6.4 Stratospheric ozoneIB Environmental Systems and Societies HL: Subtopic test

1. 1
   Australia has one of the highest rates of skin cancer in the world. Public health campaigns urge people to cover up, use sunscreen and avoid the midday Sun. Scientists explain that the Sun emits radiation across a range of wavelengths, and that stratospheric ozone absorbs most of the shortest-wavelength ultraviolet (UV) radiation before it reaches the ground.

   (a)

   Why is UV radiation more harmful to living organisms than visible light?

   [1 mark]

   • AIt has a longer wavelength and a lower frequency
   • BIt has a shorter wavelength, a higher frequency and therefore more energy
   • CIt is emitted only by the ozone layer
   • DIt travels faster than visible light

   (b)

   Which pair of effects can be caused by exposure to UV radiation?

   [1 mark]

   • AAnaemia and asthma
   • BRickets and scurvy
   • CHearing loss and arthritis
   • DSunburn and cataracts

   (c)

   Explain how exposure to UV radiation can lead to skin cancer.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Each Antarctic spring (September to October), ozone over Antarctica falls sharply, forming the "ozone hole", and then recovers by December. During the dark polar winter a vortex of very cold air isolates the stratosphere over the pole, and polar stratospheric clouds form. When sunlight returns in spring, chemical reactions on the surfaces of these clouds release reactive chlorine atoms from the breakdown products of chlorofluorocarbons (CFCs), and these chlorine atoms destroy ozone.

   (a)

   Which type of substance released from CFCs destroys stratospheric ozone?

   [1 mark]

   • AHalogens such as chlorine
   • BNoble gases such as argon
   • CNitrogen gas
   • DCarbon dioxide

   (b)

   Why does the Antarctic ozone hole form in spring rather than during the dark winter?

   [1 mark]

   • ACFCs are only released in spring
   • BThe stratosphere warms in spring and destroys ozone
   • CSunlight is needed to drive the reactions that release chlorine atoms from the stratospheric clouds formed in winter
   • DOzone formation stops in spring

   (c)

   (HL) Explain why large ozone losses occur over the poles in spring.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student is given simplified, rounded data on the global production of CFCs: about 1 100 thousand tonnes in 1986, about 400 thousand tonnes in 1996 and close to zero in 2010. The Montreal Protocol was agreed in 1987. CFC molecules can last 50 to 100 years in the atmosphere, and some CFCs remain in old refrigerators, air conditioners and insulating foam.

   (a)

   Calculate the percentage decrease in global CFC production between 1986 and 1996, and suggest why the decrease began after 1987.

   [3 marks]

   (b)

   Explain why the ozone layer is expected to recover only slowly even though production of CFCs has almost stopped.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Hydrofluorocarbons (HFCs) were developed to replace CFCs in refrigerators and air conditioners. HFCs contain no chlorine, so they cause much less ozone depletion, but many are powerful greenhouse gases: HFC-134a has a 100-year global warming potential of about 1 300 times that of carbon dioxide. The 2016 Kigali Amendment to the Montreal Protocol phases down HFCs. Demand for air conditioning is growing quickly in hot countries such as the United Arab Emirates and India. Air conditioners use large amounts of electricity, often generated from fossil fuels, and older units contain ozone-depleting substances (ODSs) or HFCs that can leak.

   (a)

   (HL) Explain how air conditioning contributes to both ozone depletion and climate change, and why replacing CFCs with HFCs only partly solved the problem.

   [6 marks]

   (b)

   (HL) Evaluate strategies for reducing the environmental impact of air conditioning in a hot country such as the United Arab Emirates.

   [6 marks]

   Total for question 4: 12 marks

End of questions