The ozone layer, a protective shield in Earth's stratosphere, absorbs harmful ultraviolet (UV) radiation from the sun. Concerns about its depletion arose in the 20th century due to human activities.
The ozone layer didn’t "disappear," but it was significantly depleted in certain regions, most notably over Antarctica, where a phenomenon called the "ozone hole" was discovered in 1985 by British scientists Joseph Farman, Brian Gardiner, and Jonathan Shanklin. The ozone hole refers to a dramatic thinning of the ozone layer, where ozone concentrations dropped to less than 220 Dobson Units (DU), far below the normal ~300 DU. This depletion was most severe during the Antarctic spring (September–November).
Causes of Ozone Depletion
- Chlorofluorocarbons (CFCs) and Other Ozone-Depleting Substances (ODS):
- CFCs, used in refrigerants, aerosols, and foam production, were the primary culprits. These stable chemicals, along with halons, methyl bromide, and hydrochlorofluorocarbons (HCFCs), were released into the atmosphere, rising to the stratosphere.
- In the stratosphere, UV radiation breaks down CFCs, releasing chlorine atoms. A single chlorine atom can destroy up to 100,000 ozone molecules through catalytic reactions, significantly reducing ozone levels.
- Polar stratospheric clouds (PSCs), which form in the extremely cold Antarctic stratosphere, enhance these reactions, making depletion more severe in polar regions.
- Human Activities:
- Industrial processes and consumer products (e.g., air conditioners, spray cans) released large quantities of CFCs from the mid-20th century onward.
- Other ODS, like halons (used in fire extinguishers) and methyl chloroform (a solvent), also contributed.
- Natural Factors (Minor Role):
- Volcanic eruptions and solar activity can influence ozone levels, but human-made ODS were the dominant cause of depletion.
Consequences of Ozone Depletion
- Increased UV Radiation: Depletion allowed more UV-B rays to reach Earth, increasing risks of skin cancer (e.g., melanoma), cataracts, and immune system suppression in humans.
- Environmental Impact: Higher UV levels harmed phytoplankton, the base of the ocean food chain, and disrupted ecosystems, particularly in polar regions.
- Agricultural and Material Damage: UV radiation damaged crops and degraded materials like plastics and paints.
