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:
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 km altitude 99% of UV radiation screened by ozone Ozone absorbs ultraviolet (UV) radiation
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…
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
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
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
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
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
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
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!