Four in 10 Americans live in counties with unhealthy air pollution levels

• Fairbanks, Alaska, Los Angeles and California cities get F rating
• American Lung Association tracks particle and ozone pollution

New research from the American Lung Association finds that more than four in 10 people - a whopping 135 million in the US - live in counties with unhealthy levels of particle or ozone pollution.

In their 22nd annual State of the Air" report, released on Wednesday, the group examined federal data on the two most widespread types of air pollution to create a comprehensive overview of toxic air across the country. The annual air quality report card" identifies the parts of the country with the most polluted air, and gives them a letter grade (from A to F). This year, it also found that people of color were three times as likely to live in the nation's most polluted places.