Glossary

NOx, VOCs, particle pollution and AQI – this glossary can help you make sense of it all.

Is there an air quality term you would like to understand?

Air Quality

The condition of air, as it relates to pollution in a particular area as measured by the Air Quality Index.

Air Quality Index (AQI)

The AQI is a scale of 0 to 500, developed by the U.S. Environmental Protection Agency and divided into several color-coded categories. The AQI scale serves as a simple tool for reporting the air quality of a particular region. A value of 101 or greater means that concentrations that violate national health-based standards for the pollutant in question (ground-level ozone or particle pollution) are either present or forecasted to be present.

Compressed Natural Gas (CNG)

Fuel source for certain buses/bus lines. "Cleaner" than gas-powered. MARTA runs CNG buses on many routes.

Nonattainment

A federal designation conferred by the U.S. EPA that signifies a geographic area in which the level of a certain air pollutant is higher than the level allowed by federal standards. A single area may have acceptable levels of one air pollutant but unacceptable levels of one or more other air pollutants.

NOx (nitrogen oxides)

Half the recipe of chemicals, along with VOCs, which when cooked by heat and sunlight makes up ground-level ozone; primarily created from combustion engines and point sources like power plants and industry.

Particle Pollution

A mixture of solids and liquid droplets that vary in size and typically includes aerosols and fine solids such as soot and dust; sources include all kinds of combustion, including vehicle exhaust, power plants, wood burning, construction activity and agriculture.

Smog

A combination of the words "smoke" and "fog"; in Georgia we use the term to describe the pollutants most prevalent here: ground-level ozone and particle pollution.

Smog Alert

A Smog Alert is a forecast made by scientists on days when the concentrations of either ozone or particle pollution, or both, are expected to reach unhealthy levels. The Clean Air Campaign distributes Smog Alert notifications on behalf of the Georgia Environmental Protection Division.

VOCs (volatile organic compounds)

The other half of the chemicals needed to create ground-level ozone; produced by things such as vapors from gasoline, paint and cleaning solvents, and natural sources like vegetation. See NOx also.