The Clean Air Act, last amended in 1990, requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for pollutants considered harmful to public health and the environment. The Clean Air Act established two types of national air quality standards:

• Primary standards set limits to protect public health, including the health of “sensitive" populations such as asthmatics, children, and the elderly.
• Secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings.

NATIONAL AMBIENT AIR QUALITY STANDARDS

The EPA has set National Ambient Air Quality Standards for six principal pollutants, which are called "criteria" pollutants and are listed below. Units of measure for the standards are parts per million (ppm) by volume and micrograms per cubic meter of air (µg/m3).  Click here for a list of the current standards.