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Ozone layer and CFCs

Content objective:

What are we learning and why are we learning this? Content, procedures, or skills.

Vocabulary objective

Tier II: High frequency words used across content areas. Key to understanding directions & relationships, and for making inferences.

Tier III: Low frequency, domain specific terms.

Building on what we already know

Make connections to prior knowledge. This is where we build from.



I. Oxygen atoms can exist by themselves or as molecules

II. How is ozone made

III. The ozone layer

IV. When is ozone good for us? Bad for us?

V. Chlorofluorocarbons (CFCs)


VII. How do we know that ozone loss isn’t natural?

VIII. What is being done about ozone depletion?

IX. Will the ozone layer recover?

Misconceptions: This phenomenon is not related to global warming.

I. Three forms of oxygen

O – atomic oxygen             not stable.                   instantly combines with other O atoms to make O2

O2 . molecular oxygen        very stable.                  this is what we breathe

O3   ozone                          Only stable for a minute.  Irritating to breathe. We don’t want it near us.

II. How is ozone made?


The ozone layer

The Earth is wrapped in a blanket of air (the atmosphere.)

About 20 to 30 km high the air is rich in naturally produced ozone gas; we call this region the ozone layer.

It’s important because it stops much of the sun’s ultra-violet (UV) rays, so that only a small percent of UV light reaches the surface.

Small amounts of UV light are good; our skin cells use it to convert natural vitamin D in our foods to an active form of Vitamin.

Too much UV light cause sunburns, and increases the risk of skin cancers.

When is ozone good for us? Bad for us?

According to this diagram, where do we humans find it useful (“good) for ozone to exist? Where do we find it not useful (“bad”)?

V. Chlorofluorocarbons (CFCs)

Many years ago scientists invented a super-useful family of chemicals called Chlorofluorocarbons (CFCs)

They are commonly known by the DuPont brand name Freon.

They were non-toxic, cheap to produce, easy to clean, and harmless to animal and plant life.

They became widely used as refrigerants, and as propellants in air conditioners, some fire extinguishers, hairspray cans, asthma inhalers

However there were unintended consequences: we later discovered that CFC molecules were floating into the upper atmosphere, where they were being broken down by UV sunlight.

See the diagram below for details. As a result of this breakdown, these gases caused ozone to break down.

Here we see the same process, animated.

CFC breaks down ozone


Every spring, a hole as big as the USA develops in the ozone layer over Antarctica, in the South Pole. A smaller hole develops each year over the Arctic, at the North Pole. It was getting thinner all over the planet.

(It is not literally a “hole”; it is a region where less ozone exists.)

Scientists have discovered that the ozone hole over Antarctica started in 1979, and that the ozone layer generally started to get thin in the early 1980s.

“UV rays can go through water and end up killing small water animals or plants, called ‘plankton’ which form the base of the food chain in oceans and seas. Whales and other fishes have plankton as their main food, and if plankton die because of these UV rays, whales will start dying too, because they will not have anything to eat. Large amounts of UV rays could damage all green plants. If the ozone layer keeps getting thinner, there could be fewer and fewer plants on Earth, then there would be less food in the whole world.”

Excess UV light could cause an epidemic of serious sunburns and skin cancers in humans. Excess UV light also damages our eyes, and can cause blindness.


The following text (sections 7, 8 and 9) is from factmonster.com, Environment, Ozone layer

VII. How do we know that ozone loss isn’t natural?

While it is true that volcanoes and oceans release large amounts of chlorine, the chlorine from these sources is easily dissolved in water and washes out of the atmosphere in rain.

In contrast, CFCs are not broken down in the lower atmosphere and do not dissolve in water. The chlorine in these human-made molecules does reach the stratosphere.

Measurements show that the increase in stratospheric chlorine since 1985 matches the amount released from CFCs and other ozone-depleting substances produced and released by human activities.

VIII. What is being done about ozone depletion?

In 1978, the use of CFC propellants in spray cans was banned in the U.S. In the 1980s, the Antarctic “ozone hole” appeared and an international science assessment more strongly linked the release of CFCs and ozone depletion. It became evident that a stronger worldwide response was needed.

In 1987, the Montreal Protocol was signed and the signatory nations committed themselves to a reduction in the use of CFCs and other ozone-depleting substances.

