stratospheric ozone depletion
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Stratospheric Ozone Depletion
IB syllabus: 5.6.1-5.6.6AP syllabusCh 17, 18
Video – The Hole Story
Syllabus Statements 5.6.1: Outline the overall structure and composition of
the atmosphere 5.6.2: Describe the role of ozone in the absorption of
UV radiation. 5.6.3: Explain the interaction between ozone and
halogenated organic gasses. 5.6.4: State the effects of UV radiation on living
tissues and biological productivity. 5.6.5: Describe three methods of reducing the
manufacture and release of ozone-depleting substances
5.6.6: Describe and evaluate the role of national and international organizations in reducing the emissions of ozone-depleting substances
vocabulary
Halogenated organic gases Pollution Non-point source pollution Replenishable natural capital
Atmospheric Structure
Layered structure – Troposphere, Stratosphere, Mesosphere, Thermosphere
Troposphere is layer next to earth’s surface – 75-80% of mass of earth’s air
Atmospheric composition 78% nitrogen, 21% oxygen, trace amounts of water, argon, carbon dioxide
Lapse rate – rate at which temperature declines with increasing altitude in the troposphere
Layers of the AtmosphereAtmospheric pressure (millibars)
0 200 400 600 800 1,000120
110
100
90
80
70
60
50
40
30
20
10
0(SeaLevel)
–80 –40 0 40 80 120Pressure = 1,000millibars atground levelTemperature (˚C)
Alti
tude
(kilo
met
ers)
Alti
tude
(mile
s)
75
65
55
45
35
25
15
5
Thermosphere
Heating via ozoneMesosphere
Stratosphere
Ozone “layer”Heating from the earth
Troposphere
TemperaturePressure
Mesopause
Stratopause
Tropopause
Ozone
Ozone is O3 formed from O + O2
Found in the lower Stratosphere as the ozone layer – good protective qualities
Found in the Troposphere as a result of human pollution – bad qualities photochemical oxidant
Ozone Formation
O3 + UV O + O2
O + O O2
O + O2 O3
It’s Replenishable
Ozone absorbs UV radiation
When UV strikes O3 it is absorbed and its energy used to break the chemical bond
O3 + UV O + O2
So UV doesn’t make it to the earth’s surface
Ozone Layer Layer in the lower stratosphere Keeps 95% of harmful UV radiation away Seasonal depletion of ozone layer above
Arctic & Antarctic, overall thinning everywhere but tropics
Depletion is serious long term threat to (1) humans, (2) other animals, (3) sun driven producers (plants) supporting food webs
CFC’s (Freons)
1. Discovered in 19302. Chemically stable, odorless, nonflamable,
nontoxic, noncorrosive dream chemical in the troposphere
3. Coolants, Propellants, Sterilants, Fumigants
4. 1974 discovered to be lowering concentrations of stratospheric ozone
5. Immediate ban called for
CFC’s II Large quantities being released – use, leaks,
production of plastics Remain in troposphere – unreactive, insoluble
very stable 11-20 years to rise to stratosphere Release high energy Cl atoms when exposed
to UV which speed up breakdown of ozone Each CFC lasts 65-385 years in stratosphere Can break down up to 100,000 molecules of
ozone
Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breakingoff a chlorine atom and leaving CFCl2.
UV radiation
Sun
Once free, the chlorine atom is off to attack another ozone moleculeand begin the cycle again.
A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O2.
The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO).
The chlorine atom attacksan ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2).
Cl
Cl
ClC
F
Cl
Cl
OO
Cl
OO
O
ClO
OO
ClO
O
Summary of ReactionsCCl3F + UV Cl + CCl2FCl + O3 ClO + O2
Cl + O Cl + O2
Repeated many times
Summary of Reactions
1. CCl3F + UV Cl + CCl2F
2. Cl + O3 ClO + O2
3. ClO + O Cl + O2
Steps 2 + 3 are repeated many times causing massive destruction of ozone
Methyl Bromide
Other major ODC Used as a pesticide and fumigant on crops Kills nematodes, fungi, weeds
Remember that ozone breaks down naturally when it absorbs UV
This speeds up that process and limits the regeneration of O3
Pollutants enhance O3 destruction disturbing the equilibrium of the O3 production system
Year
1970 1975 1990 2000 200519851955 1960 1965 1980 1995
400
350
300
250
200
150
100
Tota
l ozo
ne (D
obso
n un
its)
October monthly means
Decreasing ozone volume in fall over the poles
Seasonal Polar Thinning Seasonal loss of ozone in summers over poles Ozone hole is actually ozone thinning Sunless winters, polar vortex causes swirling
winds isolated from rest of atmosphere Ice crystals in clouds collect CFC’s and speed
