America's 10 most polluted cities, 2012 (BLOG)

While dangerous pollutants still threaten the health of millions of Americans, the United States has made great strides in clearing the ...

While dangerous pollutants still threaten the health of millions of Americans, the United States has made great strides in clearing the air, according to the American Lung Association.

In its annual State of the Air 2012 report, the organization said that between 2001 and 2010, ozone levels dropped 13%, year-round particle pollution declined 24% and short-term particle pollution 28% thanks to the Clean Air Act.

Particle pollution includes things like dust, metals, smoke, exhaust and acids, like nitrates and sulfates. Ozone, meanwhile, is created when a chemical or fossil fuel, like coal or gasoline, is partially burned and the unburned hydrocarbons, when combined with ultraviolet light, form a gas.

Amendments to the Clean Air Act in 1990, which included the promotion of the use of natural gas and low sulfur fuel, have resulted in 23,000 fewer premature deaths in 2010, averted 1.7 million asthma attacks and prevented 4.1 million lost work days, according to The Environmental Protection Agency.

But pollution still takes a great toll on public health. More than 4 out of 10 Americans, 127 million people, live in counties with dangerous levels of either ozone or particle pollution, the American Lung Association said. The result: increased incidents of all sorts of health problems, especially asthma, bronchitis and cardiovascular disease.

"We've been paying for this pollution for a long time," said Janice Nolen, the national policy advocate for the ALA.

The ALA report ranked cities by particle pollution, both short-term and year-round, as well as by ozone levels.

Many of the cities with the dirtiest air are located in the sunny valleys and basins of the West, where pollutants can stagnate and cook into photochemical smogs.

As a result, California lays claim to many of the most polluted cities. Bakersfield, in California's San Joaquin Valley, claimed the top spot as the most polluted city in the United States for 2012 for both types of particle pollution and was third in ozone levels. Los Angeles continues to be the worst city for ozone pollution, thanks to its heavy traffic and trade ports.

Those looking for the cleanest air can look no further than Santa Fe-Espanola, N.M., which took the top spot for air purity in all three categories, according to ALA's report.

10. Philadelphia
Population: 6,533,683
Cardiovascular cases: 1,660,434
Rank in most ozone-polluted cities: 16

Philadelphia is less industrial than it was but still cracked the top 10. Photo: G Widman for GPTMO

The City of Brotherly Love was once an industrial powerhouse, with heavy industries like steel, manufacturing, textiles and machinery.

Many of the factories are gone now and Philadelphia has much more of a service economy now. The industries that remain are subject to much stricter controls, according to Linda Rebarchak, a spokeswoman for the Pennsylvania Department of Environmental Protection.

Over the past few years, for example, continuous air monitors have been installed over many of the city's smokestacks to measure emissions. The monitors have helped to alert officials and factory managers to any problems in the systems, she said.

9. Louisville
Population: 1,427,483
Cardiovascular cases: 358,161
Rank in most ozone-polluted cities: Not in top 25

Lousville has cut its ozone levels by 15%. Photo: Thinkstock

Like many cities with air pollution problems, Louisville sits in a valley where air can stagnate in the summer heat.

"In the 1970s our air was pretty bad," said Thomas Nord, spokesman for the Louisville Metro Air Pollution Control District.

Through stricter regulations governing auto emissions, the city has managed to cut its ozone levels by about 15% since 1999.

8. Cincinnati
Population: 2,172,191
Cardiovascular cases: 534,359
Rank in most ozone-polluted cities: 21

Cincinnati has made pollution improvements, including its school buses. Photo: Philip Groshong / Cincinnati CVB

The Southern Ohio city has been stepping up its efforts to improve air quality over the past few years by launching several different programs, according to Megan Hummel, a spokeswoman for the Southwest Ohio Air Quality Agency.

It has retrofitted hundreds of old diesel engine school buses and replaced dozens more to reduce harmful emissions.

7. Phoenix
Population: 4,192,887
Cardiovascular cases: 981,249
Rank in most ozone-polluted cities: 19

High dust levels continue to plague Phoenix. Photo: Jill Richards / Phoenix CVB

Phoenix's intense sunlight can cook emissions into a smog soup. But efforts to cut tailpipe emissions have helped cut back ozone levels in the city considerably.

"We've had a long-term vehicle emissions inspection policy for about 25 years," said Mark Shaffer, a spokesman for the Arizona Department of Environmental Quality.

But nothing can help the area deal with its never-ending supply of dust -- a factor that helps put Phoenix in sixth place for year-round particle pollution.

6. Pittsburgh
Population: 2,447,393
Cardiovascular cases: 702,228
Rank in most ozone-polluted cities: 20

It's not Steel Town as much, but Pittsburgh is still high in emissions. Photo: Thinkstock

It's been decades since Pittsburgh's nickname, Smoky, was appropriate. As big steel exited the city's industrial landscape, the pollutants belching forth from the city's coke ovens and blast furnaces have almost all disappeared.

