Ozone Layer Depletion – How the Large Hole in the Arctic Ozone Layer Closed

ozone layer depletion close arctic upsc

The U.N. World Meteorological Organization (WMO) recently declared that Ozone depletion over the Arctic though hit a “record level” in March (the biggest since 2011), the hole has now closed.

The ozone hole’s closing was due to a phenomenon called the polar vortex, and not because of reduced pollution levels due to Covid-19 lockdowns around the world.

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What is the Ozone layer?

  • The ozone layer is a region of the Earth’s stratosphere that absorbs most of the Sun’s harmful Ultraviolet (UV) radiation.
  • In UV rays, the UV-B radiations are particularly harmful and majorly screened out by the ozone layer only.
  • This layer protects the earth from Sun’s harmful UV radiation by absorbing around 97-99% of it.

What is ozone depletion?

  • Ozone depletion is the destruction of stratospheric ozone by certain chemicals when they reach the stratosphere in a certain region.
  • The destruction has been going on for a long time because the equilibrium between the formation and destruction of ozone has been upset due to Anthropocene activities.
  • The specific examples of regional ozone depletion are the Arctic ozone hole, Antarctic ozone hole.

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What are the chemicals that cause ozone depletion?

The chemicals which destroy the ozone layer are called ozone-depleting substances. The ozone-depleting substances are

  • Chlorofluorocarbons (CFCs)
  1. The CFCs are made up of chlorine, fluorine, and carbon. These are used as refrigerants, propellants in aerosol sprays, fire extinguishers, etc.
  2. Another worrying part is CFCs cannot be removed from the atmosphere by usual scavenging processes like rain out, oxidation, etc.
  • Carbon tetrachloride
  1. It is commonly used as a cleaning agent, an industrial solvent, fire extinguishers, etc.
  2. Despite a worldwide ban, its emission rates have only increased
  • Methyl chloroforms

Methyl chloroform (also known as 1,1,1 trichloroethane) is a versatile industrial solvent used primarily to clean metal and electronic parts. It was introduced as a substitute for carbon tetrachloride in the 1950s.

  • Halons
  1. Halons contains bromine, which also destroys ozone in the stratosphere.
  2. Halons are used primarily in fire extinguishers. Halon-1301 has 10 ozone-depleting potential times that of CFC-11.
  3. Because of long atmospheric life cycles, although the use of halons in developed countries has been phased out since 1996, the atmospheric concentration of these potent, ozone destroyers is still rising.
  • The Nitrogen Oxides

Nitrogen oxides released from agricultural fertilizers, industrial emissions, etc are also potent ozone-depleting substances.

How the process of ozone depletion occurs with the above chemicals?

  • The ozone-depleting substances mentioned above release Chlorine or Bromine when they reach the stratosphere and are exposed to the UV rays.
  • The Chlorine or Bromine atoms react with the Ozone molecule and break it down to produce chlorine/bromine monoxide and oxygen.
  • The chlorine/bromine monoxide dissociates to form free chlorine/bromine molecule and hence the cycle continues that reduces ozone concentration in the stratosphere.
  • Similarly, Nitrogen oxides react with ozone to form nitrogen dioxide and oxygen. The Nitrogen dioxide further reacts with monoxide to form nitric oxide and oxygen.

Ozone depletion at the Arctic and Antarctic region

  • Ozone depletion in the Antarctic region is predominant due to the presence of polar stratospheric clouds (PSCs).
  • The ozone depletion at the Arctic has been claimed to be caused due to dramatic cooling of the upper atmosphere in the northern latitudes which increases PSCs.

What are the effects of ozone depletion or what would have happened in the absence of the ozone layer?

  • Effects on human life
  1. The exposure to UV-B radiations increases the incidence of and morbidity from eye diseases, skin cancer, and infectious diseases.
  2. In the absence of the ozone layer, people would be affected by skin cancer and weakened immune systems
  3. Radiation exposure potentially threatens the cornea and lens of the eye.
  • Effects on Plants
  1. Exposure to UV radiation in forest and grassland ecosystem is likely to result in changes in the composition of species which threatens biodiversity
  2. The psychological and developmental processes of plants are disturbed
  • Effects on aquatic ecosystems
  1. Exposure to UV radiations affect mobility and orientation mechanisms in phytoplankton which results in reducing survival rates
  2. The developmental processes of marine life are is also affected.

How the ozone depletion was detected?

  • Mario Molina and Sherwood Rowland, two USA chemists in 1974 published an article detailing threats to the ozone layer from chlorofluorocarbon (CFC) gases
  • The ground-breaking research (for which they were awarded the 1995 Nobel Prize in chemistry) by them concluded that the atmosphere had a “finite capacity for absorbing chlorine” atoms in the stratosphere
  • In 1985, a team of English scientists found a hole in the ozone layer over Antarctica that was later linked to CFCs. The “hole” is an area of the stratosphere where extremely low concentrations of ozone are present that reoccurs every year

What are the measures taken to stop the ozone depletion?

