“ Natural ” O 3 Destruction Water: H 2 O + UV light H +OH Free Radicals: Unpaired electrons...
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Transcript of “ Natural ” O 3 Destruction Water: H 2 O + UV light H +OH Free Radicals: Unpaired electrons...
“Natural” O3 Destruction
Water:H2O + UV light •H + •OH
Free Radicals:Unpaired electronsUnchargedVery reactive
Convert O3 to O2
NO
2 N2O + O2 4 NO
(soil bacteria)
NO + O3 NO2 + O2
energy +N2 + O2 2 NO
Energy = lightning or jet engine
Chlorofluorocarbons (CFCs)
• Natural means don’t account for O3 loss• Even with seasonal cycles
• Main suspect: CFCs– Cl + F + C–Man-made, gases– Unreactive (non-toxic, non-flammable,
cheap)
Uses: Coolants, propellants, styrofoam…
Related: Halons (C and F or Br – no Cl)
Inert CFCs?
Upper atmosphere = high energy UV bonds break
CFC (or halon) + UV •Cl
2 •Cl + 2 O3 2 ClO• + O2
2 ClO• ClOOCl
ClOOCl + UV ClOO• + •Cl
ClOO• Cl• + O2
Catalytic cycle
Fig.2.15
Why do we care about energy?
Reactions require energy
If light has enough E, the reaction occurs
If not, the reaction will not occur, no matter how muchlight you put in!
You won’t get a tan from standing in front of a radio- no matter how long!
In the Greenhouse (3.1)
• Avg. Temp. - Compare Earth to Venus:
Earth VenusBased on distance: 0°F 212°F
Actual 59°F 840°F
Why? Heat is held in longer by CO2 and H2Oin the atmosphere
Fig.03.02 Fig. 3.2
Greenhouse Gases
Absorb IR radiation - trap heat
CO2 & H2O (also methane, CH4)- No change in water
CO2 is on the riseMore now than 150 years agoEarth temp. has changed
Greenhouse Effect
Process where gases trap heat
Heat stays and warms the planet
Needed for life – planet would freeze otherwise
Too much = bad“Enhanced greenhouse effect”
Energy return of > 81% avg. temp. increase
History of Our Atmosphere
• Early atmosphere: 1000X CO2
• Bacteria used CO2, made sugars
6 CO2 + 6 H2O C6H12O6 + 6O2
(glucose)
Consumed Produced
How do we know?Core samples from the ocean
Bacterial remains tell temp.
Magnetic alignment tells when(relate to Earth’s magnetic core)
“Heavy water” composition of ice
More heavy water = higher temp.
Trapped bubblesTell conc. of CO2 when bubble formed
Fig.3.4
Theory:
Global warming:Caused by high CO2 and CH4 levels
Possible: High CO2 and CH4 levels are a resultof warming, not a cause
Fact: CO2 and CH4 trap heat and do contribute
Recent Evidence
Atmospheric CO2 is increasing
Global temps. are increasing
Fig. 3.5 Fig. 3.6
Other Factors
Orbital changesTemp maximaMajor and minor ice ages
Doesn’t entirely account for temp. changes
Airborne dust – volcanic activityCloud cover – weather patternsGreenhouse gases