More Americans breathing cleaner air – but not all

beautiful girl lying down of grass. Copy space

While more Americans are breathing cleaner air than in the past, many are living in cities that have worse air quality than a decade ago, Health Day News reported.

A new report from the American Lung Association (ALA) measured ozone and particle levels in the air in nearly 1,000 cities and counties in the United States between 2009 and 2011. Among the 25 most polluted cities in last year’s report, about half had improved, and many displayed the cleanest air levels since the ALA began researching air quality trends in 2000.

"The long-term trend is positive and headed to much cleaner air," said report author Janice Nolen, assistant vice president of national policy and advocacy for the American Lung Association. "(However), there is an uptick in some areas that are a concern and some areas where the problem remains very, very serious."

The other half of the 25 most polluted cities showed worse pollution than from before the report, according to Health Day News. And even the cities that had improved were still near the top of the most-polluted list.

Los Angeles had the most ozone – or smog – pollution, and Bakersfield, Calif., had the most particle – or soot – pollution.

In addition to the California cities, Houston, Dallas, Oklahoma City, Cincinnati, New York City and Washington, D.C., were among the metropolitan areas that had high levels of ozone. As for year-round levels of soot, many of the same cities in California topped the list, as well as Cincinnati and Canton in Ohio; Philadelphia and Allentown in Pennsylvania; Louisville, Ky.; St. Louis, Mo.; and Fairbanks, Alaska.

The cities that did not experience a single day of unhealthy levels of ozone or particle pollution from 2009 to 2011 were Bismarck, N.D., Rapid City, S.D., and the Fort Meyers and Palm Beach areas of Florida.

In total, 254 counties had unhealthy levels of ozone or particle pollution, and about 132 million people (42 percent of the U.S. population) live in these areas – compared to 127 million people (41 percent of the U.S. population) in the ALA’s last report.

Both ozone and particle pollution can affect respiratory health, worsening breathing and increasing the risk of asthma attacks, respiratory infections and chronic obstructive pulmonary disease (COPD).

Click here for more from Health Day News.