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