Chapter 13, Section 2: the ozone shield Standards: SEV4f ATMOSPHERE & CLIMATE CHANGE

An area in the stratosphere where ozone is highly concentrated. Ozone (O 3 ) absorbs most of the UV light that comes from the sun. WHAT IS THE OZONE LAYER?

Chlorofluorocarbons (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 Styrofoam Propellant in hair spray, deodorant, insecticides & paint In 1970’s it was discovered they may be damaging the ozone layer. WHAT CHEMICAL IS ATTRIBUTED WITH CAUSING OZONE DEPLETION?

At ground level, CFCs are stable & do not cause problems. When air currents carry them to the stratosphere they can deplete the ozone. Takes 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 years UV light from sun breaks CFC which releases a chlorine atom. The chlorine atom breaks a molecule of ozone (O 3 ) into an O 2 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. HOW DO CFC’S DEPLETE THE OZONE?

Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl 3, breaking off a chlorine atom and leaving CFCl 2. UV radiation Sun Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O 2. The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO) The chlorine atom attacks an ozone (O 3 ) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O 2 ). Cl C F O O O O O O O O O O

 1980’s scientists working in Antarctica noticed a thinning of the ozone by 50-98% that was occurring each spring. WHAT IS “THE OZONE HOLE”?

 During the dark winter months, VERY cold strong winds called polar vortex winds trap CFC’s and convert them to molecular Cl 2  In the spring, UV rays split Cl 2 and the individual Cl atoms break ozone down rapidly.  The thinning lasts for several months. HOW DOES THE OZONE HOLE FORM?

 Ozone at ground level is highly reactive and reacts with other molecules of air pollution before it can even enter the stratosphere. WHY CAN’T OZONE CREATED AT GROUND LEVEL (AKA- BAD OZONE) HELP HEAL THE OZONE THINNING?

 UV light can  Damage DNA  Premature aging  Weakened immune system  Increase chance of developing cataracts  Increase susceptibility to skin cancer WHAT ARE THE EFFECTS OF OZONE THINNING ON HUMANS?

 Oceans  Kills phytoplankton which is the bottom of the marine food chain.  Disrupts food chains  Phytoplankton removes CO 2 so if they die, CO 2 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 WHAT ARE THE EFFECTS OF OZONE THINNING ON ANIMALS & PLANTS?

 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. HOW CAN WE PROTECT THE OZONE LAYER?

 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. YOU SHOULD BE ABLE TO…