release of Cl Sun returns in spring / summer and frees large
volumes of free Cl Ozone thinning travels north to effect Aus, NZ,
S. Am., S. Af.
August 7, 2001
October 10, 2001
35
30
25
20
15
10
5
0 5 10 15Ozone partial pressure (milipascals)
Alti
tude
(kilo
met
ers)
Year1979 1982 1985 1988 1991 1994 1997 2000 2003 2006
0
5
10
15
20
25
30M
illio
n sq
uare
kilo
met
ers
Figure 18-29Page 474Area of North America
Size of Ozone thinning
Antarctic
SeptOzoneLoss
Arctic
MarchOzoneLoss
Human Health
• Worse sunburn
• More eye cataracts
• More skin cancers
• Immune system suppression
Food and Forests
• Reduced yields for some crops
• Reduced seafood supplies from reduced phytoplankton
• Decreased forest productivity for UV-sensitive tree species
Wildlife
• Increased eye cataracts in some species
• Decreased population of aquatic species sensitive to UV radiation
• Reduced population of surface phytoplankton
• Disrupted aquatic food webs from reduced phytoplankton
Air Pollution and Materials• Increased acid deposition• Increased photochemical smog• Degradation of outdoor paints and plastics
Global Warming
• Accelerated warming because of decreased ocean uptake of CO2 from atmosphere by phytoplankton and CFCs acting as greenhouse gases
What are the effects?
Effects on Humans, Plants, Animals & Global climate
A 1% loss of stratospheric ozone equals a 2% increase in skin cancers & 1% increase in cataracts worldwide.
Humans make cultural changes, others cannot
Ultraviolet A Ultraviolet B
Thin layer ofdead cells
Squamouscells
Basallayer
Melanocytecells
Basalmembrane
Bloodvessels
HairEpidermis
Sweatgland
Dermis
Squamous Cell Carcinoma Basal Cell Carcinoma Melanoma
Solutions & Protection
Must immediately stop using ozone depleting chemicals
Long recovery time afterwards due to persistence in the atmosphere
Substitutes are available for most CFC uses Hydrocarbons seem to be best for future
How can the manufacture and release of ODC be reduced?
Refrigerants can be recycled Alternatives to gas blown plastics can be
used Alternative propellents – hydroflourocarbons
– better but a potent greenhouse gas Alternatives to methyl bromide can be used
for fumigation and pesticides
Problems Existing stockpiles were ok to use after the
phase out Old CFCs continue to leak out of junked cars
and fridges Black market trade in CFCs increasing because
they are not made but still useful China, India, Mexico have increased use and
production of CFCs Full recovery expected by 2050 if current
decline continues
Montreal Protocol 1987, 36 nations in Montreal Cut emissions of CFCs by 30% between 1989 and
2000 After 1989 ozone thinning info new meetings in 1990,
1992 formed new Copenhagen protocol, 177 nations more stringent reductions required
UNEP involved in these agreements as well as an accelerated phase out for Korea, China, India
Montreal Multilateral Fund est’d for aiding transition Also studying the relative effectiveness of the
measures being taken
Year1950 1975 2000 2025 2050 2075 2100
3,000
0
6,000
9,000
12,000
15,000A
bund
ance
(par
ts p
er tr
illio
n) No protocol
1987MontrealProtocol
1992CopenhagenProtocol
Ozone depleting chemical concentration Predictions in stratosphere
In the US
Government ratified Montreal Protocol agreeing stop production of CFC propellents
Taxes levied on CFC production and use Corporations changing their ways McDonalds (1987) – stopped use of
styrofoam packaging Caused foam packaging industry to stop
use of all CFCs by 1988
Next…
Return to 1980 levels by 2050 Assume countries follow agreement and
don’t produce new ODC Ozone loss has been cooling troposphere
masking global warming’s real effects Good precedent for global cooperation
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