STRATOSPHERIC OZONE DEPLETION. Adapted from K. Sturges at MBHS

Transcription

1 STRATOSPHERIC OZONE DEPLETION Adapted from K. Sturges at MBHS

2 Ozone Layer Ozone is Good up high Stratosphere Bad nearby Troposphere Solar Radiation - range of electromagnetic waves UV shortest we see if violet- damages proteins and DNA molecules at surfaces of organisms UVA- can cause damage UVB- really bad- only 1% of UVB hits earth- responsible for sunburns and skin cancer Ozone shield Layer that protects w/o it life may not exist as we know it Absorbs UV radiation

3 Ozone Depletion in Stratosphere Ozone Protects earth from UV radiation 2012 John Wiley & Sons, Inc. All rights reserved.

4 Formation of the Ozone Shield Reaction #1: UV light + O 2 O + O Reaction #2: Free O + O 2 O 3 Reaction #3: Free O + O 3 O 2 + O 2 Reaction #4: UV light + O 3 O + O 2 The amount of ozone in stratosphere is dynamic- there is no equilibrium. Cycles of formation (reactions. 1 and 2) and destruction (reactions3 and 4)

5 OZONE DEPLETION IN THE STRATOSPHERE Ozone thinning: caused by CFCs and other ozone depleting chemicals (ODCs). Increased UV radiation reaching the earth s surface from ozone depletion in the stratosphere is harmful to human health, crops, forests, animals, and materials such as plastic and paints.

6 Ozone Depletion in Stratosphere Ozone thinning/hole First identified in 1985 over Antarctica Occurs annually between Sept and Nov because: Caused by human-produced bromine and chlorine containing chemicals (Ex: CFCs) 2012 John Wiley & Sons, Inc. All rights reserved.

7 OZONE DEPLETION IN THE STRATOSPHERE Since 1976, in Antarctica, ozone levels have markedly decreased during October and November. Figure 20-20

8 Chlorofluorocarbons (CFCs) Manmade, organic molecules in which both chlorine, fluorine or bromine atoms replace some of the hydrogen atoms. Releases chlorine/ fluorine/bromine atoms that split ozone Sources: refrigerators and air conditioners production of plastic foam cleaner for electronic parts pressurizing agent in aerosol cans

9 CFCs destroy ozone CFCs remain in the stratosphere for a century UV radiation breaks CFCs into chlorine and carbon atoms The chlorine atom splits ozone Ozone hole = decreased ozone levels over Antarctica One chlorine atom can destroy 100,000 ozone molecules

10 Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl 3, breaking off a chlorine atom and leaving CFCl 2. Cl Cl C Cl F Sun UV radiation Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. Cl Cl O O The chlorine atom attacks an ozone (O 3 ) molecule, pulling an oxygen atom off it and leaving an oxygen O molecule (O 2 ). O O Cl The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO). A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O2. Cl O O O Cl O O Stepped Art Fig , p. 486

11 OZONE DEPLETION IN THE STRATOSPHERE During four months of each year up to half of the ozone in the stratosphere over Antarctica and a smaller amount over the Artic is depleted. Figure 20-19

12 Ozone Layer Southern Hemisphere Hole Thinning of one area 50% less ozone than normal If anywhere besides the South Pole, would be drastic for human life Winter causes vortex- Cold Temps, H 2 O, other gases form stratospheric clouds Clouds provide chlorine reservoirs where chlorine (along with chlorine monoxide and methane) is trapped and not depleting O3 Spring and summer arrive, UV releases the chlorine allowing it to destroy O3

13 The Antarctic ozone hole High-altitude polar stratospheric clouds form during the dark, frigid winter Nitric acid in clouds splits chlorine off of CFCs A polar vortex (swirling winds) traps chlorine UV radiation in September (spring) sunshine dissipates the clouds and releases the chlorine The chlorine destroys the ozone December s warmer air shuts down the polar vortex Ozone-poor air diffuses, while ozone-rich air enters

14 Ozone Depletion in Stratosphere Hole over Antarctica requires two conditions: Sunlight just returning to polar region Circumpolar vortex- a mass of cold air that circulates around the southern polar region Polar stratospheric clouds form Enable chemical reactions that cause Cl and Br to destroy ozone 2012 John Wiley & Sons, Inc. All rights reserved.

15 Ozone Layer Northern Hemisphere No hole Thinning Intensifies in winter due to large particles found

16 Ozone Layer Not just in polar regions Thinning is supposed to peak Due to decline in chlorine and bromine concentrations in stratosphere by developing countries Montreal Protocol (more later) Scale use of CFCs down by 50% CFCs still produced in developing countries

17 Stratospheric Ozone Consequences Not enough ozone in stratosphere Human Health Sunburn Skin cancer Eye damage Efficiency of immune system Synergistic with other air pollutants Environmental Reduction of primary productivity in oceans Disruption of food chain (large animals first) Damage to fish, amphibians, mammals Widespread effects on major food crops Decreased plant productivity

18 Effects of Ozone Depletion Higher levels of UV-radiation hitting the earth Eye cataracts Skin cancer (right) Weakened immunity May disrupt ecosystems May damage crops and forests 2012 John Wiley & Sons, Inc. All rights reserved.

19 Recovery of Ozone Layer Montreal Protocol (1987) Reduction of CFCs Started using HCFCs (greenhouse gas) Phase out of all ozone destroying chemicals is underway globally Satellite pictures in 2000 indicated that ozone layer was recovering Full recovery will not occur until John Wiley & Sons, Inc. All rights reserved.

20 The Montreal Protocol Montreal Protocol = 196 nations agreed to cut CFC production in half by 1998 Follow-up agreements deepened cuts, advanced timetables, and addressed other ozone-depleting chemicals Industry shifted to safer, inexpensive, and efficient alternatives Challenges still face us CFCs will remain in the stratosphere for a long time Nations can ask for exemptions to the ban

21 The Montreal Protocol is a success It is considered our biggest environmental success story Research developed rapidly, along with technology Policymakers included industry in helping solve the problem Implementation of the plan allowed an adaptive management strategy Strategies responded to new scientific data, technological advances, and economic figures The Montreal Protocol can serve as a model for international environmental cooperation

22 Protecting the ozone layer International agreements reduced ozonedepleting substances The hole in the ozone has stopped growing

23 Natural Capital Degradation Effects of Ozone Depletion Human Health Worse sunburnmore eye cataracts More skin cancers Immune system suppression Food and Forests Reduced yields for some crops Reduced seafood supplies from reduced phytoplankton Decreased forest productivity for UV-sensitive tree species Wildlife Increased eye cataracts in some speciesdecreased population of aquatic species sensitive to UV radiation Reduced population of surface phytoplankton Disrupted aquatic food webs from reduced Air Pollution phytoplankton and Materials Increased acid deposition Increased photochemical smog Degradation of outdoor paints and plastics Global Warming Accelerated warming because of decreased ocean uptake of CO2 from atmosphere by phytoplankton and CFCs acting as greenhouse gases Fig , p. 488