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WHAT IS OZONE DEPLETION?

WHAT IS OZONE DEPLETION?. WHAT IS OZONE?. Triatomic form of oxygen (O 3 ) Strong oxidant (chemically reactive) In lower atmosphere = pollutant In stratosphere = protective “shield” • 90% of O 3 found b/w 15-40 km altitude • 99% of UV radiation screened by ozone

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WHAT IS OZONE DEPLETION?

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  1. WHAT IS OZONE DEPLETION?

  2. WHAT IS OZONE? • Triatomic form of oxygen (O3) • Strong oxidant (chemically reactive) • In lower atmosphere = pollutant • In stratosphere = protective “shield” • • 90% of O3 found b/w 15-40 km altitude • • 99% of UV radiation screened by ozone • Ozone absorbs ultraviolet (UV) radiation

  3. WHAT IS UV LIGHT? • Ultraviolet (UV) Radiation • Smaller wavelength, more energy • 3 types (wavelength): • 1. UVC: shortest, most energetic, most absorbed in stratosphere • 2. UVA: longest, transmitted to Earth, causes some damage • 3. UVB: MOST DANGEROUS! Strongly absorbed by O3 in stratosphere • but with less O3 there is more UVB…

  4. WHAT DAMAGE DOES LESS OZONE CAUSE? • Skin Cancer Epidemic • Most common cancer in US • Ultraviolet radiation (UVB) damages skin • 90% increase since 1970; 1 in 5 will contract; 40 – 50% over 65 • Related to ozone depletion • PROTECT YOURSELF! • • 50% of exposure by 18 • • Cumulative effect

  5. WHERE IS THE OZONE HOLE? • British Antarctic Survey scientists first measured O3 in 1957 • They published depleted levels of O3 in 1985 • Show clear decrease since 1970’s • NOT an actual “hole” but decreased concentration

  6. WHY DOES IT FORM OVER ANTARCTICA? • IT’S COLD! • Polar stratospheric clouds form ~20 km above poles in temps 195-190 K (-78 to -83 C) when sulfuric acid freezes • Polar vortex isolates air mass • Clouds hold nitrogen, removing chlorine sink (nitrogen oxides help remove Cl) • In the spring, sunlight sets off ozone depletion reactions

  7. WHAT CAUSES OZONE DEPLETION? • Hypothesis that anthropogenic CFCs have depleted O3 suggested in 1974 • Immediately controversial!! • Everyday products had CFCs • • Propellants in spray cans • • Refrigerants • • Cleaning agents • • Styrofoam

  8. Two reactions define cycle of destruction, a catalytic chain reaction: • 1. Cl + O3 ¯> ClO + O2 • 2. ClO + O ¯> Cl + O2 • Estimated that single Cl atom can go through cycle 200 times in stratosphere! • Further estimated that single Cl atom destroys ~100,000 ozone molecules in 1-2 years

  9. MONTREAL PROTOCOL 1987 • Plan for eventual reduction of global CFCs by 50% of 1986 levels; stop by 1999 • Because of dramatic evidence of destruction, timetables shortened; US ended production in 1995 • Even if all production of bad chemicals stopped today, problem would not go away • About 35% of CFC-12 will still be around in 2100, and ~15% in 2200

  10. SUMMARY • Ozone is a pollutant in lower atmosphere, and an effective measure of poor air quality. • Ozone is a GOOD thing, up in the stratosphere • We have caused a decrease in the stratospheric ozone concentration, leading to increased incidents of skin cancer, cataracts, suppressed immune system, damage to food crops • Take precautions in the sun!

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