Shankar IAS Summary: Ozone Depletion | Famous Books for UPSC Exam (Summary & Tests) PDF Download

Introduction

Ozone depletion refers to the thinning of the ozone layer in Earth’s stratosphere, primarily caused by human activities. The ozone layer is crucial for protecting life on Earth from harmful ultraviolet (UV) radiation. When this layer is damaged, more UV rays reach the Earth’s surface, leading to various environmental and health issues.

Ozone holes, notably over Antarctica, have emerged, prompting global concerns. 

The depletion of ozone can have severe consequences, including increased skin cancer rates, cataracts, and harm to ecosystems. It is a significant environmental concern that requires global attention and action.

Ozone Depletion

• It is found in two different layers of the atmosphere.
• Ozone in the troposphere is ''bad'' because it contributes to air pollution. In contrast, ozone in the stratosphere is beneficial as it provides protection against UV radiation.
• Ozone in the stratosphere is "good" because it protects life on Earth by absorbing some of the sun's harmful Ultra Violet (UV) rays decrease in the concentration of ozone in a particular region of the atmosphere of ozone hole 
• The best example of such an ozone hole is the atmosphere over the Antarctic which has only about 50 percent of the ozone that originally occurred there.

Sources

(i) Chlorofluorocarbons (CFCs):

• CFCs molecules are made up of chlorine, fluorine and carbon.
• They are used as refrigerants (66%): Propellants in aerosol sprays, foaming agents in plastic manufacturing (30%), fire extinguishing agents, solvents for cleaning electronic and metallic components, for freezing foods etc 
• CFCs has a wide and varied application due to its properties like non- corrosiveness, noninflammability, low toxicity and chemical stability, etc. the residence time of CFCs in the atmosphere estimated to be between 40 and 150 years

 The chemical reaction

• CFCs + UV radiation = freeing chlorine atoms. A free chlorine atom + ozone molecule to = chlorine monoxide (ClO). chlorine monoxide + atom of oxygen. = (O₂) and reformation of the free chlorine atom (Cl).
• The element that destroys O₃ (ie. chlorine ) is being reformed at the end of cycle.
• A single chlorine atom destroy thousands of ozone molecules before encountering reactive nitrogen or hydrogen compounds that eventually return chlorine to its reservoirs.

(ii) Nitrogen Oxides:

• The chemical reaction- Nitric oxide (NO) catalytically destroys ozone.
• Nitric oxide + ozone - Nitrogen dioxide + O₂
• Nitrogen dioxide + monoxide = Nitric oxide + O₂

Other Substances

_Bromine

• Bromine is found in compounds like halons and HBFCs, which are used in fire extinguishers. Methyl bromide, another bromine compound, is commonly used as a pesticide. 
• A single atom of bromine has the potential to destroy ozone molecules hundreds of times more effectively than a single atom of chlorine. 

_{Sulphuric acid particles}

• Sulfuric acid particles play a significant role in the atmosphere by releasing chlorine from its molecular stores. 
• Additionally, these particles convert reactive nitrogen into non-reactive forms, which helps prevent the formation of chlorine reservoirs in the atmosphere. 

Role of polar stratospheric clouds in ozone depletion

• The ice particles of the cloud provided substrates for chemical reactions which freed chlorine from its reservoirs.
• The reaction between HCl and ClNO₂ is very slow, but this reaction occurs at a faster rate in the presence of a suitable substrate which is provided by the stratospheric clouds at the poles.
• The PSCs not only activate chlorine, but they also absorb reactive nitrogen.

• If nitrogen, oxides were present they would combine with chlorine monoxide to form a reservoir of chlorine nitrate, (ClNO₂). 
• Every spring, a hole as big as the USA develops in the ozone layer over Antarctica, in the South pole 
• A smaller hole develops each year over the Arctic, at the North Pole.

Why is the ozone hole predominant at the Antarctic?

• The Antarctic stratosphere is much colder. The low temperature enables the formation of Polar stratospheric Clouds (PSCs), below 20 km
• The vortex is a ring of rapidly circulating air that confines the ozone depletion in the Antarctic region. The longevity of the Antarctic vortex is another factor, enhancing favourable conditions for the depletion of ozone. 
• The vortex remains, in fact, throughout the polar winter, well into midspring Whereas- the vortex in the Arctic disintegrates by the time the polar spring (March-April) arrives
• The ozone measurement instruments and techniques are varied, Some of them are the Dobson spectrophotometer and the filter ozonometer called M83, and total ozone mapping pectrometer (TOMS) in the Nimbus-7 satellite
• The Umheher technique- The most common measure of total ozone abundance is the Dobson unit (named after the pioneering atmospheric physical Gordon Dobson) which is the thickness of the ozone column ( compressed at Standard Temperature and Pressure (STP)) in milli-centimeters.

Arctic Ozone Depletion

• There is a clear trend of ozone depletion impacting the Arctic region.
• A significant event occurred in March 1996, representing the most extensive ozone depletion observed in the northern hemisphere, which had repercussions for Britain.
• Scientists associate this event with a historical cooling trend in the upper atmosphere of northern latitudes.
• Since the winter of 1992, there has been a consistent increase in ozone depletion across the northern hemisphere.
• The accumulation of ozone-depleting chemicals, coupled with the colder temperatures in the Arctic stratosphere, plays a crucial role in the formation of Polar Stratospheric Clouds (PSCs), exacerbating the ozone depletion issue.

Environmental Effects of Ozone

• Effects of human and animal health
• Effects on terrestrial plants
• Effects on aquatic ecosystems
• Effects on bio-geochemical cycles
• Effects on air quality
• Effects on materials

 Ozone Depleting Substances Rules

• In July 2000, The Ozone Depleting Substances (Regulation and Control) Rules, 2000 were introduced under the Environment (Protection) Act. These rules, amended in 2001, 2003, 2004, and 2005, establish deadlines for phasing out various Ozone Depleting Substances (ODSs) while regulating their production, trade, import, and export, as well as products containing ODS.

• Prohibitions and Deadlines:
  • CFCs: The rules prohibit the use of chlorofluorocarbons (CFCs) in most products after January 1, 2003, with exceptions for metered dose inhalers and specific medical uses.
  • Halons: The use of halons is restricted after January 1, 2001, except for essential needs.
  • Other ODS: Substances like carbon tetrachloride, methylchloroform, and CFCs for metered dose inhalers can be used until January 1, 2010. Methyl bromide use was allowed until January 1, 2015.
  • HCFCs: Hydrochlorofluorocarbons (HCFCs) can be used as temporary substitutes for CFCs until January 1, 2040.

Ozone Depleting Substances (Regulation and Control) Amendment Rules, 2019

• The Ozone Depleting Substances (Regulation and Control) Amendment Rules, 2019, were published under the Environment (Protection) Act of 1986. These rules reflect the commitment of the Ministry of Environment, Forest, and Climate Change (MoEFCC) to regulate ozone-depleting substances.
• Import Licence Prohibition: The amendment prohibits the issuance of import licences for HCFC-141b starting from January 1, 2020. This move is part of the broader effort to phase out harmful substances.
• Phasing Out HCFC-141b: India successfully phased out Hydrochlorofluorocarbon (HCFC)-141b, used by foam-producing businesses, by January 1, 2020, aligning with the nation's commitment to move away from ODSs in favor of environmentally friendly and energy-efficient technologies.