• SkillCat Team

Ozone

Updated: Apr 5

EPA 608 Core Chapter 2

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The Ozone Layer


In this module, we will introduce the Ozone layer and talk about how it is essential to life on Earth. Skip to quiz!


Introduction to Ozone


Recall that an atom is the basic building block of all things. Ozone is a naturally occurring gas, made up of 3 oxygen atoms bonded together.


Earth’s atmosphere is made up of several layers, as shown.


Ozone is found in the lowest two layers of Earth’s atmosphere, the Troposphere and the Stratosphere.


Formation of Ozone


Recall that the Oxygen found in air is a gas made of two Oxygen atoms.


In the atmosphere, the sun’s high energy rays break the bond between two oxygen molecules. These free oxygen atoms then bond with pairs of oxygen atoms to form Ozone.


As mentioned in the video, Ozone is found in the Troposphere and the Stratosphere.


The highest concentration of Ozone is found in the Stratosphere. Ozone found in this region is called the Ozone Layer.


Function of Ozone


Ultraviolet (UV) radiation from the sun is constantly hitting earth and is harmful for humans. The main function of Ozone is to absorb and reflect ultraviolet radiation. This occurs in the Ozone Layer in the Stratosphere.

Ozone is also found at ground level, also known as the troposphere, mainly in the form of smog. This type of ozone is created by chemical reactions from pollutant emissions and sunlight.


At ground level, it is considered a harmful pollutant because of its effects on humans and the environment. In humans, it can cause damage to lungs when inhaled. In the environment, it damages plant life in increased amounts.


To summarize, there are two types of ozone:

1. Stratospheric ozone - This ozone performs the essential function of absorbing and reflecting harmful UV rays from the sun.

2. Ground level ozone - This ozone is harmful to humans’ health.


Ozone occurs naturally in the Stratosphere and Troposphere, with the highest concentration found in the Stratosphere. Ozone is essential to life on Earth because it absorbs and reflects harmful UV rays from the sun.



Ozone Depletion


In this module, we will discuss how chemicals used in refrigeration systems destroy the ozone layer. We’ll also take a look the effects of depleting the ozone layer. Skip to quiz!


Impact of Refrigerants


In the 1970s, scientific research discovered that some human-produced chemicals were destroying the Ozone Layer. Recall that the Ozone Layer is ozone in the Stratosphere.


As mentioned in the video, the main chemicals at blame for this destruction are:

- CFCs, which stands for chlorofluorocarbons

- HCFCs, which stands for hydrochlorofluorocarbons


CFCs and HCFCs are categories of refrigerants. They were once used in almost every refrigeration and AC unit before it was discovered that they were destroying the ozone layer.


The most harmful refrigerants in terms of ozone depletion are CFCs. This is because there are more chlorine molecules in CFCs than HCFCs.


CFCs and HCFCs do not dissolve in water and do not break down easily in the atmosphere. Because of this, the chlorine in these chemicals can destroy a lot of ozone before it is broken down.


Impact of Chlorine


When CFCs and HCFCs reach the atmosphere, UV radiation breaks their bonds to release their Chlorine atoms. These free chlorine atoms bond easily with one of the Oxygen atoms in ozone molecules, breaking it apart. When the Oxygen atoms break apart, they are no longer Ozone.

When the Chlorine atom breaks apart an Oxygen atom, it destroys an Ozone molecule. This results in a Chlorine Monoxide molecule (ClO) and an Oxygen molecule (O2).


The Chlorine Monoxide molecule (ClO) will move around the atmosphere until it collides with single oxygen atoms. Single oxygen atoms bond easily with the oxygen atom from Chlorine Monoxide. This leaves Chlorine free to repeat the process of breaking up Ozone.


One Chlorine atom goes on to destroy many more Ozone molecules in the atmosphere before it disintegrates.


CFCs can last 70-100 years in the atmosphere before they are naturally broken down in the atmosphere. In this time, it repeats the process of destroying ozone. This is why a single Chlorine atom can destroy up to 100,000 Ozone molecules.


Effects of Ozone Depletion


As Ozone becomes depleted, more ultraviolet radiation is able to pass through the atmosphere.

Increased UV radiation causes:

- Increase in skin cancers in humans

- Increase in cataracts in humans

- Reduced marine life and ocean algae

- Destruction of immune systems in humans and animals

- Reduced plant life and vegetation


Of the previously mentioned impacts of ozone depletion, the most serious threats to humans are increased skin cancer and increased cataracts.


Destruction of the ozone layer will also contribute to:

- Increased ground-level ozone and smog which cause respiratory issues in humans.

- Increased erratic weather conditions


Ozone depletion poses great threats to human life on Earth. Because of this, ozone depletion is not just a national or region problem, but it is a global problem. It affects people all over the world.


Evidence of Ozone Depletion


In the mid 1970s, large amounts of chlorine in the Stratosphere were destroying the Ozone Layer. It was determined that this chlorine came from human-made gases. Before then, it was believed that natural sources, such as volcanoes, were to blame for the rise chlorine.


Volcanic activity does naturally release chlorine into the atmosphere. But according to air samples taken from the stratosphere above volcanoes, only a small amount of this chlorine makes it up to the ozone layer. Most of the volcanic chlorine stays on ground level.

