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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.

Syllabus
First assessment 2026
Course
ESS HL
Level
HL

Exam points

  • Analyse recorded and projected ozone data, including decline, stabilisation and recovery.
  • Evaluate how ozone-depleting chemicals increase surface UVB and biological risk.
  • Evaluate Montreal Protocol success through phase-out, delayed response and recovery evidence.
  • Explain why HFC climate impacts led the Kigali Amendment to require an equitable phase-out.

Covered syllabus points

6.4.1—Solar radiation spectrum6.4.2—UV radiation danger6.4.3—Stratospheric ozone protection6.4.4—UV radiation impacts6.4.5—Ozone equilibrium6.4.6—Ozone-depleting substances (ODSs)6.4.7—Ozone depletion effects6.4.8—Montreal Protocol6.4.9—Montreal Protocol success6.4.10 (HL)—ODS mechanisms6.4.11 (HL)—Polar stratospheric ozone depletion6.4.12 (HL)—HFCs6.4.13 (HL)—Air conditioning issues

Question 1

[Maximum number: 2]
Tropospheric ozone concentration in Mexico City over time

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.

Question 2

[Maximum number: 4]

Outline how decreasing stratospheric ozone may impact living organisms.

Question 3

[Maximum number: 7]
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

Question (a)

(a)

Describe the overall trend shown in the recorded annually averaged data in the stratospheric-ozone chart shown above.

[ 2 ]

Question (b)

(b)

State one chemical responsible for the trend in the recorded annually averaged data between 1980 and 1990 shown in the stratospheric-ozone chart shown above.

[ 1 ]

Question (c)

(c)

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

[ 1 ]

Question (d)

(d)

Identify the year that stratospheric ozone is predicted to return to 1980 levels in the stratospheric-ozone chart shown above.

[ 1 ]

Question (e)

(e)

Describe two reasons for the projected change in ozone levels after 2020 in the stratospheric-ozone chart shown above.

[ 2 ]
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