In The energy in the sunlight converts

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.

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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.

Decreasing Photochemical Smog

Weather patterns help dissipate photochemical smog. Precipitation can clear the primary pollutants from the air, preventing photochemical smog from forming. Warmer temperatures help air to heat and rise, moving pollutants away from the earth’s surface. However, the best way to decrease photochemical smog levels is to decrease use of fossil fuels through using non-polluting or renewable energy sources, such as hydroelectric power, nuclear power, or wind energy.

Riding bikes or using hybrid cars can also decrease pollutant emissions.

Lesson Summary

We now know that smog is the air pollutants produced from things like burning fossil fuels during motor vehicle transport, generating electricity in power plants, and producing goods in factories. Photochemical smog, produced when pollutants from the combustion of fossil fuels react with sunlight, is a secondary pollutant that has not only a harmful effect on our environment, but also on our health. Though certain weather conditions like rain and warm air naturally help us fight photochemical smog, it is up to us to make the commitment to use alternate energy sources, such as hydroelectric power or wind energy, in order to prevent this condition from getting worse

Photochemical Smog: Key Terms

Smog in Los Angeles
Smoggy Shot of Los Angeles Traffic

Smog – air pollutants produced by burning fossil fuels; creates a thick, brown haze that lies around especially polluted citiesFossil fuels – substances like coal and oil which power much of our electricity, allow us to drive cars, and are the means for powering factoriesPhotochemical smog – smog produced when pollutants from the combustion of fossil fuels react with sunlightSecondary Pollutant – a pollutant which occurs when chemicals react with each other or the atmospherePollutants – chemicals which pollute the airOzone – chemical that protects our atmosphere when located high above the Earth’s surface but is a pollutant that can harm lungs and vision when located near humansPeroxyacetyl nitrate – chemical, formed by photochemical smog, that is responsible for damaging lung tissueTemperature inversion – a condition in which air sinks to the surface, trapping smogRenewable energy sources – energy sources which are sourced from renewable resources and typically involve less pollutants than conventional energy sources; examples include wind energy and hydroelectric power

Learning Outcomes

After this lesson, check to see if you can:

  • Describe the source of smog
  • Define photochemical smog
  • Explain the potential harms of pollutants in smog
  • Recall conditions that are ideal for photochemical smog
  • Identify examples of renewable energy sources
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