Ozone Layer

What is the Ozone Layer?

Almost always the ozone has only been correlated with the hole in the ozone layer and the damages it has caused to the environment. The richness of the ozone layer that makes the hole so significant and the science behind the hole is far less popular. Schönbein in the year 1840 confirmed its existence and Jacques-Louis Soret rooted the chemical formula of ozone as O3 and proved that ozone is an allotropic form of Oxygen.

The importance of ozone is defined by the fact that it protects the earth from harmful ultraviolet rays from the sun. The ozone layer is found in the upper regions of the stratosphere where it protects the earth from the harmful ultraviolet rays of the sun. These radiations can cause skin cancer in the humans. The ultraviolet rays split the oxygen molecule into free oxygen atoms, these free oxygen atoms combine with the oxygen molecule to form ozone. This salient layer lies at distance of 12-15 miles beyond the earth surface.

The importance of ozone is defined by the fact that it protects the earth from harmful ultraviolet rays from the sun. The ozone layer is found in the upper regions of the stratosphere where it protects the earth from the harmful ultraviolet rays of the sun. These radiations can cause skin cancer in the humans. The ultraviolet rays split the oxygen molecule into free oxygen atoms, these free oxygen atoms combine with the oxygen molecule to form ozone. This salient layer lies at distance of 12-15 miles beyond the earth surface.

Ozone layer

Ozone Layer Depletion – Ozone Hole

Preparation of ozone

This allotropic form of oxygen is formed by passing dry oxygen through a salient electric current. By doing so a part of the oxygen molecules undergo dissociation and then atomic oxygen gets associated with the oxygen molecule to give 5%-10% of the allotropic form of oxygen. The product obtained is called as ozonized oxygen.

O2   \( \require{AMScd} \begin{CD} @> energy >>\end{CD} \)     O+O

O2+O    →   O3

3O2↔2O3 – energy (endothermic reaction)

Ozone is unstable and decomposes to molecular oxygen. A dynamic equilibrium is maintained between the formation and decomposition of ozone. It has been found that this protective ozone layer is getting depleted because of the presence of CFC (chlorofluorocarbon) compounds.

When CFC is released into the atmosphere, they mix with atmospheric gases and reach the stratosphere. In presence of ultraviolet rays, they are broken down to form chlorine radicals. This chlorine radical reacts with ozone to form chlorine monoxide and oxygen molecule.

CF2Cl2 (g)    \(\require{AMScd} \begin{CD} @>uv>> \end{CD} \)  Cl (g) + CF2Cl (g) (Note: Cl is in the form of radical)

(Note: Cl is in the form of radical)

Cl (g) + O3 (g) → ClO (g) + O2 (g)

This reaction breaks down the ozone. CFC compounds are agents which release chlorine radical in the atmosphere and cause damage to the ozone layer.

Ozone Structure:

Ozone Structure

Ozone 3D Ball Structure

Ozone is a polar molecule and to understand this we need to have a look at the structure of Ozone. Ozone resonates between two structures which are shown below:

Ozone layer

Ozone Structure

The middle Oxygen atom has a formal charge of +1 and the atoms at the edge have a formal charge of -1. Due to the separation of light charges and its bent geometry, it has polarity and is considered a polar molecular.

Properties of ozone:

  • Ozone in its pure state is blue in color which has a strong disturbing smell but in a limited proposition, it has a pleasant smell.
  • It has the ability to absorb the UV rays which occupy the ultraviolet region which ranges between 220-290 nm of the atmospheric spectrum.
  • This form of oxygen boils at 161.2K and forms violet-blue crystals when solidified. It melts at 80.6k.
  • This allotrope is a strong oxidizing agent as ozone is an unstable compound under normal conditions and it decomposes quickly in the presence of heat to form nascent oxygen and molecule of oxygen.

Importance of ozone layer

Ozone is harmful at ground level but high up the atmosphere ozone layer plays a vital role in the protection of all living beings. The sun propagates ultraviolet radiations which as an adverse effect on living beings. This layer absorbs the radiations and prohibits them from entering the outer surface of the earth. The ozone layer resides in the stratospheric layer of the earth’s atmosphere. The layers which occupy the lower part of the atmosphere removes the unwanted pollutants from the earth’s surface.

Ozone layer depletion:

Ozone layer

Ozone layer depletion – Ozone Hole

The reason behind ozone layer depletion is mainly due to the extensive use of ozone-depleting substances (ODS. Some ozone-depleting substances are:

  • Chlorofluorocarbons (CFC): The use of CFC’s is one of the main reasons for the depletion of the layer. They are usually used as a coolant in refrigerators and air conditioners used in cars etc. It is also used as an industrial solvent, foam products and as hospital sterilization equipment.
  • Methyl chloroform: Finds its applications usually in industries for chemical processing etc.
  • Carbon tetrachloride: Normally used as a solvent.

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Practise This Question

Which of the following is the primary reason for the depletion of ozone layer?