What Is Air Pollution? - Definition, Sources & Types

Lesson Transcript
Instructor: Elizabeth Friedl

Elizabeth, a Licensed Massage Therapist, has a Master's in Zoology from North Carolina State, one in GIS from Florida State University, and a Bachelor's in Biology from Eastern Michigan University. She has taught college level Physical Science and Biology.

Air pollution is a mixture of harmful particles and gases in the atmosphere. Learn the definition of air pollution, discover its sources, and explore the different types of air pollutants that exist. Updated: 03/03/2022

What Is Air Pollution?

Being sick is pretty lousy, isn't it? If you know someone who has a cold, you tend to steer clear of them because you don't want to catch their germs. Every time that person coughs or sneezes, their germs get put into the air and are then free to travel to the next person. Can you imagine trying to contain something like that in the air? It would be pretty difficult because, not only are the germs invisible, but they expand outward as they enter the air.

We don't think of germs as air pollution, but it really is the same idea. Air pollutants are gases and particles in the atmosphere that harm organisms and affect climate. Air pollution, then, is the release of these particles and gases into the air. For the previous example, the germs would be the pollutants, but the air wouldn't be polluted until those germs are sneezed out.

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  • 0:07 What Is Air Pollution?
  • 0:54 Sources of Air Pollution?
  • 2:02 Types of Air Pollutants
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Sources of Air Pollution

When you think of air pollution, you likely think of human activities, such as coal-burning plants and emissions from cars, planes and boats. But, air pollution also comes from natural sources. Volcanoes are a great example of a natural pollution source; they produce large amounts of particles and gases, and the eruptions send them up into the atmosphere. Forest fires are a natural process that also produce large amounts of potentially harmful gas and particulate matter.

No matter the source, there are two ways pollution can enter the air. Point source pollution is when the air pollutants come from a single source of origin, such as smokestacks at a single factory. Non-point source pollution is when the air pollutants come from many sources, such as all of the cars in the U.S.

Just like not all sources of pollution are the same, pollutants also vary in their effects. Primary pollutants are those that cause direct harm or that can react to form harmful substances in the atmosphere. Secondary pollutants are those harmful substances that are created from the reactions between primary pollutants and the components of the atmosphere.

Types of Air Pollutants

In another lesson, we learned about the Clean Air Act of 1970, which set limits on emissions and standards for air quality, provided funding for pollution control research and made it possible for citizens to sue those who violate the standards. The standards set forth in this legislation by the Environmental Protection Agency, or EPA, identified six pollutants as those that posed the greatest threat to human health. Let's look at each one.

Carbon monoxide is both odorless and colorless, and it's produced through combustion. Most carbon monoxide emissions come from vehicles, about 62%, but they also come from forest fires, lawn equipment and the burning of industrial waste. This pollutant is dangerous to human health because, even in very small concentrations, it can prevent oxygen from being delivered through your body to major organs. At higher levels, it can cause death.

Sulfur dioxide is also a colorless gas, and it's highly reactive. About 70% of sulfur dioxide emissions come from combustion at industrial power plants, like those that generate electricity from coal. Sulfur in the coal reacts with atmospheric oxygen in the air and forms the compound sulfur dioxide. Once in the air it may react further to create sulfur acid, which can fall back to Earth as acid rain. Sulfur dioxide can also cause respiratory illnesses when it's breathed in.

Nitrogen oxides are a family of gases that are also very reactive, but you can definitely see and smell these! Both nitric oxide and nitrogen dioxide are in this family, and these are the gases that contribute to the smog you see over large cities, like Los Angeles. More than half of these pollutants come from vehicle combustion emissions, with a large amount also coming from industrial combustion. Nitrogen oxides also cause respiratory illnesses.

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