The term atmosphere refers to the blanket of gases that surround the earth. These gases exist in several spherical layers.
The troposphere is the layer closest to the earth. It extends up about 4 miles above sea level at the poles and about 11 miles at the equator. Both the weather and clouds occur in the troposphere. It is a very thin layer, but it includes about 75 to 80 percent of the earth’s air mass. About 99 percent of the air we inhale consists of just two gases found in this layer: nitrogen (78 percent) and oxygen (21 percent). The remaining amount is comprised of argon, carbon dioxide, water vapor, dust and soot particles, methane, ozone, and nitrous oxide (Miller and Spoolman, 2016). Air lets our living planet breathe—it's the mixture of gases that fills the atmosphere, giving life to the plants and animals on Earth. We can breathe ordinary air all day long with no ill effects. (The average person breathes in 2 gallons of air per minute – 3,400 gallons a day.)
Several of these gases (including carbon dioxide, methane, water vapor, and nitrous oxide) are referred to as “greenhouse gases,” because they absorb and release energy that warms the troposphere. Rising and falling air currents, winds, and concentrations of greenhouse gases in the troposphere play major roles in the earth’s short-term weather and long-term climate (Miller and Spoolman, 2016).
The second layer of the atmosphere is the stratosphere, which is characterized by a slight temperature increase with altitude and the absence of clouds. The stratosphere extends between 11 and 31 miles above the earth's surface. The composition of the stratosphere is similar to that of the troposphere except it has much less water vapor and much more ozone. Much of the earth’s small amount of ozone is found in a portion of the stratosphere (the ozone layer) located about 11 to 16 miles above sea level.
Ozone, a form of oxygen, is crucial to our survival; it absorbs about 95 percent of the sun’s harmful ultraviolet radiation and keeps it from reaching earth. The ozone layer is sometimes referred to as a “global sunscreen.” It “allows us and other life-forms to exist on land and helps to protect us from sunburn, skin and eye cancers, cataracts, and damage to our immune system” (Miller and Spoolman, 2016).
The mesosphere is characterized by temperatures that quickly decrease as height increases. The mesosphere extends from about 31 to 50 miles above the earth's surface. In the thermosphere, temperature increases with altitude (Enchanted Learning, 2017).
The term air pollution refers to “the presence of chemicals in the atmosphere in concentrations high enough to harm organisms, ecosystems, or human-made materials, or to alter climate” (Miller and Spoolman, 2016). Air pollution can harm the health of people or other animals, kill plants or stop them growing properly, damage or disrupt other aspects of the environment (such as making buildings crumble), or cause some other kind of nuisance (reduced visibility or an unpleasant odor) (Woodford, 2017). It is the quantity (or concentration) of a chemical in the air that makes the difference between harmless and pollution. For example, carbon dioxide is present in the air at a typical concentration of less than 0.05 percent, and breathing it in usually does no harm. But, research has found that at only 5 to 10 percent of air, it is toxic and could kill a person in only a few minutes (Woodford, 2017).
The chemicals that pollute the air can come from either natural or human sources. Natural sources include wind-blown dust and pollutants from wildfires and volcanic eruptions. Most natural pollutants spread out over the Earth and are diluted or removed by precipitation, gravity, or cycles of the chemical itself. Most human sources of pollutants occur in urban and industrialized areas and are produced primarily by the burning of fossil fuels in power plants, industrial factories, and motor vehicles (Miller and Spoolman, 2016).
Top Ten Gases in Air Pollution
The most harmful types of gases are (Woodford, 2017):
1. Sulfur dioxide: Coal, petroleum, and other fuels are often impure and contain sulfur as well as organic compounds. When sulfur burns with oxygen from the air, sulfur dioxide is produced. Coal-fired power plants are the world's biggest source of sulfur-dioxide air pollution, which contributes to smog, acid rain, and health problems that include lung disease.
2. Carbon monoxide: This highly dangerous gas forms when fuels have too little oxygen to burn completely. It spews out in car exhausts and it can also build up to dangerous levels inside homes that have a poorly maintained gas boiler, stove, or fuel-burning appliance.
