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 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 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!