Surprise, surprise:

Is the air you breathe hazardous to your health?

Now’s your chance to find out, thanks to The American Lung Association and their thirteenth annual State of the Air report. Before checking out the worst of the worst lists, breathe in the good and not-so-good news about our air.

The good news: The report finds that in America’s most polluted cities, air quality was at its cleanest since the organization’s annual report began 13 years ago. This year’s report details the trend that standards set under the Clean Air Act to cleanup major air pollution sources—including coal-fired power plants, diesel engines, and SUVs—are working to drastically cut ozone (smog) and particle pollution (soot) from the air we breathe. Despite this progress, unhealthy levels of air pollution still exist and in some parts of the country worsened.

“State of the Air shows that we’re making real and steady progress in cutting dangerous pollution from the air we breathe,” said Charles D. Connor, American Lung Association President and CEO. “We owe this to the ongoing protection of the Clean Air Act. But despite these improvements, America’s air quality standards are woefully outdated, and unhealthy levels of air pollution still exist across the nation, putting the health of millions of Americans at stake.”

The not-so-good news: The job of cleaning the air is not finished. More than 40 percent of people in the United States live in areas where air pollution continues to threaten their health. That means more than 127 million people are living in counties with dangerous levels of either ozone or particle pollution that can cause wheezing and coughing, asthma attacks, heart attacks, and premature death. Those at greatest risk from air pollution include infants, children, older adults, anyone with lung diseases like asthma, people with heart disease or diabetes, people with low incomes and anyone who works or exercises outdoors.

10 Most Ozone-Polluted US Cities:

1. Los Angeles-Long Beach-Riverside, Calif.

2. Visalia-Porterville, Calif.

3. Bakersfield-Delano, Calif.

4. Fresno-Madera, Calif.

5. Hanford-Corcoran, Calif.

6. Sacramento-Arden-Arcade-Yuba City, Calif.-Nev.

7. San Diego-Carlsbad-San Marcos, Calif.

8. Houston-Baytown-Huntsville, Texas

9. San Luis Obispo-Paso Robles, Calif.

10. Merced, Calif.

Ozone (O₃), an extremely reactive gas molecule, is the primary ingredient of smog air pollution. It attacks lung tissue by reacting chemically with it and is very harmful to breathe.

The ozone layer—found high in the upper atmosphere (the stratosphere)—shields us from much of the sun’s ultraviolet radiation. Ozone air pollution at ground level where we can breathe it (in the troposphere) is harmful.

State of the Air 2012 finds that nearly four out of 10 people in the U.S. live in counties that received an F for air quality because of unhealthy levels of ozone air pollution, which can cause health problems that day, and even days after. When inhaled, ozone irritates the lungs, like a bad sunburn, and can cause wheezing, coughing, asthma attacks and can shorten life.

10 Cities Most Polluted by Short-Term Particle Pollution (24-hour PM2.5)

1. Bakersfield-Delano, Calif.
2. Fresno-Madera, Calif.
3. Hanford-Corcoran, Calif.
4. Los Angeles-Long Beach-Riverside, Calif.
5. Modesto, Calif.
6. Pittsburgh-New Castle, Pa.
7. Salt Lake City-Ogden-Clearfield, UT
8. Logan, UT-ID
9. Fairbanks, Alaska
10. Merced, Calif.

“We still need to fulfill the promise of clean, healthy air for everyone, and that can only become a reality through the full implementation of the Clean Air Act. The American Lung Association strongly opposes any efforts to weaken, delay, or undermine the protective standards the law provides,” said Connor.

Get more detailed information for your state by clicking here. Click here to get local up-to-date air quality reports and forecasts.

More air pollution facts from the American Lung Association: