The Ozone Layer
1.
The Earth is surrounded by layers of gases that help to protect
it from space. These layers of gases make up the Earth’s atmosphere.
The second layer of the Earth’s atmosphere is called the stratosphere.
It contains the ozone layer, which helps to protect the Earth from
ultraviolet (UV) radiation from the sun. This protection is important for
humans because ultraviolet radiation can cause skin cancer and other
serious health problems.
Questions:
1. In which layer of the atmosphere ozon can be found?
2. What is the function of ozone?
3. For several decades, scientists and environmentalists have been worried about damage to
the ozone layer. Measurements of the amount of ozone in the stratosphere have been
taken over this period and have produced some disturbing results. For example, average
levels of ozone in the stratosphere were 5% lower in the mid 1990s than in 1970. In
addition, scientists have found much higher levels of ozone destruction at the North Pole
and particularly at the South Pole. British Antarctic Survey (BAS) scientists Joseph Farman,
Brian Gardiner and Jonathan Shanklin found that ozone levels fall by more than 50% in the
Antarctic spring (September to November). Scientists call this loss of ozone the ‘ozone hole’.
Questions:
1. What does 5% refer to?
2. What are the 2 places with the largest damage of ozon layer?
4. Research into the ozone problem has produced several important findings. In 1969, Paul
Crutzen, a Dutch chemist, published an article about ozone. He was interested in finding out
which chemicals react with ozone to cause its destruction or to stop its creation. His
experiments suggested that nitrogen compounds (mixtures of chemicals containing
nitrogen) may be harmful to ozone.
Questions:
1. What happened in 1969?
2. What nitrogen compouns?
5. In 1974, two American chemists, Mario Molina and Sherwood Rowland, from the University
of California at Irvine suggested that another chemical, chlorine, may damage ozone.
Specifically, they argued that chlorofluorocarbons (CFCs), mixtures of chlorine, fluorine and
carbon, lead to the destruction of ozone. CFCs can be released into the atmosphere by
appliances such as refrigerators and air conditioners. Molina and Rowland’s research
suggested that the chlorine from the CFCs reacts with ozone and destroys it.
Questions:
1. Where is Mario Molina from?
2. What are CFCs?
6. Further research by Crutzen and by Molina and Rowland supported the arguments about the
effect of CFCs. In addition, these researchers found another chemical, bromine, has a
harmful effect on ozone. Bromine is also a product of human activity, particularly of certain
industrial processes. Because of the importance of these research findings, Crutzen, Molina
and Rowland received the Nobel Prize for Chemistry in 1995.
Questions:
1. What is another chamical harmful to ozon layere?
2. What happened in 1995?
7. Scientists and environmentalists brought these problems to the attention of governments.
As a result, it became clear that there was a need for international action. It seemed that
human activity was causing the destruction of the ozone layer. On the one hand, appliances
such as refrigerators and air conditioners, and even aerosol cans, were producing CFCs. On
the other hand, some industrial processes were producing bromine and nitrogen
compounds. Consequently, in 1987, governments from around the world agreed to start
dealing with the problems. This agreement, the Montreal Protocol, included targets for the
reduction of CFC emissions and changes to harmful industrial processes. Since 1987, the
governments have reviewed and updated the Montreal Protocol several times.
Questions:
1. What appliances produce CFCs?
2. What is Montreal Protocol?
8. Despite the progress of governments and scientists, there were still many questions to
answer about ozone. For example, scientists did not know why the ‘ozone hole’ appeared
over the Antarctic during springtime. Was it the result of human activity? Research by the
National Aeronautics and Space Administration (NASA) has helped to answer this question.
During the Antarctic winter, there is little movement of air above the South Pole. Because
there is no sunlight, the air becomes very cold. These conditions lead to the formation of
polar stratospheric clouds (PSCs). When sunlight returns in the springtime, it causes
chemical reactions in the PSCs. These reactions lead to the release of chlorine and bromine
from the PSCs. It is this chlorine and bromine that destroys large amounts of ozone.
Therefore, the ‘ozone hole’ appears naturally and not as a result of human activity. When
the Antarctic summer arrives, the PSCs disappear and new ozone forms. As a result, the
‘ozone hole’ disappears.
Questions:
1. What is formed over the South Pole during Antarctic winter?
2. What two chemicals destroy ozone layer in spring?
9. Nevertheless, the role of human activity in the reduction of overall ozone levels around the
world is still important. Therefore, the Montreal Protocol is still an essential tool. Research
has shown that changes in technology have helped to reduce CFC, bromine and nitrogen
compound emissions over recent years. As a result, levels of these harmful chemicals in the
stratosphere are not rising. Most scientists therefore expect ozone levels to stop falling.
Although it will probably take several decades, this process should eventually lead to the
recovery of ozone levels in the stratosphere.
Questions:
1. What helped to reduce the levels of CFC?
2. How long would it take for ozone layers to stop falling?
10. Unfortunately, however, solving one scientific problem can often lead to the creation of a
new one. Ozone is a greenhouse gas. Therefore, as levels of ozone have fallen over the past
few decades, scientists think these falls have tended to reduce the amount of global
warming. In other words, global warming would be worse if ozone levels had not gone
down over the past few decades. If ozone levels recover over the next few decades,
scientists think this could make global warming worse. There is clearly plenty of research for
scientists to do.
Questions:
1. True or False?
Scientists think that when levels of ozone go down, the amount of global warming goes
down as well.
If ozone levels go up again, it might reduce global warming.
Adapted from Encyclopaedia Britannica (846 words, FK = 10.7)