Transcript Document 7411923

Section 9 and 10 Ozone Depletion
• What is the threat from ozone depletion? Good
versus bad ozone.
• What causes ozone depletion?
• What happens to ozone levels over Earth’s
poles?
• Why should we be worried about ozone
depletion?
• What are solutions to this problem?
Ozone Depletion
What is ozone?
“Good” versus “bad”
ozone
Where is the “ozone
layer”
Keeps out about 95% of
UV rays
Layer has been thinning
Ozone Depletion: What Causes
Depletion?
GM Chemist discovered
Chlorofluorocarbons in
1930 (CFCs)
…also known as freon
•
•
•
•
Very stable
Nontoxic
Noncorrosive
Inexpensive
“Dream Chemical”
Ozone Depletion: What Causes
Depletion?
CFCs used for:
• Coolant in refrigerators
and air conditioners
• Propellant in aerosol
sprays
• Cleaner for electronics
• Bubbles in plastic foams
• Insulations
Former Uses of CFCs
Air Conditioners
Refrigerators
Spray cans
Cleaners for electronic parts
Sterilizing medical instruments
Fumigants for granaries and cargo ships
Ozone Depletion: What Causes
Depletion?
Too good to be true:
1974 study at UC Irvine
indicated threat to
ozone layer from CFCs
Shock to the $28 billion
per year CFC industry –
DuPont and other
chemical companies
Ozone Depletion: What Causes
Depletion?
1) CFCs remain stable in
troposphere due to
unreactivity
2) Over 11-20 years they get
lifted into stratosphere by
convection and drift
3) Once in stratosphere they
break down by UV rays
releasing highly reactive
chlorine atoms (with
others) that in a chain
reaction break apart ozone
Ozone Depletion: What Causes
Depletion?
4) Each CFC molecule lasts
in stratosphere for 65-385
years
Can convert 100,000 of O3
to O2 during that time.
DuPont and others fought
findings until 1988 when
they admitted problems.
1995 Nobel Prize Chemistry
Ozone Depletion in the Stratosphere
Fig. 21-21 p. 484
Ozone Depletion: What Causes
Depletion?
CFCs are not the only
culprit
• Halons (fire
extinguishers)
• Hydrogen chloride
(space shuttle)
• Some natural
chemicals
Ozone Depleting Chemicals
Chlorofluorocarbons (CFCs)
Halons
Methyl bromide
Carbon tetrachloride
Methyl chloroform
Hydrogen chloride
Ozone “Hole”
During 4 months each
year half of the ozone
layer above Antarctica
is depleted
1984 researchers
discovered 40-50%
reductions in later
winter (August –
November)
Ozone “Hole”
“Ozone Hole” more
accurate “ozone
thinning”
Polar Vortex: circular
winds blowing around
poles during winter
isolates atmosphere.
Warming at end of winter
releases frozen
chemicals destroying
ozone
Ozone “Hole”
Huge problem for parts of
New Zealand, Australia
South American and
South Africa
Similar “hole” but less
severe over Arctic during
late winter early spring
Loss of the Ozone Layer:
Reasons for Concern
 Increased incidence and severity of sunburn
 Increase in eye cataracts
 Increased incidence of skin cancer
 Immune system suppression
Refer to
Fig. 21-23 p. 486
 Increase in acid deposition
 Lower crop yields and decline in productivity
Skin Cancers
Fig. 21-25 p. 487
Solutions: Protecting the Ozone Layer
1987 Montreal Protocol
36 nations:
Goal: reduce CFCs by
35% by 2000
1992 Copenhagen
Protocol accelerated
phase out
Good news: substitutes do
exist
If all of the ozone-depleting substances were
banned tomorrow, it would take about 90-150
years for Earth to recover to pre-1975 levels.
Solutions: Protecting the Ozone Layer
CFC substitutes
Montreal Protocol
Copenhagen Protocol
Fig. 21-27 p. 489