Glossary for Grades 6-12

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acid rain — air pollution produced when acid chemicals are incorporated into rain, snow, fog, or mist. The “acid” in acid rain comes from sulfur oxides and nitrogen oxides, products of burning coal and other fuels and from certain industrial processes. The sulfur oxides and nitrogen oxides are related to two strong acids:  sulfuric acid and nitric acid. When sulfur dioxide and nitrogen oxides are released from power plants and other sources, winds blow them far from their source. If the acid chemicals in the air are blown into areas where the weather is wet, the acids can fall to Earth in the rain, snow, fog, or mist. In areas where the weather is dry, the acid chemicals may become incorporated into dusts or smokes. Acid rain can damage the environment, human health, and property.

aerosols — liquid particles suspended in the air.

air pollution — the introduction of contaminants into the atmosphere.

Air Quality Index (AQI)— an index for reporting how clean or dirty the local air is and what health effects people should be concerned with. The AQI focuses on health effects that occur within a few hours or days after exposure to polluted air. The AQI is used for five major air pollutants regulated by the Clean Air Act. These are ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen oxides. For each of these pollutants, EPA has established national air quality standards to protect against harmful health effects.

air shed—  the geographic region that shares an air supply.

alternative fuels — any fuel source other than gasoline or diesel such as alcohols, electricity, natural gas, or propane. Many alternative fuels are cleaner burning than fossil fuels and may, in the future, be used in place of fossil fuels.

Ambient Air Monitoring Program — a program designed by the EPA that collects air samples to determine a locality’s compliance with air quality standards, to activate emergency control procedures that prevent or alleviate air pollution episodes, to observe pollution trends throughout a region, to provide a database for research. The EPA's ambient air quality monitoring program is carried out by State and local agencies and consists of three major categories of monitoring stations, State and Local Air Monitoring Stations (SLAMS), National Air Monitoring Stations (NAMS), and Special Purpose Monitoring Stations (SPMS), that measure the criteria pollutants. Additionally, a fourth category of a monitoring station, the Photochemical Assessment Monitoring Stations (PAMS), which measures ozone precursors (approximately 60 volatile hydrocarbons and carbonyl) has been required by the 1990 Amendments to the Clean Air Act.

anthropogenic— of relating to, or resulting from the influence of human beings on nature.

area source— Area source emissions are those air pollutants emitted from many individually small activities such as gasoline service stations, small paint shops, and consumer use of solvents.  Area sources also include open burning associated with agriculture, forest management, and land clearing activities.  

atmosphere — the whole mass of air surrounding the earth.

attainment area — a geographical area in which levels of a criteria air pollutant meet the health-based primary standard (national ambient air quality standard) for the pollutant. An area may have on acceptable level for one criteria pollutant, but may have unacceptable levels for others. Thus, an area could be both attainment and nonattainment at the same time. Attainment areas are defined using federal pollutant limits set by EPA.

biogenic emissions — all pollutants that are emitted from non-human sources, such as trees and vegetation, oil and gas seeps, and microbial activity.

biosphere — the portion of the earth that contains all living organisms.

carbon cycle — the movement of carbon through the atmosphere, biosphere, and hydrosphere.

carbon dioxide — a colorless, odorless gas formed during breathing, combustion, and decay of organic matter. A greenhouse gas, it traps heat and makes the Earth habitable.

carbon monoxide — a colorless, odorless, poisonous gas produced when carbon-containing substances such as coal, oil, gasoline, wood, or natural gas do not burn completely.

chlorofluorocarbons (CFCs) — these chemicals and some related chemicals have been used in great quantities in industry, for refrigeration and air conditioning, and in consumer products. CFCs and their relatives, when released into the air, rise into the stratosphere, where they take part in chemical reactions which result in reduction of the stratospheric ozone layer. The 1990 Clean Air Act includes provisions for reducing releases (emissions) and eliminating production and use of these ozone-destroying chemicals.

climate — a general description of the average temperature and rainfall conditions of a region over a period of time.

combustion — burning or the production of heat and light energy through a chemical process.

criteria pollutants — as defined by the EPA, six air pollutants that are the most widespread and harmful. They are: particulate matter, sulfur dioxide, carbon monoxide, nitrogen oxides, and lead.

