Ozone Layer Depletion

JUL 30

Mains   > Environment & Ecology   >   Ozone depletion   >   Ozone depleting agents


  • Recently, a study claimed that a new ozone hole has been detected over the tropics, at latitudes of 30 degrees South to 30 degrees North.


  • According to the study, the ozone hole is located at altitudes of 10-25 km over the tropics.
  • The study suggested that the tropical ozone hole is about seven times larger than Antarctica's and it also appears across all seasons, unlike that of Antarctica, which is visible only in the spring.
  • The tropical ozone hole, which makes up 50 percent of Earth’s surface, is likely to cause skin cancer, cataracts, and other negative effects on the health and ecosystems of tropical regions.


  • The ozone layer is a region of high ozone concentration in the stratosphere, 15 to 35 kilometres above Earth's surface.
  • The ozone layer acts as an invisible shield and protects the earth from harmful ultraviolet (UV) radiation from the sun. In particular, the ozone layer protects the earth from UV radiation known as UV-B, which causes sunburn.
  • Long-term exposure to high levels of UV-B threatens human health and damages most animals, plants and microbes, so the ozone layer protects all life on Earth.
  • Ozone:
    • Ozone is a pale blue gas composed of three oxygen atoms bonded together.
    • Ozone is found in two layers of the atmosphere.
    • The ozone found in the troposphere(bad ozone) is near the earth’s surface and is harmful to life (causes breathing issues in humans) and plants (damages crops and plants.) Urban smog comprises the bad ozone.
    • The good ozone is found in the stratosphere which also hosts the ozone layer. It is called good as it absorbs the sun’s harmful ultraviolet radiation

Dobson Unit:

  • The Dobson Unit is the most common unit for measuring ozone concentration.
  • One Dobson Unit is the number of molecules of ozone that would be required to create a layer of pure ozone 0.01 millimeters thick at a temperature of 0 degrees Celsius and a pressure of 1 atmosphere (the air pressure at the surface of the Earth).


  • Ozone absorbs UV-B radiation from the sun.
  • When an ozone molecule absorbs UV-B, it comes apart into an oxygen molecule (O2) and a separate oxygen atom (O).
  • Later, the two components can reform the ozone molecule (O3).


  • Ozone layer depletion refers to the thinning of the protective ozone layer in the atmosphere.
  • This happens when certain chemicals come into contact with ozone and destroy it.
  • In the mid-1970s, scientists realised that the ozone layer was threatened by the accumulation of gases containing halogens (chlorine and bromine) in the atmosphere. Then, in the mid-1980s, scientists discovered a “hole” in the ozone layer above Antarctica – the region of Earth’s atmosphere with severe depletion.
  • Manmade chemicals containing halogens were determined to be the main cause of ozone loss.
  • These chemicals are collectively known as ozone-depleting substances (ODSs).
  • ODSs were used in literally thousands of products in people’s daily lives around the world.
  • The most important ODSs were chlorofluorocarbons (CFCs), which at one time were widely used in air conditioners, refrigerators, aerosol cans, and in inhalers used by asthma patients.
  • Other chemicals, such as hydrochlorofluorocarbons (HCFCs), halons and methyl bromide also deplete the ozone layer. Most of the computers, electronics and parts of our appliances were cleaned with ozone-depleting solvents. Car dash boards, insulation foams in our houses and office buildings, water boilers and even shoe soles were made using CFCs or HCFCs.


  • When a CFC molecule reaches the stratosphere, it eventually absorbs UV radiation, causing it to decompose and release its chlorine atoms.
  • One chlorine atom can destroy up to 100,000 ozone molecules.
  • Too many of these chlorine and bromine reactions disrupt the delicate chemical balance that maintains the ozone layer, causing ozone to be destroyed faster than it is created.



  • Effects on Human:
    • Ozone layer depletion increases the amount of UVB that reaches the Earth’s surface.
    • Studies show that UVB causes non-melanoma skin cancer.
    • Also, UVB has been linked to the development of cataracts, a clouding of the eye’s lens.
  • Effects on Plants:
    • UVB radiation affects the physiological and developmental processes of plants.
    • Despite mechanisms to reduce or repair these effects and an ability to adapt to increased levels of UV, plant growth can be directly affected by UV radiation.
  • Effects on Marine Ecosystems:
    • Phytoplanktons form the foundation of aquatic food webs. Phytoplankton productivity is limited to the euphotic zone, the upper layer of the water column in which there is sufficient sunlight to support net productivity.
    • Exposure to solar UVB radiation has been shown to affect both orientation and motility in phytoplankton, resulting in reduced survival rates for these organisms.
    • Scientists have demonstrated a direct reduction in phytoplankton production due to ozone depletion-related increases in UVB.
    • UVB radiation has been found to cause damage to early developmental stages of fish, shrimp, crab, amphibians, and other marine animals.
  • Effects on Biogeochemical Cycles:
    • Increases in UVB radiation could affect terrestrial and aquatic biogeochemical cycles, thus altering both sources and sinks of greenhouse and chemically important trace gases (e.g., carbon dioxide, carbon monoxide, carbonyl sulfide, ozone, and possibly other gases).
    • These potential changes would contribute to biosphere-atmosphere feedbacks that mitigate or amplify the atmospheric concentrations of these gases.


