1. Climate Change and Ozone Loss
AP Environmental Science

2. Stratospheric Ozone Depletion

3. Altitude (kilometers) Ozone concentration (ppm)40 25 35 20
Stratosphere 30
Benefical Ozone 25
Stratospheric ozone 15
Altitude (kilometers) 20
Altitude (miles) 10 15 10 5
Troposphere
Harmful Ozone 5
Photochemical ozone 5 10 15 20
Ozone concentration (ppm)

4. Atmospheric Ozone
Ozone is a gas found in the upper atmosphere that blocks some UV radiation.
97% of the ozone is in the stratosphere
Most forms over tropics
Slow circulation currents carry the marjority of it to the poles= thickest layer above poles 4

5. Stratospheric Ozone Cont’d
A concentration of pollution at the poles and other factors caused chlorine pollution to be concentrated in Antarctica.
When the sun returns in the spring, the energy liberates the chlorine from ice.
Chlorine causes ozone (O3) to be broken down into oxygen (O2). 5

6. Importance of Ozone Essential for terrestrial life Reduces sunburn
Prevents tropospheric ozone
How?

7. Formation of Ozone
Formed in the stratosphere by the reaction of UV radiation striking an oxygen molecule
The oxygen molecule splits and forms oxygen atoms.
Atomic oxygen can now react with molecular oxygen to form ozone
Atomic oxygen can also react with ozone to produce oxygen gas
These reactions generally balance each other so that the concentration of ozone in the stratosphere remains fairly constant, which keeps the amount of UV radiation reaching Earth fairly constant.

8. Ultraviolet Radiation
UV-A: Causes skin tanning
UV-B: Causes blistering sun-burns and is associated with skin cancer
UV-C: Found only in the stratosphere and is responsible for ozone formation

9. Ozone Depletion in Stratosphere
Thinning of the ozone layer was discovered in 1985.
Occurs seasonally an is due to the presence of human-made compounds containing halogens (chlorine, bromine, fluorine, or iodine)
Measurements indicate that the ozone over the Antarctic has decreased as much as 60% since the late 1970s with an average net loss of about 3% worldwide

10. Ozone Depleting Chemicals
Main Culprit: Chlorofluorocarbons (CFCs)
Others:
Methyl bromide (fumigant)
Halons (fire extinguishers)
Carbon tetrachloride (solvent)
Methyl chloroform (cleaning solvent and propellant)
N-propyl bromide (solvent)

11. CFCs
First manufactured in the 1920s, they are used as refrigerants (ie Freon), aerosol propellants, electrical part cleaning solvents, and in the manufacture of foam products and insulation.
By 1974, nearly 1 million tons of CFC gases were produced each year, and the chemicals were making $8 billion worth of business.
The largest single source of CFCs to the atmosphere is leakage from air conditioners.
The average life span of CFC in the environment is 200 years

12. The Ozone Depletion Reaction
CFC molecule enters stratosphere & UV radiation causes it to decompose and produce atomic Chlorine
The atomic Cl reacts with ozone to produce Chlorine Monoxide (ClO)
The ClO then reacts with more O3 to produce even more atomic Cl…Chain Reaction
Thus, 1 Cl atom released from a CFC can ultimately destroy over 100,000 ozone molecules.

13. Sun UV radiation Cl C F Cl Cl O Cl Cl O O O Cl O O Stepped Art
Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breaking off a chlorine atom and leaving CFCl2.
Once free, the chlorine atom is off to attack another ozone molecule
and begin the cycle again.
UV radiation Cl C F Cl Cl O Cl
A free oxygen atom pulls
the oxygen atom off
the chlorine monoxide
molecule to form O2.
The chlorine atom attacks an ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen
molecule (O2). Cl O O O Cl O
The chlorine atom and
the oxygen atom join to
form a chlorine monoxide
molecule (ClO). O
Stepped Art
Fig , p. 486 13

14. Also…
Bromine is found in much smaller quantities than chlorine, but is about 50x more effective in its job at destroying ozone.
It is responsible for 20% of the problem.
Found in halons which are used in fire extinguishers

15. OZONE DEPLETION IN THE STRATOSPHERE
During four months of each year up to half of the ozone in the stratosphere over Antarctica and a smaller amount over the Arctic is depleted. 15

16. Seasonal Thinning at the Poles
Ozone thinning (hole)
Polar vortex
Fig p. 475

17. Effects of Ozone Depletion
During the 1998 Antarctic spring, a hole 3x the size of Australia developed in the ozone layer, allowing more UV radiation to reach Earth’s surface.
-Harmful effects of UV include:
Increased incidence and severity of sunburn
Increase in eye cataracts
Increased incidence of skin cancer
Immune system suppression
Increase in acid deposition
Stratosphere cooling
Increases in mutations (changes in DNA structure)
Lower crop yields and decline in productivity

18. Risks from Increased UV Radiation
A 1% decrease in ozone is expected to produce a 5-7% increase in skin cancer.
Malignant Melanoma,
Garrison, 2005 18

19. Decreased Phytoplankton Productivity
As southern hemisphere summer begins.
Due to increased influx of UV rays through ozone hole over Antarctica.
Phytoplankton around Antarctica form the base of a food chain critical to whales and remove much CO2 from atmosphere.
Garrison, 2005 19

20. Strategies for Reducing Ozone Depletion
Montreal Protocol (1987)
Designed to protect st. ozone layer
Stipulated that production and consumption of compounds that deplete ozone were to be phased out by 2000
The Montreal Protocol was passed in 1989.
CFC levels in the atmosphere decreased and the ozone layer is beginning to recover.
They are still legal in many developing countries 20

21. Variation of CFC-11 Levels from 1977-1996
A leveling off & slight dip in CFC levels appears to be happening as a result of CFC phase out after treaty.
Garrison, 2005 21

22. Alternatives HCFC replaces chlorine with hydrogen
Still capable of destroying ozone; less effectively because it breaks down more in troposhere
Alternatives to halons in fire extinguishers
He, Ammonia, Propane, Butane can be used as coolants

23. Characteristics of Global Warming and Ozone Depletion
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

24. The Ultimate Proof of Global Warming
Let me be brief.