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  • Air pollution consists of chemicals or particles in the air that can harm the health of humans, animals, and plants. It also damages buildings. Pollutants in the air take many forms. They can be gases, solid particles, or liquid droplets.

    Sources of Air Pollution

    Pollution enters the Earth's atmosphere in many different ways. Most air pollution is created by people, taking the form of emissions from factories, cars, planes, or aerosol cans. Second-hand cigarette smoke is also considered air pollution. These man-made sources of pollution are called anthropogenic sources.

    Some types of air pollution, such as smoke from wildfires or ash from volcanoes, occur naturally. These are called natural sources.

    Air pollution is most common in large cities where emissions from many different sources are concentrated. Sometimes, mountains or tall buildings prevent air pollution from spreading out. This air pollution often appears as a cloud making the air murky. It is called smog. The word "smog" comes from combining the words "smoke" and "fog."

    Large cities in poor and developing nations tend to have more air pollution than cities in developed nations. According to the World Health Organization (WHO), some of the worlds most polluted cities are Karachi, Pakistan; New Delhi, India; Beijing, China; Lima, Peru; and Cairo, Egypt. However, many developed nations also have air pollution problems. Los Angeles, California, is nicknamed Smog City.

    Indoor Air Pollution

    Air pollution is usually thought of as smoke from large factories or exhaust from vehicles. But there are many types of indoor air pollution as well.

    Heating a house by burning substances such as kerosene, wood, and coal can contaminate the air inside the house. Ash and smoke make breathing difficult, and they can stick to walls, food, and clothing.

    Naturally-occurring radon gas, a cancer-causing material, can also build up in homes. Radon is released through the surface of the Earth. Inexpensive systems installed by professionals can reduce radon levels.

    Some construction materials, including insulation, are also dangerous to people's health. In addition, ventilation, or air movement, in homes and rooms can lead to the spread of toxic mold. A single colony of mold may exist in a damp, cool place in a house, such as between walls. The mold's spores enter the air and spread throughout the house. People can become sick from breathing in the spores.

    Effects On Humans

    People experience a wide range of health effects from being exposed to air pollution. Effects can be broken down into short-term effects and long-term effects.

    Short-term effects, which are temporary, include illnesses such as pneumonia or bronchitis. They also include discomfort such as irritation to the nose, throat, eyes, or skin. Air pollution can also cause headaches, dizziness, and nausea. Bad smells made by factories, garbage, or sewer systems are considered air pollution, too. These odors are less serious but still unpleasant.

    Long-term effects of air pollution can last for years or for an entire lifetime. They can even lead to a person's death. Long-term health effects from air pollution include heart disease, lung cancer, and respiratory diseases such as emphysema. Air pollution can also cause long-term damage to people's nerves, brain, kidneys, liver, and other organs. Some scientists suspect air pollutants cause birth defects. Nearly 2.5 million people die worldwide each year from the effects of outdoor or indoor air pollution.

    People react differently to different types of air pollution. Young children and older adults, whose immune systems tend to be weaker, are often more sensitive to pollution. Conditions such as asthma, heart disease, and lung disease can be made worse by exposure to air pollution. The length of exposure and amount and type of pollutants are also factors.

    Effects On The Environment

    Like people, animals, and plants, entire ecosystems can suffer effects from air pollution. Haze, like smog, is a visible type of air pollution that obscures shapes and colors. Hazy air pollution can even muffle sounds.

    Air pollution particles eventually fall back to Earth. Air pollution can directly contaminate the surface of bodies of water and soil. This can kill crops or reduce their yield. It can kill young trees and other plants.

    Sulfur dioxide and nitrogen oxide particles in the air, can create acid rain when they mix with water and oxygen in the atmosphere. These air pollutants come mostly from coal-fired power plants and motor vehicles. When acid rain falls to Earth, it damages plants by changing soil composition; degrades water quality in rivers, lakes and streams; damages crops; and can cause buildings and monuments to decay.

    Like humans, animals can suffer health effects from exposure to air pollution. Birth defects, diseases, and lower reproductive rates have all been attributed to air pollution.

