Ozone is a molecule that occurs naturally; it is a colourless gas and has a very harsh odour. The molecule is composed of three atoms of oxygen, and its chemical formula of ozone is O₃. It occurs less commonly than oxygen. Out of say 10 million molecules of air, nearly 2 million would be that of normal oxygen, however, ozone would make up for only 3.

The accumulation of oxygen in the atmosphere resulted in the formation of the ozone layer in the upper atmosphere or the stratosphere. The layer of ozone filters the incoming rays in the cell-damaging UV part of the spectrum. Thereby, the development of the ozone layer comes from the formation of more advanced forms of life.

In 1913, Charles Fabry and Henri Buisson, two French Physicists discovered the ozone layer.

Table of Contents

• Ozone layer Definition
• How is Ozone created?
• Where is the ozone layer located?
• Ozone layer Hole
• Ozone layer Depletion
• Ozone layer Depletion – Causes
• Ozone layer Depletion – Effects
• Ozone layer Recovery – Ozone layer Healing
• Montreal Protocol

Ozone layer Definition – What is the Ozone layer?

The ozone layer is a thin blanket around the atmosphere of the Earth that protects and absorbs the harmful ultraviolet rays arriving from the sun.

Relative to the other components of the atmosphere, there is a high concentration of ozone (O3) in this layer. The layer of ozone comprises less than 10 parts per million of ozone, whereas the average concentration of ozone in the atmosphere, on the whole, is close to 0.3 parts per million.

How is Ozone created?

In the stratosphere of the Earth, the ozone is generated when ultraviolet light strikes oxygen molecules having two atoms of oxygen (O₂). This causes them to split into independent oxygen atoms. Then the atomic oxygen unites with that of the O₂ that is not broken for the creation of ozone (O₃).

These ozone molecules are unstable, when they are hit by the UV light, splitting O₂ molecule occurs generating individual oxygen atoms. It is a continuous process referred to as the ozone-oxygen cycle.

The chemical reaction is as expressed below –

O + O₂ O₃

The concentrations of ozone are the highest in the 20 – 40 km region, wherein it can range from 2 to 8 parts per million.

Where is the ozone layer located?

This layer is a commonly used term for a high concentration of the ozone seen in the stratosphere, approximately 15-30 km above the surface of the earth. Mainly, the layer is seen in the lower part of the stratosphere. Having said that, the thickness of the layer geographically and seasonally varies. The layer covers Earth and shields the life that sustains on Earth. It does so by absorbing the harmful UV-B (Ultraviolet-B) rays from the sun.

Close to 90% of the ozone of the atmosphere is seen in the stratosphere, which extends from 10 to 18 km to about 50 km over the surface of the earth. The temperature of the atmosphere in the stratosphere increases as we go higher. This process is generated by the absorption of solar rays by this ozone layer. The ozone layer is effective in blocking almost all the solar rays from reaching the surface of the Earth having a wavelength less than 290 nm. This is inclusive of ultraviolet (UV) and other radiation that can possibly threaten life on Earth.

The layer absorbs 97-99% of the medium frequency UV light from the Sun in the wavelength range 200 nm – 315 nm.

Ozone layer hole

In the 1970s, Frank Sherwood Rowland and Mario Molina, two chemists, found an association between the disintegration of ozone in the stratosphere and the CFCs (chlorofluorocarbons).

The chemicals comprising bromine and chlorine atoms are given out to the atmosphere as a result of a range of human activities. These chemicals integrate with some weather conditions causing reactions to occur in the ozone layer, thus the ozone molecules are destroyed.

This depletion of the ozone layer is a global phenomenon. Particularly, the acute depletion of the ozone layer above the Antarctic is usually called the ozone hole. In recent times, the increased depletion of the ozone has begun to occur over the Arctic too.

Ozone layer depletion

The depletion of the ozone layer corresponds to the eventual thinning of the ozone layer of the Earth in the upper atmosphere as a result of the release of the chemical compounds comprising gaseous bromine or chlorine from different sources and activities. This thinning is mostly evident in the polar areas, particularly over Antarctica.

When environmental issues are discussed, the depletion of ozone is the main concern, as it tends to increase the amount of UV rays reaching the surface of the Earth. This raises the rate of eye cataracts, skin cancer and other immune system and genetic related damage to the system.

In 1987, the approved Montreal Protocol was one of the main agreements, which were enacted to stop the production of the chemical that potentially depleted the ozone layer. With continued global cooperation on the issue, the layer is on the road to recovery.

Ozone layer depletion – Causes

Whenever there is a natural imbalance between the production and destruction of the stratospheric ozone, ozone depletion starts occurring. Even though the natural processes can temporarily lead to ozone loss, the bromine and chlorine liberated by man-made compounds such as the CFCs are now being considered as the primary reason for the depletion. In 1974, it was first indicated that the man-made groups of compounds called the CFCs (Chlorofluorocarbons) were probably the main reason for ozone depletion.

CFCs (Chlorofluorocarbons)

The CFCs are non-flammable, non-toxic and non-carcinogenic in nature. They comprise fluorine, chlorine and carbon atoms.

