Glossary
Ammonia (NH3)
A colorless gas with a pungent odor, released from agricultural activities (e.g., livestock waste) and decomposition of organic matter, contributing to particulate matter formation.
Example:
Large-scale livestock farms can release significant amounts of ammonia from animal waste, which then reacts in the air to form fine particulate matter.
Ammonium (NH4)
An ion formed when ammonia reacts with atmospheric acids (like sulfuric or nitric acid), contributing significantly to the formation of secondary particulate matter.
Example:
The reaction of atmospheric ammonium with other pollutants forms fine solid particles that contribute to haze and respiratory problems.
COx (Carbon oxides)
Compounds composed of carbon and oxygen, including carbon monoxide (CO) and carbon dioxide (CO2), often produced by combustion processes.
Example:
Incomplete combustion in a poorly maintained furnace can produce dangerous levels of COx, specifically carbon monoxide.
Carbon Monoxide (CO)
A colorless, odorless, and highly toxic gas produced by the incomplete combustion of carbon-containing fuels.
Example:
Running a car in an enclosed garage can quickly lead to dangerous levels of carbon monoxide, which can be fatal.
Clean Air Act
A foundational U.S. federal law enacted to control air pollution by regulating emissions from both stationary and mobile sources.
Example:
The Clean Air Act significantly reduced lead levels in the atmosphere by phasing out leaded gasoline.
Coal Combustion
The process of burning coal, primarily for electricity generation, which is a significant source of pollutants like CO2, SO2, mercury, and particulates.
Example:
A power plant relying on coal combustion for energy production must manage emissions of sulfur dioxide to prevent acid rain.
Fossil Fuel Combustion
The burning of ancient organic matter (coal, oil, natural gas) to release energy, serving as a major anthropogenic source of air pollutants.
Example:
Driving a car involves fossil fuel combustion, releasing a mix of carbon oxides, nitrogen oxides, and hydrocarbons.
Hydrocarbons
Organic compounds made exclusively of hydrogen and carbon atoms, many of which are volatile and contribute to air pollution, especially ozone formation.
Example:
The evaporation of gasoline from a fuel tank releases hydrocarbons into the atmosphere, contributing to smog.
NOx (Nitrogen oxides)
A group of highly reactive gases containing nitrogen and oxygen, such as NO and NO2, primarily formed during the combustion of fossil fuels at high temperatures.
Example:
Power plants and vehicles release NOx, which contributes to the formation of smog and acid rain.
Nitric Acid (HNO3)
A strong acid formed in the atmosphere from nitrogen dioxide and water, contributing to acid rain.
Example:
The formation of nitric acid in the atmosphere contributes to acid rain, which can harm aquatic ecosystems.
Nitric Oxide (NO)
A gas formed during high-temperature combustion processes, which can react further in the atmosphere to form nitrogen dioxide and contribute to smog.
Example:
The high temperatures inside a car engine during operation produce nitric oxide, a precursor to urban haze.
Nitrogen Dioxide (NO2)
A reddish-brown gas formed from nitric oxide, contributing to smog, acid rain, and respiratory issues.
Example:
The brown haze often visible over cities is partly due to high concentrations of nitrogen dioxide from vehicle exhaust.
Ozone (O3)
In the troposphere (ground-level), it is a harmful secondary pollutant formed from NOx and VOCs in sunlight, causing respiratory issues and damaging plants.
Example:
On hot, sunny days, urban areas often experience high levels of ground-level ozone, leading to 'ozone action day' warnings.
Particulates (Particulate Matter - PM)
Tiny solid or liquid particles suspended in the air, classified by size (e.g., PM10, PM2.5), with smaller particles posing greater health risks due to deeper lung penetration.
Example:
Smoke from a wildfire contains a high concentration of fine particulates, which can cause respiratory problems and reduce visibility.
Primary Pollutants
Pollutants emitted directly into the atmosphere from an identifiable source.
Example:
A car's exhaust pipe directly releases carbon monoxide as a primary pollutant into the air.
SOx (Sulfur oxides)
Compounds of sulfur and oxygen, like SO2 and SO3, predominantly released from the burning of sulfur-containing fossil fuels, especially coal.
Example:
Industrial facilities burning high-sulfur coal emit SOx, a major precursor to acid rain.
Secondary Pollutants
Pollutants formed in the atmosphere when primary pollutants react with other substances, often in the presence of sunlight or water.
Example:
Ozone in urban smog is a secondary pollutant, formed from reactions involving nitrogen oxides and VOCs.
Sulfur Dioxide (SO2)
A pungent gas released primarily from the burning of sulfur-containing fossil fuels, contributing to acid rain and particulate matter.
Example:
Volcanic eruptions can release large amounts of sulfur dioxide, impacting regional air quality and contributing to atmospheric haze.
Sulfur Trioxide (SO3)
A gas formed from sulfur dioxide, which readily reacts with water vapor in the atmosphere to form sulfuric acid.
Example:
Once sulfur trioxide is formed in the atmosphere, it quickly combines with atmospheric moisture to create acid rain.
Sulfuric Acid (H2SO4)
A strong acid formed in the atmosphere from sulfur trioxide and water, a major component of acid rain.
Example:
Acid deposition from sulfuric acid can damage forests, acidify lakes, and corrode buildings.
Volatile Organic Compounds (VOCs)
Organic chemicals that evaporate easily at room temperature, released from various sources like paints, solvents, and industrial processes, playing a key role in ozone formation.
Example:
The strong smell of fresh paint is due to the release of volatile organic compounds into the air.