    Global Warming

    Global warming is an environmental phenomenon caused by natural and anthropogenic air pollution. It refers to rising air and ocean temperatures around the world. This temperature rise is at least partially caused by an increase in the amount of greenhouse gases in the atmosphere. Greenhouse gases trap heat energy in the Earths atmosphere. (Usually, more of Earths heat escapes into space.)

    Carbon dioxide is a greenhouse gas that has had the biggest effect on global warming. Carbon dioxide is emitted into the atmosphere by burning fossil fuels (coal, gasoline, and natural gas). Humans have come to rely on fossil fuels to power cars and planes, heat homes, and run factories. Doing these things pollutes the air with carbon dioxide.

    Other greenhouse gases emitted by natural and artificial sources also include methane, nitrous oxide, and fluorinated gases. Methane is a major emission from coal plants and agricultural processes. Nitrous oxide is a common emission from industrial factories, agriculture, and the burning of fossil fuels in cars. Fluorinated gases, such as hydrofluorocarbons, are emitted by industry. Fluorinated gases are often used instead of gases such as chlorofluorocarbons (CFCs). CFCs have been outlawed in many places because they deplete the ozone layer.

    Worldwide, many countries have taken steps to reduce or limit greenhouse gas emissions to combat global warming. The Kyoto Protocol, first adopted in Kyoto, Japan, in 1997, is an agreement between 183 countries that they will work to reduce their carbon dioxide emissions. The United States has not signed that treaty.


    In addition to the international Kyoto Protocol, most developed nations have adopted laws to regulate emissions and reduce air pollution. In the United States, debate is under way about a system called cap and trade to limit emissions. This system would cap, or place a limit, on the amount of pollution a company is allowed. Companies that exceeded their cap would have to pay. Companies that polluted less than their cap could trade or sell their remaining pollution allowance to other companies. Cap and trade would essentially pay companies to limit pollution.

    In 2006 the World Health Organization issued new Air Quality Guidelines. The WHOs guidelines are tougher than most individual countries existing guidelines. The WHO guidelines aim to reduce air pollution-related deaths by 15 percent a year.


    Anybody can take steps to reduce air pollution. Millions of people every day make simple changes in their lives to do this. Taking public transportation instead of driving a car, or riding a bike instead of traveling in carbon dioxide-emitting vehicles are a couple of ways to reduce air pollution. Avoiding aerosol cans, recycling yard trimmings instead of burning them, and not smoking cigarettes are others.

    air pollution
    China is one of the most rapidly developing nations in the world. It also has one of the highest rates of air pollution.

    Greenhouse Gases
    There are five major greenhouse gases in Earth's atmosphere.

    • water vapor
    • carbon dioxide
    • methane
    • nitrous oxide
    • ozone

    London Smog
    What has come to be known as the London Smog of 1952, or the Great Smog of 1952, was a four-day incident that sickened 100,000 people and caused as many as 12,000 deaths. Very cold weather in December 1952 led residents of London, England, to burn more coal to keep warm. Smoke and other pollutants became trapped by a thick fog that settled over the city. The polluted fog became so thick that people could only see a few meters in front of them.

    The United States conducted tests of nuclear weapons at the Nevada Test Site in southern Nevada in the 1950s. These tests sent invisible radioactive particles into the atmosphere. These air pollution particles traveled with wind currents, eventually falling to Earth, sometimes hundreds of miles away in states including Idaho, Utah, Arizona, and Washington. These areas were considered to be "downwind" from the Nevada Test Site.

    Decades later, people living in those downwind areascalled "downwinders"began developing cancer at above-normal rates. In 1990, the U.S. government passed the Radiation Exposure Compensation Act. This law entitles some downwinders to payments of $50,000.

  • Term Part of Speech Definition Encyclopedic Entry
    acid rain Noun

    precipitation with high levels of nitric and sulfuric acids. Acid rain can be manmade or occur naturally.

    aerosol can Noun

    container of liquid material under high pressure. When released through a small opening, the liquid becomes a spray or foam.

    air pollution Noun

    harmful chemicals in the atmosphere.

    Encyclopedic Entry: air pollution
    anthropogenic source Noun

    caused by people.

    asthma Noun

    disease that makes it difficult to breathe.

