Stratospheric ozone
Stratospheric ozone is a layer of ozone (O₃) molecules located in the Earth's stratosphere, approximately 10 to 30 miles above the Earth's surface. It plays a critical role in absorbing the majority of the Sun's harmful ultraviolet (UV) radiation.
Ozone-Depleting Substances (ODS):
- Chlorofluorocarbons (CFCs): These man-made chemicals, once commonly used in refrigerants, air conditioners, and aerosol propellants, are major contributors to ozone depletion.
- Halons and Other Chemicals: Other substances, such as bromine compounds (halons), also contribute to ozone layer depletion.
Ozone Depletion:
- The Ozone Hole: Ozone depletion is most prominent in the polar regions, particularly over Antarctica, where the ozone layer has become significantly thinner, leading to the so-called "ozone hole."
- Mechanism: CFCs and other ozone-depleting substances are released into the atmosphere, where they eventually reach the stratosphere. Ultraviolet light breaks down these chemicals, releasing chlorine and bromine atoms, which then destroy ozone molecules in a catalytic process.
Cl + O₃ → ClO + O₂
ClO + O → Cl + O₂
These reactions continue, leading to a significant loss of ozone.
Consequences of Ozone Depletion:
- Increased UV Radiation: A thinner ozone layer allows more harmful UV radiation to reach Earth's surface, which can increase the incidence of skin cancers, cataracts, and weakened immune systems in humans.
- Environmental Impact: Elevated UV levels can harm marine ecosystems, particularly phytoplankton, which are at the base of the ocean food chain. It can also damage terrestrial plant life, affecting crop yields and forest productivity.
Montreal Protocol
The Montreal Protocol is an international treaty that regulates the production, trade and use of chlorofluorocarbons (CFCs) and other ODSs. It is regarded as the most successful example yet of international cooperation in management and intervention to resolve a significant environmental issue. As the protocol phased out CFCs and halons, other substances (e.g., hydrochlorofluorocarbons or HCFCs) were introduced as alternatives. Some of these alternatives, like HFCs (hydrofluorocarbons), do not deplete ozone but are potent greenhouse gases contributing to climate change. The protocol has since been amended to address these concerns.
Success:
- CFC production has been largely eliminated.
- The ozone layer is on track to recover by the mid-21st century.
Key Amendments:
- Kigali Amendment (2016): Focused on phasing out hydrofluorocarbons (HFCs), which are powerful greenhouse gases.