The important CFCs are –

• CFC-11 (trichlorofluoromethane – CFCl3)
• CFC-12 (dichloro-difluoromethane – CF2Cl2)
• CFC-113 (trichloro-trifluoroethane – C2F3Cl3)
• CFC-114 (dichloro-tetrfluoroethane – C2F4Cl2)
• CFC-115 (chloropentafluoroethane – C2F5Cl)

CFCs find applications as coolants in air conditioners and refrigeration, production of foam, solvents in cleaners, propellants in aerosols. The man-made CFCs are the primary cause for the depletion of the stratospheric ozone.

Launching Rockets

Rocket launches globally may need some firm regulations to avert notable damage caused to the stratospheric ozone layer of the Earth in the coming times, as per recent research. The upcoming ozone loss from uncontrolled launches can gradually increase the loss as a result of the CFCs. Reactive trace-gas molecules referred to as radicals can dominate the ozone destruction in the stratosphere; one radical in the stratosphere can destroy close to 10,000 molecules of ozone before it is deactivated and eliminated from the stratosphere.

Ozone layer Depletion Effects

Effect of Ozone layer depletion on Human and Animal Health

The growing and continuous perforation of the UV-B rays from the sun is most likely to have an acute impact on the health of life on Earth and potential risks of skin cancer, eye diseases and related infectious diseases.

The harmful UV rays are known to damage the lens and cornea of the eye. Persistent exposure to the UV-B can result in cataracts of the cortical and posterior subcapsular form.

Further, the UV-B rays can have an adverse effect on the immune system, leading to several infectious diseases. There is a likelihood in the light-skinned human population to develop NMSC (nonmelanoma skin cancer). Research conducted on animals indicates that UV exposure reduces the immune response to skin cancers, antigens and infectious agents.

Effect of Ozone layer depletion on Aquatic Life

Increased exposure to UV rays can have a severe impact on the productivity of the aquatic ecosystem, given more than 30% of the animal protein for the world for human consumption is derived from the sea exclusively. Increased exposure in the subtropics and tropics can have an influence on the distribution of the phytoplankton that is known to form the base of the aquatic food webs.

Further, UV-B can damage the initial stage of development of aquatic entities such as crab, shrimp and other such entities. The adverse effects on aquatic entities would be undermined larval development and reduced reproductive capacity.

Effect of Ozone layer depletion on Terrestrial plants

UV-B rays are known to have an effect on the developmental and physiological processes of plants. As per experts, an increase in the UV-B levels can require the use of more UV-B tolerant cultivators and thus producing new tolerants in agriculture.

In grasslands and forests, the increased UV-B rays can lead to changes in the composition of species, hence changing the biodiversity across ecosystems. Additionally, UV-B can affect the community of plants indirectly, leading to alterations to the form of plants and more changes. The changes are said to have significant inferences for plant pathogens, competitive balance and biogeochemical cycles.

Effect of Ozone layer depletion on Climate change

Climate change and ozone depletion are interlinked in more ways than one. However, ozone depletion does not constitute the main reason for climate change. The atmospheric zone absorbs the solar UV rays that warm up the stratosphere. Additionally, it absorbs the infrared rays that are emitted by the surface of Earth, thus trapping heat effectively in the troposphere. Consequently, the climate affects the changes in the concentrations of ozone with the altitude at which the ozone change takes place.

The main ozone loss that has been studied in the lower stratosphere is a result of human-produced bromine and chlorine-containing gasses.

The ozone increases on the other hand, which are evaluated to have taken place in the troposphere as a result of surface-pollution gasses having a warming effect on the surface of the Earth. This contributes to the greenhouse effect.

Ozone layer Recovery – Ozone layer Healing

The depletion of the ozone as a result of different human-generated activities produced bromine and chlorine compounds that are eventually expected to vanish by the mid 21st century; the compounds slowly are being eliminated from the stratosphere by natural phenomenon.

This accomplishment is courtesy of the milestone international accord of controlling the production and the use of ozone-depleting substances. In order to achieve the predicted recovery, complete compliance is vital.

In the absence of the Montreal Protocol and related Amendments, the sustained use of the CFCs (chlorofluorocarbons) and the other ozone-depleting substances would increase the quantity of stratospheric bromine and chlorine by folds in the mid-2050s in comparison to that of the 1980s. These abundances of the substances could cause large losses of the ozone.

In the present scenario, with the ongoing international project aiming at reducing the human-caused emissions of the ozone-depleting gasses, the total troposphere concentrations of the bromine and chlorine-containing compounds began to reduce in 1995.

With all other factors becoming constant, the ozone layer can be expected to revert to normalcy in the middle of the next century, as per reports.

Montreal Protocol

The Montreal Protocol is an international agreement or treaty which was adopted on 16th September 1987 in Montreal. The main objective of it was the regulation of the production and use of chemicals which contributed towards the depletion of the ozone layer of the Earth. At the start, around 46 countries had signed it, which then went on to be signed by close to 200 signatories.

Courtesy of the agreement, it was observed that the ozone hole in Antarctica gradually was recovering. As per some climate projections, the ozone layer shall revert to what it was in the 1980s anywhere by 2050-2070.

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Read more:

• Why Is The Ozone Layer Important For The Existence Of Life On Earth?
• What Are The 2 Types Of Ozone?
• What If Earth Had No Ozone Layer?
• Where Is Bad Ozone Found?