3. Carbon dioxide: This gas is central to everyday life and isn't normally considered a pollutant: we all produce it when we breathe out and plants such as crops and trees need to "breathe" it in to grow. However, carbon dioxide is also a greenhouse gas released by engines and power plants. Since the beginning of the Industrial Revolution, it's been building up in the Earth's atmosphere and contributing to the problem of global warming and climate change.
4. Nitrogen oxides: Nitrogen dioxide and nitrogen oxide are pollutants produced as an indirect result of combustion, when nitrogen and oxygen from the air react together. Nitrogen oxide pollution comes from vehicle engines and power plants, and plays an important role in the formation of acid rain, ozone and smog. Nitrogen oxides are also indirect greenhouse gases.
5. Volatile organic compounds (VOCs): These carbon-based (organic) chemicals evaporate easily at ordinary temperatures and pressures, so they readily become gases. That's precisely why they're used as solvents in many different household chemicals such as paints, waxes, and varnishes. Unfortunately, they're also a form of air pollution: they're believed to have long-term (chronic) effects on people's health and they also play a role in the formation of ozone and smog.
6. Particulates: These are the sooty deposits in air pollution that blacken buildings and cause breathing difficulties. In cities, most particulates come from traffic fumes.
7. Ozone: In the stratosphere (upper atmosphere), a band of ozone protects us by screening out harmful ultraviolet radiation (high-energy blue light) beaming down from the sun. At ground level, it's a toxic pollutant that can damage health. It forms when sunlight strikes a cocktail of other pollution and is a key ingredient of smog.
9. Unburned hydrocarbons: When petroleum and other fuels that are made of organic compounds burn properly, they're completely converted into harmless carbon dioxide and water; when they burn incompletely, they can release carbon monoxide or float into the air in their unburned form, contributing to smog.
10. Lead and heavy metals: Lead and other toxic "heavy metals" can be spread into the air either as toxic compounds or as aerosols (when solids or liquids are dispersed through gases and carried through the air by them) in such things as exhaust fumes and the fly ash (contaminated waste dust) from incinerator smokestacks.
Carbon dioxide emission
The Biggest Contributors to Air Pollution
So, what are the biggest contributors to air pollution? There are three that are most significant (Woodford, 2017).
1. Motor vehicles: There are something like a half billion cars on the road today. Virtually all of them are powered by gasoline and diesel engines that burn petroleum to release energy. Petroleum is made up of hydrocarbons (large molecules built from hydrogen and carbon) and, in theory, burning them fully with enough oxygen should produce nothing worse than carbon dioxide and water. In practice, fuels aren't pure hydrocarbons and engines don't burn them cleanly. As a result, exhausts from engines contain all kinds of pollution, notably particulates (soot of various sizes), carbon monoxide, nitrogen oxides, volatile organic compounds (VOCs), and lead—and indirectly produce ozone. Mix this together and energize it with sunlight and you get the sometimes brownish, sometimes blueish fog of pollution we call smog, which can hang over cities for days on end.
2. Power plants: Renewable energy sources such as solar panels and wind turbines are helping us generate a bigger proportion of our power every year, but the overwhelming majority of electricity (around 70 percent in the United States, for example) is still produced by burning fossil fuels such as coal, gas, and oil, mostly in conventional power plants. Just like car engines, power plants should theoretically produce nothing worse than carbon dioxide and water; in practice, fuels are dirty and they don't burn cleanly, so power plants produce a range of air pollutants, notably sulfur dioxide, nitrogen oxides, and particulates. (They also release huge amounts of carbon dioxide, a key cause of global warming and climate change when it rises and accumulates in the atmosphere.)
3. Industrial plants and factories: Plants that produce the goods we all rely on often release small but significant quantities of pollution into the air. Industrial plants that produce metals such as aluminum and steel, refine petroleum, produce cement, synthesize plastic, or make other chemicals are among those that can produce harmful air pollution. Most plants that pollute release small amounts of pollution continually over a long period of time, though the effects can be cumulative.
