Ozone - La Cañada Unified School District

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Ozone Hole
Mark Ewoldsen, Ph.D.
Advanced Placement Environmental Science Teacher
La Cañada High School
1
Two Atmosphere Layers
• Stratosphere is above Troposphere
–Ozone Layer blocks UV radiation
• Troposphere is where we live
–Weather occurs here
• 72% of all air is below the cruising
altitude of commercial airliners
(33000 ft)
2
Stratospheric Ozone
(Good)
vs.
Tropospheric Ozone
(Bad)
3
Ozone – Two Faces
• Stratosphere – Good Ozone
–Blocks UV radiation
–Hole caused by depletion due to
CFC’s
• Troposphere – Bad Ozone
–Pollution
• Photochemical smog
• Eye irritant
4
Harmful effects of UV radiation
• Skin cancer such as melanoma(ultraviolet
radiation can destroy acids in DNA)
• Suppression of immune systems
5
matrix.ucdavis.edu/tumors/tradition/ gallery-ssmm.html
Harmful effects of UV radiation
• Skin cancer such as melanoma(ultraviolet
radiation can destroy acids in DNA)
• Suppression of immune systems
• Cataracts and sun burning
7
www.snec.com.sg/clinical_services/ cataract.asp
http://www.wep.org.au/info/files/images/Amelia_and_the_kids.jpg
Harmful effects of UV radiation
• Skin cancer such as melanoma(ultraviolet
radiation can destroy acids in DNA)
• Suppression of immune systems
• Cataracts and sun burning
• Adverse impact on crops and animals
• Reduction in the growth of ocean
phytoplankton
• Cooling of the Earth's stratosphere and possibly
some surface climatic effect
• Degradation of paints and plastic material
10
Good
Ozone
13
Ozone Formation
• Ozone forms a
layer in the
• O2 + hv  O + O
stratosphere,
thinnest in the
tropics (around • (1) O + O2 O3
the equator) and
denser towards
• wavelength ~ 240 nm
the poles.
http://www-imk.fzk.de/topoz-iii/ataglanz/ozonbild.html
http://www-imk.fzk.de/topoz-iii/ataglanz/ozonzerst.html
Natural
Ozone Hole
• Winter = no sunlight
• Air in the polar
vortex can get very
cold -80C
• Special clouds called
Polar Stratospheric
Clouds form as nitric
acid trihydrate
• PSCs are crucial for
ozone loss to occur
Since there is no sunlight, the air within the polar vortex can get very cold
The ozone hole builds up over the winter months,
peaking at around September and breaking up
again by December, this data set from 2005
July
August
September
October
November
December
Destroying Good Ozone
19
20
Destroying Good Ozone
• Chloroflourocarbons were first created in 1928 as
non-toxic, non-flamable refrigerants, and were first
produced commercially in the 1930's by DuPont
• In 1974, a laboratory study demonstrated the ability
of CFC's to catalytically breakdown Ozone in the
presence of high frequency UV light
• Cl + O3 -> ClO + O2 ClO + O3 ---> 2 O2 + Cl
• In a 1985, a study summarized data that had been
collected by the British Antartic Survey showing
that ozone levels had dropped to 10% below
normal January levels for Antarctica.
•
http://www.nas.nasa.gov/About/Education/Ozone/history.html
21
A single chlorine atom
removes about 100,000
ozone molecules before
it is taken out of
operation by other
substances
22
The frozen crystals that make up polar stratospheric
clouds provide a surface for the reactions that free
chlorine atoms in the Antarctic stratosphere
Ultraviolet light hits a chlorofluorocarbon
(CFC) molecule, such as CFCl3, breaking
off a chlorine atom and leaving
CFCl2.
Sun
Cl
Cl
C
Cl
F
UV radiation
Once free, the chlorine atom is off
to attack another ozone molecule
and begin the cycle again.
Cl
Cl
O
The chlorine atom attacks
an ozone (O3) molecule,
pulling an oxygen atom
Cl
off it and leaving
an oxygen
O
molecule (O2).
O
O
The chlorine
Cl
atom and the
O
oxygen atom join
to form a chlorine
O
monoxide molecule (ClO) O
O
A free oxygen atom pulls
the oxygen atom off
the chlorine monoxide
molecule to form O2.
Cl
O
O
http://www.clas.ufl.edu/users/dlsmith/Lecture_11.html
http://www.mmscrusaders.com/newscirocks/ozone/cfc.jpg
26
27
Montreal Protocol
• An international treaty designed to protect the
ozone layer
– phasing out production of number of substances
believed to be responsible for ozone depletion
– Effective January 1, 1989
– Five revisions
•
•
•
•
•
1990 (London)
1992 (Copenhagen)
1995 (Vienna)
1997 (Montreal)
1999 (Beijing)
28
Area of North America
Area of Antarctica
30
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