Context- The ozone hole over Antarctica is one of the biggest on record, roughly three times the size of Brazil. It’s a natural phenomenon, but scientists are concerned climate change could begin reopening ozone holes.

Ozone

• Ozone (O₃) is a gas naturally found in the atmosphere, constituted by three oxygen atoms.
• Originating from the Greek word óζειν (ozein), which means “to smell”, ozone’s pungent odor can be detected even in low concentrations.

Distribution in the Atmosphere:

Tropospheric Ozone:

• Located in the troposphere, extending up to 10–15 kilometers (6-9 miles) from the Earth’s surface.
• Accounts for about 10% of the Earth’s ozone.

Stratospheric Ozone:

• Located between the top of the troposphere and around 50 kilometers (31 miles) altitude.
• Comprises about 90% of Earth’s ozone, with the highest concentration, referred to as the “ozone layer”, found between 15 and 35 km altitude.
• Continually produced and destroyed in reactions initiated by solar ultraviolet radiation.

Ozone Production & Destruction:

In the Stratosphere:

• Ozone is formed when ultraviolet radiation splits an oxygen molecule (O₂) into two separate oxygen atoms, which then individually combine with other oxygen molecules to create ozone.
• Its destruction involves reactions with a variety of natural and human-produced chemicals, such as those containing hydrogen, nitrogen, chlorine, and bromine.

In the Troposphere:

• Ozone production is majorly a result of reactions involving hydrocarbon and nitrogen oxide gases, all dependent on sunlight.
• Human activities like fossil fuel combustion and deforestation increase the pollutants that facilitate tropospheric ozone production.
• Ozone in this layer is destroyed by natural chemical reactions, human-produced chemicals, and interactions with surfaces like soils and plants.

Significance:

Stratospheric Ozone (Good Ozone):

• UV Shield: Absorbs harmful UV radiation, protecting against skin cancer, cataracts, and environmental damage.
• Protection Efforts: The Montreal Protocol reduces human-caused ozone-depleting substances.

Tropospheric Ozone (Bad Ozone):

• Formation: Created from human-emitted pollutants.
• Effects on 
  • Health: Causes respiratory issues and exacerbates heart and lung conditions.
  • Environment: Harms crops, forests, and contributes to global warming.

Natural Ozone:

• Naturally exists in the atmosphere, aiding in removing pollutants and regulating stratospheric temperatures.

Causes of Ozone depletion

Through Human Activities

• Primarily caused by human-emitted gases, particularly halogens like chlorine and bromine.
• ODSs: These are specific halogen source gases, like CFCs, responsible for ozone depletion and regulated by the Montreal Protocol.
• CFCs & HCFCs: Used in refrigeration and air conditioning. Emissions have been controlled and reduced, thanks to international regulations.
• Halons and Methyl Bromide: Used in fire suppressants and fumigation; contribute significantly to ozone depletion.

The “ozone hole” over Antarctica arises due to:

• Unique Conditions: Antarctica has specific meteorological and chemical conditions that enhance ozone destruction.
• Halogen Gases: These are uniformly distributed, but their effects are more pronounced in Antarctica.
• Cold Temperatures: Polar stratospheric clouds (PSCs), which play a key role in ozone depletion, form at very low temperatures more commonly reached in Antarctica.
• Isolation: Antarctic air is more isolated in winter, intensifying conditions for ozone depletion.
• Role of PSCs: These clouds amplify the abundance of reactive chlorine gases, leading to ozone destruction.
• Nitric Acid Removal: Large PSC particles cause nitric acid removal, prolonging ozone destruction.

Measures for controlling ozone-depleting substances (ODSs):

• The Vienna Convention (1985) was an international treaty signed by 26 nations, aiming to protect the ozone layer from human-induced degradation. It primarily set a foundation for research and information exchange regarding the ozone layer.
• The Montreal Protocol (1987) was the actionable response to the Vienna Convention. It specifically targeted and set controls on ozone-depleting substances (ODSs). Nations were bound legally to reduce the production and consumption of these substances. Over the years, the Protocol was fortified with amendments to adjust to the evolving scientific understanding and emerging challenges:
  • London Amendment (1990): It set ambitious targets, aiming to phase out the most harmful ODSs by 2000 in developed countries and by 2010 in developing ones.
  • Copenhagen Amendment (1992): Recognizing the urgency, this amendment further accelerated the phaseout dates for several ODSs. It also introduced controls on HCFCs, which were less harmful alternatives to earlier ODSs but still posed some risks.
  • Kigali Amendment (2016): This amendment addressed hydrofluorocarbons (HFCs). While HFCs don’t deplete the ozone, they have significant global warming potentials and thus contribute to climate change.

Impact of Ozone Layer Depletion on UV Radiation:

• Depletion of the ozone layer increases ultraviolet (UV-B) radiation at Earth’s surface.
• UV-B is harmful, causing sunburn and increasing skin cancer risks.
• Ozone absorbs and reduces UV-B; less ozone means more UV-B reaches us.
• UV exposure is indicated by the UV Index (UVI). A decrease in ozone leads to a higher UVI.
• UV levels have risen over time, especially in areas like Antarctica due to the ozone hole.
• Increased UV affects human health, causing eye issues, skin disorders, and influencing Vitamin D production.
• Recovery of the ozone layer is underway, but UV-related health risks will persist for decades.