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

2. Disruption of Biogeochemical Cycles
Carbon cycle—addition of carbon dioxide to the troposphere mostly by burning fossil fuels
Have potential to warm earth’s atmosphere
Nitrogen cycle—release of nitrogen oxides & gaseous ammonia by burning fossil fuels and using nitrogen fertilizer
Have the potential to lower pH of soils, streams, & lakes
Sulfur cycle—release of sulfur dioxide from petroleum refining and burning of coal
Forms sulfuric acid as a component of acid rain

3. 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

4. UV and the Atmosphere

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

6. UV and Ozone
UV radiation is absorbed during the process of formation and destruction of ozone and oxygen
O2 and O3 are continuously breaking down and reforming – dynamic equilibrium
UV causes O2 to break down into monoatomic O
Oxygen atoms are very reactive so they can combine with an oxygen molecule to form ozone (O3).

7. Ozone and Halogenated Organic Gases
Halogens – Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At).
Halogenated organic gases are stable unless exposed to UV – these released halogens react with monoatomic oxygen and slow ozone formation, disturbing the equilibrium

8. Sources CFCs (chlorofluorocarbons) HCFCs (hydrofluorocarbons)
Halons (fire extinguishers – release bromine atoms)
Methyl Bromide (pesticide – releases bromine atoms)

9. 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

10. 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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11. 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

12. Seasonal Ozone Thinning

13. Seasonal Ozone Thinning
Steady winds create a circular pattern over the earth’s poles creating a polar vortex
CFCs & ODCs cannot react with ozone in the dark, so they accumulate each winter
Upon return of sunlight in spring, large numbers of chlorine atoms are released, destroying 40-50% of ozone above Antarctica
When vortex breaks up, masses of ozone-depleted air move away from poles

14. 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

15. Solutions? Recycle refrigerants
Alternatives to glass-blown plastics, alternative propellants (propane)
Alternatives to methyl bromide
Aerosol cans use liquified petroleum gas (LPG)

16. Montreal Protocol Montreal Protocol (1987)
international agreement on reduction of emission of ozone-depleting substances (CFCs and later added halons)
Most countries followed the rules but China and India continued to produce and use huge amounts of CFCs. But they have since both agreed to phase out the use of CFCs.
unfortunately CFCs have a long lifespan and it has been estimated that the levels will not return to normal before 2050
London Agreement (1990) and Copenhagen Treaty (1992) offered more restrictions on CFC emissions
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17. Montreal Protocol