(Source: Conserve Energy Future)
The Harms from Air Pollution
1. Negative effect on human health: Air pollution is a major contributor to lung diseases such as bronchitis, emphysema, and asthma and to various forms of cancer. The World health Organization estimates that three million persons die prematurely each year due to the ill effects of air pollution.
2. Negative effects on agriculture: Air pollution (in common with water pollution) can seriously affect the growth of plants. For example, absorption of high levels of sulfur compounds from the air can destroy plant cells and reduce agricultural productivity. One can easily find chemical residues (everything from toxic heavy metals such as lead to cocktails of brake fluids and other chemicals) in plants that grow alongside highways.
3. Acid rain: Most coal-burning power plants, metal ore smelters, oil refineries, and other industrial facilities emit sulfur dioxide, particulates, and nitrous oxides. These substances can form secondary acidic substances that descend on the earth in rain, snow, fog, and cloud vapor. This acid rain can be very harmful to plant life and productivity and severely damage aquatic and wetland ecosystems. It can contaminate drinking water and fish and animals and be ingested by humans.
4. Depletion of the ozone layer: In the 1980s, atmospheric scientists detected a thinning in the ozone layer over the South Pole. After scientific investigation, it was determined that the reduction was a result of air pollutants from human behavior – specifically the release of nontoxic, aerosol gas molecules called chlorofluorocarbons (CFC) (described above). CFCs are used in many types of aerosol cans, refrigerator coolants, and fire extinguishers and are released into the atmosphere. Because they are nontoxic and chemically inactive, this was thought to be safe. However, it was discovered that they do break down when they encounter the very intense ultraviolet radiation found in the stratosphere and ultimately lead to a decrease in ozone molecules – weakening the protection afforded to everything on Earth by the ozone layer (Spooner, 2012).
5. Climate change: In the early 1900s, climatologists (scientists who seek to understand all aspects of climate and climate change from short-term, localized situations to long-term global situations) detected noticeable climate change. Initially, it was considered unlikely that humans could do anything sufficiently powerful to alter climate. However, as climate science continued to evolve and as patterns of change increased, climatologists (in the last 50 years or so) have reached the conclusion that human activities are contributing to observed changes in Earth’s climate system. Our planet’s “warming” is largely a result of the distribution of greenhouse gases into the atmosphere (Spooner, 2012). This profoundly important development is described in more detail on the “Climate Change” page.
What Can Be Done
The starting points for doing something about air pollution are the same as with all of the environmental issues covered in this section of the website:
Become more knowledgeable about this issue.
Discuss this issue with others; learn from them and help them learn from you.
Consider the recommendations made by the New Hampshire Department of Environmental Services (
* Conserve energy – remember to turn off lights, computers, and electric appliances when not in use.
* Use energy efficient light bulbs and appliances.
* Participate in your local utility’s energy conservation programs.
* Limit driving by carpooling, using public transportation, biking and walking.
* Combine errands for fewer trips.
* Keep your automobile well tuned and maintained. Follow the manufacturer’s instructions on routine maintenance, such as changing the oil and filters, and checking tire pressure and wheel alignment.
* Avoid excessive idling of your automobile.
* Use electric or hand-powered lawn care equipment.
* Be careful not to spill gasoline when filling up your car or gasoline powered lawn and garden equipment.
* Run dishwashers and clothes washers only when full.
* Choose environmentally friendly cleaners.
* Use water-based or solvent free paints whenever possible and buy products that say "low VOC".
* Seal containers of household cleaners, workshop chemicals and solvents, and garden chemicals to prevent volatile organic compounds from evaporating into the air.
* Purchase and use low-polluting outboard marine engines and personal watercraft (4-stroke and direct fuel injection 2-stroke outboard marine engines).
* Advocate for emission reductions from power plants and more stringent national vehicle emission standards.
