The 2009 report was based on data collected at some 900 monitoring sites across the country during a three-year period from 2005 through 2007. Researchers measured the air quality of different areas using three criteria -- long-term particle pollution, short-term particle pollution and ozone concentration. All three forms of pollution have been shown to have negative health effects.
And according to the report, "air pollution remains widespread and dangerous" with nearly every major city burdened by some type of pollution from either ozone or particle pollution.
The rankings even included a few surprising locations that now have dirty air and were previously considered pristine.
Pittsburgh and Bakersfield, Calif., had the most particle pollution -- a mix of tiny specks of soot, dust, ash, and aerosols in the air. Meanwhile, Los Angeles topped the ozone rankings-- a dubious distinction that means that it could well be the smoggiest place in the country.
Cities and counties from coast to coast were ranked numerically based on their air pollution levels and these same communities were also graded A through F in a national air quality "report card."
The findings suggest that despite a growing "green" movement in the United States, the air you breathe can put your health at risk.
Air Not as Clean as It Seems
A lot of Americans feel comfortable about air pollution, and we often think that it's a problem in a few well-known places, said Dr. Norman H. Edelman, chief medical officer for the American Lung Association.
"This report suggests that some places we consider clean are not," he said.
Two locations in Utah, for example, earned listings among the top polluted cities. "Everyone assumes that Salt Lake City must be a clean place, but it's not it's counterintuitive," suggested Edelman.
Salt Lake City ranked sixth nationwide in a listing of cities most polluted by short-term particle pollution, and its neighbor to the north, Logan, Utah, came in at the number eight spot.
Pittsburgh topped the list of cities most polluted by short-term exposure to particles. It's still a dangerous city for particulate pollution, pointed out Edelman.
"This catches my eye because we ordinarily think they've cleaned up their act," he said.
Where Pollution Is at Its Peak
Three California spots -- Fresno, Bakersfield and Los Angeles -- ranked second, third and fourth in the nation for short-term particle pollution, while Birmingham, Ala., came in fifth.
Communities ranking high on this list have short-term spikes in particle pollution that can last anywhere from a few hours to several days. And it's these short-term spikes that increase the number of emergency room visits for asthma and other respiratory diseases, along with upping the risk of heart attacks, strokes, and early death among residents.
The sources of particle pollution can range from woodstoves and diesel trucks to coal-fired power plants and heavy highway traffic -- to name a few. And while particle pollutants come in different sizes, the ones that do the most damage are the extremely tiny ultrafine particles.
These teeny particles can creep deep into the lungs where they cause irritation and inflammation, and can be troublesome to people with existing respiratory problems such as asthma and chronic obstructive pulmonary disease.
But it's also suspected that these same tiny particles might escape the lungs and make their way into the bloodstream, where they can they have body-wide effects, especially on the heart.
Cheyenne, Wyo., was the cleanest place in the United States for long-term particle pollution. Santa Fe, N.M., was second in this category, Honolulu was third, with Great Falls, Mont., and Flagstaff, Ariz., tied for fourth.
Fargo had the distinction of being the cleanest city in the land in this year's report. It was the only location to earn a place on all three clean city lists.
More Americans Living With Polluted Air
One big contrast between the 2009 report and the data from the previous year was for ozone. This year the American Lung Association found that some 175 million Americans live in locations with unhealthy ozone levels while a year ago only 92.5 million residents did so.
Numerous studies have shows that ozone exposure, over long periods of time, can harm human health. Last month, a study conducted at the University of California, Berkeley showed that long-term exposure to ground-level ozone is linked to an increased risk of death from respiratory ailments. Other studies have implicated ozone-heavy smog in heart disease.
The number of people affected by high levels of ozone has nearly doubled in part as a result of tighter standards for it adopted by the Environmental Protection Agency (EPA) in March of 2008.
Although the new EPA ozone standards were put in place in 2008, the data collected between 2005 and 2007 was recalculated against the stricter guidelines. And even with these new ozone thresholds, many scientists don't feel they are stringent enough to protect human health.
Still, there are improvements. While Los Angeles led the list of American cities for ozone levels, the city continues to make consistent improvements in reducing this threat.
"I was pleasantly surprised to see that L.A.'s hard work over the years has paid off. They've made concentrated efforts to clear up their ozone and really taken it seriously," said Janice Nolen, assistant vice president of national policy for the American Lung Association. But she admits that Los Angeles will likely remain number one in ozone for some time because of its geography.
"Heat and sunlight make a difference to ozone. And if you add lots of mountains and the traffic in Los Angeles, this allows ozone to cook more and the air there is less likely to move out," explained Nolen.
In fact, warm and sunny locations tend to have more ozone formation and seem to dominate the rankings for this pollutant: Six out of the top 10 cities in the country for ozone were in California, two were in Texas and both Arizona and North Carolina had one of the most polluted ozone communities.
And while ozone in most cities nationwide have been improving -- by either decreasing or leveling off -- that's not the case in Las Vegas and Dallas, two places where ozone levels have been on the rise over the last decade.
Air Pollution a Complex Problem
While it's worthwhile to learn how your community fared in the report, it might not always reveal the extent of the problem.
"Air pollutants are not just generated locally," pointed out Jonathan Levy, an associate professor of environmental health at the Harvard School of Public Health in Boston, who is not connected the American Lung Association report.
"These are complicated pollutants that are hard to wrestle down, and they're not always a local phenomenon, "said Levy. In other words, he explained, the city you live in might not emit lots of pollutants, but sometimes you are just unlucky enough to live downwind from a place that does and people are exposed to high levels.
Weather patterns, for example, affect where pollution ends up and can push it away from its original source.
But no matter where you live, you can take steps to ease pollution. The experts encourage you to drive less and use mass transportation more, as well as using less electricity in your home.
To check the air quality in your city or community, visit www.stateoftheair.org or www.lungusa.org.