Ozone Layer Depletion

ozone layer
  • Ozone is a form of oxygen. Oxygen occurs in three different forms in the atmosphere: as oxygen atoms (O), as oxygen molecules (O2) and as zone(O3).
  • Ozone’s unique physical properties allow the ozone layer to act as our planet’s sunscreen, providing an invisible filter to help protect all life forms from the sun’s damaging UV (ultraviolet)rays.
  • Most incoming UV radiation is absorbed by ozone and prevented from reaching the Earth’s surface. Without the protective effect of ozone, life on Earth would not have evolved the way it has.

Ultraviolet radiation

  • Ultraviolet radiation is the one form of radiant energy coming out from the sun. The sun emits a range of energy known as the electromagnetic spectrum. The various forms of energy, or radiation, are classified according to wavelength (measured in nanometres where one nm is a millionth of a millimetre).
  • The shorter the wavelength, the more energetic the radiation. In order of decreasing energy, the principal forms of radiation are gamma rays, x-rays, UV (ultraviolet radiation), visible light, infrared radiation, microwaves, and radio waves. Invisible Ultraviolet is so named because it occurs next to violet in the visible light spectrum.
  • The three categories of UV radiation are:
    • UV-A between 320 and 400 nm
    • UV-B between 280 and 320 nm
    • UV-C between 200 and 280 nm

Role of Ozone in absorbing these radiations

  • UV-B and C are highly energetic and are dangerous to life on earth. UV-A being less energetic is not dangerous.
  • Fortunately, UV-C is absorbed strongly by oxygen and by ozone in the upper atmosphere. UV-B is also absorbed by ozone layer in the Stratosphere and only 2-3% of it reaches the earth’s surface.
  • The ozone layer, therefore, is highly beneficial to plant and animal life on earth in filtering out the dangerous part of sun’s radiation and allowing only the beneficial part to reach earth.
  • Any disturbance or depletion of this layer would increase UV-B and UV-C radiation reaching the earth’s surface leading to dangerous consequences.

Ozone Depletion

  • Ozone depletion occurs when the natural balance between the production and destruction of stratospheric ozone is tipped in favour of destruction.
  • Although natural phenomenon can cause temporary ozone loss, chlorine and bromine released from synthetic compounds is now accepted as the main cause of a net loss of stratospheric ozone in many parts of the world since 1980.
  • There is strong evidence that global ozone depletion is occurring.
  • The evidence is in the observations of the Antarctic ozone “hole” and atmospheric records indicating seasonal declines in global ozone levels.

About ozone hole

  • Ozone layer is the common term for the high concentration of ozone that is found in the stratosphere (layer of the atmosphere between around 10- 50 km altitude).
    • Atmospheric ozone absorbs ultraviolet (UV) radiation from the sun, particularly harmful UVB-type rays.
  • Ozone hole refers to a region in stratosphere where concentration of ozone becomes extremely low.
    • Such holes are spotted over both the Poles.
    • Ozone depletion at North pole is much smaller in size, owing to warmer temperatures at North Pole than at the South Pole.
    • Ozone depletion is directly related to the formation of Polar vortex (in stratosphere).
      • During winter, temperatures in the vortex usually drop below 195 K (-78°C), and polar stratospheric clouds (PSCs) form.
      • PSCs provide a surface for ozone-depleting substances such as chlorine-containing CFCs, HCFCs, bromine-containing halons etc. to reach stratosphere.
      • At the poles, ODSs attach to ice particles in PSCs. When the sun comes out again in the polar spring, the ice particles melt, releasing the ozone-depleting molecules from the ice particle surfaces.
      • Once released, these ozone-destroying molecules harm and break apart the molecular bonds in UV radiation-absorbing ozone.
    • During the Southern Hemisphere spring season (August – October) the ozone hole over the Antarctic increases in size, reaching a maximum between mid-September and mid-October.
    • Ozone depletion slows when temperatures in stratosphere start to rise, in late Southern Hemisphere spring, the polar vortex weakens and breaks down.
      • This is because in warmer temperatures fewer PSCs form and they don’t persist as long, limiting the ozone-depletion process.

