Air Quality (Outdoor [Ambient] and Indoor)

Ambient air pollution (outdoor air pollution) consists of a complex mixture of gases, particulate matter, and liquids. The air pollutants include the six criteria pollutants (carbon monoxide, ozone, lead, nitrogen oxides, particulate matter, and sulfur dioxide), toxic (also known as hazardous) air pollutants, and greenhouse gas emissions, which affect human health, the environment including the various ecosystems, and the stratospheric ozone layer. The pollutants come from a variety of sources, general and specific, and are affected by weather and local topographical conditions. Indoor air quality is in a separate section in this chapter. (See endnotes 1, 17.)