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World Ozone Day

Date = September 16 — observed annually
Established = 1994 by the United Nations General Assembly.
Purpose = To raise awareness about the importance of the ozone layer and promote actions to protect it from ozone-depleting substances.
Ozone Layer = A region of the stratosphere rich in ozone (O₃) that absorbs most of the Sun’s harmful ultraviolet (UV) radiation.
Key Agreement = The Montreal Protocol on Substances that Deplete the Ozone Layer was adopted on 16 September 1987.
First observed = 16 September 1995.
2026 Theme = “From science to global action”.

International Day for the Preservation of the Ozone Layer

International Day for the Preservation of the Ozone Layer is observed every year on 16 September.
Also called as World Ozone Day.

Ozone Layer = A region of the stratosphere rich in ozone (O₃) that absorbs most of the Sun’s harmful ultraviolet (UV) radiation.
Ozone layer location: Stratosphere.
Chemical formula of ozone: O₃
Major function: Absorbs harmful ultraviolet (UV) radiation, particularly UV-B.
Ozone-depleting substances (ODS): Mainly CFCs (chlorofluorocarbons), halons and related chemicals.
Ozone hole: Most prominently observed over Antarctica.
Vienna Convention: Adopted in 1985; provides the framework for international cooperation on ozone protection.
Montreal Protocol: Adopted in 1987 under the Vienna Convention.
India: India is a party to both the Vienna Convention and Montreal Protocol.
Vienna Convention (1985) → framework for ozone protection
Montreal Protocol (1987) → phase-out of ozone-depleting substances

The Shield: Located primarily in the stratosphere (15-35 km above Earth), ozone (O₃) absorbs 97–99% of incoming medium-frequency ultraviolet (UV-B) radiation.
Impact of Depletion: Excess UV radiation causes skin cancers, cataracts, immune system damage in humans, and severe disruptions to marine ecosystems (phytoplankton) and agricultural crop yields.

16 September → World Ozone Day → Montreal Protocol → 1987 → Ozone layer → Stratosphere → O₃ → UV radiation → CFCs

Do not confuse ozone depletion with global warming.
Ozone depletion primarily concerns increased UV radiation reaching Earth.
While global warming is mainly associated with the enhanced greenhouse effect.
Measurement Unit: Dobson Unit (DU).
Conversion: = 1DU = 0.01 mm
Normal Thickness = 300-400 DU.
Ozone Hole Definition: An area where total column ozone drops below 220 DU.
Discovery of Ozone Layer: Discovered in 1913 by French physicists Charles Fabry and Henri Buisson.
Discovery of the Ozone Hole (1985): Detected over Antarctica by British Antarctic Survey scientists Joseph Farman, Brian Gardiner, and Jonathan Shanklin.