1. Ozone depletion O 3 very pale bluish gas very powerful oxidising agent pungent smelling odor absorbs UV light detection: [O 3 ] in a sample of air can be measured using UV spectroscopy; the more UV is absorbed the higher [O 3 ] in upper stratosphere; 15 to 45 km

2. Ozone depletion Two functions absorbs UV – 290 – 320 nm; UV causes sunburn, skin cancer, eye cataracts reduces plant growth, O 3 destroys apparatus for photosynthesis can cause genetic mutations causes loss of plankton Ozone production releases energy which produces an increase in temperature in stratosphere which gives it stability

3. Ozone: Ozone: natural cycle (stratosphere) formation of ozone: O 2 + uv  O  + O  (uv = 242 nm) O 2 + O   O 3 natural depletion of ozone O 3 + O   2O 2 O 3 + uv  O 2 + O  (uv = 290 – 320 nm) rate of formation = equal to rate of depletion = steady state both types of reactions are slow

4. Ozone: Ozone: evidence for depletion Antartica, autumn 2003 ozone hole = area having less than 220 Dobson units (if 100 DU of ozone were brought to the Earth's surface, it would form a layer 1 millimeter thick)

5. Ozone Ozone: evidence of depletion

6. Ozone Ozone: depletion http://www.epa.gov/ozone/science/hole/size.html

7. Ozone Ozone: man-made depletion nitrogen oxides: sources: combustion, airplanes, nitrogenous fertilisers CFCs = chlorofluorocarbons used in: refrigerators, air conditioners, blowing agents, solvents, dry cleaning agents chemically stable, low toxicity, volatile, insulating, fire suppressive, low cost end up in stratosphere as they are not broken down Cl  free radical produced by uv - photodissociation Cl  acts as catalyst in ozone depletion – catalytic depletion

8. ChloroFluoroCarbons: ChloroFluoroCarbons: useful compounds chemically stable; long atmospheric life-time low toxicity low cost to manufacture volatile liquids good solvents insulating fire-oppressive

9. Ozone Ozone: anthropogenic depletion

10. Ozone depletion Ozone depletion: equations photodissociation: C- Cl is weakest bond CCl 2 F 2  CClF 2  + Cl  catalytic depletion: Cl  + O 3  ClO + O 2 ClO + O   Cl  + O 2

11. Ozone depletion: Ozone depletion: alternatives to CFCs Hydrocarbons such as propane and 2- methyl propane as refrigerant coolants: no halogens fluorocarbons: stronger C-Hal bonds hydrochlorofluorocarbons: hydrogen makes it more stable; fewer halogen free radicals released hydrofluorocarbons: stronger C-F bond

12. Ozone depletion: Ozone depletion: alternatives to CFCs Alternatives should still have other useful properties of CFS’s but propane and 2- methyl propane as refrigerant coolants: greenhouse gases/flammable fluorocarbons: greenhouse gases hydrofluorocarbons: still some depletion