Photochemical Smog: Definition, Formation & Effects

Photochemical Smog: Definition, Formation & Effects
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  • 0:00 What Is Smog?
  • 1:10 How Is Photochemical…
  • 1:30 What Makes up…
  • 2:04 Conditions for…
  • 2:35 Decreasing Photochemical Smog
  • 3:09 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb
In this lesson, we will learn about photochemical smog, a common type of pollutant. We'll cover what photochemical smog is, how it is different from other types of pollution, how it is formed, and how to decrease it.

What Is Smog?

Picture the City of Angels, Los Angeles, California. At first we might think of famous movie stars, palm tree-lined boulevards, and surfing. However, another image might also come to mind, one that isn't as fun, and that's smog. Not so pretty, smog is the thick, brown haze that lies around especially polluted cities like Los Angeles.

Photochemical smog is a type of smog. But what exactly is smog? Smog is formed from combustion, or burning, of fossil fuels like coal and oil. Fossil fuels power much of our electricity, allow us to drive cars, and are the means for powering factories that manufacture everyday goods. Smog is especially common in cities with a lot of cars and traffic, like LA. Smog isn't just found in the United States, though. Developing nations like China, India, and the Middle East also have high levels of air pollution.

Smog, itself, is the pollutants given off by burning fossil fuels. Photochemical smog is a type of secondary pollutant that occurs when the chemicals given off react with sunlight in the atmosphere.

How Is Photochemical Smog Formed?

Photochemical smog is produced when pollutants from the combustion of fossil fuels react with sunlight. The energy in the sunlight converts the pollutants into other toxic chemicals. In order for photochemical smog to form, there must be other pollutants in the air, specifically nitrous oxides and other volatile organic compounds (VOCs).

What Makes up Photochemical Smog?

When nitrous oxides and VOCs interact with sunlight, secondary pollutants are formed, such as ozone and peroxyacetyl nitrate. These secondary pollutants are what we have been calling photochemical smog. You might think, 'Hey, isn't ozone good for protecting our atmosphere?' Well, it is, but only at levels high above the surface. When ozone is near humans, it can cause serious problems with our lungs and vision. Peroxyacetyl nitrate is one of the chemicals that is responsible for damaging lung tissue, and photochemical smog forms plenty of it.

Ideal Conditions for Photochemical Smog

Anything that burns fossil fuels in the presence of sunlight can produce photochemical smog. Motor vehicles, during the morning commute in cities, produce a lot of pollutants. When the sun is out, it is the perfect incubator for this type of smog. Photochemical smog is also more prevalent in valleys. The mountains block fresh air from coming into the area and create a basin that photochemical smog will easily get trapped in. Temperature inversion is a condition in which air sinks to the surface, trapping the smog.

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