IB ESS HL 6.4 Stratospheric Ozone Questions

Practise IB ESS HL 6.4 by analysing ozone records and evaluating chemical controls, biological effects and international recovery policy.

Exam points

Interpret ozone charts by describing long-term decline, stabilisation and projected recovery against 1980 levels.
Explain how stratospheric ozone absorbs UV, then link depletion to skin, eye and phytoplankton harm.
Identify ODS sources and explain how released halogens catalyse ozone breakdown.
Distinguish ozone depletion from global warming by comparing their gases, mechanisms and effects.
Evaluate Montreal Protocol success using ozone-hole trends, recovery projections and compliance limits.
Evaluate ODS controls and substitutes by weighing ozone benefits against costs and other environmental effects.
Explain why HFC replacements require Kigali controls despite reducing ozone harm.

Covered syllabus points

6.4.1—Solar radiation spectrum 6.4.2—UV radiation danger 6.4.3—Stratospheric ozone protection 6.4.4—UV radiation impacts 6.4.5—Ozone equilibrium 6.4.6—Ozone-depleting substances (ODSs)6.4.7—Ozone depletion effects 6.4.8—Montreal Protocol 6.4.9—Montreal Protocol success 6.4.10 (HL)—ODS mechanisms 6.4.11 (HL)—Polar stratospheric ozone depletion 6.4.12 (HL)—HFCs 6.4.13 (HL)—Air conditioning issues

[Maximum number: 2]

Figure:Tropospheric ozone concentration in Mexico City over time

Outline why a high concentration of ozone in the troposphere is a direct problem for humans, while in the stratosphere it is a benefit to humans.

[Maximum number: 4]

Outline how decreasing stratospheric ozone may impact living organisms.

[Maximum number: 7]

Figure 2: Observed and projected changes in global stratospheric ozone

Figure:Observed and projected changes in global stratospheric ozone

Key:
- Annually averaged data
- Average of atmospheric model projections

(a)

Describe the overall trend shown in the recorded annually averaged data in Figure 2.

[ 2 ]

(b)

State one chemical responsible for the trend in the recorded annually averaged data between 1980 and 1990 shown in Figure 2.

[ 1 ]

halons/CFCs/HCFCs/HBFCs/ $\mathrm{N}_{2} \mathrm{O}$ /methyl bromide/methyl chloroform/carbon tetrachloride/ chlorine/bromine;

Note: do not credit HFCs/ODSs

(c)

Outline one impact of low concentrations of stratospheric ozone on humans.

[ 1 ]

(d)

Identify the year that stratospheric ozone is predicted to return to 1980 levels in Figure 2.

[ 1 ]

(e)

Describe two reasons for the projected change in ozone levels after 2020 in Figure 2.

[ 2 ]

[Maximum number: 1]

Figure:Observed and projected changes in global stratospheric ozone

Key:
- Annually averaged data
- Average of atmospheric model projections

State one chemical responsible for the trend in the recorded annually averaged data between 1980 and 1990 shown in Figure 2.

halons/CFCs/HCFCs/HBFCs/ $\mathrm{N}_{2} \mathrm{O}$ /methyl bromide/methyl chloroform/carbon tetrachloride/ chlorine/bromine;

Note: do not credit HFCs/ODSs

[Maximum number: 3]

Figure:Mean ozone-hole area from 1979 to 2016

(a)

State where the ozone hole referred to in the ozone-hole chart shown above is located.

[ 1 ]

(b)

Describe the changes in mean ozone hole area between 1979 and 2016.

[ 2 ]

[Maximum number: 1]

Identify one method to reduce ozone-depleting substances.

[Maximum number: 9]

The Montreal Protocol on Substances that Deplete the Ozone Layer (1987) is one of the most successful international agreements on a major environmental issue.

Discuss the validity of this statement.