Air samples taken in the stratosphere provide the strongest evidence that it is refrigerant chemicals that are destroying the ozone.


Air samples of the stratosphere contain significantly increased amounts of CFCs and HCFCs, as well as carbon monoxide. As we discussed, carbon monoxide is formed when chlorine bonds with oxygen as it breaks apart an ozone molecule.


These samples match with the increased use and emissions of refrigerant chemicals over the same time period.


Ozone depletion is due to Chlorine-containing refrigerants and gases in the atmosphere. Specifically, this is CFCs and HCFCs. The most harmful types of refrigerants are CFCs.


Evidence of ozone depletion is found in air samples from the Stratosphere. Because of the importance of ozone to sustaining life on Earth, ozone depletion is a global problem.



Question #1: Ozone has __ molecules of oxygen.

  1. 2

  2. 3

  3. 8

  4. 10

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Answer: 3

Ozone is composed of 3 molecules of oxygen.


Question #2: What is the major function of ozone in the stratosphere?

  1. Absorb and reflect UV rays from the sun

  2. Create UV rays by using rays from the sun

  3. Direct UV rays from the sun to humans

  4. Convert UV rays into energy for humans

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Answer: Absorb and reflect UV rays from the sun

Ozone is essential to life on earth because it absorbs and reflects harmful UV rays from the sun.


Question #3: Ground level ozone is what absorbs and reflects harmful UV rays from the sun.

  1. True

  2. False

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Answer: False

Ozone in the Stratosphere absorbs and reflects harmful UV rays from the sun, not ground level ozone. Ground level ozone is actually harmful for humans when inhaled.


Question #4: The majority of ozone is located in the Troposphere.

  1. True

  2. False

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Answer: False

The majority of ozone is located in the Stratosphere, not the Troposphere.


Question #5: What molecule destroys the ozone layer?

  1. Carbon

  2. Chlorine

  3. Calcium

  4. Fluorine

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Answer: Chlorine

Chlorine is the molecule in refrigerants responsible for destroying the ozone layer.


Question #6: One molecule of chlorine can destroy how many molecules of ozone?

  1. 3000

  2. 100,000

  3. 300,000

  4. 10,000,000

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Answer: 100,000

One molecule of chlorine can destroy 100,000 molecules of ozone.


Question #7: Three molecules of chlorine can destroy how many molecules of ozone?

  1. 3000

  2. 100,000

  3. 300,000

  4. 10,000,000

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Answer: 300,000

One molecule of chlorine can destroy 100,000 molecules of ozone. So, 3 molecules of chlorine can destroy three times that, or 300,000 molecules of ozone.


Question #8: Who does ozone depletion affect?

  1. People who close to areas with a lot of ozone

  2. People in the United States

  3. People in high altitudes

  4. People all over the world

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Answer: People all over the world

Ozone depletion is a global problem and affects everyone living on earth.


Question #9: In which of the following ways does ozone depletion affect humans?

  1. Increased risk of heart disease

  2. Increased risk of skin cancer

  3. Increased risk of nose cancer

  4. Increased risk of cataracts

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Answer: Increased risk of skin cancer

Increased risk of cataracts

When ozone is depleted, there is not enough ozone present to absorb and reflect harmful UV rays from the sun. This increases risk of skin cancer and cataracts in humans.


Question #10: Which of the following are effects of ozone depletion?

  1. Increasing toxicity in the oceans

  2. Increasing acidity in the air

  3. Decreasing crop yields

  4. Increasing crop yields

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Answer: Decreasing crop yields

Decreasing crop yields is an effect of ozone depletion. This is due to increased UV rays from the sun that damage plant life.


Question #11: Which of the following are effects of ozone depletion?

  1. Threat to wild and marine life

  2. Human structures can be damaged

  3. Cars will be affected

  4. Increasing invasive plant species

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Answer: Threat to wild and marine life

Ozone depletion also affects animals on land and sea.


Question #12: Is there evidence that refrigerants are in the stratosphere?

  1. Yes

  2. No

  3. Inconclusive

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Answer: Yes

Yes, air samples taken from the stratosphere confirm that refrigerants such as CFCs and HCFCs make it to the stratosphere, where they destroy ozone.


Question #13: Can chlorine in the stratosphere be from natural sources, such as volcanoes?

  1. Yes, chlorine in the stratosphere is primarily from natural sources such as volcanoes

  2. Yes, chlorine can come from natural sources such as volcanoes, but they are not the primary source

  3. No, all chlorine comes from refrigerants released

  4. There is no chlorine in the stratosphere

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Answer: Yes, chlorine can come from natural sources such as volcanoes, but they are not the primary source

Chlorine is released from natural sources such as volcanoes. But the rise of chlorine in the atmosphere is the refrigerants that have been released.


Question #14: What is the primary source of chlorine in the Stratosphere?

  1. Volcanoes

  2. Natural sources such as earthquakes

  3. Emissions of refrigerant chemicals such as CFCs and HCFCs by humans

  4. There is no chlorine in the stratosphere

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Answer: Emissions of refrigerant chemicals such as CFCs and HCFCs by humans

The primary source of the rise of chlorine in the atmosphere is the refrigerants that have been released by humans.



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