Release into the atmosphere of various gases, finely divided solids, or finely dispersed liquid aerosols at rates that exceed the natural capacity of the environment to dissipate and dilute or absorb them. (source #7)

The U.S. AQI is EPA’s index for reporting air quality. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality. (source #16)

An area that does not meet ambient air quality standards. (source #6)

A part of Earth’s atmosphere that absorbs lots of the sun’s ultraviolet radiation. It is made of a gas called ozone, which is a molecule of three oxygen atoms. (source #1)

An almost colorless, gaseous form of oxygen with an odor similar to weak chlorine. In the present-day stratosphere, this natural balance has been altered, particularly by the introduction of man-made chlorofluorocarbons. If the ozone decreases, the ultraviolet radiation at the Earth's surface will increase. (source #2)

Organic compounds (e.g. ethylene, propylene, benzene, styrene, acetone) which evaporate readily and contribute to air pollution directly or through chemical or photochemical reactions to produce secondary air pollutants. (source #8)