America's most polluted cities

This time of year, many Americans are concerned with sunburns. In some areas, they should pay more attention to smog.

The reason? Though it's often invisible, air pollution is a threat to 186 million Americans, according to a new report released by the American Lung Association.

The annual report -- State of the Air 2009 -- found that six in 10 Americans live in counties where ozone or particle pollution has reached dangerous levels.

Both types of pollution can be deadly and have been linked to worsening respiratory conditions like asthma, emphysema and bronchitis, and there is evidence that particle pollution increases risk of heart attacks and strokes.

In compiling this list, the American Lung Association ranked US metropolitan statistical areas -- geographic entities defined by the US Office of Management and Budget for use by federal agencies in collecting, tabulating and publishing federal statistics -- using the highest weighted average for any county within that MSA. Grading was based on the Environmental Protection Agency's determination of violations of the national ambient air quality standard.

Though overall air pollution is down compared to previous years, the problem is still widespread. Visalia and Fresno, two mid-size towns in central California ranked high for short-term and year-round particle pollution.

Birmingham, Ala., and Cincinnati were listed in the top 10 of metro areas with unhealthy levels of year-round particle pollution. In the Southwest, the Houston, Dallas and Phoenix metro areas had high ozone levels.

Residents of Los Angeles, Bakersfield, Calif., and Pittsburgh, Pa., might want to pay close attention to the ALA's rankings. These metro areas were deemed the most polluted in the nation.

The Los Angeles metro area -- known for its thick smog -- ranks this year as the most ozone-polluted. Pollutants produced by car exhaust and smokestacks form the raw ingredients for the production of ozone.

Nearby Bakersfield, Calif., ranked as the city with the most year-round particle pollution and had ozone levels second only to Los Angeles. The Pittsburgh metro area, an industrial hub in western Pennsylvania, had the highest short-term particle pollution and the second highest year-round levels.

Short-term and year-round particle counts reflect the amount of tiny solid and liquid particles in the air, most often emitted from diesel-powered vehicles, steel mills and coal-fired power plants, among other sources.

It's an unenviable distinction, but also a serious public health issue, says Dr. Norman H. Edelman, chief medical officer for the ALA.

"As of now, half of Americans live in an area where they are at risk," he says. Federal and state governments are working to improve air quality, and such efforts were recently bolstered by increased funding in the stimulus package. But short of moving to Fargo, N.D., Wahpeton, Minn., Lincoln, Neb., or Honolulu, Hawaii, or one of the other towns and cities ranked as the cleanest by the ALA, Americans have few choices but understanding and avoiding risks in affected areas.

Air Quality and Your Health

Many Americans fail to realize they're exposed to unhealthy air pollution levels or confuse ozone pollution symptoms like a runny nose, cough and watery eyes with allergies or a cold. Worse yet, there are no diagnostic tests that indicate heightened risk.

"Ozone gets into your airway and doesn't leave a trace," says Edelman. Researchers believe that it actually behaves similarly to cigarette smoke by burning the airway and possibly causing inflammation in the lungs and blood vessels. Such inflammation can worsen respiratory conditions.

Unlike ozone pollution, which causes immediate but less benign symptoms, particle pollution is silent until manifested through long-term conditions like emphysema and asthma. Particle pollution has also been linked to worsened asthma, lung cancer, heart attacks, strokes and increased premature mortality.

Edelman recommends avoiding the outdoors when the air quality has been measured as unsafe. This is particularly important for at-risk populations, which include children and those with respiratory conditions. Several government agencies, including the Environmental Protection Agency and the National Weather Service, maintain a Web site that tracks pollution monitors placed across the country.

In 2008, the threshold for dangerous ozone levels was lowered from .08 parts per million to .075 ppm. The shift means that nearly 83 million more Americans live in counties where ozone monitors registered too many unhealthy days of air pollution.

Cleaning Up the Air

This has not escaped the attention of the current administration, which allocated $300 million in stimulus funds for state and federal clean diesel programs. Lydia Wegman, director of health environmental impacts division at the EPA, says that such efforts have improved in recent years as state and local agencies "have developed a lot more knowledge of strategies for controlling air pollution."

Despite its top ranking on ALA's list, Wegman cites Los Angeles as a leading example. In 2006, the Los Angeles and Long Beach ports adopted a long-term plan to reduce particulate matter pollution by targeting diesel vehicles.

Sam Atwood, a spokesman for the South Coast Air Quality Management District in the Los Angeles area, says taming pollution has proved difficult since the area's two ports handle 40 per cent of the country's foreign imports.

Trucks and trains are then put into action in transporting those goods, leading to further air pollution. Emissions created by the area's 16 million residents and 11 million vehicles are another major consideration, as is the warm weather, which tends to trap pollution close to the ground.

Despite those challenges, Los Angeles has slowly improved its ozone and year-round particle pollution levels in the past decade. By 2010, California will also have reduced its diesel emissions by nearly 75 per cent as compared to 2000 levels, according to Mike Scheible, deputy executive officer of the state's Air Resources Board.

To be sure, there is significant economic incentive for improving air quality. A study done in 2007 by the South Coast Air Quality Management District found that achieving federal air quality standards in the Los Angeles area would cost $2.3 billion per year but save $14.6 billion.

That figure reflects a range of annual costs, including crop damage, lost work days and premature deaths.