    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    attribute Verb

    to think to be caused by.

    birth defect Noun

    physical disorder present at birth and not developed later.

    bronchitis Noun

    irritation of the main air passages to the lungs.

    cancer Noun

    growth of abnormal cells in the body.

    cap and trade Noun

    system for reducing air pollution by placing limits on how much companies can pollute without having to pay for it.

    carbon dioxide Noun

    greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.

    chemical Noun

    molecular properties of a substance.

    chlorofluorocarbon (CFC) Noun

    chemical compound mostly used in refrigerants and flame-retardants. Some CFCs have destructive effects on the ozone layer.

    cigarette Noun

    thin roll of tobacco for smoking.

    coal Noun

    dark, solid fossil fuel mined from the earth.

    coal-fired power plant Noun

    power plant that makes electricity by burning coal.

    colony Noun

    network of mold cells considered as one organism.

    combat Verb

    to fight.

    concentrated Adjective

    items gathered closely together in one place.

    consider Verb

    to think about.

    contaminate Verb

    to poison or make hazardous.

    crop Noun

    agricultural produce.

    Encyclopedic Entry: crop
    current Noun

    steady, predictable flow of fluid within a larger body of that fluid.

    Encyclopedic Entry: current
    decade Noun

    10 years.

    decay Verb

    to rot or decompose.

    degrade Verb

    to lower the quality of something.

    developed country Noun

    a nation that has high levels of economic activity, health care, and education.

    developing world Noun

    nations with low per-capita income, little infrastructure, and a small middle class.

    downwind Adjective

    in the direction of the wind.

    downwinder Noun

    person who was accidentally exposed to radioactive particles from the Nevada Test Site.

    ecosystem Noun

    community and interactions of living and nonliving things in an area.

    Encyclopedic Entry: ecosystem
    emission Noun

    discharge or release.

    emit Verb

    to give off or send out.

    emphysema Noun

    disease of the lungs.

    exceed Verb

    to go beyond the limit.

    exhaust Noun

    gases and particles expelled from an engine.

    factory Noun

    one or more buildings used for the manufacture of a product.

    fluorinate Verb

    to add or combine with the element fluorine (F).

    fog Noun

    clouds at ground level.

    Encyclopedic Entry: fog
    fossil fuel Noun

    coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.

    garbage Noun

    trash or waste material.

    gas Noun

    state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

    gasoline Noun

    liquid mixture made from oil and used to run many motor vehicles.

    global warming Noun

    increase in the average temperature of the Earth's air and oceans.

    Encyclopedic Entry: global warming
    greenhouse gas Noun

    gas in the atmosphere, such as carbon dioxide, methane, water vapor, and ozone, that absorbs solar heat reflected by the surface of the Earth, warming the atmosphere.

    haze Noun

    group of solid and liquid particles in the air that makes it difficult to see.

    heart disease Noun

    illness affecting the heart and circulatory system.

    hydrofluorocarbon Noun

    greenhouse gas often used as an industrial cooling material.

    illness Noun

    disease or sickness.

    immune system Noun

    network of chemicals and organs that protects the body from disease.

    incident Noun

    event or happening.

    indoor air pollution Noun

    harmful chemicals coming from or accumulating inside a building.

    insulation Noun

    material used to keep an object warm.

    irritation Noun

    condition of unpleasant sensitivity.

    kerosene Noun

    flammable liquid used as fuel.

    kidney Noun

    organ that removes the waste products from blood and helps regulate general health.

    Kyoto Protocol Noun

    (1997) international agreement to reduce greenhouse gas emissions.

    liquid Noun

    state of matter with no fixed shape and molecules that remain loosely bound with each other.

    liver Noun

    organ that removes toxins from the blood, converts sugar to glycogen, and produces bile needed for digestion.

    London Fog of 1952 Noun

    (December 5December 9, 1952) severe smog that killed between 4,000 and 12,000 people in London, England. Also called the Great Smog.

    long-term effects Noun

    results of an incident or behavior that last for years or a lifetime.

    lung Noun

    organ in an animal that is necessary for breathing.

    man-made Noun

    produced by people.

    methane Noun

    chemical compound that is the basic ingredient of natural gas.

    mold Noun

    type of fungi that forms on the surface of materials.

    motor vehicle Noun

    method of transportation that is run by an electric or gas engine.

    mountain Noun

    landmass that forms as tectonic plates interact with each other.

    natural gas Noun

    type of fossil fuel made up mostly of the gas methane.

