1. Stratospheric Ozone Depletion
By: Natalie Bahou & Yasmeen Al-Qadi
Stratospheric Ozone Depletion
By: Natalie Bahou & Yasmeen Al-Qadi

2. Definition of ozone depletion
Ozone layer depletion is the reduction of the amount of ozone in the stratosphere, caused by substances formed from breakdown of ozone depleting substances (manufactured chemicals).

3. Overall structure and composition of the atmosphere
Layers within the atmosphere (from the ground up) and their characteristics
Troposphere -
0-12km thick;
75% of all gases in atmosphere;
all weather happens here;
temperature falls with altitude
Stratosphere -
12-50 km thick
temperature increases with altitude (gets warmer!)
horizontal winds (jet stream)
contains ozone layer

4. Mesosphere -
50-80km thick
temperature falls with altitude
meteor showers happen here
Thermosphere -
aurora borealis and aurora australis
ionosphere here (reflects radio waves for communications)
can be very very hot (2000 C+) !
Exosphere -
outermost layer of earth’s atmosphere
550km+ above earth’s surface
satellites orbit here

6. The role of ozone in the absorption of ultraviolet radiation
allows UVa and UVb through, but blocks UVc waves
UVa - causes wrinkles
UVb - causes skin cancer
UVc - worst one because of damage to organisms/tissues
O2 + O + UV → O3
the energy provided by incoming UV light changes O2 → O3

9. The interaction between ozone and halogenated organic gases
HOG’s are usually stable but break down into halogen atoms (F, Cl, Br, I, At) which are highly reactive (CFC = chlorofluorocarbon; Cl and F are halogens; organic = contains carbon, therefore CFC = halogenated organic compound)
How ozone is depleted by CFC’s:
UV radiation breaks off a chlorine atom from a CFC molecule.
The chlorine atom attacks an ozone molecule (O3), breaking it apart and destroying the ozone.
The result is an ordinary oxygen molecule (O2) and a chlorine monoxide molecule (ClO).

10. sources of HOG’s - fire extinguishers, refrigerators, AC units
The chlorine monoxide molecule (ClO) is attacked by a free oxygen atom releasing the chlorine atom and forming an ordinary oxygen molecule (O2).
The chlorine atom is now free to attack and destroy another ozone molecule (O3). One chlorine atom can repeat this destructive cycle thousands of times.
sources of HOG’s - fire extinguishers, refrigerators, AC units

11. The effects of ultraviolet radiation on living tissues and biological productivity
reacts with melanin in skin to cause sunburn & skin cancer
overexposure degrades immune system (but how?)
required for production of vitamin D (a good thing)
interferes with photosynthesis in producers (esp. phytoplankton)
zooplankton then gain less energy from phytoplankton, and food chain suffers (i.e. productivity decreases)

13. Three methods of reducing the manufacture and release of ozone‑depleting substances
Ozone-depleting substances: CFC’s, halogenated organic gases
Reduce-Regulate-Restore model
Reduce:
replace gas-blown plastics because…
replace CFC’s with CO2, propane, or air
replace aerosol propellants
replace methylbromide pesticides with something other than GHG’s
don’t use aerosol hair products or deodorant - use alternatives (gel, mousse, roll-ons etc)

14. Regulate:
recover and recycle CFC’s from refrigerators and AC units
HCFC’s are better because they don’t persist as long in the atmosphere; however, they are still harmful to the ozone layer (just less so than CFC’s)
legislate to have refrigerators returned to the manufacturer in order to recover materials used in building them
capture CFC’s from scrap cars AC units
Restore:
remove chlorine from the stratosphere or add ozone (not exactly feasible!)
ozone layer is slowly replenishing itself as long as we continue the ban (see below)

15. The role of national and international organizations in reducing the emissions of ozone‑depleting substances
UNEP (United Nations Environment Programme) forges agreements on:
ITIHC (International Trade in Harmful Chemicals)
air pollution
contamination of international waterways
provide information to countries and public on disadvantages of pollution

16. 1987 Montreal Protocol
international agreement on the emission of ozone- depleting substances
froze production and consumption of CFC’s with goal of zero production by year 2000
LEDC’s granted a longer time to implement the treaty
China and India have not met their quotas under the MP because of their rapid economic growth and high demand for refrigeration & AC’s
good example of a successful international cooperative effort to alter human impact on the environment