Learn how air pollution can harm your health and the environment, and what EPA is doing to protect the air we breathe.

The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) for six common air pollutants (also known as “criteria air pollutants”).

National Ambient Air Quality Standards (NAAQS) for ground-level ozone, or ozone pollution, specify a maximum allowed measurement for ozone (O3) to be present in outdoor air.

The Clean Air Act requires EPA to designate areas in the United States after the agency sets a new National Ambient Air Quality Standard (NAAQS) or revises an existing standard