  • The Vienna Convention
  1. The Vienna Convention for the Protection of the Ozone Layer was signed in 1985.
  2. Under the convention UN member countries recognized the importance of curbing damage to the ozone layer.
  3. Countries agreed to adopt the Montreal Protocol to further the goals of the Vienna Convention.
  • Montreal Protocol
  1. It was signed in 1987 and came into force in 1989.
  2. The protocol aimed to control the consumption and production of anthropogenic ozone-depleting substances (ODSs) and some hydrochlorofluorocarbons (HCFCs).
  3. The Protocol was signed in 1987 by 197 parties to control the use of ozone-depleting substances (mainly chlorofluorocarbons (CFCs)).
  4. The protocol has provisions to reduce the production and consumption of ODSs.
  5. It phases down the use of ODSs in a stepwise, time-bound manner with different timetables for developed and developing countries
  6. Both groups of nations have time-bound, binding, and measurable commitments under the protocol, making it effective.

The Montreal protocol has been the single most successful environment agreement

Its success reflects in

  1. Largest number of countries (for an environmental treaty) signing and ratifying the protocol
  2. The reduction in ozone depletion rates worldwide
  3. levelling off or decrease in the atmospheric concentrations of the most important chlorofluorocarbons and related chlorinated hydrocarbons.
  4. Parties to the Protocol having been able to phase out 98% of ODSs compared to levels in 1990
  5. NASA scientist’s document revealing that Ozone depletion in the Antarctic region has declined 20 percent since 2005: the first direct proof that Antarctic ozone is recovering because of the CFC phase-down.
  6. The United Nations confirmed in 2018 that the ozone layer would heal completely in the (non-polar) Northern Hemisphere by the 2030s, followed by the Southern Hemisphere in the 2050s and polar regions by 2060.
  7. Kigali agreement (2016)
    1. Motivated by the success of the protocol, the Kigali agreement amended the Montreal protocol to include Greenhouse Gas HFC.
    2. This was done to complement the Kyoto protocol which lacks near-universal ratification of the Montreal protocol.
    3. Around 197 countries agreed at Kigali to reduce the use of HFCs by roughly 85% of their baselines by 2045.

India and Montreal Protocol

  • India became a signatory to the protocol in 1992
  • As per the National Strategy for ODS Phaseout, the Environment Ministry has notified the Ozone Depleting Substances (Regulation and Control) Rules 2000. These are
  • The Rules prohibit the use of CFCs in manufacturing various products
  • They provide for the mandatory registration of ODS producers, sellers, importers and stockists
  • Also, The Government of India has granted full exemption from payment of Customs and Excise duties on capital goods required for ODS phase out projects funded by the Multilateral Fund.
  • The National Ozone Unit (NOU) has undertaken comprehensive public awareness campaign to ensure that both the public and the companies responsible for actually phasing out the ODS understand and support the policies to protect the ozone layer.

What are the issues with the current ozone depletion control regime?

  • According to the UN study named ‘Scientific Assessment of Ozone Depletion: 2018’, the ozone layer is recovering only at a rate of 1-3% per decade
  • Recent detection of rogue CFC-11 production has brought forth the loopholes in implementation
  • Ozone-depleting substances have long lifetimes making them persist in the atmosphere for a very long time to the tune of centuries.
  • The expected revival of the ozone layer is 2060 which is a very long period.
  • The current geopolitical conditions threaten the Kigali agreement.

How the Large Hole in the Arctic Ozone Layer Is Now Closed?

  • To be clear, the hole’s appearance and repair were not caused by human activity.
  • Scientists from Copernicus Atmosphere Monitoring Service (CAMS), who have been monitoring the area, attribute the ozone hole to something more natural.
  • A large low-pressure area made from swirling cold air—known as a polar vortex—was particularly strong for several weeks in March.
  • This caused cold air to remain trapped in the North Pole, the by-product of which was the formation of high altitude clouds that cause chemical reactions to stimulate ozone depletion once sunlight returns.
  • So, now that the polar vortex is starting to break down, the air between the ozone-depleted and ozone-rich layers are mixing once again. This has caused the hole to heal itself as ozone levels begin to rise once again.

Way forward

  • Though we have seen success, continued adherence to the protocol is necessary as the situation is in early recovery condition.
  • Finance and technology transfer from developed countries to developing countries is necessary to adopt technologies necessary to adhere to the protocol.
  • Research and development are necessary to find substances to bring about a balance between ozone security and global warming reduction.
  • The environmental issues are hardly a matter of widespread public debate. This scenario must change as it is necessary for accelerated and initiated public actions to reduce ozone depletion and global warming.

Practice Question for Mains

What is ozone Depletion? Critically discuss the success of the Montreal protocol in arresting ozone depletion. (250 words)

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