Outdoor air quality in the U.S. has improved since the 1990s, but many challenges remain in protecting public health from air quality problems. Ground-level ozone, the main component of smog, and particle pollution that can penetrate deep into the lungs are just two of the many threats to air quality and public health in the U.S.
- Page last reviewed: April 2, 2014
- Page last updated: April 2, 2014
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