Stratospheric Ozone and Its Importance

Stratospheric Ozone

• Ozone's Role

  • Absorbs UV-C and much of UV-B radiation.
  • Essential for life on land; prevents significant tissue damage and mutations in DNA.

• Health Benefits

  • Prevents skin cancer and cataracts caused by UV-B and C radiation.

• Comparison

  • Tropospheric ozone: Respiratory irritant, damaging to plant tissue, precursor to photochemical smog.

Ozone Absorption Mechanism

• UV-C radiation breaks down O₂ into two free oxygen atoms (O).
• A free oxygen atom combines with an O₂ molecule to form ozone (O₃).
• UV-C can also break down ozone (O₃) back into O and O₂, maintaining a cycle that absorbs UV radiation.

Polar Stratospheric Clouds (PSC)

• Formed during Antarctica spring melt at -100°F from water and nitric acid (HNO₃).
• In PSCs, chlorine nitrate (ClONO₂) and hydrochloric acid (HCl) react to release free Cl atoms, which are harmful to ozone, maintaining ozone depletion.

Reducing Ozone Depletion

• Phasing Out CFCs
  • Main strategy for reducing anthropogenic ozone depletion.
  • The Montreal Protocol (1987) initiated global phase-out of CFCs in products like refrigerators and aerosols.
  • CFCs replaced with HCFCs - less damaging but still harmful.
  • Transition to HFCs (not ozone-depleting but still greenhouse gases).
  • Future replacements are HFOs, which have shorter atmospheric lifetimes.

Anthropogenic Sources

• CFCs
  • Primary human-caused ozone breakdown agents.
  • Used in refrigerants and aerosol propellants.
• Breakdown Process
  • UV radiation releases chlorine from CFCs.
  • Chlorine reacts with ozone (O₃), converting it to O₂ and perpetuating the cycle of ozone depletion.