; Bakersfield, Calif.; Sacramento, Calif.; and Washington-Baltimore.

Twelve cities increased their average number of high ozone days, including Fresno, Calif., Dallas-Fort Worth, Las Vegas, Phoenix, New York City and Denver. Rising temperatures create conditions favorable to forming ozone. Communities will need more help to reduce ozone pollution in the warmer temperatures expected from the changing climate.

Challenges Remain: More Safeguards Needed to Protect Health

Thanks to the Clean Air Act, some of the most polluted cities have made extraordinary headway.

Even with this progress, air pollution remains a pervasive public health threat in the United States. Safeguards are necessary to protect the health of the millions of Americans who live where dangerous levels of either ozone or particle pollution can cause wheezing and coughing, asthma attacks, heart attacks and premature death. While everyone needs protection, those at greatest risk from air pollution include infants, children, older adults, anyone with lung disease like asthma, people with heart disease or diabetes, people with low incomes and anyone who works or exercises outdoors.

The American Lung Association calls for several steps to safeguard the air everyone breathes:

  • Strengthen the outdated ozone standards. The EPA must adopt an up-to-date ozone limit that follows the current health science and the law to protect human health. Strong standards will drive much needed cleanup of ozone pollution across the nation.
  • Adopt a strong final Clean Power Plan. The EPA needs to issue tough final requirements to reduce carbon pollution from power plants.
  • Protect the Clean Air Act. Congress needs to ensure that the protections under the Clean Air Act remain effective and enforced. States should not be allowed to “opt out” of Clean Air Act protections.
  • Fund the work to provide healthy air. Congress needs to adequately fund the work of the EPA and the states to monitor and protect the nation from air pollution.

“Through the history of this report we’ve seen tremendous improvement in air quality, yet we’ve also discovered that air pollution is a more serious threat to our health than we previously knew,” said Wimmer. “We have cleaner air today than we did 16 years ago – testament that the Clean Air Act works. Congress must allow the Clean Air Act to continue to protect our health, and ensure that the EPA and states can protect Americans from air pollution.”

To see how your community ranks in “State of the Air 2015,” to learn how to protect yourself and your family from air pollution, and to join the fight for healthy air, visit:

Nation’s Most Polluted Cities

Top 10 U.S. Cities Most Polluted by Short-term Particle Pollution (24-hour PM 2.5)

Metropolitan Statistical Areas

  1. Fresno-Madera, Calif.
  2. Bakersfield, Calif.
  3. Visalia-Porterville-Hanford, Calif.
  4. Modesto-Merced, Calif.
  5. Los Angeles-Long Beach, Calif.
  6. San Jose-San Francisco-Oakland, Calif.
  7. Salt Lake City-Provo-Orem, Utah
  8. Logan, UT-ID
  9. Fairbanks, Alaska
  10. Pittsburgh-New Castle-Weirton, Penn.-Ohio-West Va.

Top 10 U.S. Cities Most Polluted by Year-Round Particle Pollution (Annual PM 2.5)

Metropolitan Statistical Areas

  1. Fresno-Madera, Calif.
  2. Bakersfield, Calif.
  3. Visalia-Porterville-Hanford, Calif.
  4. Modesto-Merced, Calif.
  5. Los Angeles-Long Beach, Calif.
  6. El Centro, Calif.
  7. San Jose-San Francisco-Oakland, CA
  8. Cincinnati-Wilmington-Maysville, OH-KY-IN
  9. Pittsburgh-New Castle-Weirton, Penn.-Ohio-W.Va.
  10. Cleveland-Akron-Canton, OH

Top 10 Most Ozone-Polluted Cities

Metropolitan Statistical Areas

  1. Los Angeles-Long Beach, Calif.
  2. Visalia-Porterville-Hanford, Calif.
  3. Bakersfield, Calif.
  4. Fresno-Madera, Calif.
  5. Sacramento-Roseville, Calif.
  6. Houston-The Woodlands, Texas
  7. Dallas-Fort Worth, Texas-Okla.
  8. Modesto-Merced, Calif.
  9. Las Vegas-Henderson, Nev.-Ariz.
  10. Phoenix-Mesa-Scottsdale, Ariz.


The American Lung Association “State of the Air 2015” report uses the most recent quality-assured air pollution data, collected by federal, state and local governments and tribes in 2011, 2012, and 2013. These data come from official monitors for the two most widespread types of pollution, ozone and particle pollution. The report grades counties, ranking cities and counties based on scores calculated by average number of unhealthy days (for ozone and for short-term particle pollution) and by annual averages (for year-round particle pollution).