Stratospheric ozone depletion refers to the decrease in the concentration of ozone (O₃) in the Earth’s stratosphere, particularly in the region known as the ozone layer. The ozone layer is crucial because it absorbs most of the Sun’s harmful ultraviolet (UV) radiation, protecting life on Earth.
Key points about stratospheric ozone depletion:

1. Causes: The primary cause of ozone depletion is the release of ozone-depleting substances (ODS), such as chlorofluorocarbons (CFCs), halons, and hydrochlorofluorocarbons (HCFCs). These substances were commonly used in refrigerants, aerosol sprays, and industrial solvents.
2. Chemical reactions: When ODS reach the stratosphere, UV radiation breaks them down, releasing chlorine and bromine atoms. These atoms catalyze the destruction of ozone molecules, leading to a decrease in ozone concentration.
3. Antarctic ozone hole: The most severe ozone depletion occurs over Antarctica during the Southern Hemisphere spring (September to November), forming what is known as the “ozone hole.”
4. Consequences: Ozone depletion allows more UV radiation, particularly UV-B, to reach the Earth’s surface. Increased UV exposure can lead to various health issues, such as skin cancer, cataracts, and weakened immune systems. It also harms plants and marine ecosystems.
5. Montreal Protocol: In 1987, the international community adopted the Montreal Protocol, an agreement to phase out the production and consumption of ODS. The protocol has successfully reduced the use of these substances and slowed ozone depletion.
6. Recovery: The Montreal Protocol has allowed stratospheric ozone levels to recover to pre-1980 levels by the middle of the 21st century. However, factors such as climate change and the continued use of some ODS substitutes may affect the recovery process.

Stratospheric ozone depletion is a global environmental issue that has been addressed through international cooperation and the implementation of the Montreal Protocol. Continued monitoring and adherence to the protocol are essential for the long-term protection of the ozone layer and life on Earth.