STRATOSPHERIC OZONE DEPLETION
Adapted from K. Sturges at MBHS
Ozone LayerOzone is…
◦ “Good up high”
◦ Stratosphere
◦ “Bad nearby”
◦ Troposphere
Solar Radiation - range of electromagnetic waves◦ UV – shortest we see if violet- damages proteins and DNA molecules at
surfaces of organisms
◦ UVA- can cause damage
◦ UVB- really bad- only 1% of UVB hits earth- responsible for sunburns and skin cancer
◦ Ozone shield
◦ Layer that protects w/o it life may not exist as we know it
◦ Absorbs UV radiation
Ozone Depletion in Stratosphere
◦ Ozone Protects earth from UV radiation
© 2012 John Wiley & Sons, Inc. All rights reserved.
Formation of the Ozone Shield
Reaction #1: UV light + O2 O + O
Reaction #2: Free O + O2 O3
Reaction #3: Free O + O3 O2 + O2
Reaction #4: UV light + O3O + O2
The amount of ozone in stratosphere is dynamic- there is no
equilibrium.
Cycles of formation (reactions. 1 and 2) and destruction (reactions3
and 4)
OZONE DEPLETION IN THE STRATOSPHERE
◦Ozone thinning: caused by CFCs and other ozone
depleting chemicals (ODCs).
◦ Increased UV radiation reaching the earth’s surface from
ozone depletion in the stratosphere is harmful to human health,
crops, forests, animals, and materials such as plastic and
paints.
Ozone Depletion in Stratosphere
◦ Ozone thinning/hole
◦ First identified in 1985 over
Antarctica
◦ Occurs annually between Sept
and Nov because:
◦ Caused by human-produced
bromine and chlorine containing
chemicals (Ex: CFCs)
© 2012 John Wiley & Sons, Inc. All rights reserved.
OZONE DEPLETION IN THE STRATOSPHERE
◦ Since 1976, in Antarctica, ozone levels have markedly decreased during October and November.
Figure 20-20
Chlorofluorocarbons (CFCs)
◦Manmade, organic molecules in which both chlorine, fluorine or bromine atoms replace some of the hydrogen atoms.
◦ Releases chlorine/ fluorine/bromine atoms that split ozone
◦ Sources:◦ refrigerators and air conditioners
◦ production of plastic foam
◦ cleaner for electronic parts
◦ pressurizing agent in aerosol cans
CFCs destroy ozone
◦ CFCs remain in the stratosphere for a
century
◦ UV radiation breaks CFCs into chlorine
and carbon atoms
◦ The chlorine atom splits ozone
◦ Ozone hole = decreased ozone levels
over Antarctica
One chlorine atom can destroy
100,000 ozone molecules
SunOnce free, the chlorine
atom is off to attack
another ozone molecule
and begin the cycle
again.
A free oxygen atom pulls
the oxygen atom off
the chlorine monoxide
molecule to form O2.
The chlorine atom and
the oxygen atom join to
form a chlorine monoxide
molecule (ClO).
UV radiation
Cl Cl
ClC
F
The chlorine atom attacks an
ozone (O3) molecule, pulling
an oxygen atom off it and
leaving an oxygen
molecule (O2).
Cl
Cl
OO
O
Cl
ClO
ClO
OO
OO
Ultraviolet light hits a chlorofluorocarbon
(CFC) molecule, such as CFCl3, breaking
off a chlorine atom and leaving CFCl2.
O
Fig. 20-18, p. 486
Stepped Art
OZONE DEPLETION IN THE STRATOSPHERE
◦ During four months of
each year up to half of the
ozone in the stratosphere
over Antarctica and a
smaller amount over the
Artic is depleted.
