Atmosphere & climate change

1. Atmosphere & climate change Chapter 13, Section 2: the ozone shield Standards: SEV4f

2. What is the ozone layer? • An area in the stratosphere where ozone is highly concentrated. • Ozone (O3) absorbs most of the UV light that comes from the sun.

3. What chemical is attributed with causing ozone depletion? Chlorofluorcarbons (CFCs) • When first invented, were valued because they are • Nonpoisonous • Nonflammable • Do not corrode • Were used for decades as • Coolants in refrigerators & air conditioners • Component of Sytrofoam • Propellant in hair spray, deodorant, insecticides & paint • In 1970’s it was discovered they may be damaging the ozone layer.

4. How do cfc’s deplete the ozone? • At ground level, CFCs are stable & do not cause problems. • When air currents carry them to the stratosphere they can deplete the ozone. • Takes 10-20 years for the CFC’s to make it to the stratosphere and they get recycled while they are up there so they are persistent for 60-120 years • UV light from sun breaks CFC which releases a chlorine atom. • The chlorine atom breaks a molecule of ozone (O3) into an O2 molecule and an oxygen atom (O) which the chlorine attaches to and creates chlorine monoxide (ClO) • Chlorine monoxide (ClO) hits another ozone and the chlorine breaks off again and attacks another ozone molecule. • 1 chlorine from CFC can destroy 100,000 ozone molecules.

5. Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breaking off a chlorine atom and leaving CFCl2. Sun Cl Cl Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. C Cl F UV radiation Cl Cl O O A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O2. The chlorine atom attacks an ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2). Cl Cl O O O O O The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO) Cl O O O

6. What is “the ozone hole”? • 1980’s scientists working in Antarctica noticed a thinning of the ozone by 50-98% that was occurring each spring.

7. How does the ozone hole form? • During the dark winter months, VERY cold strong winds called polar vortex winds trap CFC’s and convert them to molecular Cl2 • In the spring, UV rays split Cl2 and the individual Cl atoms break ozone down rapidly. • The thinning lasts for several months.

8. Why can’t ozone created at ground level (aka- bad ozone) help heal the ozone thinning? • Ozone at ground level is highly reactive and reacts with other molecules of air pollution before it can even enter the stratosphere.

9. What are the effects of ozone thinning on humans? • UV light can • Damage DNA • Premature aging • Weakened immune system • Increase chance of developing cataracts • Increase susceptibility to skin cancer

10. What are the effects of ozone thinning on animals & plants? • Oceans • Kills phytoplankton which is the bottom of the marine food chain. • Disrupts food chains • Phytoplankton removes CO2 so if they die, CO2 levels would go up in atmosphere (global climate change) • Freshwater • Kill amphibian eggs • Survivors suffer birth defects • Populations decline • Land Plants • Interferes with photosynthesis • Reduces crop yield

11. How can we protect the ozone layer? • Montreal Protocol (1987) • Meeting of several nations calling for reduction or elimination of CFCs in products. • Many manufacturers are switching to non-CFC propellants in aerosol cans. • You can help by: • Not buying Styrofoam products • If air conditioner leaks, fix it to prevent release to air.

12. You should be able to… • Describe the process by which chlorofluorcarbons destroy ozone molecules in the stratosphere. • Describe the process by which the ozone hole forms over Antarctica in the spring. • List five harmful effects that UV radiation could have on plants or animals as a result of ozone thinning. • Explain why it will take years for the ozone layer to recover, even though the use of CFCs has declined significantly.