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Atmosphere

A thin layer of gases surrounding the Earth that absorbs radiation, moderates climate, and transports water, nutrients, and contaminants.

Primary Pollutants

Pollutants that are directly harmful and can react to form harmful substances, such as soot and carbon dioxide.

Secondary Pollutants

Pollutants that form when primary pollutants react with atmospheric components, e.g., tropospheric ozone and sulfuric acid.

Point Sources

Specific spots where large quantities of pollutants are discharged, like power plants and factories.

Non-point Sources

Diffuse sources of pollution consisting of many small contributors, such as automobiles.

Criteria Air Contaminants

Pollutants that pose significant threats to human health, including sulfur dioxide, nitrogen dioxide, ammonia, particulate matter, lead, carbon monoxide, and volatile organic compounds.

Sulfur Dioxide (SO2)

A colorless gas with a strong odor, emitted from coal-burning power plants and can form acid precipitation.

Nitrogen Dioxide (NO2)

A very reactive, foul-smelling reddish-brown gas that contributes to smog and acid precipitation from vehicle engines and industrial combustion.

Particulate Matter

Solid or liquid particles suspended in the atmosphere that can damage respiratory tissue when inhaled.

Lead

A particulate pollutant added to gasoline and produced by industrial metal smelting, harmful to the nervous system.

Carbon Monoxide (CO)

A colorless, odorless gas produced primarily by incomplete combustion, posing health risks even in small concentrations.

Tropospheric Ozone (O3)

Ground-level ozone, a secondary pollutant and major component of smog, formed from reactions involving sunlight, heat, nitrogen oxides, and volatile organic compounds.

Volatile Organic Compounds (VOCs)

A diverse group of air pollutants commonly found from vehicle exhaust and various industrial processes.

Smog

Unhealthy mixtures of air pollutants over urban areas, including industrial (gray air) smog and photochemical smog.

Dust Storms

Natural sources of outdoor air pollution caused by unsustainable farming and grazing, resulting in the transport of large amounts of dust.

Industrial Smog

Smog produced from burning coal or oil, characterized by a gray appearance, and reduced by regulations in developed countries.

Photochemical Smog

Summer smog from light-driven reactions of primary pollutants and normal atmospheric compounds, such as those from vehicles.

Asian Brown Cloud

A two-mile thick layer of pollution over Asia that reduces sunlight and poses health risks.

Air Quality Monitoring

A method of tracking and regulating air pollutant emissions to mitigate outdoor air pollution.