Ozone Depletion
Ozone depletion is the thinning of the stratospheric ozone layer (located 15–35 km above Earth's surface) caused by catalytic destruction of ozone (O₃) molecules by anthropogenic chemicals, particularly chlorofluorocarbons (CFCs), halons, hydrochlorofluorocarbons (HCFCs), and methyl bromide. The ozone layer shields life on Earth from harmful ultraviolet-B (UV-B) radiation; its depletion increases risks of skin cancer, cataracts, immune suppression, and damage to phytoplankton. The Montreal Protocol (1987) successfully phased out most ozone-depleting substances, and the ozone layer is gradually recovering.
Key Formula
Cl• + O3 → ClO• + O2; ClO• + O• → Cl• + O2 (net: O3 + O• → 2O2, Cl• regenerated as catalyst)
LaTeX: Cl^\bullet + O_3 \rightarrow ClO^\bullet + O_2; \quad ClO^\bullet + O^\bullet \rightarrow Cl^\bullet + O_2
| Symbol | Meaning | Unit |
|---|---|---|
| Cl• | Chlorine radical (catalyst, from CFC photolysis) | reactive species |
| O₃ | Ozone molecule being destroyed | Dobson Units (DU) in column |
| ClO• | Chlorine monoxide radical (intermediate) | reactive species |
| O• | Atomic oxygen | reactive species |
Worked Example
Problem
The Antarctic ozone hole in 1987 showed a column ozone value of 180 Dobson Units (DU), compared to a normal level of 300 DU. Calculate the percentage ozone depletion.
Solution
Step 1: Depletion = Normal − Observed = 300 − 180 = 120 DU. Step 2: Percentage depletion = (Depletion / Normal) × 100 = (120 / 300) × 100.
Answer
40% ozone depletion — a severe ozone hole condition.
Major Ozone-Depleting Substances and Their Ozone Depletion Potential (ODP)
| Substance | Chemical Formula | ODP (CFC-11 = 1) | Primary Use | Phase-Out Status |
|---|---|---|---|---|
| CFC-11 (reference) | CCl₃F | 1.0 | Refrigerants, foams | Phased out (Montreal Protocol) |
| CFC-12 | CCl₂F₂ | 0.82 | Refrigerators, aerosols | Phased out |
| Halon-1301 | CBrF₃ | 10.0 | Fire extinguishers | Phased out |
| HCFC-22 | CHClF₂ | 0.055 | Air conditioning | Phase-out by 2040 (developing nations) |
| Methyl bromide | CH₃Br | 0.66 | Agricultural fumigant | Mostly phased out |
Interactive Tools
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Related Terms
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Carbon Footprint
A carbon footprint is the total amount of greenhouse gases, primarily carbon dioxide and methane, emitted directly or indirectly by an individual, organisation, event, or product, expressed as CO₂ equivalent (CO₂e). It is a widely used metric to quantify human contribution to climate change, encompassing energy use, transportation, food consumption, and manufacturing processes. Reducing carbon footprints is central to climate mitigation strategies outlined in international agreements such as the Paris Accord.
Renewable Energy
Renewable energy is energy derived from naturally replenishing sources that are virtually inexhaustible on human timescales, including solar, wind, hydroelectric, geothermal, and biomass energy. Unlike fossil fuels, renewable sources produce little to no greenhouse gas emissions during operation, making them essential for decarbonising the global energy system. India aims to achieve 500 GW of renewable energy capacity by 2030 under its Nationally Determined Contributions to the Paris Agreement.
From Greek "ozein" (to smell) — named by Christian Friedrich Schönbein in 1840 for the distinctive smell produced during electrical discharges. "Depletion" derives from Latin "deplere" (to empty out) — "de" (thoroughly) + "plere" (to fill). The stratospheric ozone layer itself was discovered by French physicists Charles Fabry and Henri Buisson in 1913.