Outdoor air quality has improved since the 1990s, but many challenges remain in protecting Americans from air quality problems. Ground-level ozone, the main part of smog, and particle pollution are just two of the many threats to air quality and public health in the United States.
Learn about physical activity and air quality. Check out our new infographic!
- Page last reviewed: April 2, 2014
- Page last updated: April 6, 2017
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