“ Natural ” O 3 Destruction

“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