The American Lung Association recently issued its“State of the Air: 2008” report for the United States, examining trends in air pollution and respiratory diseases, like asthma and chronic bronchitis, in major U.S. cities from 2004 to 2006.

Within the report are rankings of the “Most Polluted” and “Cleanest” cities. The research focuses on two of the most widespread air pollutants: ozone, the primary ingredient of smog, and particle pollution, found in sources like dirty truck exhaust.

Below are some highlights of the top five winners (or, losers?):

MOST POLLUTED

Most Polluted: Ozone: “The five worst cities for ozone all saw good improvement in their ozone levels during 2004-2006, including Los Angeles and Houston—two cities with most infamous smog problems.”

1. Los Angeles, Calif.
2. Bakersfield, Calif.
3. Visalia, Calif.
4. Houston, Tex.
5. Fresno, Calif.

Most Polluted: Year-Round Particle Pollution: “Aggressive emissions controls in the Los Angeles basin dropped the year-round particle levels by just under one-third during
this decade…. Several cities that also reduced year-round particle pollution dropped off the ’25 most polluted’ list this year, including New York City, Chicago, Philadelphia and Indianapolis.”

1. Los Angeles, Calif.
2. Pittsburgh, Penn.
3. Bakersfield, Calif.
4. Birmingham, Ala.
5. Visalia, Calif.

Most Polluted: Short-Term Particle Pollution: “For the first time, a city not in California—Pittsburgh—moved to the top of a most polluted list… Most cities curtailed the number of days with dangerous levels of short-term particle pollution.”

1. Pittsburgh, Penn.
2. Los Angeles, Calif.
3. Fresno, Calif.
4. Bakersfield, Calif.
5. Birmingham, Ala.

CLEANEST

(Cities were listed alphabetically – not ranked – for least ozone and short-term particle pollution.)

Least Polluted: Year-round Particle Pollution:

1. Cheyenne, Wyo.
2. Santa Fe, N.Mex.
3. Honolulu, Hawaii
4. Great Falls, Mont.
5. Farmington, N.Mex.