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The Ozone Hole

Since the 80’ the scientists have noticed a great reduction of the ozone in a wide area above the Antarctic. This phenomenon called “the ozone hole” which is defined as that geographic area where the total amount of stratospheric ozone is less than 220 Dobson Unit (DU). The DU counts the quantity of stratospheric ozone in a scale which is called total column ozone. Specifically, 100 DU are equal to 1mm of an ozone layer if that was spread above the Earth’s surface (Gentekakis, 2010). It is shown at picture 1, the ozone hole in 1985 and how much was extended after 30 years above the Antarctic.

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 Picture 1.         Ozone hole in October 1985.        Ozone hole in September 2015. “NASA Ozone Watch”

 

The stratospheric ozone is constantly in a balance between the reactions of its creation and its disintegration. The UV radiation, oxygen molecules and oxygen atoms are the main reasons why this balance exists (Eq. 1). The significance of stratospheric ozone is simple. Ozone trammels the UV radiation that enters the Earth’s surface in order to reduce its harmful effects for life. So, the ozone is actually operating like an invisible filter. It absorbs most of the harmful ultraviolet rays of the sun and allows only a portion to reach the earth surface.

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O2 + hv* -> O + O

O + O3 + M*2 -> O3 + M

O3 + hv -> O2 + O (Eq. 1) (Gentekakis, 2010)

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But how the ozone hole was created? It is caused by the Chlorofluorocarbons (CFCs) or Hydro chlorofluorocarbons (HCFCs), which are very stable chemical compounds and they can exist in the troposphere from 10 to 150 years. CFCs were used as propellant gases and refrigeration appliances in air conditioners, for instance. However, the stratosphere can be considered as a ‘keeper’ of the CFCs because, there, they can be photodegraded by the UV radiation, setting free chlorium atoms (Cl). Those atoms disintegrate the ozone, resulting in its reduction. A chlorium atom can disintegrate multiple ozone molecules as it is shown at equation 2.

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CCl3F + hv -> CCl2 + Cl

Cl + O3 -> ClO + O2

ClO + O -> Cl + O2   (Eq.2) (Gentekakis, 2010)

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The ozone is very important as it protects against the sunlight and absorbing a great portion of UV radiation. The creation of the ozone hole has negative effects on both human health -eyes and skin- and on the environment -ecosystems and climate. During the summer, most people enjoy the sun without using sunscreen and they get sunburns (Picture 2). Furthermore, exposure to UV causes inflammation of the cornea and long-term exposure to UV can also lead to cataracts. UV destroys the immune system of the body and makes it less able to fight diseases. People with a damaged immune system will be more prone to skin cancer, parasitic skin infections, herpes, hepatitis and other diseases (Picture 3) (Allen, 2001).

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                                                    Picture 2. Sunburn                

 

 

 

 

 

 

 

                                      

 

                                                    

 

                                                 

 

                                                   Picture 3. Melanoma

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 As for the environment, the lack of ozone can affect the climate and both plants and aquatic organisms. The impact on the climate is dramatic. Elevated temperatures in the lower layers of the atmosphere and on the surface of the earth is caused by the increased quantities of ultraviolet and infrared radiation that are more easily reached on Earth by the hole. This exacerbates the global problem of temperature rise. In addition, as ozone UV absorption produces heat, ozone depletion will cause a significant increase in cold in the upper layers of the atmosphere. Plants may have consequences on their growth rate for instance, those which are growing in shady parts will be less able to tolerate increased exposure to radiation because they do not have great resistant to UV radiation. Aquatic organisms may be, as well, influenced by the high levels of UV. The radiation can hinder the growth and reproduction of phytoplankton, resulting in a steep decline in its population, which will lead to the destruction of the aquatic food chain, since this is the basis for it (Picture 4) (Hader et.al., 2011).

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                                        Picture 4. Aquatic food chain. 

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The ozone holes show the permanent damage of our planet’s atmosphere. Scientists have discovered the existence of another ozone hole above the Artic zone of the planet, which -fortunately- is less intense and there is, also, a significant reduce of ozone concentration above the north eternal land of the earth. However, there are promising results according to the latest records of the ozone hole above the Antarctic, which show that the hole has shrunk. The planet is gradually recovering, as it is illustrated at picture 5, a NASA research program for ozone monitoring (https://www.youtube.com/watch?v=lBu3vltczRw).

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                    Picture 5. Ozone hole from 1979-2012. “NASA Ozone Watch”   

 

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