AP Environmental Science 9.1: Stratospheric Ozone
Practice AP Environmental Science questions on stratospheric ozone, UV radiation, CFCs, ozone depletion, skin cancer, and cataracts.
- Syllabus
- Effective Fall 2025
- Course
- AP Environmental Science
Exam points
- explain how stratospheric ozone absorbs UV radiation and protects life from skin cancer and cataracts
- describe how CFCs and polar atmospheric processes can contribute to stratospheric ozone depletion
Covered syllabus points
9.1 Stratospheric Ozone Depletion question 1
[Maximum number: 7]
Ozone (O3) is an atmospheric trace gas that occurs naturally in the stratosphere. It is also formed as a consequence of human activity in the troposphere, immediately above Earth's surface. The location of ozone in the atmosphere determines whether the gas protects or damages the environment.
Question (a)
(a)
Identify the type of solar radiation that is absorbed by stratospheric ozone, and describe one human health benefit that results from the absorption of this solar energy.
[ 2 ]
and describe one human health benefit that results from the absorption of this solar energy.
(2 points: 1 point for identifying ultraviolet (UV, UV-B, or UV-C) radiation as the type absorbed by stratospheric ozone and 1 point for a correct description of a health benefit resulting from the absorption of UV radiation in the stratosphere; only the first type of solar radiation and health effect can earn points)
The following are acceptable human health benefits resulting from the absorption of UV radiation in the stratosphere:
- Low rates of skin cancer (e.g., basal cell carcinoma, squamous cell carcinoma, melanoma)
- Low rates of sunburns
- Low rates of eye damage (e.g., cataracts)
Question (b)
(b)
The absorption of solar energy by stratospheric ozone causes ozone molecules to undergo chemical decomposition and formation. Describe the chemical processes that lead to this natural balance between decomposition and formation of stratospheric ozone (you may use chemical equations in your answer).
[ 2 ]
(2 points: 1 point for a correct description of the chemical decomposition of stratospheric ozone and 1 point for a correct description of the formation of stratospheric ozone)
Correct descriptions of the chemical decomposition of stratospheric ozone include one of the following:
- Ozone absorbs UV radiation, producing an oxygen molecule and an oxygen atom
- Ozone molecules absorb UV radiation, producing oxygen molecules
- \(\mathrm{O}_{3}+\mathrm{UV} \rightarrow \mathrm{O}_{2}+\mathrm{O}\)
- \(2 \mathrm{O}_{3}+\mathrm{UV} \rightarrow 3 \mathrm{O}_{2}\)
Correct descriptions of the chemical formation of stratospheric ozone include one of the following:
- An oxygen molecule reacts with an oxygen atom to form ozone
- Oxygen molecules absorb UV radiation, forming ozone molecules
- \(\mathrm{O}_{2}+\mathrm{O} \rightarrow \mathrm{O}_{3}\)
- \(3 \mathrm{O}_{2}+\mathrm{UV} \rightarrow 2 \mathrm{O}_{3}\)
OR:
The chemical decomposition and formation of stratospheric ozone may be described together:
- Ozone absorbs UV radiation producing an oxygen molecule and an oxygen atom, which then react to form ozone
- \(\mathrm{O}_{3}+\mathrm{UV} \rightarrow \mathrm{O}_{2}+\mathrm{O} \rightarrow \mathrm{O}_{3}\)
(Note: This combined explanation earns both points.)
Question (c)
(c)
The Montreal Protocol of 1987 provided a global framework to phase out chlorofluorocarbon (CFC) production and use. Although the Montreal Protocol has led to a dramatic decrease in CFCs released into the atmosphere, stratospheric ozone destruction has decreased only slightly.
Explain the process by which CFC lead to the destruction of stratospheric ozone. (You may use chemical equations in your answer.)
Explain why the rapid decrease in CFC emissions has not led to a similarly rapid decrease in the destruction of stratospheric ozone.
[ 3 ]
The Montreal Protocol of 1987 provided a global framework to phase out chlorofluorocarbon (CFC) production and use. Although the Montreal Protocol has led to a dramatic decrease in CFCs released into the atmosphere, stratospheric ozone destruction has decreased only slightly.
Explain the process by which CFCs lead to the destruction of stratospheric ozone. (You may use chemical equations in your answer.)
(2 points: 1 point for a correct description of the decomposition of CFCs and 1 point for a correct description of the reaction of ozone with chlorine)
Correct descriptions of the decomposition of CFCs include one of the following:
- Absorption of UV radiation by CFC molecules releases chlorine atoms
- \(\mathrm{CCl}_{3} \mathrm{~F}+\mathrm{UV} \rightarrow \mathrm{CCl}_{2} \mathrm{~F}+\mathrm{Cl}\)
Correct descriptions of the destruction of stratospheric ozone include one of the following:
- Chlorine atoms break down ozone molecules
- \(\mathrm{Cl}+\mathrm{O}_{3} \rightarrow \mathrm{ClO}+\mathrm{O}_{2}\)
Explain why the rapid decrease in CFC emissions has not led to a similarly rapid decrease in the destruction of stratospheric ozone.
(1 point can be earned for a correct explanation linking the absence of a rapid decrease in the destruction of stratospheric ozone with one of the following):
- The slow migration of CFCs into the stratosphere.
- The long lifetime of CFCs and/or chlorine in the stratosphere.
- The continued release of other ozone-depleting substances.
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