Ozone Layer Depletion

Ozone is a highly reactive gas comprising of three oxygen atoms. Both ozone and oxygen are constantly formed, destroyed, and reformed in the ozone layer as UV light breaks the bonds between atoms, creating free oxygen atoms. Thus, the concentration of ozone fluctuates depending on seasons and latitudes.

The two primary sources of ozone depletion are:

1. Man-made Sources

It is responsible for almost 90% of the total depletion. It occurs mainly due to the excessive release of chlorine and bromine from ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs), halons, carbon tetrachloride (CCl₄), hydrochlorofluorocarbons (HCFCs), and methyl bromide (CH₃Br).

Here is a list of some main ozone-depleting compounds, along with their sources:

2. Natural Sources

Sun-spots and stratospheric winds are the two major natural causes of ozone depletion. Together, they contribute not more than 1-2% of the total depletion of the ozone layer. Their effect is temporary.

Aerosols such as chlorofluorocarbons (CFCs) released from various human-made sources make their way into the stratosphere by destroying the troposphere and the ozone layer. The mechanism is given below:

CFCs are broken up by ultraviolet radiations (UV-A, UV-B, AND UV-C) from the sun releasing chlorine. Once the chlorine is released, it reacts with ozone (O₃) to form chlorine monoxide (ClO) and oxygen (O₂).

Cl + O₃ = ClO + O₂

When a molecule of chlorine monoxide (ClO) meets an oxygen atom, it breaks up, releasing chlorine.

ClO + O = Cl + O₂

The free radical of chlorine again reacts with other ozone molecules. It destroys its structure, thus producing a catalytic cycle of chlorine.

Based on the Environmental Protection Agency (EPA) report, one chlorine atom can destroy more than 100,000 ozone molecules, thus destroying them more quickly than produced naturally. Later it was discovered that bromine and specific bromine-containing molecules such as bromine monoxide were almost 40 times more potent than chlorine at destroying ozone.

Some of the main consequences or impacts of ozone layer depletion on earth are given below:

• Damage to Human Heath: If the ozone layer is completely depleted, humans will get directly exposed to intense UV light from the sun. Overexposure to UV rays is responsible for skin cancer, cataracts, sunburns, immune deficiency disorders, and rapid aging.
• Affecting Growth of Plants: Many crops such as barley, wheat, corn, oats, rice, tomatoes, and cauliflower are vulnerable to intense UV light, causing a reduction in their growth rate, flowering, and photosynthesis.  
• Skin and Eye Cancer in Animals: Like humans, animals exposed to UV light for an extended period can cause skin and eye cancer.
• Threat to Marine Life: The growth of certain marine planktons decreases when exposed to high UV light. Since planktons appear at a higher level of the food chain, the entire marine ecosystem gets disturbed. Also, severe reproductive defects are found in the fishes, thus decreasing their population.
• Causing Chemical Degradation: Man-made chemicals such as plastics, wood, fabrics, and rubber get hugely degraded on exposure to UV light.

In 1987, Montreal Protocol was proposed to stop the production, use, and import of ozone-depleting substances to minimize their concentration in the atmosphere. It was aimed at protecting the atmospheric ozone layer. It was a landmark agreement to phase out all those substances that have been ratified by all 197 United Nations (UN) member countries.

• Some of the crucial ways to prevent ozone layer depletion are listed below:
• Replacing halon-based fire extinguishers with other foam-based forms
• Discouraging to buy refrigerators and air conditioners that use CFCs as a refrigerant
• Servicing old electrical equipment like air conditioners and air coolers reduces the release of chlorofluorocarbons.
• Discouraging the use of cleaning solvents containing CFCs or ammonia and encouraging natural and eco-friendly cleaning products
• Minimizing the use of personal vehicles and using public transport reduces greenhouse gases that deplete the ozone layer.
• Prohibiting the use of air pollutants such as nitrous oxide that decompose ozone into nitrogen dioxide (NO₂) and oxygen gas (O₂)
• Avoid the use of fossil fuels and increasing dependence on renewable sources of energy.

• Ozone layer depletion is the depletion of the stratospheric ozone layer of the earth.
• Artificial sources producing ozone-depleting substances are the leading cause of ozone-depletion
• Its depletion causes an increased UV light to reach the earth’s surface.
• Increased UV light is the reason behind several health problems like skin cancer, cataracts, sunburns, immune deficiency disorders, and aging in humans and animals.
• We should be well aware of the harmful effects and the agents that cause ozone layer depletion and take appropriate measures to reduce and avoid their use.
• We should pledge to preserve nature and make it sustainable to live.