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OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
The good,the bad &
the ugly
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Driving Questions
1. Why is ozone important?
2. How is it formed?
3. How is it destroyed?
4. How is it different in the stratosphere vs. the troposphere?
5. If stratospheric ozone is decreasing and tropospheric ozone is increasing, why not just build a REALLY big chimney?
Issues to be Considered:
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Greenhouse Gases
1. Carbon Dioxide (CO2)
2. Nitrous Oxide (N2O)
3. Methane (CH4)
4. Ozone (O3)
5. Chlorofluorocarbons (CCFs)
and
Water VaporClick me
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ultraviolet Radiation
0
0.5
1
1.5
2
2.5
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Wavelength (µm)
Radiation
uv-b
.280 µ
m
uv-a
.315 µ
m.4
00 µ
m
uv-c
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Formation
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Maxima
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Why the Stratosphere?
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Formation
• When an oxygen molecule absorbs a photon of light with a wavelength shorter than 0.2 µm the energy splits the molecule into two oxygen atoms.
O2 + h —> O + O• One of these atoms can react with another oxygen
molecule to form an ozone molecule.
O + O2 + M —> O3 + MUp to 98% of the sun's high-energy ultraviolet light(UV-B and UV-C) are absorbed by the destruction and formation of atmospheric ozone.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Formation
O2 + h —> O + O
2 (O + O2 + M —> O3 + M)
3O2 —> 2O3
Net production
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Destruction
• Ozone, on the other hand, absorbs photons of light with a wavelength between 0.2-0.3 µm that splits the molecule into an oxygen atom and an oxygen molecule.
O3 + h —> O2 + O• The oxygen atom react with another ozone molecule to
form two oxygen molecules.
O + O3 —> O2 + O2
2 O3 —> 3O2
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Catalytic Reactions
• The term catalytic means that X can react with and remove ozone while X itself is regenerated in the process
O3 + X —> XO + O2
XO + O3 —> X + 2O2
2 O3 —> 3 O2
O3 + X —> XO + O2
XO + O —> X + O2
O + O3 —> 3 O2
and
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Formation
• Ozone has a natural photochemical balance between formation and destruction as other gases participate. Example: Nitrogen oxides
NO2 —> NO + O
O + O2 —> O3
NO + O —> NO2
O + O2 —> 2O2
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Formation
• But chlorofluorocarbons shift this balance:
Cl2CF2 + UV light —> ClCF2 + Cl
• Then there is a catalytic destruction of ozone:
Cl + O3 —> ClO + O2
ClO + O3 —> Cl + O2
• The net effect of this pair of fast reactions is to turn two ozone molecules into three normal molecules of oxygen. The (catalyst) atomic chlorine is recovered in the second reaction, making it available to start over. In fact, each chlorine atom can destroy hundreds of thousands of ozone molecules!
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Lifetime of CFC1. Emitted into atmosphere as gas.2. Disperses rapidly throughout Northern hemisphere in ~1
year3. After a few years is uniformly mixes throughout whole
troposphere.4. Movement into stratosphere is slow. Some leaks upwards to
region where sufficient UV light is available to break bonds and release Cl.
5. Each atom of Cl participates in thousands of catalytic reactions, destroying hundreds of thousands of ozone molecules.
6. Ultimately each Cl atom reacts with methane to produce HCl.
7. Some of the HCl is transported back into the troposphere and gets rained out, the rest gets broken apart and the Cl cycle begins again.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Depletion Potential
•The Ozone Depletion Potential (ODP) is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11.
o Thus, the ODP of CFC-11 is defined to be 1.0.
o Other CFCs and Hydrochlorofluorocarbons (HCFC’s) have ODPs that range from 0.01 to 1.0.
o Halons have ODPs ranging up to 10.
o Carbon tetrachloride (CCl4) has an ODP of 1.2, and methyl chloroform's ODP is 0.11.
o Hydrofluorocarbons (HFCs) have zero ODP because they do not contain chlorine.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Column Measure
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Problems with Ozone Depletion• More than 90% of
non-melanoma skin cancers are related to UV-B exposure.
• 1% ozone decrease produces a ~2% increase in UV-B.
• Each 2% increase in UV-B is epidemiological linked with a 2%-5% increase in basal-cell cancer cases and a 4-10% increase in squamous cell cancer.
http://www.skincancer.org/
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Problems with Ozone Depletion
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Problems with Ozone Depletion
A national UV Index is issued daily to advise the public on the strength of the sun's UV rays.
The chart to the right shows the levels of the UV Index, your time to burn in the sun without sunscreen, and what you can do to protect yourself.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Problems with Ozone Depletion
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Problems with Ozone Depletion
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Hole Discovery
In 1985 Farmen et al. published a paper containing this figure. It showed a dramatic decrease in total ozone abundance during October over the Antarctic station at Halley Bay.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Ozone Hole Discovery
Moreover the amount of ozone column has decreased steadily.
0
50
100
150
200
250
1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Ozone Column (Dobson Units)
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Changing Ozone Concentrations
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Changing Ozone Concentrations
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Changing Ozone Concentrations
0
5
10
15
20
25
30
1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001
Ozone Hole Area (10^6 km^2)
The ozone hole is defined geographically as the area wherein the total ozone amount is less than 220 Dobson Units.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
So Why an Ozone “Hole”?
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Role of Polar Stratospheric Clouds
Source: Turco, Earth Under Siege
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
0
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35
0 5 10 15Ozone (partial pressure)
HEIGHT (km)
8/4/01
9/28/01
10/2/01
10/14/01
Ozone depletion depends on altitude
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
Ozone depletion depends on altitude and is highly influenced by temperature.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of Michigan
Changing Ozone Concentrations
Last Updated: April 18, 2023
QuickTime™ and aGIF decompressor
are needed to see this picture.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
• UV radiation is weaker and the photolysis of O2 is less important.
• Near the surface the production of ozone is still initiated by sunlight, but the reactors are volatile organic compounds (VOCs) and nitrogen oxides (NOx = NO + NO2)
Meanwhile, down near the surface
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
NO2 —> NO + O
O + O2 + M —> O3 + M
NO + O3 —> NO2 + O2
Meanwhile, down near the surface
Net result, no ozone buildup.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
• VOCs produce “radical organics” (RO2) that interfere with the NO chemistry, basically producing extra atomic oxygen
RO2 + NO —> NO2 + RO
NO2 —> NO + O
O + O2 + M —> O3 + M
Meanwhile, down near the surface
Net result, ozone buildup.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
Meanwhile, down near the surface
QuickTime™ and aGIF decompressor
are needed to see this picture.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
Meanwhile, down near the surface
QuickTime™ and aGIF decompressor
are needed to see this picture.
OZONE
Stratospheric
Tropospheric
Summary
Basics
Issues
©2003, Perry Samson, University of MichiganLast Updated: April 18, 2023
Ozone Control