emission — a discharge or release of pollutants into the air, such as from a smokestack or automobile engine.

energy — the ability to do work. Forms of energy include sunlight and the chemical bonds present in fuels.

energy-efficiency — the usable power from fuels or machines in relation to the amount of waste heat given off. The more waste heat, the less efficient the machine or fuel is.

environment — the combination of all external conditions and influences relating to the life, development, and survival of all living things.

fossil fuels — coal, oil, and natural gas formed from the remains of ancient plant and animal life

fuel cells — a device that converts hydrogen and oxygen into water, producing heat and energy which can be used to power motors, lights, or other electrical devices. Depending on the type, they may in the future be used to power everything from automobiles to homes to large power plants.

global warming — the term given to the possibility that the Earth’s average temperature is increasing due to excess carbon dioxide and other greenhouse gases in the atmosphere.

greenhouse effect — trapping of heat in the atmosphere by greenhouse gases which makes the Earth warm and habitable.

greenhouse gases — compounds such as carbon dioxide, water vapor, methane, sulfur hexafluoride (SF₆), nitrous oxides (N₂O), ozone (O₃), and several classed of halogenated hydrocarbons that trap heat in the atmosphere.

hazardous air pollutants (HAPs) — chemicals that cause serious health and environmental effects. Health effects include cancer, birth defects, nervous system problems, and death due to massive accidental releases such as occurred at the pesticide plant in Bhopal, India. Hazardous air pollutants are released by sources such as chemical plants, dry cleaners, printing plants, and motor vehicles (cars, trucks, buses, etc.).

hydrocarbons — compounds that consist of carbon and hydrogen. They are found in fossil fuels, glues, paints, and solvents.

hydrologic cycle — the movement of water from evaporation into the atmosphere and back to the Earth’s surface as precipitation.

infrared light — radiation of a longer wavelength than red light. It is invisible, but can be felt as heat.

lead (Pb) — a heavy metal that is soluble in water and can be easily absorbed in the body, where it accumulates. One of the six criteria pollutants, it was commonly used in gasoline until it was banned in the 1980s.  

mobile source — pollution sources that move around, such as cars, trucks, and buses.

monitoring— measurement of air pollution. EPA, state and local agencies measure the types and amounts of pollutants in community air. The 1990 Clean Air Act requires certain large polluters to perform enhanced monitoring to provide an accurate picture of their pollutant releases. Enhanced monitoring programs may include keeping records on materials used by the source, periodic inspections, and installation of continuous emission monitoring systems (CEMS). Continuous emission monitoring systems will measure, on a continuous basis, how much pollution is being released into the air. The 1990 Clean Air Act requires states to monitor community air in polluted areas to check on whether the areas are being cleaned up according to schedules set out in the law.

National Ambient Air Quality Standards (NAAQS)— standards set by the EPA for pollutants considered harmful to public health and environment. The Clean Air Act established two types of air quality standards: primary and secondary standards. Primary standards set limits to protect public health, including the health of “sensitive” populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect the public welfare, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings.

nitrogen oxides — gases that form when nitrogen and oxygen combine, such when fossil fuels are burned at high temperatures or when lightning strikes.

Non-attainment area — a geographic area in which the level of a criteria air pollutant is higher than the level allowed by the federal standards. A single geographic area may have acceptable levels of one criteria air pollutant but unacceptable levels of one or more other criteria air pollutants; thus an area can be both attainment and non-attainment at the same time. It has been estimated that 60% of Americans live in non-attainment areas.

ozone (O₃) — a colorless gas made of three oxygen atoms. Stratospheric ozone is formed when ultraviolet (UV) radiation breaks apart O₂ and is important in blocking most harmful UV radiation from reaching the surface of the Earth. Ground-level ozone is a pollutant, a major component of smog. It is formed when nitrogen oxides react with sunlight and volatile organic compounds.  

particulate matter — a criteria air pollutant. Particulate matter includes dust, soot, and other tiny bits of solid materials that are released into and move around in the air. Particulates are produced by many sources, including burning of diesel fuels by trucks and buses, incineration of garbage, mixing and application of fertilizers and pesticides, road construction, industrial processes such as steel making, mining operations, agricultural burning (field and slash burning), and operation of fireplaces and woodstoves. Particulate pollution can cause eye, nose, and throat irritation and other health problems.

