6.4 Stratospheric ozone

Guiding questions

How does the ozone layer maintain equilibrium?
How does human activity change this equilibrium?

Click here for a set of vocabulary flashcards covering all SL and HL content in topic 6.4.

Click here for flashcards that address only the SL content.

SL and HL knowledge statements

6.4.1 The Sun emits electromagnetic radiation in a range of wavelengths, from low frequency radio waves to high frequency gamma radiation.

6.4.2 Shorter wavelengths of radiation (namely, UV radiation) have higher frequencies and, therefore, more energy, so pose an increased danger to life.

6.4.3 Stratospheric ozone absorbs UV radiation from the Sun, reducing the amount that reaches the Earth’s surface and, therefore, protecting living organisms from its harmful effects.

6.4.4 UV radiation reduces photosynthesis in phytoplankton and damages DNA by causing mutations and cancer. In humans, it causes sunburn, premature ageing of the skin and cataracts.

6.4.5 The relative concentration of ozone molecules has stayed constant over long periods of time due to a steady state of equilibrium between the concurrent processes of ozone formation and destruction.

6.4.6 Ozone-depleting substances (ODSs) destroy ozone molecules, augmenting the natural ozone breakdown process.

This video explains the science behind ODSs’ destruction of stratospheric ozone.

6.4.7 Ozone depletion allows increasing amounts of UVB radiation to reach the Earth’s surface, which impacts ecosystems and human health.

6.4.8 The Montreal Protocol is an international treaty that regulates the production, trade and use of chlorofluorocarbons (CFCs) and other ODSs. It is regarded as the most successful example yet of international cooperation in management and intervention to resolve a significant environmental issue.

6.4.9 Actions taken in response to the Montreal Protocol have prevented the planetary boundary for stratospheric ozone depletion being crossed.

I’ve included this brief video about the Montreal Protocol even though it’s almost ten years old simply because SIR DAVID ATTENBOROUGH!

This short video summarizes what happened with the seasonal hole in the stratospheric ozone layer as a result of the Montreal Protocol.

Knowledge statements for HL only

6.4.10 ODSs release halogens, such as chlorine and fluorine, into the stratosphere, which break down ozone.

6.4.11 Polar stratospheric ozone depletion occurs in the spring due to the unique chemical and atmospheric conditions in the polar stratosphere.

6.4.12 Hydrofluorocarbons (HFCs) were developed to replace CFCs as they can be used in similar ways and cause much less ozone depletion, but they are potent GHGs. They have since been controlled by the Kigali Amendment to the Montreal Protocol.

6.4.13 Air conditioning units are energy-intensive, contribute to GHG emissions and traditionally have contained ODSs.

Practical activities

6.4.13a Application of skills: Review the alternatives to air conditioning units.
6.4.13b Application of skills: Use databases to collect data on the use of air conditioning units in different societies and present this data graphically, considering the reasons for the differences per capita.
Add from existing PSOW booklet.

Possible engagement opportunities

Turn these into CAS suggestions connected to the UN SDGs.

Discuss the extent to which the Montreal Protocol sets a precedent for how environmental issues can be addressed at a global scale.
Present findings on alternatives to air conditioning to the school leadership.

Happy learning!