Ozone 1 Ozone Two Faces Troposphere Bad Ozone

Ozone 1

Ozone – Two Faces • Troposphere – Bad Ozone –Pollution • Photochemical smog • Eye irritant • Stratosphere – Good Ozone –Blocks some UV radiation –Hole caused by depletion due to ODC’s (Ozone Depleting Chemicals) 2

O 2 + uv O + O 2 O 3 COPY THIS CHART!!

Natural destruction of the ozone. . … COPY THIS CHART!!

Continuous cycle!

Ozone production in the stratosphere is important as it blocks some UV radiation UVA – very little is blocked by the ozone layer UVB – partially blocked by the ozone layer, causes burning & skin cancer 6

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Anthropogenic disruption of the stratospheric ozone cycle is caused by …… 8

Production of……. Ozone Depleting Chemicals (ODCs) 9

Ozone Depleting Chemicals (ODCs) • Chlorofluorocarbons (CFCs) (most common) • Halons • Methyl Bromide fumigant used in agriculture to control pests • Carbon Tetrachloride (CCl 4) 10

http: //www. mmscrusaders. com/newscirocks/ozone/cfc. jpg 11

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

http: //www. clas. ufl. edu/users/dlsmith/Lecture_11. html

A single chlorine atom removes about 100, 000 ozone molecules before it is taken out of operation by other substances 15

There is a seasonal fluctuation in the ozone hole above Antarctica. The ozone hole builds up over the winter months, peaking at around September and breaking up again by December. July August September October Why? November December

• Winter = no sunlight at poles • Air in the polar vortex can get very cold - 80 C • Special clouds called Polar Stratospheric clouds form • PSCs are crucial for ozone loss to occur The frozen crystals that make up polar stratospheric clouds provide a surface for the reactions that free chlorine atoms in the Antarctic stratosphere

September 21 -30, 2006 the average area of the ozone hole was the largest ever observed, at 10. 6 million square miles

Why should we be concerned about more UV B radiation reaching the surface of Earth? 20

effects of more UV radiation • • • Skin cancer such as melanoma Cataracts and sun burning Suppression of immune systems Lower crop yields Reduction in the growth of ocean phytoplankton • Deeper penetration into bodies of water • Degradation of paints and plastic material 21

melanoma matrix. ucdavis. edu/tumors/tradition/ gallery-ssmm. html

cataract www. snec. com. sg/clinical_services/ cataract. asp

Solutions? 24

an international treaty designed to protect the ozone layer by phasing out the production of numerous substances believed to be responsible for ozone depletion. Five revisions 1990 (London) 1992 (Copenhagen) 1995 (Vienna) 1997 (Montreal) 1999 (Beijing) 25

Hopefully closed by end of the century 26