parts per million (ppm) — an expression of concentration. It is the number of units of one substance in a million units of all particles of the mixture. For example, 10 units of SO₂ in one million units of air is 10 ppm.

pH — a scale used to designate whether a substance is acidic or basic (alkaline), expressed as the logarithmic concentration of hydrogen atoms (H+). pH 7 is neutral. Substances below pH 7 are more acidic, while those above pH 7 are more basic.

point source emission — pollutants emitted from a definite source, such as a factory or an automobile.

pollution — unwanted chemicals or other materials found in the air. Pollutants can harm health, the environment, and property. Many air pollutants occur as gases or vapors, but some are very tiny particles: dust, smoke, or soot.

precipitation — any form of moisture that condenses in the air and falls to the ground as rain, snow, sleet, etc.

primary pollutants — air pollutants that are emitted directly into the atmosphere as a by-product of fuel combustion.

primary standard —  standards set by EPA to establish limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly.

Reid Vapor Pressure (RVP)—  a common measure of gasoline volatility. Volatility is the property of a liquid fuel that defines its evaporation characteristics. EPA regulates the vapor pressure of all gasoline during the summer months (June 1 to September 15) in order to reduce evaporative emissions that contribute to smog.

secondary pollutants —air  pollutants that are formed in the atmosphere from the chemical reactions of primary pollutants or other pollutants.

secondary standard —standards set limits to protect public welfare, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings.

smog — a mixture of pollutants, principally ground-level ozone, produced by chemical reactions in the air involving smog-forming chemicals. A major portion of smog-formers come from burning of petroleum-based fuels such as gasoline. Other smog-formers, volatile organic compounds, are found in products such as paints and solvents. Smog can harm health, damage the environment, and cause poor visibility. Major smog occurrences are often linked to heavy motor vehicle traffic, sunshine, high temperatures, and calm winds or temperature inversion. Smog is often worse away from the source of the smog-forming chemicals, since the chemical reactions that result in smog occur in the sky while the reacting chemicals are being blown away from their sources by winds.

source — any place or object from which pollutants are released. A source can be a power plant, factory, dry cleaning business, gas station, or farm. Cars, trucks, and other motor vehicles are sources, and consumer products and machines used in industry can be sources too. (See also stationary sources and mobile sources).

State Implementation Procedures (SIP) — a detailed description of the programs a state will use to carry out its responsibilities under the Clean Air Act. State implementation plans are collections of the regulations used by a state to reduce air pollution. The Clean Air Act requires that EPA approve each state implementation plan. Members of the public are given opportunities to participate in review and approval of SIPs.

stationary source — pollution sources that stay in one place, such as factories or gas stations.

stratosphere — the layer of air that extends from about 7 to 31 miles above the earth's surface. As the stratosphere rises, the temperature increases gradually to about 32^oF. Clouds rarely form in this layer.

sulfur dioxide — one of the six criteria pollutants, formed from burning sulfur-containing compounds, such as coal and metal refining.

temperature inversion — one of the weather conditions that are often associated with serious smog episodes in some portions of the country. In a temperature inversion, air doesn’t rise because it is trapped near the ground by a layer of warmer air above it. Pollutants, especially smog and smog-forming chemicals, including volatile organic compounds, are trapped close to the ground. As people continue driving, and sources other than motor vehicles continue to release smog-forming pollutants into the air, the smog level keeps getting worse.

toxic — something that can be poisonous or deadly if it is eaten, touched, or inhaled in large enough amounts.

troposphere — the lowest and densest part of the earth’s atmosphere, extending from the Earth’s surface to about 7 miles in altitude. It is where life resides and where most weather changes occur.

ultraviolet light — radiation with a wavelength shorter than violet light and with more energy. It is invisible to humans, but the increased energy can result in damaged tissues.

visible light — the part of the spectrum that can be seen by humans.

volatile organic compounds (VOCs) — major air pollutants present in the atmosphere as vapor such as hydrocarbon fragments and evaporated organic compounds such as paint, gasoline, and cleaning solutions. They are a major component in the formation of smog.

water vapor — small particles of water that are suspended in the atmosphere.

weather — the state of the atmosphere with respect to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness.