WORKSHEET 7

Activity - The Ups and Downs of Ozone

A balloon-borne sonde measures ozone as it climbs through the atmosphere to about 35km.

1. Draw a graph of ozone reading versus year from Table 1 in the space provided below (with ozone reading on the vertical axis and year on the horizontal axis).
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
2. Draw a graph of ozone reading versus month for each year from Table 2 in the space provided below(with ozone reading on the vertical axis and month on the horizontal axis). Use a different colour for each year.

1. What does your first graph tell you about what has happened to the thickness of the ozone layer during the period 1956 to 1996?
   
   
   
   
   
   
   
   
   
2. From your second graph, what changes do you observe in recent years (1992 and 1996) compared with 1957 and 1967?
   
   
   
   
   
   
   
   
   
   
   
3. What does the graph tell you about the timing each year of the Antarctic ozone hole?
   
   
   
   
   
   
   
   
   
   
4. Explain in your own words how CFCs damage the ozone layer.
   
   
   
   
   
   
   
   
   
   
   
   
5. List some of the things we could do to decrease the damage to the ozone layer.
   
   
   
   
   
   
   
   
   
   
   
   
6. Why is the ozone layer important to our health?
   
   
   
   
   
   
   
   
   
   

Since the late 1970s, the ozone layer has been damaged. This means that more of the sun's harmful UV radiation is able to reach the earth's surface. This radiation can cause sunburn, skin cancer and eye diseases. Go to the following link for more information about UV radiation.

Damage to the ozone layer is caused by CFCs (chlorofluorocarbons), that in the past were used as refrigerants, in spray cans, in the plastics industry and for cleaning electronic circuit boards. Halons, used as fire extinguishing chemicals, also destroy ozone.

Ozone depletion occurs over much of the planet. The depletion over Antarctica (the Antarctic Ozone Hole) peaks in spring, when sunlight activates chemical reactions in which chlorine released from the CFCs rapidly destroys ozone molecules. These reactions happen on ice crystals in the very cold, high-altitude clouds above Antarctica.

See this animated model to understand how ozone is destroyed by CFCs

Fact file

Ozone is a pale blue gas irritating to the nose and throat; it is explosive and toxic. It is produced and destroyed naturally in the atmosphere and until recently, this resulted in a nicely balanced equilibrium. It is formed when oxygen molecules absorb ultraviolet radiation with wavelengths less than 240 nanometres and is destroyed when it absorbs ultraviolet radiation with wavelengths greater than 290 nanometres.

The thickness of the ozone layer is measured in Dobson units. Divide the reading of stratospheric ozone in Dobson Units by 100 and you have the thickness in millimetres of a layer of pure ozone gas at ground level formed from all the ozone in the stratosphere at the time. For example, in August 1996, the ozone that made up the ozone layer if brought down to the ground, would form a layer of pure ozone gas just 1.72 millimetres thick if evenly spread around the world.

Further information may be found at the following link: Ozone information.

This activity is courtesy of
the Cooperative Research Centre for Southern Hemisphere Meteorology