Nowadays, the economy is driven by the service and tech industries. Yet, it still remains a major transportation hub and diesel engines power much of the truck, train and boat traffic that moves through the area.

As a result, harmful emissions are a particular problem. The city has a high rate of lung diseases, especially emphysema with nearly 43,000 cases and cardiovascular disease with more than 700,000 cases, according to the American Lung Association.

5. Fresno, Calif.
Population: 1,081,315
Cardiovascular cases: 231,750
Rank in most ozone-polluted cities: 4

Fresno is No. 5 on the list but also pushed neighboring cities higher. Photo: Rod Gavorian Photography / Fresno CVB

Fresno is the biggest city in California's San Joaquin Valley and produces a lot of the surrounding area's air pollution.

The biggest culprit: traffic. A busy Interstate runs the length of the Central Valley and provides a steady stream of cars and trucks. Much of the smog drifts South to cities like Visalia and Hanford, but there is also a phenomenon known as the "Fresno Eddy," said Jaime Holt, chief communications officer for the San Joaquin Valley Air Quality District.

"It's kind of a whirlpool that pushes back some of the pollution back into Fresno air space," she said.

There's also few public transportation options so most everyone drives. And with a sky-high unemployment rate -- 17.3% in February -- many of the passenger cars are old.

4. Visalia, Calif.
Population: 442,179
Cardiovascular cases: 89,570
Rank in most ozone-polluted cities: 2

Visalia's irrigation has been a source of pollution. Photo: Marek Warszawski / Fresno Bee / MCT / Getty Images

Lying just south of Fresno, the skies of this small city bear the brunt of some of the pollution produced by its larger neighbor.

But Visalia can't blame it all on Fresno. Agricultural lands surrounding the town depend heavily on irrigation and many of the pumps bringing water to dry farmlands burn diesel, which produces both particle pollution and ozone.

"Over the past few years, most of those diesel pumps have been switched over to electricity," said Holt of the Valley's Air Quality District.

Air quality has also improved, she said, because the agency has used federal and state grants to pay residents to replace wood-burning stoves and fireplaces with gas or electricity.

3. Los Angeles
Population: 17,877,006
Cardiovascular cases: 4,109,426
Rank in most ozone-polluted cities: 1

L.A. is looking to cut back on pollution from its ports. Photo: Los Angeles CVB

One of Los Angeles' biggest pollution problems is its ports.

"Forty-three percent of all the imports in the country come through here," said Sam Atwood, spokesman for the South Coast Air Quality Management District. "Once the cargo comes in, it gets put on a truck, moved to warehouses and taken to trains. Almost everything is powered by diesel."

There have been several efforts made to cut back on this diesel-related pollution. One is the voluntary slowing of ships as they come into port, starting from about 24 nautical miles out. By doing so, the ships burn less fuel and produce lower emissions.

2. Hanford, Calif.
Population: 152,982
Cardiovascular cases: 31,019
Rank in most ozone-polluted cities: 5

Neighboring Fresno and older cars have polluted Hanford. Photo: Hanford Conference & Visitor Agency

This small metro area should boast azure skies but, too often, the polluted air from Fresno, its neighbor to the North, drifts in, said Jaime Holt, chief communications officer for the San Joaquin Valley Air Quality District.

It doesn't help that many of the local residents are also driving older cars that often produce much higher levels of the components that create smog.

One solution to that problem is a recently instituted smog check program called "Tune in, Tune up" run by the Air Quality District.

The state agency sets up in a big empty parking lot and gives free smog tests. "The cars that can't pass get a $500 voucher for a major tune up," said Holt.

1. Bakersfield, Calif.
Population: 839,631
Cardiovascular cases: 173,566
Rank in most ozone-polluted cities: 3

Bakersfield has reduced pollution, but it's still No. 1. Photo: Bakersfield Convention & Visitors Bureau

Bakersfield sits in a bowl surrounded on three sides by the Sierras and the California coastal ranges. Air drifts down the valley from other cities and lingers, allowing pollutants to build up, according to Jaime Holt, chief communications officer for the San Joaquin Valley Air Quality District. Making matters worse, the sun bakes the air, causing photochemical smog. And the dry weather adds dust particles to the mix.

But there have been efforts to clean up Bakersfield's act. Regulations governing emissions from surrounding oil and gas producers that took effect in 2003 have helped to significantly reduce pollution in the area, said Holt.

Area farmers have also changed many of their practices. They now refrain from cultivating when the ground is too dry, for example, in order to reduce dust. And regulations limiting residential use of fireplaces and wood stoves have also helped.

"We have some crystal clear days here now, where you can see snow in the Sierras," said Holt. "But then they can go away for weeks at a time."