1. T HE T HIN B LUE B LANKET Environmental Science 2.1

2. O ZONE S HIELD – N ATURAL S UNSCREEN Halo of blue is created when sunlight is scattered by Earth’s atmosphere When UV light strikes an oxygen molecule (O 2 ), it splits the molecule to create free oxygen atoms Free oxygen atoms attach to O 2 in the air, forming ozone (O 3 ) Most of Earth’s ozone forms a protective filter within the stratosphere Ozone breaks down in the presence of certain chemicals Variations in amount of UV and upper atmosphere temp. cause natural swings in ozone concentration If system is balanced, rate of ozone formation is equal to rate of destruction (equilibrium)

3. CFC S – R ISKS AND B ENEFITS OF T ECHNOLOGY Chlorofluorocarbons (CFCs) – compounds that contain carbon, fluorine, and chlorine Nontoxic Nonflammable Inexpensive Old coolants were dangerous Methyl chloride leaks caused many deaths in 1920s First safe coolant was CFC-12 (freon) CFCs slowly rise into the stratosphere, where sun’s UV rays split chlorine from the CFC molecules, and chlorine attacks the ozone molecules History of CFCs – p. 93

4. B IOLOGICAL E FFECTS Stratospheric ozone prevents most of the Sun’s UV rays from reaching Earth UVB radiation is harmful to most organisms and is absorbed ONLY by ozone UVB causes premature aging of the skin, skin cancer, and cataracts Increase in UVB exposure lowers response of immune system Sunlight is necessary for photosynthesis, but UV light is not UVA and UVB decrease photosynthesis, growth, and reproduction of phytoplankton

5. W ARNING N OT H EEDED World Plan of Action on the Ozone Layer was created in 1977 to encourage countries to ban use of CFCs in aerosols CFCs were essential industrial chemicals, and alternatives were not readily available 1985 – 50% decrease in ozone concentration over Antarctica Ozone being destroyed faster than natural processes can replace it Increased incidents of skin cancer

6. M ONTREAL P ROTOCOL Chlorine is major cause of ozone destruction 35 countries signed the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987 Goal is total elimination of production and use of the chemicals that deplete the ozone layer Stratospheric ozone level is lowest since measurement began in 1978 UVB radiation at highest level

7. F INDING A LTERNATIVES Use of all new CFCs has been banned in industrialized countries Recycled CFCs may still be used to maintain existing equipment High cost of CFC substitutes has encouraged illegal marketing A/C units and refrigerators now contain HCFCs, which contain hydrogen Less destructive to ozone layer b/c less stable and fewer molecules reach stratosphere Production must stop by 2030

8. Halons – stable chemicals that contain bromine, fluorine, and carbon Destroying ozone much faster than CFCs Halons in fire extinguishers are being replaced with CO 2 CO 2 not suitable for all fires