Answers may demonstrate:

Understanding concepts and terminology such as ozone depleting substances (halogenated organic gases/chlorofluorocarbons CFCs); Use in aerosols, gas-blown plastics, pesticides, flame retardants and refrigerants; ozone destruction and reformation and dynamic equilibrium; ozone holes; management strategies, laws, legislation implemented in response to Montreal Protocol; multilateral fund; black market ODS; development of alternatives and their impacts; HFCs; ozone depleting substances not covered by Montreal Protocol (e.g. dichloromethane); other international environmental agreements (e.g. Kyoto protocol/Paris agreement/COP agreements/CITES etc);

Breadth in addressing and linking a range of strategies, laws, legislation implemented in response to Montreal Protocol and their success in reducing ozone depletion; relative success of other international agreements;

Examples national laws and regulations to decrease production and consumption of CFCs; including recycling refrigerants, developing alternatives to CFCs (such as HFCs), gas-blown plastics, halogenated pesticides, propellants and aerosols; examples of illegal markets and continued use; examples of other international environmental agreements;

Balanced Analysis evaluating the extent to which the protocol has been successful in terms of international cooperation; speed and extent of ozone recovery; impacts of alternatives; degree of international cooperation; comparison with other international environmental agreements.

A conclusion that is consistent with and supported by analysis and examples given e.g.: Compared with many of the UN attempts to produce international agreements regarding climate change the Montreal Protocol has been significantly more successful particularly in the extent of international support attained. However, the degree of success in specifically restoring the ozone layer may be limited due to black market sales and impacts of new ODS not covered by the Protocol.

The following guide for using the markbands suggests certain features that may be offered in responses. The five headings coincide with the criteria in each of the markbands (although ESS terminology has been conflated with 'understanding concepts') This guide simply provides some possible inclusions and should not be seen as requisite or comprehensive. It outlines the kind of elements to look for when deciding on the appropriate markband and the specific mark within that band.

Section B, part (c) markbands
0: The response does not reach a standard described by the descriptors below and is not relevant to the question.

1–3: The response contains:
• minimal evidence of knowledge and understanding of ESS issues or concepts
• fragmented knowledge statements poorly linked to the context of the question
• some appropriate use of ESS terminology
• no examples where required, or examples with insufficient explanation/relevance
• superficial analysis that amounts to no more than a list of facts/ideas
• judgments/conclusions that are vague or not supported by evidence/argument.

4–6: The response contains:
• some evidence of sound knowledge and understanding of ESS issues and concepts
• knowledge statements effectively linked to the context of the question
• largely appropriate use of ESS terminology
• some use of relevant examples where required, but with limited explanation
• clear analysis that shows a degree of balance
• some clear judgments/conclusions, supported by limited evidence/arguments.

7–9: The response contains:
• substantial evidence of sound knowledge and understanding of ESS issues and concepts
• a wide breadth of knowledge statements effectively linked with each other, and to the context of the question
• consistently appropriate and precise use of ESS terminology
• effective use of pertinent, well-explained examples, where required, showing some originality
• thorough, well-balanced, insightful analysis
• explicit judgments/conclusions that are well-supported by evidence/arguments and that include some critical reflection.

[Maximum number: 2]

The hole in the ozone layer over Antarctica, discovered in the 1980s, was caused by chlorofluorocarbons (CFCs). The Montreal Protocol requires the use of hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs) instead of CFCs (Figure 3). However, these two gases are also linked to environmental problems (Figure 4).

Figure 3:Comparison of the effects of CFCs, HCFCs and HFCs

Figure 4:HCFCs and HFCs cause less damage than CFCs but still affect the environment

Outline why governments agreed to phase out the use of HFCs from 2019 in the Kigali Amendment to the Montreal Protocol.

All question bank results loaded

Covered syllabus points

Question 1

Question 2

Question 3

Question (a)

Question (b)

Question (c)

Question (d)

Question (e)

Question 4

Question 5

Question (a)

Question (b)

Question 6

Question 7

Question 8