O3zone StoryTerry Deshler, Atmospheric Science

• Formation• Importance• Loss

– Before 1985

– After 1985

• Recovery• Relationship to global warming

• The end

Relationship to Global Warming • Peripheral• Ozone has a slight greenhouse effect, but

• Loss of ozone over Antarctica may have intensified the polar vortex and reduced the warming expected in Antarctica

• CFCs are a significant green house gas

• Reduction of CFCs largest single human action mitigating the current warming

The End?• No, we have to limit the release of CFCs

into the atmosphere from now on.

• The good news - the atmosphere will cleanse itself of present atmospheric chlorine.

• The bad news - it will take another 50 years to see the ozone hole above Antarctica disappear.

Ozone Formation

• O2 + h O + O

• Then, O + O + M O2 + M

• or O + O2 + M O3 + M (Ozone created)– Where will this primarily occur?

• Also, O3 + h ( > 310 nm) O2 + O

• and O3 + h ( < 310 nm) O2* + O* (UV absorption)

• O2* + O2 2O2 + thermal energy (Excess energy dumped

• O2* O2 + h ( = 1.3 m) in ozone layer)

Importance of ozone• Absorbs DNA damaging UV radiation

– This UV affects both animals and plants

• SH/NH differences - In summer UV radiation is 50% more intense in SH than NH. Australia - world leader in skin cancer– Reasons – 10% - Earth is closer to sun in SH summer than

NH summer– 20% - Antarctic ozone loss/clearer atmosphere– 20% - Unknown

Food Preservation

• 100 BC - 1700s, Early methods: Drying, Salting, Cool cellars/Spring houses, Pickling, Fermenting, Canning.

• Cooking -> could eat spoiled food - spices to hide the flavor.

• 1803 Ice Boxes - Thomas Moore invented the insulated box, with ice was in a separate container above the food storage area. Relied on stores of natural ice from frozen lakes and rivers.

• 1850s - Methods to artificially produce ice were developed.

• 1890 - Warm weather/rain lead to a shortage of natural ice. Spurred the development of mechanical refrigeration.

Refrigeration• 1918 - Kelvinator, First refrigerator introduced to American market.

• 1920s - Refrigerators used ammonia (NH4), sulfur dioxide (SO2), (toxic, odorous), and methyl chloride (CH3Cl), (toxic, no odor) - silent killer.

• 1928 - Thomas Midgley, Fridgidaire, dichlorodifluoromethane (CCl2F2)

• 1929 - Fridgidaire and DuPont joined to produce CCl2F2, and CFCl3 as Freon.

1974 - Molina and Rowland - simple question - What happens to CFCs released into the atmosphere? (awarded Nobel prize Chemistry 1995)

CCl3 F (F-11) + h ( < 240 nm, z > O3 layer) CCl2F + ClCCl2F2 (F-12) + h ( < 240 nm, z > O3 layer) CClF2 + Cl

• Then• Cl + O3 ClO + O2

• ClO + O Cl + O2

• Net: O3 + O O2 + O2

• This would occur above ozone layer altitudes above 30 km

Reservoir molecules

• 1975 - 1980 – Predicted ozone losses above 30 km were not observed. Reservoir molecules discovered.

– Cl + CH4 HCl + CH3

– ClO + NO2 ClONO2

– HCl and ClONO2 are reservoir species.1984 – Models predict 10% ozone loss in 100 years for current CFC production rates.

Ozone Profiles

McMurdo Station,

Antarctica

1986 - 1994

1994

1986 1987 1988

1989 1990 1991

1992 1993

Late winterspring

During Winter

Catalytic Cycle Polar Stratosphere– PSC particle + HCl + ClONO2 Cl2

– Cl2 + h Cl + Cl

– 2 [ Cl + O3 ClO + O]

– ClO + ClO + M ClOOCl + M (M=N2 or O2)

– ClOOCl + h Cl + ClOO

– ClOO + M Cl + O2 + M– h = Sun’s return

• Net 2O3 + h 3O2

• A single Cl atom can destroy more than100,000 ozone molecules.

• This cycle will continue until the NO2 and OH lost in the form of HNO3 in polar stratospheric clouds is replenished by mid latitude air, thus converting Cl back to its reservoir species.

Nitric acid/waterIce

Nitric acid/waterIce

Molina &Rowland,1974

ReservoirMoleculesDiscovered

MontrealProtocol, andamendments

Antarctic ozone holediscovered

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Foam ExpansionSolventsPropellants

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1974Ozone Depletion

Hypothesis

1986Base Year for

Montreal Protocol

1996CFC PhaseoutComplete in

Developed Countries

CFCs HCFCs HFCs

Refrigerants

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An Industry in Transition

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Compliments of Paul Newmanand the Goddard automailer

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