Figure 20-19
Ozone Layer
◦ Southern Hemisphere ‘Hole’
◦ Thinning of one area
◦ 50% less ozone than normal
◦ If anywhere besides the South Pole, would be drastic for
human life
◦ Winter causes vortex-
◦ Cold Temps, H2O, other gases form stratospheric clouds
◦ Clouds provide chlorine reservoirs where chlorine (along
with chlorine monoxide and methane) is trapped and not
depleting O3
◦ Spring and summer arrive, UV releases the chlorine allowing it
to destroy O3
The Antarctic ozone hole
◦ High-altitude polar stratospheric clouds form during the dark, frigid winter
◦ Nitric acid in clouds splits chlorine off of CFCs
◦ A polar vortex (swirling winds) traps chlorine
◦ UV radiation in September (spring) sunshine dissipates the clouds and
releases the
chlorine
◦ The chlorine destroys the
ozone
◦ December’s warmer air
shuts down the polar vortex
◦ Ozone-poor air diffuses,
while ozone-rich air enters
Ozone Depletion in Stratosphere
◦ Hole over Antarctica requires two conditions:
◦ Sunlight just returning to polar region
◦ Circumpolar vortex- a mass of cold air that circulates around
the southern polar region
◦ Polar stratospheric clouds form
◦ Enable chemical reactions that cause Cl and Br to destroy
ozone
© 2012 John Wiley & Sons, Inc. All rights reserved.
Ozone Layer
◦ Northern Hemisphere
◦ No hole
◦ Thinning
◦ Intensifies in winter due to large particles found
Ozone Layer
◦ Not just in polar regions
◦ Thinning is supposed to peak 2010-
◦ Due to decline in chlorine and bromine concentrations in stratosphere by developing countries
◦ Montreal Protocol (more later)
◦ Scale use of CFCs down by 50%
◦ CFCs still produced in developing countries
Stratospheric Ozone ConsequencesNot enough ozone in stratosphere
◦Human Health◦ Sunburn◦ Skin cancer◦ Eye damage◦ Efficiency of immune system◦ Synergistic with other air pollutants
◦ Environmental◦ Reduction of primary productivity in oceans◦ Disruption of food chain (large animals first)◦ Damage to fish, amphibians, mammals◦ Widespread effects on major food crops◦ Decreased plant productivity
Effects of Ozone Depletion
◦ Higher levels of UV-radiation
hitting the earth
◦ Eye cataracts
◦ Skin cancer (right)
◦ Weakened immunity
◦ May disrupt ecosystems
◦ May damage crops and forests
© 2012 John Wiley & Sons, Inc. All rights reserved.
Recovery of Ozone Layer
◦Montreal Protocol (1987)
◦ Reduction of CFCs
◦ Started using HCFCs (greenhouse gas)
◦ Phase out of all ozone destroying chemicals is underway globally
◦ Satellite pictures in 2000 indicated that ozone layer was
recovering
◦ Full recovery will not occur until 2050
© 2012 John Wiley & Sons, Inc. All rights reserved.
The Montreal Protocol
◦ Montreal Protocol = 196 nations agreed to cut CFC production in
half by 1998
◦ Follow-up agreements deepened cuts, advanced timetables,
and addressed other ozone-depleting chemicals
◦ Industry shifted to safer, inexpensive, and efficient alternatives
◦ Challenges still face us
◦ CFCs will remain in the stratosphere for a long time
◦ Nations can ask for exemptions to the ban
The Montreal Protocol is a success
◦ It is considered our biggest environmental success story
◦ Research developed rapidly, along with technology
◦ Policymakers included industry in helping solve the problem
◦ Implementation of the plan allowed an adaptive management
strategy
◦ Strategies responded to new scientific data, technological
advances, and economic figures
◦ The Montreal Protocol can serve as a model for international
environmental cooperation
Protecting the ozone layer
International agreements reduced ozone-depleting substances
The hole in the ozone has stopped growing
Human Health• Worse
sunburn• More eye
cataracts• More skin
cancers• Immune system
suppressionFood and Forests
• Reduced yields for some
crops• Reduced seafood supplies from reduced
phytoplankton• Decreased forest productivity for UV-sensitive tree
speciesWildlife
• Increased eye cataracts in some
species• Decreased population of aquatic species sensitive to UV
radiation• Reduced population of surface
phytoplankton• Disrupted aquatic food webs from reduced
phytoplanktonAir Pollution and Materials• Increased acid
deposition• Increased photochemical smog• Degradation of outdoor paints and
plasticsGlobal Warming
• Accelerated warming because of decreased ocean uptake of CO2
from atmosphere by phytoplankton and CFCs acting as greenhouse gases
Effects of Ozone Depletion
Natural Capital Degradation
Fig. 20-21, p. 488