
International day for the preservation of the Ozone layer is celebrated on September 16 as proclaimed by the United Nations General Assembly to commemorate the date of signing of the Montreal Protocol on substances that deplete the ozone layer in 1987. The Montreal Protocol is a global agreement to preserve the ozone layer in the stratosphere by phasing out the production and consumption of ozone-depleting substances (ODS).
The Ozone layer or Ozone shield is located in the stratosphere between 15 km and 30 km above the Earth’s surface. It has a high concentration of ozone in relative to the other parts of the atmosphere. The Ozone layer blocks the entrance of harmful UV radiations from the Sun and protects the living beings on Earth. In particular, ozone layer protects living organisms on Earth from UV-B radiations. Long-term exposure to high levels of UV-B threatens the health of humans and damage other living organisms. Therefore, Ozone layer is vital for preserving life on Earth.
Ozone absorbs UV-B radiations and gives oxygen molecule and separate oxygen atom. Later, they can reform the ozone molecule. Ozone is being formed and destroyed all the time. There is a balance between the natural processes of ozone production and destruction and this balance maintains a consistent ozone concentration in the stratosphere. When UV-C radiations emitted from the Sun reach the Stratosphere,it will be completely absorbed by oxygen molecules. UV-C splits oxygen molecules into oxygen atoms and these oxygen atoms then react with other oxygen molecules to produce ozone. So, these reactions increase the amount of ozone in the stratosphere. Gases such as nitrogen and hydrogen in the stratosphere participate in reaction cycles that destroy ozone converting it back into oxygen. So, these reactions decrease the amount of ozone in the stratosphere. Human activities disturb the natural balance of the ozone producing and destroying reactions which lead to ozone depletion.

Halogen source gases which are prominent Ozone depleting gases, are released to the atmosphere by certain industrial processes and consumer products. These gases bring chlorine and bromine to the stratosphere, which cause depletion of the ozone layer. For example, chlorofluorocarbons (CFCs), once used in almost all refrigeration and air conditioning systems break apart to release ozone-depleting chlorine atoms. Other examples of human-produced ozone-depleting gases are the “halons,” which are used in fire extinguishers contain ozone-depleting bromine atoms. Chlorofluorocarbon (CFC), carbon tetrachloride (CCl4) and methyl chloroform (CH3CCl3) are prominent chlorine containing gases that are emitted by human activities and destroy stratospheric ozone. The most prominent bromine containing halogen source gases that deplete the ozone layer are “halons” and methyl bromide (CH3Br). These ozone depleting substances create holes in the ozone layer and harmful UV radiations enter the Earth surface via these ozone holes and create issues such as skin cancers, cataracts, reduced crop production which in turn lead to food scarcity and affects food chains. In the oceans, lakes and rivers UV-B has adverse effects on many different aspects of the biology of organisms across the food web.

The scientific confirmation of the depletion of ozone layer which could give arise to various issues on living organisms prompted cooperation of International communities to develop solutions to protect the ozone layer. Vienna Convention for the protection of Ozone layer was adopted and signed by 28 countries on 22nd of March 1985. Under the Vienna Convention, the Montreal Protocol on substances that deplete the Ozone Layer is the landmark multilateral environmental agreement that regulates the production and consumption of man-made ozone depleting substances (ODS).
At present, CFC which is a prominent ozone depleting substance has been completely phased out from refrigeration, air conditioning, aerosols, inhalers and also halons are phased out from fire extinguishers and also methyl bromide is phased out from pesticides. These ozone depleting substances are replaced with environment friendly alternatives.
While scientists and researchers find new solutions and create earth-friendly products, there are things that we all can do to reduce the emission of ozone depleting substances;
- Buy ‘ozone friendly’, ‘HCFC free’ or ‘energy efficient’ products.
- Try to replace older equipment that release ozone depleting substances or service older equipment (not CFC free) regularly as their malfunctions cause CFC to escape into the atmosphere.
- Check for leaks in air conditioners of your home and vehicle and repair them.
Montreal protocol has been successful in protecting the ozone layer by phasing out the release of ozone depleting substances. Whilst the damage to the ozone layer due to human activities has not been recovered yet, thanks to the Montreal protocol and the collaborative effort of nations around the world, there is scientific evidence that the ozone layer is healing itself.
Written by
Sandini Gihansa
1st year undergraduate
Biological Science,
Faculty of Science,
University of Colombo.
References:
- https://ozone.unep.org/ozone-and-you#policy-1
- https://www.genevaenvironmentnetwork.org/resources/updates/international-day-for-the-preservation-of-the-ozone-layer/
- https://csl.noaa.gov/assessments/ozone/2006/chapters/Q7.pdf
- https://www.un.org/en/observances/ozone-day
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