✔ The Antarctic ozone hole closed early on December 1, 2025, marking the second consecutive year of relatively smaller ozone holes compared to the large and long-lasting ones seen between 2020 and 2023.
✔ Data from Copernicus, the European Earth observation agency, indicates that the 2025 hole was the smallest in five years, fuelling hopes for long-term recovery.
● Present Status (2025):
✔ The hole peaked at just over 21 million sq km in September 2025, which is significantly below the historical record of over 29 million sq km set in 2006.
✔ Scientists credit this positive trend to the global ban on ozone-depleting substances (ODS).
● About Ozone Hole:
✔ It is a seasonal thinning of the stratospheric ozone layer, primarily in the southern polar region, usually occurring during the austral spring (September to November).
✔ Ozone (O₃) in the stratosphere forms a protective shield that absorbs harmful ultraviolet (UV) radiation, especially UV-B (280–320 nm) and UV-C (<280 nm).
● Causes:
✔ Ozone depletion is primarily caused by human-induced emissions of chemicals like chlorofluorocarbons (CFCs), which destroy ozone molecules.
✔ Under strong UV-C radiation, they release halogen atoms—mainly chlorine (Cl) and bromine (Br)
✔ One chlorine atom can destroy ~1 lakh ozone molecules and bromine from halons is 50–100 times more potent than chlorine
● Why Ozone Hole Forms Over Antarctica
✔ Formation of Polar Stratospheric Clouds (PSC) at extreme cold temperatures (-70 to -800 C), which contain ice crystals, nitric acid (HNO₃), and water.
✔ In winter, sunlight is absent. CFCs break down slowly, and chlorine is “stored” in inactive forms such as - ClONO₂ (chlorine nitrate) and HCl.
o On PSC surfaces, these convert to Cl₂, an active form
✔ As sunlight returns in spring, UV light splits Cl₂ to Chlorine atom, resulting in massive, sudden catalytic destruction of ozone, forming the ozone hole.
✔ Antarctica develops a strong polar vortex—a circular wind pattern trapping air. This isolates the region, preventing mixing with warmer ozone-rich air from lower latitudes.
● Global Initiatives:
✔ Vienna Convention (1985) was established as a framework convention to promote cooperation among nations by exchanging information on the effects of human activities on the ozone layer.
o It was the first convention of any kind to be signed by every country involved, reaching universal ratification in 2009
✔ Montreal Protocol:
o This agreement followed the Vienna Convention to implement specific control actions and phase out ozone-depleting substances.
