O3zone
A story in three acts
• Introducing three oxygen atoms in one
molecule - O3zone - our hero
• Narrator - Terry Deshler
Can you answer the ozone quiz?
If not stay tuned.
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How does ozone form?
Why is ozone important?
Is ozone being lost over Antarctica?
If so, why Antarctica and not over Laramie?
Is ozone loss caused by human activity?
Does ozone loss occur above the Arctic?
Will ozone recover soon?
Is ozone loss related to global warming?
Ozone Formation
• O2 + hν → O + O
• Then, O + O + M → O2 + M
• or O + O2 + M → O3 + M (Ozone created)
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Where will this primarily occur?
• Also, O3 + hν (λ > 310 nm) → O2 + O
• and O3 + hν (λ < 310 nm) → O2* + O* (UV absorption)
• O2* + O2 → 2O2 + thermal energy (Excess energy dumped
• O2* → O2 + hν (λ = 1.3 µm)
in ozone layer)
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Our setting the atmosphere
Our setting the atmosphere
Our setting the atmosphere
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Our setting the atmosphere
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
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Is ozone being lost over
Antarctica? (data time)
– YES!
– So let us introduce our
vocabulary / cast of
characters
Polar ozone loss (act I)
cast in order of appearance
• Chlorofluorocarbons (CFCs) - Truck
drivers, good for cool places
• Ultraviolet (UV) light - Truck breakers
• Chlorine - Useful guys, but can be bad “hit molecules”
• Reservoir molecules - Foster homes
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.
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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.
CFCs - Truck drivers
• 1928 - First totally safe molecule for mechanical
refridgerators - Thomas Midgley,
dichlorodifluoromethane (CCl2F2), Fridgidaire and
DuPont joined to produce CCl2F2, and CCl3F as
Freon (F12, F11).
• 1941 - Automobile air conditioning - Packard
• 1943 - Bug bomb used in WWII → CFCs became
propellants for aerosol spray cans.
• 1940 - 1960 - Uses of Freon boomed.
• 1970s - CFC production 600,000 tons annually
growing 10% per year. Uses with immediate releases
to the atmosphere - 66%, refrigeration - 20%
The Awakening
• 1971 - Lovelock - Electron Capture Device
coupled with Gas Chromatography -> First
capability to detect molecule concentrations on
the order of ppt (parts per trillion = 10-12).
• 1974 - Molina and Rowland - simple question What happens to CFCs released into the
atmosphere?
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UV - Truck breakers
• 1974 - Molina and Rowland - simple question What happens to CFCs released into the
atmosphere? (awarded Nobel prize Chemistry 1995)
– CCl3 F (F-11) + hν (λ < 240 nm, z > O3 layer) → CCl2F + Cl
– CCl2F2 (F-12) + hν (λ < 240 nm, z > O3 layer) → CClF2 + Cl
• Then
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• Net:
Cl + O3
ClO + O
O3 + O
→
→
→
ClO + O2
Cl + O2
O2 + O2
• This would occur above ozone layer
above 30 km
altitudes
Reservoir molecules - Foster homes for bad guys
• 1975 - 1980 – Predicted ozone losses above 30
km were not observed. Reservoir molecules
discovered.
HCl + CH3
– Cl + CH4 →
– ClO + NO2 →
ClONO2
– HCl and ClONO2 are reservoir species.
• 1984 – Models predict 10% ozone loss in 100
years for current CFC production rates.
Ozone loss (Act II) - Cast
• Polar stratospheric clouds (nitric acid
clouds) - Natural and beautiful, but home
wreckers
• Return of the Sun - A rebirth, but not for
everything
• Catalytic cycle - Steal and keep stealing
(making a second appearance)
• Stratospheric polar vortex - Isolation cell
to keep the bad guys in, and the pacifists out
• The Arctic - Lady in waiting or ?
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Ozone Loss Polar Regions the subtle act
• Polar ozone loss requires the release of Cl from
the reservoir molecules, HCl, ClONO2
• Based on ozone profiles the Cl release must
occur at relatively low altitudes.
• Gas phase chemistry cannot do it.
• ⇒ Something new
Heterogeneous chemistry
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The photolysis has to wait for the
return of light in late winter
Happens during dark winter
Catalytic Cycle Polar Stratosphere
–
PSC particle + HCl + ClONO2 → Cl2
–
Cl2 + hν
– 2[
Cl + O3
– ClO + ClO + M
–
–
ClOOCl + hν
ClOO + M
→
→
→
Cl + Cl
ClO + O]
ClOOCl + M (M=N2 or O2)
→
→
Cl + ClOO
Cl + O2 + M
→
3O2
– hν = Sun’s return
• Net
2O3 + hν
• 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.
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Nitric acid/water
Ice
Nitric acid/water
Ice
Ozone loss (Act III) - Cast
• Montreal Protocal and amendments Laws to limit the formation of new radicals
• Trend of stratospheric chlorine - Together
we can defeat the bad guys
• Global warming - It is the same
atmosphere, but is there any other
connection?
Antarctic
ozone hole
discovered
Molina &
Rowland,
1974
Montreal
Protocol, and
amendments
Reservoir
Molecules
Discovered
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Measurements continue
at McMurdo:
• To maintain good records in anticipation
of ozone recovery.
• To test quantitative models of ozone loss.
– This last aspect is focus of current
measurements.
McMurdo
Antarctica
78°S - 1989
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.
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Postscript
• The ozone loss story is a positive one
• A global problem created by local human
activities was identified, and reasonable
solutions adopted by the worlds leading
countries to reduce and eventually
eliminate the problem.
• Is there a relation to global warming?
• Physically - minimal.
• Politically - the actions on ozone loss
may serve as a model to direct future
decisions by world leaders
Tropospheric
Chlorine
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