Join forces with groups and organizations that are knowledgeable about environmental issues in general (BEAT!) and about this issue in particular. Organizations have greater access to scientific expertise, have larger budgets, have more contacts with the media, and have the force of combining many voices into one.
Advocate for policies that show understanding and respect for natural processes. Examples are educational programs and policies that encourage energy efficiency and greater use of renewable energy sources such as biomass, hydropower, geothermal power, wind power, and solar power by individuals, families, companies, and the government. Strict emission standards for automobiles and emission control devices are a necessity.
Advocate for government agencies and government leaders at all levels to conscientiously try to fulfill their responsibilities toward protection and conservation of the environment.
Examine the values and political position on this issue of candidates running for political office. Federal support for a strong Environmental Protection Agency is very important. Support for a meaningful Department of Environmental Quality in North Carolina is very important. Support by North Carolina’s governor and state legislature for taking a scientific approach to consideration of energy sources is absolutely critical. Look for candidates that emphasize the importance of environmental impact in making decisions about what to do or not do.
Conserve Energy Future. 2017 “Air Pollution Facts.”
G. Tyler Miller and Scott E. Spoolman. 2016 Environmental Science (15th edition). Boston: Cengage Learning.
New Hampshire Department of Environmental Services. 2017 "What Can I Do To Help Reduce Air Pollution."
Alecia M. Spooner. 2012 Environmental Science for Dummies. Hoboken, NJ: John Wiley and Sons.
Chris Woodford. 2018 “Explain That Stuff: Air Pollution.”
Read and See More on Air Pollution:
Nicholas Bakalar. 2017 “Even Safe “Pollution Levels Can Be Deadly.” New York Times, June 28. www.nytimes.com/2017/06/28/well/even-safe-pollution-levels-can-be-deadly.html?rref=collection%2Ftimestopic%2FAir%20Pollution&action=click&contentCollection=science®ion=stream&module=stream_unit&version=latest&contentPlacement=10&pgtype=collection
Fine particulates and ozone in the air increase the risk of premature death.
Alina Bradford. “Live Science: Pollution Facts and Types of Pollution.”
A brief overview of land, air, water, and light pollution.
A. Crimmins; J. Balbus; J.L. Gamble; C.B. Beard; J.E. Bell; D. Dodgen; R.J. Eisen; N. Fann; M.D. Hawkins; S.C. Herring; L. Jantarasami; D.M. Mills; S. Saha; M.C. Sarofim; J. Trtanj; L. Ziska. 2016 The Impacts of Global Change on Human Health: A Scientific Assessment. Washington, D.C.: United States Global Change Research Program. s3.amazonaws.com/climatehealth2016/low/ClimateHealth2016_FullReport_small.pdf
A comprehensive review of the effects of air pollution on human health.
Umair Irfan. 2014 “Air Pollution and Extreme Weather Combine to Kill.” Scientific American, September 3. www.scientificamerican.com/article/air-pollution-and-extreme-weather-combine-to-kill/
A mix of extreme temperature and air pollution can be a deadly force.
National Institute of Environmental Health Sciences. 2017 "Air Pollution.”
A brief look at air pollution with links to much good information.
State Climate Office of North Carolina. 2017 “Air Quality.”
A brief examination of the way air quality is measured in North Carolina.
The Guardian. “Air Pollution: A Dark Cloud of Filth Poisons the World’s Cities.” 2016
An international look at air pollution problems around the world.
(Sample Scholarly Article) Marilena Kampa and Elias Castenas. 2008 “Human Health Effects of Air Pollution.” Environmental Pollution 151:362-367. www.sciencedirect.com/science/article/pii/S0269749107002849
A comprehensive look at health problems caused by air pollution.
(Video) Romain Lacombe: “Global Pandemic – Air Pollution”
Air pollution is a global pandemic that's underway. It's a major health challenge yet nobody talks about it. It affects everyone but we usually ignore it cause we can't actually "see" it. Now it's time to talk about it and find a way to solve it together.
Sample Scholarly Journals:
Environmental Health Perspectives
Journal of Air Pollution and Health