U.S. Environmental Protection AgencyOffice of Air Quality, Planning and Standards
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Clean Air and Dirty Air
On a clear breezy day, the air smells fresh and clean. Clean air is air that has no harmful levels of pollutants (dirt and chemicals) in it. Clean air is good for people to breathe.

On a hot day with no wind, the air can feel heavy and have a bad smell. Once in a while, the air can even make your chest feel tight, or make you cough. When too much dirt and chemicals get into the air, the air is dirty or polluted. Dirty air is not good for people to breathe.

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