Lecture Notes on Ozone Depleting Substances (ODS) and Methyl Bromide

Introduction to Ozone Depleting Substances

• ODS: Chemicals contributing to the depletion of the ozone layer.
• Methyl Bromide: Still used in agriculture, particularly in Southern California for strawberries.
  • Strawberry Cultivation:
    • Grown under black plastic to prevent moisture loss, keep soil warm, and keep fruit clean.
    • Methyl bromide used for pest control by injecting it into the soil.
    • Diffuses into the air, contributing to ozone layer depletion.
  • Future ban on methyl bromide is expected.

Historical Context and Actions Taken

• Freon: Another ODS, usage began in 1930.
  • Increased usage in the 40s, 50s, 60s.
  • Problem identified in 1970s, worsened until the 1980s.
• Regulation and Effects:
  • Freon levels in the air peaked in the early 2000s and are now decreasing.
  • Antarctic ozone hole continued to worsen until recently but shows signs of improvement.

Atmospheric Structure

• Troposphere: First 10 miles of the atmosphere, where weather and climate occur.
• Stratosphere: Contains the ozone layer.
  • Lack of mixing between the two layers.
  • ODS like freon take ~20 years to reach the stratosphere from the troposphere.

Freon and Its Impact

• Characteristics of Freon:
  • Colorless, odorless, non-toxic, non-flammable, and highly stable.
• Lifetime:
  • Takes 20 years to reach the stratosphere.
  • Has a 100-year lifetime, continually destroying ozone.
  • Chlorine atoms act like Pac-Man, destroying ozone for 80 more years.
• Current Status:
  • Freon levels in the troposphere are declining.
  • Still entering the stratosphere, affecting ozone.
  • Recent data shows the Antarctic ozone hole stabilizing.

Timeline for Resolution

• Estimates: 50-70 years for freon to be eliminated from the atmosphere.
• Conclusion: Ozone depletion is on the path to resolution, but slowly.

Current Implications

• Human Health:
  • Increased need for sunscreen due to remaining ozone depletion.
  • Australia faces severe impacts with a 400% rise in skin cancer rates.
  • Strict outdoor regulations for children in several Australian states.

Closing Remarks

• Ozone depletion is a unique environmental issue with a global consensus on a solution.
• While improvements are underway, precautions remain necessary for current generations until the solution fully takes effect.