  • Vienna Convention for the Protection of the Ozone Layer:
    • The scientific confirmation of the depletion of the ozone layer prompted the international community to establish a mechanism for cooperation to take action to protect the ozone layer.
    • This was formalized in the Vienna Convention for the Protection of the Ozone Layer, which was adopted and signed by 28 countries, on 22 March 1985.
    • In September 1987, this led to the drafting of The Montreal Protocol on Substances that Deplete the Ozone Layer.
  • Montreal Protocol
    • The principal aim of the Montreal Protocol is to protect the ozone layer by taking measures to control total global production and consumption of substances that deplete it, with the ultimate objective of their elimination on the basis of developments in scientific knowledge and technological information.
    • The Protocol requires the control of nearly 100 chemicals, in several categories.
    • For each group or annex of chemicals, the Treaty sets out a timetable for the phase-out of production and consumption of those substances, with the aim of eventually eliminating them completely.
    • In 1994, the United Nations General Assembly proclaimed 16 September the International Day for the Preservation of the Ozone Layer, commemorating the date of the signing, in 1987, of the Montreal Protocol on Substances that Deplete the Ozone Layer.
    • On 16th September 2009, the Vienna Convention and the Montreal Protocol became the first treaties in the history of the United Nations to achieve universal ratification.
    • Kigali Amendment
      • The Parties to the Montreal Protocol on Substances that Deplete the Ozone Layer reached agreement at their 28th Meeting of the Parties on 15 October 2016 in Kigali, Rwanda to phase-down hydrofluorocarbons (HFCs).


  • UNEP’s Division of Technology, Industry, and Economics OzonAction Programme provides industry, government, and other stakeholders in developing countries with information exchange services, training, and networking. In addition to these core clearinghouse services, the Programme also provides assistance with Country Programmes and Institutional Strengthening projects.


India’s achievements in implementation of Montreal Protocol

  • India, as Party to the Montreal Protocol since June 1992, has been successfully implementing the Montreal Protocol and its ozone depleting substances phase out projects and activities in line with the phase out schedule of the Protocol.
  • India has phased out Chlorofluorocarbons, Carbon tetrachloride, Halons, Methyl Bromide and Methyl Chloroform for controlled uses in line with the Montreal Protocol.
  • Currently Hydrochlorofluorocarbons are being phased out as per the accelerated schedule of the Montreal Protocol. 
  • Hydrochlorofluorocarbons Phase out Management Plan (HPMP) Stage-II is currently under implementation from 2017 and will be completed by 2023.
  • On 27 September,2022, India officially ratified the Kigali Amendment of the Montreal Protocol, joining 125 other countries in the fight to phase out hydrofluorocarbons (HFCs) — harmful greenhouse gases used in refrigeration and air-conditioning that are known to accelerate global warming.
  • In 2019 India Cooling Action Plan (ICAP) is launched by Ozone Cell of Union Minister for Environment, Forest and Climate Change(MoEFCC).
    • ICAP aims to provide sustainable cooling while keeping in mind, at the same time, the need to protect the ozone layer.
    • It provides a 20-year perspective, with projections for cooling needs in 2037-38.


  • Ensuring that existing restrictions on ozone-depleting substances are properly implemented and global use of ozone-depleting substances continue to be reduced.
  • Ensuring that banks of ozone-depleting substances (both in storage and contained in existing equipment) are dealt with in an environmentally-friendly manner and are replaced with climate-friendly alternatives.
  • Ensuring that permitted uses of ozone-depleting substances are not diverted to illegal uses.
  • Reducing use of ozone-depleting substances in applications that are not considered as consumption under the Montreal Protocol.
  • Ensuring that no new chemicals or technologies emerge that could pose new threats to the ozone layer (e.g. very short-lived substances).


Q. Discuss the causes and impacts of ozone layer depletion. Also evaluate the initiatives taken at national and global level for mitigation of ozone layer depletion.