CR

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.