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WHAT IS OZONE DEPLETION?. WHAT IS OZONE? Triatomic form of oxygen (O 3 ) Strong oxidant (chemically reactive) In lower atmosphere = pollutant In stratosphere.

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Presentation on theme: "WHAT IS OZONE DEPLETION?. WHAT IS OZONE? Triatomic form of oxygen (O 3 ) Strong oxidant (chemically reactive) In lower atmosphere = pollutant In stratosphere."— Presentation transcript:

1 WHAT IS OZONE DEPLETION?

2 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 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 O 3 in stratosphere but with less O 3 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 O 3 in 1957 They published depleted levels of O 3 in 1985 Show clear decrease since 1970s NOT an actual hole but decreased concentration

6 WHY DOES IT FORM OVER ANTARCTICA? ITS COLD! Polar stratospheric clouds form ~20 km above poles in temps 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 O 3 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 + O 3 ¯ > ClO + O 2 2. ClO + O ¯ > Cl + O 2 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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