What is the Ozone Layer?
The ozone layer is referred to as a specific region in the Earth’s stratosphere that acts as a shield against the incoming ultraviolet rays of the sun. The ozone layer absorbs around 97-99% of the medium-frequency ultraviolet light emitted by the sun. The ozone layer is composed of 3 atoms of oxygen and is represented as O3. The stratosphere contains large amounts of ozone. Curiously enough, the ultraviolet radiation itself forms the ozone layer. Ozone forms when a radiation or electrical discharge causes the oxygen (O2) molecule to split into two different atoms so that they can individually join with other atoms and form ozone (O3).
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What is the Ozone Layer Depletion?
The ozone layer depletion came to the public eye after the creation of a chemical compound known as chlorofluorocarbons or CFCs (formerly used in refrigerators, aerosols, and air conditioners). CFCs are light and can move up in the air and reach the stratosphere. Here the chlorofluorocarbons react with the ozone layer in the presence of ultraviolet radiation and cause it to break down into oxygen molecules. The result is the depletion of the Ozone Layer. After an International Treaty signed in 1973, the use of CFCs was lowered and subsequently banned. In the 1980s, it was observed that the ozone layer in an area of the Antarctic stratosphere had hit low levels coming at around as low as 33 per cent of pre-1975 levels. This area became known as the Ozone hole.
How is the Ozone Layer Getting Depleted?
One of the major causes of ozone layer depletion is because of the chemical chlorofluorocarbons or CFCs. CFCs are generally composed of carbon, fluorine and chlorine. They are quite durable and can sustain harsh conditions. CFCs generally don’t react but only react with sunlight when it breaks down to release chlorine.
CF2Cl2+ UV light →CF2Cl + Cl
This chlorine reacts with the Ozone layer and forms oxygen and chlorine monoxide. The ozone depletion reactions are:
Cl + O3 → ClO + O2
When chlorine monoxide reacts with another molecule of oxygen, it breaks up again and releases chlorine which can again react with ozone and cause further depletion.
ClO + O → Cl + O2
However, it is not just CFCs that can deplete the ozone layer. Many climatic and natural circumstances can also result in ozone depletion. For example, when the Antarctic hole was spotted, scientists discovered a number of reasons why the ozone hole formed in Antarctica.
In summers, methane and nitrogen dioxide reacts with chlorine atoms and chlorine monoxide. Thus, there is a shrinking of chlorine which sinks down and thus, prevents ozone depletion.
ClO (g) + NO2 (g) → ClONO2 (g)
Cl (g) + CH4 (g) → CH3 (g) + HCl (g)
However, when winter comes, special clouds form over the Antarctic region. These are polar stratospheric clouds and they provide a nice surface for chlorine nitrates to get hydrolysed. After hydrolysis, it forms hypochlorous acid, which reacts with HCl and forms molecular chlorine.
ClONO2(g) + H2O(g) → HOCl (g) + HNO3 (g)
ClONO2(g) + HCl (g) → Cl2 (g) + HNO3 (g)
When in spring, the sun emerges in Antarctica, the sun breaks down these clouds causing the release of chlorine and thus, initiating the ozone depletion process.
HOCl (g) →OH (g) + Cl(g)
Cl2 (g) →2Cl(g)
What are the effects of Ozone Layer Depletion?
Ozone Layer depletion can result in many negative effects on human beings, plant and animal life and the ecology as a whole. Some of the negative impacts of ozone depletion are:
Ozone Layer Depletion Effect on Human Beings
If the ozone layer gets depleted, more UV rays enter the atmosphere. When these UV rays come in contact with the human skin, it can cause malignant skin cancers. It can also cause cataracts. In our body, Vitamin D is synthesized when it reacts with UV rays. Excess vitamin D can also raise blood calcium levels, increasing mortality rates.
Ozone Layer Depletion Effect on Animals
High UV rays have shown that there has been epidermal damage in whales due to the thinning of the ozone layer. More sun damage has been noticed in many aquatic animals due to ozone layer depletion.
Ozone Layer Depletion Effect on Plants
Increased UV rays can affect plant life by damaging them under extreme exposure of UV rays. Plant growth will be affected as well.
1. Can the Ozone Layer Depletion be Prevented?
Ozone layer depletion can be prevented if we take a few precautions like:
Vehicular emissions create smog which can harm the ozone layer. Hence, public transport should be availed or emission-free traveling like walking and cycling should be encouraged.
Avoiding CFCs - Hydrofluorocarbons have replaced CFCs as a safer alternative and so, we should upgrade our refrigerators and air conditioners to eco-friendly substitutes.
Reducing pesticides use: Many pesticides contain harmful chemicals that can react with the ozone layer. We should use more environmentally friendly chemicals.
Waste management: It is important for us to learn proper waste management techniques so that our waste does not produce more contaminants causing air pollution.
2. Does the Ozone Layer Recover itself?
It is possible for the ozone to repair itself. There are many natural processes which can destroy the ozone layer. Similarly, the constant breakdown of oxygen (O2) molecules which then combines with oxygen and forms O3. Hence, there are always creative and destructive processes happening on the ozone layer. However, if we lower the man-made objects that cause ozone depletion, then the ozone layer can slowly repair itself and fill up the ozone hole. A 2015 NASA image shows that the Ozone layer has recovered from the state it was in the year 1998.