    Encyclopedic Entry: natural gas
    natural source Noun

    caused by nature or the environment.

    nausea Noun

    impulse to vomit.

    nerve Noun

    part of the nervous system that registers sensation and touch.

    Nevada Test Site Noun

    testing site for nuclear weapons and other military products in the southern Nevada desert. Nuclear weapons testing was discontinued there in 1992.

    nitrogen oxide Noun

    one of many chemical compounds made of different combinations of nitrogen and oxygen.

    nitrous oxide Noun

    greenhouse gas used in medicine and the manufacture of rockets. Also known as laughing gas or happy gas.

    nuclear weapon Noun

    explosive device that draws power from the splitting and combining of atomic nuclei.

    obscure Verb

    to darken or partially block.

    odor Noun


    oxygen Noun

    chemical element with the symbol O, whose gas form is 21% of the Earth's atmosphere.

    ozone layer Noun

    layer in the atmosphere containing the gas ozone, which absorbs most of the sun's ultraviolet radiation.

    Encyclopedic Entry: ozone layer
    particle Noun

    small piece of material.

    phenomenon Noun

    an unusual act or occurrence.

    pneumonia Noun

    infection where lungs fill with fluid.

    pollutant Noun

    chemical or other substance that harms a natural resource.

    public transportation Noun

    methods of movement that are available to all community members for a fee, and which follow a fixed route and schedule: buses, subways, trains and ferries.

    Radiation Exposure Compensation Act Noun

    (1990) law providing money to people who developed cancer as a result of exposure to radiation in the atmosphere near nuclear test sites.

    radioactive particle Noun

    atom or part of an atom with excess energy that decays and changes the properties of the atom. Also called a hot particle.

    radon Noun

    chemical element with the symbol Rn.

    recycle Verb

    to clean or process in order to make suitable for reuse.

    reduce Verb

    to lower or lessen.

    regulate Verb

    to determine and administer a set of rules for an activity.

    rely Verb

    to depend on.

    reproductive rate Noun

    number of live offspring produced by a single female per reproductive cycle, usually a year.

    respiratory disease Noun

    illness having to do with the lungs and breathing.

    sewer system Noun

    network of drains disposing liquid and solid waste.

    short-term effect Noun

    results of an incident or behavior that last days or months and do not return.

    smog Noun

    type of air pollution common in manufacturing areas or areas with high traffic.

    Encyclopedic Entry: smog
    smoke Noun

    gases given off by a burning substance.

    soil Noun

    top layer of the Earth's surface where plants can grow.

    soil composition Noun

    material, including chemicals, air, and moisture, that make up a section of earth.

    solid Noun

    state of matter with a fixed shape and molecules that vibrate but do not move.

    spore Noun

    reproductive unit of some organisms.

    sulfur dioxide Noun

    greenhouse gas that can cause acid rain.

    temperature Noun

    degree of hotness or coldness measured by a thermometer with a numerical scale.

    Encyclopedic Entry: temperature
    temporary Adjective

    not lasting or permanent.

    toxic mold Noun

    airborne particles released by mold (not the mold itself) that can cause health problems for people and animals.

    treaty Noun

    official agreement between groups of people.

    unpleasant Adjective

    offensive or foul.

    ventilation Noun

    movement or circulation of fresh air in a closed environment. Also called air circulation.

    volcanic ash Noun

    fragments of lava less than 2 millimeters across.

    Encyclopedic Entry: volcanic ash
    volcano Noun

    an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.

    Encyclopedic Entry: volcano
    wildfire Noun

    uncontrolled fire that happens in a rural or sparsely populated area.

    World Health Organization (WHO) Noun

    United Nations agency responsible for health.

    yard Noun

    land surrounding a house or building.

    yard trimmings Noun

    grass, leaves, and small branches left over from mowing and cutting back local vegetation. Also called yard waste.

    yield Verb

    to produce or result in.