ozone depletion in the stratosphere the other story ch. 19
TRANSCRIPT
Ozone Depletion in the Stratosphere
The other storyCh. 19
APES
• Everything away except a writing utensil
Alt
itu
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(k
ilom
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rs)
Ozone concentration (ppm)
Alt
itu
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(m
iles)Stratospheric ozone
Stratosphere
Troposphere
40
35
30
25
20
15
10
5
00 5 10 15 20
0
5
10
15
20
25
Photochemical ozone
Beneficial Ozone
Harmful Ozone
*
What does the ozone layer do?
Protects Earth from dangerous UV
What does the ozone layer do?
• Protects Earth from dangerous UV – Cause mutations
• Higher rate skin cancer, cataracts, and immune system problems
– Essential for life: affect plants & marine ecosystems in unknown ways
– Prevents tropospheric ozone
Stratospheric Ozone Absorbs: • ALL UV-C radiation (most energetic – most lethal)• MOST UV-B radiation, but NO UV-A radiation
Consequence: Increase UV (UVB) reaching Earth’s surface
Human – Sunburn– Skin Cancer– Cataracts– Efficiency in immune
system
Ecosystem– Reducing of primary
productivity in oceans– Disrupt food chains– Damage
fish/amphibians/mammals
– Widespread effects on major food crops
– Decrease plant productivity
– Impair/destroy phytoplankton
Class of Chemicals Primarily Responsible for Thinning of Stratospheric Ozone Layer
Class of Chemicals Primarily Responsible for Thinning of Stratospheric Ozone Layer
• Chlorofluorocarbons (CFCs)– Coolant/refrigerant/air conditioner– Aerosol or propellant– Foam-blowing plastics/insulation (styrofoam)– Solvent/Cleaners
• Halocarbons– Fire retardants (fire extinguishers)– Soil fumigant/pesticide– Solvents– Foam blowing insulation
Class of Chemicals Primarily Responsible for Thinning of Stratospheric Ozone Layer
• Chlorofluorocarbons (CFCs) – AKA Freons– Wonder Chemical – Inexpensive– Stable in troposphere
• Chemically unreactive• odorless• nonflamable• nontoxic,• non corrosive
Class of Chemicals Primarily Responsible for Thinning of Stratospheric Ozone Layer
• Others– Hydrobromoflurocarbons (HBFCs)
• Fire extinguishers
– Methyl bromide • fumigant
– Hydrogen chloride • Emitted by space shuttles
– Carbon tetrachloride, methyl chloroform, n-propyl bromide, hexachlorobutadiene
• Cleaning solvents
HOW do CFCs Break Down Ozone?*
1. CFCs & others released into troposphere
2. CFCs move/drift upward into stratosphere
3. UV radiation breaks apart CFCs releasing Chlorine (bromine/fluorine)
4. Sunlight causes chemical reaction allowing Cl to attack O3 creating O2
THUS reducing O3 levels
HOW do CFCs Break Down Ozone?*
CCl3F+UV Cl+CCl2F
Cl + O3 ClO + O2
ClO + O CL + O2
SunOnce 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).
UV radiation
Cl Cl
ClC
F
The chlorine atom attacks an ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2).
Cl
Cl
OO
O
Cl
ClO
ClO
OO
OO
Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breaking off a chlorine atom and leaving CFCl2.
O
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How Do We Know This is Happening?
Predicted by Mario Molina & Sherwood Rowland
How Do We Know This is Happening?
• James Lovelock predicted haze came from human sources
• Presented at conference with meteorologists & chemists
Original Hypothesis
Nitrogen Dioxide Neutralizes Some Chlorine
Still Significant (though lower) levels of ozone depletion
Hypothesis Changes
Seasonal Thinning of Ozone at the Poles
During four months of each year up to half of the ozone in the stratosphere over Antarctica and a smaller amount over the Artic is depleted.
Seasonal Thinning of Ozone at the Poles
• Polar stratospheric clouds - high-altitude clouds of ice particles in ozone layer
• Ice particles provide solid surface for reactions
Seasonal Thinning at the Poles
Ozone thinning (hole)
Polar vortex
Seasonal Thinning of Ozone at the Poles
Final Hypothesis
Additional Evidence
• Airplane flew through ozone hole
Ozone Depletion Occurs Worldwide
Montreal Protocol• 1987• 36 nations• 50% reduction in CFC (not
others) production by 1998• Phase out CFCs in developed
countries by 1996• Phase out use of CFCs in
developing countries by 2005
Copenhagen Protocol• Montreal Protocol Amendment• 1992• 93 countries • Accelerated phase out – by 1996
PREVENTION!!
International Cooperation
• Reach 1980 levels by 2068• 1950 levels by 2108
Ozone Depletion
Projected worse over Antarctic and Arctic between 2010 & 2019
Characteristics of Global Warming and Ozone Depletion
Global Warming
CO2, CH4, NOx (greenhouse gases)
Absorbs infrared (IR) radiation
Raising the earth’s surface temperature
Decrease burning of fossil fuels
Ozone Depletion
O3, O2, and CFCs
Absorbs ultraviolet (UV) radiation
Decreasing O3 concentration in the stratosphere
Eliminate CFCs