Impacts of Ozone layer depletion

  • Effects on Human and Animal Health: Increased penetration of solar UV-B radiation is likely to have a profound impact on human health with potential risks of eye diseases, skin cancer and infectious diseases.
  • Effects on Terrestrial Plants: It is a known fact that the physiological and developmental processes of plants are affected by UV-B radiation.
    • Scientists believe that an increase in UV-B levels would necessitate using more UV-B tolerant cultivars and breeding new tolerant ones in agriculture.
    • In forests and grasslands increased UV-B radiation is likely to result in changes in species composition (mutation) thus altering the biodiversity in different ecosystems.
  • Effects on Aquatic Ecosystems:
    • While more than 30% of the world’s animal protein for human consumption comes from the sea alone, it is feared that increased levels of UV exposure can have adverse impacts on the productivity of aquatic systems.
    • High levels of exposure in tropics and subtropics may affect the distribution of phytoplankton which form the foundation of aquatic food webs.
  • Effects on Bio-geo-chemical Cycles: Increased solar UV radiation could affect terrestrial and aquatic bio-geo-chemical cycles thus altering both sources and sinks of greenhouse and important trace gases, Ex. carbon dioxide (CO2), carbon monoxide (CO), carbonyl sulphide (COS), etc.
  • Effects on Air Quality: Reduction of stratospheric ozone and increased penetration of UV-B radiation result in higher photodissociation rates of key trace gases that control the chemical reactivity of the troposphere.
  • Effects on Materials:
    • Increased levels of solar UV radiation are known to have adverse effects on synthetic polymers, naturally occurring biopolymers and some other materials of commercial interest.
    • UV-B radiation accelerates the photodegradation rates of these materials thus limiting their lifetimes.


Which are the Ozone Depleting Substances (ODS) presently used in India? 

* Chlorofluorocarbons (CFCs)–12 for Refrigeration, Chillers and Metered Dose Inhalers.
* Hydrochlorofluorocarbons (HCFCs) – 22 for Air Conditioners.
* Carbon Tetrachloride (CTCs) for as a solvent process agent mainly in the metal cleaning and textile industries. It is also used as feedstock in the manufacture of CFCs and DV Acid Chloride.

Which ODS is no longer produced in India?

Halons, which were earlier used in fire extinguishers. Halons continue to be used in Defence sector, which is exempt from Montreal Protocol. The production of CFCs has also been stopped since 2008.

What are the commonly used ODS alternatives?

ODS Alternatives

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  • During the last few years, intense research has yielded many substitute chemicals as replacements to currently used chlorofluorocarbons (CFCs), Halons, CTC, and Methyl chloroform.
  • The Government of India has entrusted the work relating to ozone layer protection and implementation of the Montreal Protocol to the Ministry of Environment & Forests (MOEF). The MOEF has set up an Ozone Cell as a national unit to look after and render necessary services to implement the Protocol and its ODS phaseout program in India.
  • The MOEF has also established an Empowered Steering Committee, which is supported by four Standing Committees, namely the Technology and Finance Standing Committee, Standing Committee for Small Scale, Tiny and Unorganized industries, Standing Committee on Implementation of ODS phaseout projects and Monitoring and Evaluation Committee. The Empowered Steering Committee is responsible for the implementation of the Montreal Protocol provisions, review of various policy and implementation options, project approvals and project monitoring.

Regulatory Framework

  • India has provided for protection and improvement of the environment in its Constitution. Article 51-(g) of the Constitution says that every citizen of India must protect and improve the natural environment including forests, lakes, rivers and wildlife and have compassion for living creatures. The constitutional provisions are implemented through environmental protection laws of the country.
  • Environment is a concurrent subject thus allowing control of both the State Government and the Central Government on policies, regulations and action plans. In the recent past, the Honorable Supreme Court of India has ordered initiatives for protection of environment and prevention of pollution. This order can be passed based on Public Interest Litigation. The Environment Protection Act, 1986 empowers the Central Government to protect and improve the environment and prevent, control and abate environmental pollution. The Regulations and Controls relating to Ozone Layer protection namely, Ozone Depleting Substances (Regulations and Control) Rules, 2000 have also been issued by the Central Government under the Environment Protection Act, 1986.
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