New report card: How bad is the air where you live?

The American Lung Association's (ALA) annual State of Air report shows that air quality worsened from 2010 to 2012, when 47% of U.S. residents lived in areas where pollution levels could make it dangerous to breathe.

For the 15th annual report, ALA analyzed levels of ozone (commonly referred to as "smog") and particle pollution (often referred to as "soot" or "ash") using data that the Environmental Protection Agency (EPA) obtained at various official monitoring sites from 2010 to 2012.

They found that about 147.6 million of the nation's residents, or 47%, lived in counties where the level of ozone, short-term particles, or year-round particles was unhealthful. Moreover, nearly 27.8 million residents—or 9% of the population—lived in a county where all three pollution levels were unhealthful.

Related: Long-term pollution exposure may cause more hospitalizations

As in previous State of the Air reports, most of the cities with the highest air pollution were located in California.

According to the report, the most ozone-polluted cities in the United States are:

1. Los Angeles-Long Beach, Calif.;
2. Visalia-Porterville-Hanford, Calif.;
3. Bakersfield, Calif.;
4. Fresno-Madera, Calif.; and
5. Sacramento-Roseville, Calif.

Meanwhile, the cities most populated by short-term particle pollution are:

1. Fresno-Madera, Calif.
2. Visalia-Porterville-Hanford, Calif.;
3. Bakersfield, Calif.;
4. Los Angeles-Long Beach, Calif.; and
5. Modesto-Merced, Calif.

The cities most populated by year-round particle pollution are:

1. Fresno-Madera, Calif.
2. Visalia-Porterville-Hanford, Calif.;
3. Bakersfield, Calif.;
4. Los Angeles-Long Beach, Calif.; and
5. Modesto-Merced, Calif.

How does your city fare? ALA's interactive map of U.S. pollution

Previous ALA reports had found modest improvements in air quality nationwide, but this report found that the quality was worsening. Specifically, it found that, although overall particle pollution continues to decrease, levels of ozone (or smog) were much worse than in the 2013 report.

Only four cities made this year's list of the "cleanest cities" in America, which includes cities that had no days with unhealthy ozone or particle pollution levels and were among the cities with lowest long-term particle pollution levels. The four qualifying cities were:

• Bangor, Maine;
• Bismarck, N.D.;
• Cape Carol-Fort Myers, Fla.; and
• Salinas, Calif.

Sources: ALA report, 4/24; ALA release, 4/30; Grossman, TIME, 4/30

Check out the Daily Briefing's archive of stories on city rankings, including:

• The cities where residents are most likely to have heart attacks
• Gallup IDs America's 10 most—and least—obese cities
• RWJF names the most—and least—healthy counties in your state