• Overview: Ozone, a molecule comprising three oxygen atoms, predominantly resides in the stratosphere, situated 10 to 50 kilometres above Earth’s surface.
  • Concentration: Despite being present in low concentrations, even at its densest, the ozone layer has only a few molecules of ozone per million air molecules.

Importance of Ozone

  • UV Protection: The ozone layer acts as a shield, protecting life on Earth from the sun’s harmful ultraviolet (UV) rays.
  • Health and Environment: UV radiation can lead to skin cancer, other diseases, and deformities in both plants and animals, making the ozone layer crucial for sustaining life.

Discovery of Depletion

  • Antarctica Findings: In the early 1980s, scientists discovered a significant drop in ozone levels in Antarctica during September-November, compared to the 1950s.
  • Ozone Hole: The discovery of the “ozone hole” over Antarctica in 1985 highlighted the severity of ozone depletion as a global environmental issue.

Causes of Depletion

  • Geographic and Chemical Factors: Unique meteorological and chemical conditions in the Antarctic stratosphere during specific months cause significant ozone depletion.Montreal Protocol: The 1987 Montreal Protocol initiated the phase-out of chlorofluorocarbons (CFCs) and other ozone-depleting substances. By 2005, the consumption of regulated chemicals had decreased by 90-95% among the 197 signatory nations.

Controlled Chemicals

  • Halo-carbons: CFCs and Halons, initially considered wonder gases for their stability, contribute significantly to ozone depletion. For example, CFC-11, CFC-12, and CFC-115 have atmospheric lifetimes of 50, 102, and 1,700 years, respectively.Halon 1301: Primarily used in fire extinguishers, it remains in the atmosphere for 65 years.
  • Carbon Tetrachloride: A solvent with a 42-year atmospheric lifetime.
  • Hydrochlorofluorocarbons (HCFCs): Developed as replacements for CFCs, HCFCs also deplete ozone, with lifetimes ranging from 1.4 to 19.5 years.
  • Other Chemicals: Substances like Methyl chloroform, Hydrobromofluorocarbons (HBFCs), Methyl bromide, and Bromochloromethane (BCM) are also controlled under the Montreal Protocol.


Climate Change Co-benefit: The reduction of ozone-depleting substances also mitigates climate change, as many of these chemicals are potent greenhouse gases.

Greenhouse Gas Impact: Several ozone-depleting substances are significantly more dangerous than carbon dioxide, a major driver of global warming. Reducing these substances helps address both ozone depletion and climate change.

Legacy Editor Changed status to publish June 3, 2024