Ozone Depletion

Chapter 4: Ozone Depletion

Outline

  • Stratosphere and UV Light

  • Ozone Hole

  • Sunscreens

  • Chlorofluorocarbons (CFCs)

  • Montreal Protocol

The Zones of the Atmosphere

  • Stratosphere

    • Located 10-30 miles from the Earth

    • Contains almost no water vapor but has 1000 times more ozone than the troposphere

    • Ozone absorbs ultraviolet (UV) light, warming the upper part of the stratosphere

    • Ozone protects all life on Earth by blocking UV radiation that can damage living tissues

    • Ozone is depleted by pollutants including Freon and bromine

Stratospheric Science

  • Ozone Definition:

    • Ozone is a molecule made up of three oxygen atoms (O₃)

    • Ozone concentration varies with altitude, with peak concentrations occurring between 30 and 35 kilometers

  • Good Ozone vs. Bad Ozone:

    • Good Ozone:

      • Found in the stratospheric layer (10-30 miles up)

      • Filters harmful UV light

    • Bad Ozone:

      • Found at ground level

      • Created by chemical reactions between air pollutants

      • Considered a pollutant itself

Ultraviolet Light (UV)

  • UV Spectrum:

    • UV-C: 100-280 nm (most harmful)

    • UV-B: 280-315 nm

    • UV-A: 315-400 nm

    • Wavelengths smaller than 280 nm are absorbed by the ozone layer

  • Health Effects of UV Light:

    • Vitamin D Activation:

      • Initiated by UV light exposure, crucial for calcium metabolism

    • Retinal Protection:

      • Only 1% of UV radiation reaches the retina due to filtering by the cornea and lens

    • Health Risks:

      • Cataract Formation

      • Melanoma: Different types of skin cancer, most severe form

      • Premature Aging of the Skin

      • Weakened Immune System

  • Susceptibility Index for Skin Cancer:

    • Comparative yearly melanoma disease instances and skin cancer susceptibility scores in 2018

      • New Zealand: 10.00, 2,473 cases

      • Australia: 9.67, 12,265 cases

      • Switzerland: 5.89, 2,484 cases

      • Sweden: 5.79, 2,911 cases

      • Norway: 5.71, 1,506 cases

      • Netherlands: 5.60, 4,804 cases

      • Denmark: 5.57, 1,596 cases

      • Slovenia: 5.19, 533 cases

      • USA: 4.62, 72,000 cases

      • Great Britain: 4.60, 14,445 cases

      • Finland: 4.59, 1,208 cases

      • Czech: 4.38, 2,194 cases

      • Germany: 4.36, 16,884 cases

      • Ireland: 4.02, 859 cases

      • Belgium: 3.79, 1,941 cases

Ozone Measurement

  • Dobson Spectrometer:

    • Total ozone content can be observed using satellites or instruments on the ground

    • Ground-based: Dobson instrument

    • Satellite-based: TOMS (Total Ozone Mapping Spectrometer)

    • Dobson Unit (DU):

      • The optimal amount of ozone equivalent to the height of two pennies

Stratospheric Ozone Depletion

  • Discovered in 1985 that stratospheric ozone levels over the South Pole were declining rapidly during September and October, known as the Antarctic Ozone Hole

    • This depletion has occurred since at least 1960

    • Causative Agents:

      • Chlorofluorocarbons (CFCs) were identified as the primary cause

      • At ground level, ozone is considered a pollutant, while in the stratosphere, it functions as a shield against UV radiation

    • The detrimental effects of depletion:

      • A 1% decrease in ozone correlates to an increase of approximately one million extra human skin cancers globally

      • Decreased agricultural production and diminished plankton populations leading to impacts on the food chain

Chlorofluorocarbons (CFCs)

  • Origin and Use:

    • First synthesized in 1928 by General Motors

    • Initially developed as a safer alternative for refrigerants

    • CFCs used in aerosol sprays, foam production, solvents, and refrigeration

  • Mechanism of Ozone Destruction:

    1. Release of CFCs:

      • CFCs are released into the atmosphere

    2. Ascend into the Ozone Layer:

      • CFC molecules rise into the stratosphere

    3. UV Radiation Interaction:

      • UV radiation splits CFCs, releasing chlorine (Cl)

    4. Ozone Depletion:

      • Chlorine radicals destroy ozone molecules

    5. Resulting Increase in UV Radiation:

      • More ozone depletion results in increased UV reaching the Earth, which is linked to higher skin cancer rates

The Ozone Hole

  • Notable Size:

    • The ozone hole over Antarctica is reported to be approximately three times the size of Brazil

  • Unique Antarctic Conditions:

    • The polar vortex during dark polar winters creates strong winds over Antarctica leading to unique atmospheric conditions

    • Extremely low temperatures (-85°C or -121°F) foster the formation of polar stratospheric clouds (PSCs), which are crucial for ozone-depleting reactions

Nobel Prize Recognition

  • Awarded in 1995 to:

    • Paul J. Crutzen

    • Mario J. Molina

    • Sherwood Rowland

    • For their contributions to understanding the chemical processes leading to ozone depletion

International Responses and Treaties

  • As evidence of ozone depletion mounted, nations began to restrict ozone-depleting chemicals

  • Montreal Protocol:

    • Established in 1987 with a coalition of 24 nations

    • A landmark international treaty aimed at phasing out the production of ozone-depleting substances, including CFCs

    • Represented a significant achievement in international environmental policy, holding nations accountable to reduce and eventually eliminate harmful chemicals

  • Current Status:

    • Aerosol cans no longer use CFCs as propellants

    • Air conditioning units are transitioning to CFC-free alternatives

    • All UN recognized nations have ratified the treaty

    • Continued efforts to eliminate ozone-depleting chemicals remain critical, as CFCs persist in the stratosphere for 60 to 120 years, slowing recovery of the ozone layer.