Ozone Layer
The ozone layer is a region of Earth's stratosphere, concentrated approximately 15–35 km above the surface, where ozone (O₃) molecules are present at relatively high concentrations (2–8 ppm), absorbing 97–99% of the Sun's medium-frequency ultraviolet radiation. Ozone is continuously formed when UV radiation (wavelength < 240 nm) splits O₂ molecules into oxygen atoms that then react with other O₂ molecules, and destroyed by catalytic cycles involving chlorine, bromine, nitrogen, and hydrogen radicals. Depletion of the ozone layer by synthetic chlorofluorocarbons (CFCs) — culminating in the discovery of the Antarctic ozone hole in 1985 — led to the Montreal Protocol (1987), which has successfully reduced stratospheric chlorine loading and begun the layer's recovery.
Key Formula
Chapman cycle: O2 + hν → 2O; O + O2 + M → O3 + M
LaTeX: \text{Chapman cycle: } O_2 + h\nu \rightarrow 2O; \quad O + O_2 + M \rightarrow O_3 + M
| Symbol | Meaning | Unit |
|---|---|---|
| h\nu | Photon of UV radiation (wavelength < 240 nm) | eV |
| O | Atomic oxygen (reactive intermediate) | mol |
| O_2 | Molecular oxygen (diatomic) | mol |
| O_3 | Ozone (triatomic oxygen) | mol |
| M | Third body molecule (N₂ or O₂) that absorbs excess energy | mol |
Ozone Layer Key Facts and Depletion Timeline
| Parameter | Value / Event | Year / Unit | Significance | Source |
|---|---|---|---|---|
| Peak ozone altitude | 25–30 km | Above sea level | Maximum O₃ concentration | NOAA |
| Ozone column (healthy) | 300 Dobson Units | DU | Baseline global average | WMO |
| Antarctic ozone hole min | ~100 DU | DU | Severe depletion over Antarctica | NASA (1994) |
| CFCs banned (Montreal) | 1987 | Year | International treaty signed | UNEP |
| Ozone hole area (max) | ~29.9 million km² | km² | Record size (September 2000) | NASA |
| Expected full recovery | ~2065–2080 | Year | Per WMO/UNEP assessment | WMO 2022 |
Interactive Tools
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Related Terms
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, extending from the tropopause (approximately 12 km at mid-latitudes) to the stratopause at about 50 km altitude. Unlike the troposphere, temperature in the stratosphere increases with altitude — from about −56°C at the tropopause to approximately 0°C at the stratopause — due to the absorption of ultraviolet radiation by the ozone layer concentrated within it. This temperature inversion creates very stable conditions that suppress vertical mixing, making the stratosphere nearly cloud-free and home to the polar vortex and stratospheric jet streams; it is also the layer traversed by high-altitude commercial aircraft.
Atmosphere (Earth)
The Earth's atmosphere is the layer of gases retained by Earth's gravity surrounding the planet, extending from the surface to approximately 10,000 km altitude where it gradually merges with the interplanetary medium. It consists primarily of nitrogen (78.09%), oxygen (20.95%), argon (0.93%), and carbon dioxide (0.04%), plus trace gases and variable amounts of water vapor. The atmosphere performs critical functions including regulating surface temperature through the greenhouse effect, protecting life from harmful ultraviolet radiation via the ozone layer, enabling weather and climate systems, and providing the oxygen and carbon dioxide essential for respiration and photosynthesis.
Troposphere
The troposphere is the lowest layer of Earth's atmosphere, extending from the surface to approximately 8–9 km at the poles and 16–18 km at the equator, and containing about 80% of the atmosphere's total mass and virtually all of its water vapor and weather. Temperature generally decreases with altitude at the environmental lapse rate of approximately 6.5°C per 1,000 m (the standard atmosphere value), until reaching the tropopause, a temperature inversion that caps the troposphere. All significant weather phenomena — clouds, precipitation, thunderstorms, cyclones, and jet streams — occur within the troposphere, making it the most meteorologically active layer.
From Greek "ozein" (to smell), referencing the distinctive sharp smell of ozone gas. The molecule O₃ was named by German chemist Christian Friedrich Schönbein in 1840, who first isolated and identified it. The term "ozone layer" came into meteorological and atmospheric science usage in the early 20th century, particularly after Gordon Dobson's measurement campaigns in the 1920s established the ozone column depth measurement unit (Dobson unit) named after him.