Since that time, the treaty has been amended to ban CFC production after 1995 in the developed countries, and later in developing. Today, over 160 countries have signed the treaty. Beginning January 1, 1996, only recycled and stockpiled CFCs will be available for use in developed countries like the US. This production phaseout is possible because of efforts to ensure that there will be substitute chemicals and technologies for all CFC uses.

IX. Will the ozone layer recover?

We can’t make enough ozone to replace what’s been destroyed, but provided that we stop producing ozone-depleting substances, natural ozone production reactions should return the ozone layer to normal levels by about 2050.

It is very important that the world comply with the Montreal Protocol; delays in ending production could result in additional damage and prolong the ozone layer’s recovery.

Misconceptions: Ozone and global warming.

Many people mistakenly equate CFCs with global warming.

Too much CFCs in the air leads to damage of the ozone layer.

Too many greenhouses gases in the air – CO2, methane, nitrous oxide (N2O) – leads to global warming.

These are distinct phenomenon. We should avoid confusing them.

CFCs are a greenhouse gas, so it could contribute to both problems. However, the great majority of greenhouse effect comes from other gases. CFCs aren’t affecting that issue very much.

Learning Standards

Massachusetts Curriculum FrameworksMassachusetts Curriculum Frameworks

Grades 6–8: Overview of Science and Engineering Practices

Examine and interpret data to describe the role human activities have played in the rise of global temperatures over time; construct, analyze, and/or interpret graphical displays of data and/or large data sets to identify linear and nonlinear relationships; distinguish between causal and correlational relationships in data; consider limitations of data analysis.

8.MS-ESS3-5. Examine and interpret data to describe the role that human activities have played in causing the rise in global temperatures over the past century.

High School. HS-ESS3-5. Analyze results from global climate models to describe how forecasts are made of the current rate of global or regional climate change and associated future impacts to Earth systems.
Clarification: Climate model outputs include both climate changes (such as precipitation and temperature) and associated impacts (such as on sea level, glacial ice volumes, and atmosphere and ocean composition).

A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas

Disciplinary Core Ideas

LS2.C: Ecosystem Dynamics, Functioning, and Resilience
A complex set of interactions within an ecosystem can keep its numbers and types of organisms relatively constant over long periods of time under stable conditions. If a modest biological or physical disturbance to an ecosystem occurs, it may return to its more or less original status (i.e., the ecosystem is resilient), as opposed to becoming a very different ecosystem. Extreme fluctuations in conditions or the size of any population, however, can challenge the functioning of ecosystems in terms of resources and habitat availability. (HS-LS2-2),(HS-LS2-6)

Moreover, anthropogenic changes (induced by human activity) in the environment—including habitat destruction, pollution, introduction of invasive species, overexploitation, and climate change—can disrupt an ecosystem and threaten the survival of some species. (HS-LS2-7)

Cross Cutting Concepts

Cause and Effect:  Empirical evidence is required to differentiate between cause and correlation and make claims about specific causes and effects. (HS-LS2-8),(HS-LS4-6)

Scale, Proportion, and Quantity: The significance of a phenomenon is dependent on the scale, proportion, and quantity at which it occurs. (HS-LS2-1)

Using the concept of orders of magnitude allows one to understand how a model at one scale relates to a model at another scale. (HS-LS2-2)

Stability and Change: Much of science deals with constructing explanations of how things change and how they remain stable. (HS-LS2-6),(HS-LS2-7)

Next Generation Science Standards

HS-ESS3-4. Evaluate or refine a technological solution that reduces impacts of human activities on natural systems.

HS-ESS3-5. Analyze geoscience data and the results from global climate models to make an evidence-based forecast of the current rate of global or regional climate change and associated future impacts to Earth’s systems.
[Clarification: Examples of evidence, for both data and climate model outputs, are for climate changes (such as precipitation and temperature) and their associated impacts (such as on sea level, glacial ice volumes, or atmosphere and ocean composition).]

[Assessment Boundary: Assessment is limited to one example of a climate change and its associated impacts.]

HS-ESS3-6. Use a computational representation to illustrate the relationships among Earth systems and how those relationships are being modified due to human activity.

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