Ozone Cycle

A natural process in the Earth's stratosphere (upper atmosphere) involving the continuous formation and destruction of ozone (O₃). Crucial for life on Earth as the ozone layer absorbs most of the harmful ultraviolet (UV) radiation from the sun.

Key Processes:

1. Formation of Atomic Oxygen: High-energy UV radiation from the sun breaks apart oxygen molecules (O₂) into two individual oxygen atoms (O): O₂ + UV → O + O
2. Formation of Ozone: These highly reactive single oxygen atoms then collide with other oxygen molecules (O₂) to form ozone (O₃): O + O₂ + M → O₃ + M (where 'M' is a third molecule like nitrogen (N₂) or oxygen (O₂) that absorbs excess energy, stabilizing the ozone molecule).
3. Destruction of Ozone (Natural): Ozone (O₃) is unstable and naturally breaks down in two main ways:
   • Absorption of UV radiation: O₃ + UV → O₂ + O
   • Reaction with atomic oxygen: O₃ + O → 2O₂

Diagram

The Ozone Layer:

• A region in the stratosphere (approximately 10 to 50 km above the Earth's surface) where the concentration of ozone is relatively high.
• This layer acts as a shield, absorbing most of the harmful UV-B and UV-C radiation from the sun, preventing it from reaching the Earth's surface.
• UV-B radiation can cause skin cancer, cataracts, and damage to plants and marine life. UV-C is even more harmful but is almost completely absorbed by the ozone layer and the atmosphere.
• As a result of the ozone cycle, energy from UV rays is dissipated as heat.

Ozone Depletion (Human Impact):

• Certain human-made chemicals, particularly chlorofluorocarbons (CFCs), halons, and other ozone-depleting substances (ODS), can catalyze the destruction of ozone in the stratosphere.
• These stable chemicals rise into the stratosphere, where they are broken down by UV radiation, releasing chlorine or bromine atoms.
• These halogen atoms act as catalysts in a chain reaction, where a single chlorine atom can destroy thousands of ozone molecules:
  • Cl + O₃ → ClO + O₂
  • ClO + O → Cl + O₂ (The chlorine atom is regenerated and can destroy more ozone)
• This catalytic destruction leads to a thinning of the ozone layer, commonly referred to as the "ozone hole" (most prominent over the Antarctic).

Consequences of Ozone Depletion:

• Increased levels of harmful UV-B radiation reaching the Earth's surface.
• Increased risk of skin cancer and cataracts in humans.
• Damage to the immune system.
• Harm to terrestrial and aquatic ecosystems, including reduced plant growth and damage to phytoplankton.
• Impacts on air quality.

International Efforts:

• The Montreal Protocol is an international treaty designed to phase out the production and consumption of ozone-depleting substances. It has been largely successful in reducing the rate of ozone depletion.

Written by Kasiban Parthipan