Our Environment · Lesson 5 of 8
How Do Our Activities Affect The Environment? — Ozone Layer And How It Is Getting Depleted
“Ozone is harmful in the wrong place and lifesaving in the right one—location really matters.”
• Distinguish molecular oxygen from ozone. • Explain how ozone forms from oxygen under the action of ultraviolet radiation. • Explain how ozone high in the atmosphere protects organisms from harmful ultraviolet radiation. • Connect chlorofluorocarbons with depletion of atmospheric ozone. • Explain why reducing ozone-depleting chemicals requires coordinated environmental action.
The same element can form substances with very different effects. Ordinary molecular oxygen is essential for aerobic life, while ozone can be poisonous near living organisms. Yet high in the atmosphere ozone performs a life-protecting function by absorbing harmful ultraviolet radiation.
Ozone Layer And How It Is Getting Depleted
Oxygen And Ozone
Molecular oxygen is O₂, meaning each molecule contains two oxygen atoms. Ozone is O₃, meaning each molecule contains three oxygen atoms. Although both contain only oxygen atoms, their properties are different because the atoms are arranged in different molecular forms.
| Substance | Formula | Key Role In This Lesson |
|---|---|---|
| Molecular oxygen | O₂ | Essential for aerobic forms of life |
| Ozone | O₃ | Poisonous near living organisms but protective high in the atmosphere |
Protective Role Of The Ozone Layer
At higher levels of the atmosphere, ozone shields Earth's surface from ultraviolet radiation from the Sun. Excess ultraviolet exposure is highly damaging to organisms and is associated with effects such as skin cancer in humans.
The importance of ozone therefore depends strongly on location. Ozone itself can be harmful near organisms, but an ozone-rich region high in the atmosphere reduces the amount of damaging ultraviolet radiation reaching the surface.
Formation Of Ozone
Ozone forms through a two-stage process driven by high-energy ultraviolet radiation. First, ultraviolet radiation splits some O₂ molecules into free oxygen atoms. Then a free oxygen atom combines with an O₂ molecule to form O₃.
Reading The Ozone Formation Process
The first equation requires energy from ultraviolet radiation. The second uses the reactive free oxygen atom to build ozone. These equations describe the pathway by which ozone is produced in the upper atmosphere.
Ozone Depletion
The amount of ozone in the atmosphere began to decline sharply during the 1980s. This decline was linked to synthetic chemicals called chlorofluorocarbons, or CFCs. Their uses included refrigeration and fire extinguishers.
Chlorofluorocarbons are synthetic chemicals associated with depletion of atmospheric ozone and historically used in applications such as refrigeration and fire extinguishers.
When the ozone layer is damaged, more harmful ultraviolet radiation can reach Earth's surface. Because UV can damage organisms, depletion of ozone is not merely an atmospheric chemistry issue; it is an ecosystem and health concern.
International Action
International action was taken to restrict CFC production and encourage CFC-free refrigeration. The broader scientific lesson is that atmospheric problems cross political boundaries and often require coordinated action.
A Strategy For Ozone Questions
Separate three ideas that are often mixed together. First, distinguish O₂ from O₃. Second, explain ozone formation using the two equations. Third, explain environmental significance: ozone high in the atmosphere absorbs harmful UV, while CFC-related depletion reduces that protection.
Problem
A student says O₂ and O₃ are the same because both contain oxygen. Correct the statement.
- 1.Both substances contain oxygen atoms.
- 2.O₂ has two oxygen atoms per molecule, while O₃ has three.
- 3.Different molecular forms can have different properties.
- 4.O₂ is essential for aerobic life; ozone is harmful near organisms but protective high in the atmosphere.
Problem
Describe the two steps that form ozone.
- 1.High-energy UV acts on O₂.
- 2.An O₂ molecule is split into free oxygen atoms: O₂ → O + O.
- 3.A free oxygen atom combines with another O₂ molecule.
- 4.O + O₂ → O₃.
- 5.The product is ozone.
Problem
Explain why CFC-driven ozone depletion is a concern for ecosystems.
- 1.CFCs are linked with a decrease in atmospheric ozone.
- 2.Ozone high in the atmosphere normally absorbs harmful UV radiation.
- 3.Less ozone means less UV shielding.
- 4.More damaging UV can reach organisms at Earth's surface.
- 5.Therefore ozone depletion can harm living systems.
Quiz
What is the molecular formula of ozone?
What is the first step in ozone formation?
Why is ozone high in the atmosphere important?
Which chemicals are linked with ozone depletion in this lesson?
Which statement resolves the apparent contradiction about ozone?
Practice Problems
- Compare O₂ and O₃ in terms of composition and environmental role.
- Write and explain the two equations involved in ozone formation.
- Explain why a decrease in ozone can increase biological damage even though ozone itself can be poisonous.
- Describe the link between CFC use and concern about ultraviolet radiation reaching Earth's surface.
- A student writes, 'CFCs are dangerous because they are ultraviolet rays.' Correct the statement and explain the actual relationship.
Key Takeaways
• Molecular oxygen is O₂, while ozone is O₃, and the two forms have different properties. • Ozone high in the atmosphere absorbs harmful ultraviolet radiation and protects life at Earth's surface. • Ultraviolet radiation can split O₂ into free oxygen atoms, which then combine with O₂ to form O₃. • CFCs are linked to depletion of the ozone layer. • Damage to the ozone layer is concerning because it allows more harmful ultraviolet radiation to reach organisms. • International controls on ozone-depleting chemicals illustrate the need for coordinated environmental action.