Ozone Depletion - In-Depth Notes

Atmospheric Structure and Ozone Layer

  • Stratosphere (15-50 km from Earth):

    • Contains very little water vapor but has 1000 times more ozone than the troposphere.
    • Ozone in this layer absorbs ultraviolet (UV) light, warming the upper stratosphere.
    • Ozone is crucial for protecting life on Earth from harmful UV radiation.
    • Pollutants such as Chlorofluorocarbons (CFCs) and bromine contribute to ozone depletion.

  • Stratospheric Ozone:

    • Peak ozone concentrations are found at altitudes of 30 to 35 kilometers.
    • "Good" Ozone: Located in the stratosphere, filters harmful UV light.
    • "Bad" Ozone: Ground level ozone, produced by chemical reactions between pollutants.

Ultraviolet Radiation (UV)

  • Types of UV Light:

    • UV-C: 100-280 nm (Very harmful, but mostly absorbed by the atmosphere)
    • UV-B: 280-315 nm (Can cause skin damage)
    • UV-A: 315-400 nm (Less harmful but still contributes to skin aging and damage)

  • Health Effects of UV Radiation:

    • Essential for Vitamin D activation but can lead to:
    • Cataracts and skin cancers (including melanoma)
    • Premature skin aging
    • Immunosuppression
    • In adults, only 1% of UV radiation reaches the retina, as most is filtered out by the eye's cornea and lens.

Ozone Depletion

  • Historical Context:
    • Ozone depletion first observed in 1985 over Antarctica.
    • Depletion has been attributed to the release of CFCs since at least 1960.
    • A 1% drop in ozone could lead to an additional 1 million skin cancer cases annually worldwide.

Causes of Ozone Layer Depletion

  • Chlorofluorocarbons (CFCs):
    • Initially used as refrigerants and in aerosol sprays since the late 1920s.
    • CFCs rise into the stratosphere where UV radiation releases chlorine atoms, which destroy ozone molecules:
    • 1 CFC molecule can destroy 100,000 ozone molecules before it is broken down.

The Ozone Hole

  • Formation Over Antarctica:
    • Polar vortex creates extreme cold temperatures (-85 ºC) facilitating the formation of polar stratospheric clouds (PSCs) that enhance ozone depletion.
    • Recent ozone holes can be several times larger than countries (e.g., three times the size of Brazil).

International Response and Regulation

  • Montreal Protocol (1987):
    • An international treaty designed to phase out ozone-depleting substances, including CFCs.
    • Banned the use of CFCs in aerosol cans and encouraged the development of CFC-free alternatives.
    • Universal ratification by UN nations shows global commitment to protect the ozone layer.
    • CFCs have a long atmospheric lifespan (60-120 years), meaning recovery of the ozone layer is a long-term process and is still ongoing.