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Ozone layer

Ozone layer

The ozone layer filters the Sun´s harmful UV radiation, therefore it is indispensable for life on Earth.

Geography

Keywords

ozone layer, ozone shield, ozone molecule, ultraviolet radiation, protecting shield, UV-A, UV-C, UV-B, oxygen, oxygen molecule, ozone hole, troposphere, stratosphere, mesosphere, biology, geography, chemistry

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Scenes

Ozone layer

  • troposphere
  • stratosphere
  • mesosphere
  • ozone layer
  • 50–80 km
  • 12–50 km
  • 0–12 km
  • 15–30 km

Ozone is a triatomic molecule, consisting of three oxygen atoms. It is a poisonous gas.

In the presence of water, atmospheric oxygen molecules are split into oxygen atoms by short wave ultraviolet radiation. When oxygen molecules combine with atomic oxygen, ozone is produced.
The troposphere also contains some ozone, but in large quantities it is found at a 15-30 km height, in the ozone layer. The importance of this layer lies in filtering most of the ultraviolet radiation of the Sun that would be deadly for living organisms. It also reflects the Earth´s radiated heat and thus it plays a role in the planet´s heat regulation.

Ozone is split into oxygen molecules and oxygen atoms by long-wave ultraviolet radiation or visible light and with the help of freons (chlorofluorocarbon). When the amount of ozone decreases in the ozone layer, the atmosphere´s ultraviolet-protecting ability is also decreased. This phenomenon is usually referred to as a ´hole´ in the ozone layer.

The density of ozone in the atmosphere varies with time.

Ozone is mostly produced in the ozone layer above the tropical zone. After March it is transported towards higher latitudes. On the northern hemisphere it can reach the North Pole, while in the southern hemisphere it can only get until the 50th-60th latitude – due to the very strong air currents at these latitudes.

After November the density gradually decreases on the southern hemisphere (since it is summer there, radiation increases). The ozone layer can become so thin that the shield protecting the Earth can be broken. However, after March more and more ozone is produced (since the radiation decreases).

Thinning of the ozone layer is a natural process. However, if ozone keeps decomposing due to the accumulation of freon in the atmosphere, the hole will get larger and harder to recover.

The ozone layer, a protecting shield

  • ultraviolet radiation
  • UV-A - Long-wave (400-320 nanometre), relatively low energy ultraviolet radiation. Most of it reaches the Earth´s surface. In large quantities it may cause DNA damage in cells, and be carcinogenic.
  • UV-B - Medium-wavelength (320-280 nanometre) ultraviolet radiation with greater energy than UV-A. Only a small amount of it reaches the Earth´s surface, as it is absorbed by the ozone layer. It facilitates the production of Vitamin D in the human body. In large quantities it is known to cause DNA damage and to be carcinogenic.
  • UV-C - Short-wave (280-100 nanometre), great energy UV radiation. It does not reach the Earth´s surface, as it is absorbed by atmospheric oxygen. Since it severely damages DNA, life could spread from water and evolve on dry land only when the atmosphere became capable of filtering UV-C radiation.
  • ozone layer
  • O₂ -› O₃
  • O₃ -› O₂

UV-C and UV-B absorption

  • oxygen molecule
  • UVC radiation
  • ozone molecule
  • The oxygen molecule breaks down.
  • The oxygen atom unites with the oxygen molecule to form ozone.
  • UVB radiation
  • The ozone molecule breaks down.
  • The oxygen atom and the ozone molecule convert into oxygen molecules.

Ozone depletion

Animation

  • ozone layer
  • 15–30 km
  • UV-A - Long-wave (400-320 nanometre), relatively low energy ultraviolet radiation. Most of it reaches the Earth´s surface. In large quantities it may cause DNA damage in cells, and be carcinogenic.
  • UV-B - Medium-wavelength (320-280 nanometre) ultraviolet radiation with greater energy than UV-A. Only a small amount of it reaches the Earth´s surface, as it is absorbed by the ozone layer. It facilitates the production of Vitamin D in the human body. In large quantities it is known to cause DNA damage and to be carcinogenic.
  • UV-C - Short-wave (280-100 nanometre), great energy UV radiation. It does not reach the Earth´s surface, as it is absorbed by atmospheric oxygen. Since it severely damages DNA, life could spread from water and evolve on dry land only when the atmosphere became capable of filtering UV-C radiation.
  • oxygen molecule
  • UVC radiation
  • ozone molecule
  • The oxygen molecule breaks down.
  • The oxygen atom unites with the oxygen molecule to form ozone.
  • UVB radiation
  • The ozone molecule breaks down.
  • The oxygen atom and the ozone molecule convert into oxygen molecules.

Narration

The ozone layer is found at an altitude of 15 to 30 km above the Earth´s surface. Its thickness varies.

It is the protective shield around our planet; its function is to absorb the Sun´s harmful ultraviolet (UV-C) radiation. This radiation damages the epidermis or skin of living organisms, as well as the DNA. Without the ozone layer, there would be no life on Earth. In general, a natural dynamic equilibrium exists between the processes of formation and decomposition of ozone.

The diatomic oxygen content of the atmosphere breaks down due to the high-energy UV-C radiation; the resulting atoms then bind to oxygen molecules, thus forming triatomic ozone molecules. These are unstable molecules which break down due to ultraviolet radiation.

For a number of decades, the equilibrium has been disrupted by human activities. It is mainly due to industrial processes that harmful materials, such as chlorine, fluorine and bromine, have been released into the atmosphere, and these have caused the ozone layer to become thinner. The term ´Ozone hole´ does not actually mean that the ozone layer is completely broken, just that it has become much thinner.
The largest Ozone hole is located over Antarctica; here the thickness of the ozone layer is about one third of the original. There is also a significant thinning over the North Pole.

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