Ozone depletionOzone depletion O3

very pale bluish gas very powerful oxidising agent pungent smelling odor absorbs UV light detection: [O3] in a sample of air can be

measured using UV spectroscopy; the more UV is absorbed the higher [O3]

in upper stratosphere; 15 to 45 km

Ozone depletionOzone depletionTwo functions absorbs UV – 290 – 320 nm; UV

causes sunburn, skin cancer, eye cataracts reduces plant growth, O3 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

Ozone:Ozone: natural cycle (stratosphere) formation of ozone: O2 + uv O + O (uv = 242 nm) O2 + O O3

natural depletion of ozone O3 + O 2O2

O3 + uv O2 + O (uv = 290 – 320 nm)

rate of formation = equal to rate of depletion = steady state both types of reactions are slow

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)

OzoneOzone: evidence of depletion

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

                                                                           

        

                                                                           

        

                                                                           

        

OzoneOzone: 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

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

OzoneOzone: anthropogenic depletion

Ozone depletionOzone depletion: equations photodissociation: C- Cl is weakest bond

CCl2F2 CClF2 + Cl

catalytic depletion:    Cl + O3 ClO + O2

   ClO + O Cl + O2

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

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