Earth 2

Thursday, April 15, 1999
Announcements: Homework assignment was collected. The purpose of the homework...to show that it is very difficult to have CO2 levels decrease in the future while the population is growing.

Lecture notes:

STRATOSPHERIC OZONE

• Stratospheric Ozone is not the same as Global Warming

Ozone

• Ozone is actually O3--triotomic oxygen molecules
• In order to have O3, you must first have normal oxygen (O2)
• Before 2 billion years ago, if you examined rocks with iron in them, you would see that the Fe wasn't in the oxidized form. This meant that there wasn't enough O2 in the atmosphere.
• Presently, Fe in rocks is oxidized at the surface (rust). This happens because photosynthesis is occurring (CO2 + H2O + CH20 + O2)

What Happens...How is Ozone produced?

• Oxygen interacts with incoming solar energy in the UV Wavelength
• Oxygen is actually split during this process...O2--> O + O
• The split oxygen molecules rapidly recombine to form O2 again, HOWEVER, recombination produces O + O2 + m --> O3 + m (this recombination is caused by catalysts)
• Catalyst-element involved in (enable or speeds up) reactions that aren't changed at the end of the reaction
• This is how ozone is produced!
• O3 --> absorbs UV radiation

Possible Feedback

UV Light

• Damages tissue molecules
• Responsible for DNA Mutations
• Causes Cancer
• Stimulates the absorption of Vitamin B

• Ozone is a selective absorber at the UV Wavelength

Ozone Layer

• The stratosphere is 20-25 km thick
• The ozone layer is only .3 cm--> 300 Dobson Units

Catalysts

These are all natural sources

Together these produce a steady state balance

• Hydrogen (H)
• Hydroxyl (OH)
• Nitrous Oxide (NO)
• Bromine (Br)
• Chlorine (Cl)

Sources

Catalysts are found in:

• NaCl (table salt)
• Major volcanic eruptions-->Dust & gas penetrate the stratosphere, circulate, and eventually are evenly distributed throughout the world. The chlorine in this mixture physically destroys the ozone

Human Sources

• Chloroflourocarbons (CFC-11, CFC-12)
• trade name: FREON...which is a great coolant (air conditioners, refrigerators) and solvent (cleaner)
• CFC's have Cl in them, which enter the atmosphere and destroy the stratosphere
• CFC's are subject to photolysis

Various Reactions

O3 + M --> M + O2

MO + O --> O2 + M

O3 + O --> 2O2

O3 + Cl --> ClO + O

ClO + O --> O2 + Cl

O3 + O --> 2O2

One More Reaction

ClO + NO2 --> CLNO3

Cl + CH4 --> HCl + CH3

• This puts chlorine into other reservoirs
• This is a relatively stable reaction

• The air in this region cannot communicate with other air masses
• In Antartica, winds are circulating around. ClNO3 & HCl combine --> Cl2 which gets deposited on ice crystals in the polar stratospheric clouds
• In the Spring, Sun --> Photolysis...Cl2 --> Cl + Cl
• This doesn't just affect Antartica. There is a 2% - 4% decrease in the ozone layer globally

What to Do?

• The ozone layer was discovered in 1985 by the British Antartic Survey

1985-Vienna Convetion decides there is a definite problem

1986-Montreal Protocol signed, limiting CFC production and cutting production 1/2 by 2000

1990-London Amendment plans to totally phase out CFC production & other catalysts

1991-Copenhagen Amendment lists all ozone destroying catalysts & suggests Cl levels will eventually return to normal

Mitigation Strategy

CO2 - Global Warming

• Mitigate
• Adapt
• Do Nothing

Ozone

• Why was action taken immediately
• NO WINNERS...ONLY LOSERS
• TECHNOLOGY