WASHINGTON, DC - The United States has made progress in cleaning up air pollution, but 154.5 million people, about half the population, live where the air is so polluted with smog and particles that it is often dangerous to breathe, the American Lung Association said today.

Sunrise over the Houston Ship Channel. Nearly half the people in the United States, 48.2 percent, live in counties that received an "F" for air quality due to unhealthy ozone levels, finds the report. (Photo by Cam17) In its annual report on air quality, State of the Air 2011, the American Lung Association says that the Clean Air Act is working and warns against legislators who are trying to weaken the law.

"State of the Air tells us that the progress the nation has made cleaning up coal-fired power plants, diesel emissions and other pollution sources has drastically cut dangerous pollution from the air we breathe," said Charles Connor, American Lung Association president and chief executive.

"We owe our cleaner air to the Clean Air Act," Connor said. "We have proof that cleaning up pollution results in healthier air to breathe. That's why we cannot stop now. Half of our nation is still breathing dangerously polluted air. Everyone must be protected from air pollution."

The threats to the Clean Air Act are coming from the Republican, not the Democratic, side of Congress, in bills to strip the U.S. EPA of funding and curtail its powers to regulate air emissions.

Senator Barbara Boxer, a California Democrat who chairs the Environment and Public Works Committee, said, "During the recent budget debate, the American Lung Association and other leading public health organizations joined me in successfully defeating GOP efforts to repeal Clean Air Act safeguards, and we must continue to fight to protect our landmark environmental laws."

"The Clean Air Act has been one of most successful and effective environmental laws ever enacted in this country," said Boxer. "This report shows significant progress has been made, but it also indicates that more work needs to be done to protect the health and safety of children and families."

The State of the Air 2011 report grades cities and counties based on the color-coded Air Quality Index developed by the U.S. Environmental Protection Agency to help alert the public to daily unhealthy air conditions.

The report uses the most recent EPA data collected from 2007 through 2009 from official monitors for ozone and particle pollution, the two most widespread types of air pollution.

Counties are graded for ozone, or smog, the most widespread air pollutant. They are also graded for year-round particle pollution and short-term particle pollution levels.

All metro areas in the list of the 25 cities most polluted by ozone showed improvement over the previous report, and 15 of those cities experienced the best year yet.

All but two of the 25 cities most polluted with year-round particle pollution improved over last year's report.

But only 11 cities among those most polluted by short-term spikes in particle pollution experienced improvement.

The report identified Honolulu, Hawaii and Santa Fe-Espanola, New Mexico as the cleanest cities - the only two cities in the nation that were among the cleanest for year-round particle pollution and also had no days when ozone and daily particle pollution levels reached unhealthy ranges.

Los Angeles-Long Beach-Riverside, California remains the metropolitan area with the worst ozone problem, although great improvements have been made since the report was first issued 12 years ago. In fact, eight of the 10 most ozone-polluted cities are in California, the report shows.

Nearly half the people in the United States, 48.2 percent, live in counties that received an "F" for air quality due to unhealthy ozone levels, finds the report.

Ground-level ozone, or smog, is the most widespread air pollutant, created by the reaction of sunlight on emissions from vehicles, power plants and other sources. When ozone is inhaled, it irritates the lungs. It can cause immediate health problems and continue days later. Ozone can cause wheezing, coughing, asthma attacks and even premature death.

Bakersfield, California tops both lists of cities polluted by short-term and annual particle pollution. Bakersfield and Hanford, California were the only two cities where year-round particle levels worsened over the previous report.

Nearly 60 million Americans, 19.8 percent, live in counties with too many unhealthy spikes in particle pollution levels, and 18 million people live with unhealthy year-round levels of particle pollution.

Particle levels can spike dangerously for hours to weeks on end or remain at unhealthy levels on average every day all year long.

"Particle pollution kills," said Norman Edelman, M.D., the American Lung Association's chief medical officer.

"When you breathe these microscopic particles, you are inhaling a noxious mix of chemicals, metals, acid aerosols, ash and soot that is emitted from smokestacks, tailpipes, and other sources. It is as toxic as it sounds and can lead to early death, asthma exacerbations, heart attacks, strokes and emergency room visits in substantial numbers," said Dr. Edelman.

"Science clearly has proven that we need to protect the health of the public from the dangers of particle pollution," he said.

Only 10 counties received an "F" for year-round particle pollution, a reflection of progress made under the Clean Air Act.

The Lung Association is advocating against weakening or blocking enforcement of the Clean Air Act, including steps to strip legal authority and funding from the EPA.

"Such moves would undermine the cleanup that remains, including the long-overdue cleanup of power plants EPA recently proposed," the association said today.

As the Lung Association pointed out in its March report on toxic air pollution from coal-fired power plants, that the pollution from over 440 coal-fired power plants in 46 states are among the biggest contributors to ozone and particle pollution in the country.

These power plants also produce 84 known hazardous air pollutants such as arsenic, mercury, dioxins, formaldehyde and hydrogen chloride, which blow across state lines polluting the air thousands of miles away from the plants.

Since this pollution spreads across state lines, the EPA's ability to enforce federal clean air standards is the only protection many communities have.

NATION'S MOST POLLUTED CITIES

10 Most Ozone-Polluted Cities

1. Los Angeles-Long Beach-Riverside, California
2. Bakersfield-Delano, California
3. Visalia-Porterville, California
4. Fresno-Madera, California
5. Sacramento-Arden-Arcade-Yuba City, California-Nevada
6. Hanford-Corcoran, California
7. San Diego-Carlsbad-San Arcos, California
8. Houston-Baytown-Huntsville, Texas
9. Merced, California
10. Charlotte-Gastonia-Salisbury, North Carolina-South Carolina

10 Cities Most Polluted by Short-term Particle Pollution

1. Bakersfield-Delano, California
2. Fresno-Madera, California
3. Pittsburgh-New Castle, Pennsylvania
4. Los Angeles-Long Beach-Riverside, California
5. Salt Lake City-Ogden-Clearfield, Utah
6. Provo-Orem, Utah
7. Visalia-Porterville, California
8. Birmingham-Hoover-Cullman, Alabama
9. Hanford-Corcoran, California
10. Logan, Utah-Idaho

10 Cities Most Polluted by Year-Round Particle Pollution

1. Bakersfield-Delano, California
2. Los Angeles-Long Beach-Riverside, California
3. Phoenix-Mesa-Glendale, Arizona
4. Visalia-Porterville, California
5. Hanford-Corcoran, California
6. Fresno-Madera, California
7. Pittsburgh-New Castle, Pennsylvania
8. Birmingham-Hoover-Cullman, Alabama
9. Cincinnati-Middletown-Wilmington, Ohio-Kentucky-Indiana
10. Louisville-Jefferson County-Elizabethtown-Scottsburg, Kentucky-Indiana