Ozone Depletion
The ozone layer and its importance, the substances that deplete it, the Antarctic ozone hole, and the Montreal Protocol success story.
Key Takeaways
- The stratospheric ozone layer absorbs harmful ultraviolet (UV) radiation.
- Ozone-depleting substances (ODS) like CFCs destroy ozone; the 'ozone hole' is over Antarctica.
- The Montreal Protocol (1987) is the most successful environmental treaty, phasing out ODS.
Core concept
The ozone (O₃) layer in the stratosphere acts as the Earth's sunscreen, absorbing most of the Sun's harmful ultraviolet (UV-B) radiation. Certain man-made chemicals rise to the stratosphere and destroy ozone, thinning this shield — most dramatically over Antarctica.
Static foundation — how depletion happens
Ozone-depleting substances (ODS) — chiefly CFCs (chlorofluorocarbons), halons and HCFCs — release chlorine and bromine atoms in the stratosphere. Each chlorine atom can destroy thousands of ozone molecules in a catalytic chain reaction, worsened by polar stratospheric clouds in the Antarctic winter/spring.
'Good up high, bad nearby'
Stratospheric ozone protects life by blocking UV — its loss is harmful. Tropospheric (ground-level) ozone is a pollutant and greenhouse gas formed in smog. Same molecule, opposite roles depending on where it is.
Vienna Convention, Montreal & Kigali
| Instrument | Year | What it does |
|---|---|---|
| Vienna Convention | 1985 | The framework treaty for protecting the ozone layer (no binding targets) |
| Montreal Protocol | 1987 | Binding phase-out of ODS (CFCs, halons); universally ratified |
| Kigali Amendment | 2016 | Phases DOWN HFCs — potent greenhouse gases (a CLIMATE measure) |
Value addition — a rare success
The Montreal Protocol is the only UN treaty ratified by every country and is on track to restore the ozone layer by around the middle of this century. The Kigali Amendment cleverly uses the same machinery to tackle HFCs — refrigerant gases that don't harm ozone but are strong warmers — linking ozone protection to climate action.
Prelims trap zones
- Stratospheric ozone is protective; tropospheric ozone is a pollutant.
- The Montreal Protocol (1987), not the Vienna Convention (1985), contains the binding phase-out.
- The Kigali Amendment targets HFCs — greenhouse gases — not ozone-depleting substances.
Knowledge Check
2 questions · check your understanding
1. Which international agreement is chiefly responsible for phasing out ozone-depleting substances?
2. The Kigali Amendment (2016) deals with the phase-down of:
Prelims Pointers
- Ozone-depleting substances include CFCs, halons, HCFCs, carbon tetrachloride and methyl bromide.
- The Vienna Convention (1985) is the framework; the Montreal Protocol (1987) has the phase-out commitments.
- The Kigali Amendment (2016) phases down HFCs — potent greenhouse gases (a climate, not ozone, measure).
- Ozone is measured in Dobson Units.
Mains Angle
- 'The Montreal Protocol is a model for global environmental cooperation.' Discuss.
- Distinguish between stratospheric and tropospheric ozone.
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