1. The Ozone hole – Dobson Units and CFC replacements

2. What is a Dobson Unit? One Dobson units equals one-hundredth of a millimeter thickness of ozone layer at standard temperature and pressure (STP).

3. Dobson Units Ozone measured by Earth Probe TOMS over 43.00 Degrees Latitude -74.00 Degrees Longitude on 2004/09/16 is 275 Dobson Units

4. http://toms.gsfc.nasa.gov/

6. Why are there ozone holes above and below the poles? Conditions Cold Light – dark periods (summer winter) Swirling vortex of air

7. Free radical sequestering We left our discussion at the ‘sequestering’ of ClO. and Cl. ClO. + NO 2 → ClONO 2 Cl. + CH 4 → HCl + CH 3 Sequestered molecules can be “rained out when stratospheric and wet tropospheric air mix in the upper troposphere.” T.G Spiro and W.M. Stigliani

8. Cold: Absorption on ice (solid surface) However, the danger occurs when these can’t be rained out. Further danger occurs when solid surfaces are present. ClONO 2 and HCl can be absorbed in ICE ClONO 2 + HCl → Cl 2 + HNO 3 ClONO 2 + H 2 O → HOCl + HNO 3

9. Light: Formation of Radicals From previous slide: ClONO 2 + HCl → Cl 2 + HNO 3 ClONO 2 + H 2 O → HOCl + HNO 3 What happens to Cl 2 in light and HOCl in light?

10. Why are there ozone holes above and below the poles? Conditions Cold Light – dark periods (summer winter) Swirling vortex of air Ice formation Allows for accumulation of ClONO 2 Keeps ice crystals suspended in stratosphere

11. CFC Substitutes and the ‘Protocols’ Montreal protocol (1987) – 31 countries agree to cut CFC production by 50% by the year 2000 London Protocol (1990) ban CFC production by 2000 Helsinki and Copenhagen (1992) – ban CFC production by 1996.

12. Ozone hole appears Ozone hole disappears

13. Substitutes HFC’s C H H F C F F F C H H H C Cl F HCFC-141b HFC-134a Replaces CFC-12 Replaces CFC-11 95% less Damaging Than CFC11 Refrigerant Blowing Agent

14. CFC Replacements What substitutes did you find? Refrigeration and Foaming agents