1. Atmosphere Composition of air Nitrogen (78%) Oxygen (21%)
Water vapor (0.01-4%)
Argon (< 1%)
Carbon dioxide (0.037%)

2. Ozone Oxygen molecules interact with UV radiation from sun
Keeps about 95% of the sun’s harmful UV radiation from reaching earth’s surface
Stratospheric ozone is essential to life on earth
Tropospheric ozone forms photochemical smog

3. UV and the Atmosphere

4. UV and Ozone
Some UV radiation from the sun is absorbed by stratospheric ozone causing it to break apart.
Under normal conditions the ozone molecule will reform
This is a dynamic equilibrium

5. Ozone and Halogenated Organic Gases
Halogens – Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At).
Halogen atoms (such as chlorine) increase destruction of ozone in a repetitive cycle, allowing more UV radiation to reach the Earth

6. Ozone Depleting Substances
CFCs (chlorofluorocarbons)
Aerosols, gas-blown plastics, refrigerants
Halons (fire extinguishers – release bromine atoms)
Methyl Bromide (pesticide – releases bromine atoms)

7. CFCs
Chlorofluorocarbons (CFCs)—stable, odorless, nonflammable, nontoxic, & noncorrosive chemicals
Coolants in refrigerators & air conditioners (freon)
Largest source - leaking car air conditioners
Propellants in aerosol spray cans
Cleaners for electronic parts such as computer chips

8. UV and Living Organisms
The effects of UV on living tissues includes:
Mutation during cell division
Health effects (sunburn, skin cancer, eye cataracts, & damage to immune system)
Damage to photosynthetic orgamisms (phytoplankton and their comsumers)
Decreases productivity

9. Ozone Depletion
CFC molecules break down under the influence of UV radiation releasing high energy chlorine atoms which speed up the breakdown of ozone into oxygen
Causes ozone in various parts of the stratosphere to be destroyed faster than it is produced
CFC molecules last on average years
Each chlorine molecule released can convert 100,000 molecules of ozone into oxygen
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10. Results of Ozone Depletion
Increased UV radiation reaching earth’s surface
Increase in acid deposition & photochemical smog
Lower yields of key crops (corn, rice, cotton, soybeans, wheat)
Decline in forest productivity (reducing CO2 uptake, enhancing global warming)
Increased breakdown & degradation of paints, plastics, & outdoor materials
Reduction in productivity of surface-dwelling phytoplankton in oceans

11. Solutions?
Reduce manufacture and release of ozone-depleting substances
Recycle refrigerants
Alternatives to glass-blown plastics, halogenated pesticides, propellants and aerosols
Develop non-propellant alternatives

12. Ozone Thinning
40-50% of ozone in upper stratosphere over Antarctica was destroyed after 1976
Takes years for CFCs to reach the stratosphere
Peak production of CFCs occurred in 1989
In 2000, ozone thinning above Antarctica covered an area 3x the size of the continental US

13. Montreal Protocol
UNEP (United Nations Environment Programme) – provides information,
forges international agreements, studies the effectiveness of these agreements, and the difficulties implementing and enforcing them
Montreal Protocol on Substances that Deplete the Ozone Layer (1987)
international agreement on reduction of use of ozone-depleting substances National governments complying with the agreement made national laws and regulations to decrease the consumption and production of halogenated organic gases (such as CFCs)

14. Montreal Protocol

15. Significance of Montreal Protocol
The best example of international cooperation on an environmental issue
An example of many experts in their different fields coming together to research the problem and find solutions
The first to recognize that different countries could phase out ODCs at different times depending on their economic status
The first with regulations that were carefully monitored

16. Unfortunately…..
Though most countries followed the rules, China and India were still producing huge amounts of CFCs—their need for refrigerators and ACs is growing due to fast economic growth
China has agreed to phase out ODC production 2 years ahead of schedule and India has as well
Because CFS have a long life, chlorine did not reach its peak until 2005
It will take until 2050 to return to pre-ODC levels