Top 10 Dirtiest U.S. Cities

More stringent regulations and clean air initiatives have helped with the air quality problem the United States faces, but over 175 million people in the U.S.—roughly 58 percent—still suffer from pollution levels that are often dangerous, according to the American Lung Association.

The most common kinds of air pollution fall into two categories: ozone (smog) and particle pollution (soot). Breathing either does not do a body good. Air pollution is a serious health threat that affects all exposed to it. It can lead to large variety of lung ailments and can have a severe impact on cardiovascular health–it speeds up aging and it can be deadly. Some of the biggest sources of air pollution are dirty power plants, old diesel vehicles and heavy equipment, and ocean-going vessels.

Ozone (O3) is a highly reactive gas molecule composed of three oxygen atoms. Although in the upper atmosphere ozone is essential (it protects us from much of the sun’s ultraviolet radiation, thank you ozone)–ozone air pollution at our level is harmful and causes serious health problems by attacking lung tissue and causing inflammation and other damage.

In the America Lung Association State of the Air Report 2010, American cities were ranked according to ozone levels, as well as short-term and year round particle pollution levels. The cities are ranked by the air quality in the most polluted county in the metropolitan area. Here are the ten cities with the highest levels of ozone, number 1 being the worst–with any other rankings they scored for particle pollution.

1o. Charlotte-Gastonia-Salisbury, NC-SC

9. San Luis Obispo-Paso Robles, CA

8. San Diego-Carlsbad-San Marcos, CA
Ranked 17th for short-term particle pollution.

7. Houston-Baytown-Huntsville, TX
Ranked 16th for year round particle pollution.

Ozone is in the atmosphere from raw gases that come out of tailpipes, smokestacks and many other sources. These essential raw ingredients for ozone are nitrogen oxides (NOx) and hydrocarbons, also called volatile organic compounds (VOCs). They are produced primarily when fossil fuels like gasoline, oil or coal are burned or when some chemicals, like solvents, evaporate.

6. Hanford-Corcoran, CA
Ranked 8th for year round particle pollution and 10th for short-term particle pollution.

5. Sacramento-Arden-Arcade-Yuba City, CA-NV
Ranked 6th for short-term particle pollution.

4. Fresno-Madera, CA
Ranked 6th for year round particle pollution and 2nd for short-term particle pollution.

3. Visalia-Porterville, CA
Ranked 3rd for year round particle pollution and 8th for short-term particle pollution.

2. Bakersfield, CA
Ranked 2nd for year round particle pollution and 1st for short-term particle pollution.

1. Los Angeles-Long Beach-Riverside, CA
Ranked 4th for year round particle pollution and 3rd for short-term particle pollution.

Since ozone is  a secondary pollutant (not formed directly by the burning of fossil fuels, but from nitrogen oxides produced by such combustion, and that then react in the presence of sunlight) it is the biggest problem in areas that are sunny and hot. In addition, LA is a low basin surrounded by mountains, with an enormous amount of automobile traffic.

Here are just a few steps you can take to improve air quality:

• Drive less: 6 tips to Go Car Free
• Don’t burn wood or trash (read about green fire logs).
• Use less electricity.
Make sure your school system requires clean buses.

Related: Global Warming Skeptics: What About Air Pollution?, Top 10 Countries Killing the Planet


Ellie M
Ellie M3 months ago


Mary T.
Mary T4 years ago

sad moving the the 4th most dirtiest city in the US...oh well

John S.
Past Member 6 years ago

Interesting, thought it would be different.

An Mi
Anna M6 years ago

And Bill M. is exactly right! Too many cars, poor city planning (suburban sprawl) and poor public transportation are ruining air quality, wasting millions of hours of people's time in interstate gridlock, and uglifying the areas surrounding cities. In America, where the population is nothing compared with places like China, much of this is preventable-- get out of the cars, give people public transport, and stop building all over the place-- concentrate it and make things walkable-- there's a novel idea.

An Mi
Anna M6 years ago

Gosh, California, that's too bad. Sadly, even these cities would be clean in comparison to many many places in other countries. I don't even want to look at the list of dirtiest cities in China...just remembering them makes me start coughing. :-(

Julie F.
Julie F7 years ago

Sad that the majority of these are in Cali!

Clemente V.
Clemente V.7 years ago

Yep, I knew Houston was there

Ruth Bruno
Ruth Bruno7 years ago

thank you

jane richmond
jane richmond7 years ago

Thrilled NYC didn't make the list.

Bill M.
Bill M.7 years ago

This happens when you have too many cars, low suburban development density, and not enough transportation alternatives. The irony is that although individual cars produce less pollution than four dedcades ago the increase in the number of vehicles and number of vehicles per capita more than offset improvements in technology.