Upload
alair
View
39
Download
0
Tags:
Embed Size (px)
DESCRIPTION
E 4. Ozone depletion in stratosphere. Describe the formation and depletion of ozone in the stratosphere by natural processes. List the ozone-depleting pollutants and their sources. Discuss the alternatives to CFCs in terms of their properties. Ozone depletion. O 3 very pale bluish gas - PowerPoint PPT Presentation
Citation preview
E 4. Ozone depletion in stratosphere
Describe the formation and depletion of ozone in the stratosphere by natural processes.
List the ozone-depleting pollutants and their sources.
Discuss the alternatives to CFCs in terms of their properties.
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
The Structures of different forms of oxygen
UV Wavelengths
Bonds in Oxygen and ozone are broken when they absorb UV radiation (only if sufficient energy)
O2 is stronger than ozone so is broken by UV of shorter wavelengths
UV Wavelengths
The energy Ephoton of a photon of light is related to its frequency f:
Ozone depletionOzone depletionTwo functions absorbs UV – 290 – 320 nm; UV
causes sunburn, skin cancer, eye cataracts (=clouding of the eye – can lead to blindness)
reduces plant growth as 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 molecules in the Earths atmosphere absorbs UV light
Ozone:Ozone: natural cycle (stratosphere) formation of ozone:
O2(g) + uv O(g) + O(g) (uv = 242 nm)
O2(g) + O(g) O3(g) natural depletion of ozone
O3(g) + O(g) 2O2(g)
O3(g) + uv O2(g) + O(g) (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
fertilisersNO(g) + O3(g) NO2(g) + O2(g)
NO2(g) + O (g) NO(g) + O2(g)
CFCs = chlorofluorocarbonsused in: refrigerators, air conditioners, blowing agents, solvents, dry cleaning agentschemically 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 depletionOzone depletion: equations catalytic depletion:
NO + O3 NO2 + O2
NO2 + O NO + O2
When added:
O3 + O 2O2
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 have all useful properties of
CFS’s but some issues: propane and 2- methyl propane as refrigerant
coolants: greenhouse gases/flammable fluorocarbons: greenhouse gases but not
flammable hydrochlorofluorocarbons: still some depletion as
has Cl, and also greenhouse gases
Environmental Impact of Ozone Depletion Ozone protects the Earths surface from
dangerous high-energy UV radiation Induces skin cancer and eye problems Damages aquatic life