Stratospheric Ozone Depletion

IB syllabus: 5.6.1-5.6.6AP syllabusCh 17, 18

Video – The Hole Story

Syllabus Statements 5.6.1: Outline the overall structure and composition of

the atmosphere 5.6.2: Describe the role of ozone in the absorption of

UV radiation. 5.6.3: Explain the interaction between ozone and

halogenated organic gasses. 5.6.4: State the effects of UV radiation on living

tissues and biological productivity. 5.6.5: Describe three methods of reducing the

manufacture and release of ozone-depleting substances

5.6.6: Describe and evaluate the role of national and international organizations in reducing the emissions of ozone-depleting substances

vocabulary

Halogenated organic gases Pollution Non-point source pollution Replenishable natural capital

Atmospheric Structure

Layered structure – Troposphere, Stratosphere, Mesosphere, Thermosphere

Troposphere is layer next to earth’s surface – 75-80% of mass of earth’s air

Atmospheric composition 78% nitrogen, 21% oxygen, trace amounts of water, argon, carbon dioxide

Lapse rate – rate at which temperature declines with increasing altitude in the troposphere

Layers of the AtmosphereAtmospheric pressure (millibars)

0 200 400 600 800 1,000120

110

100

90

80

70

60

50

40

30

20

10

0(SeaLevel)

–80 –40 0 40 80 120Pressure = 1,000millibars atground levelTemperature (˚C)

Alti

tude

(kilo

met

ers)

Alti

tude

(mile

s)

75

65

55

45

35

25

15

5

Thermosphere

Heating via ozoneMesosphere

Stratosphere

Ozone “layer”Heating from the earth

Troposphere

TemperaturePressure

Mesopause

Stratopause

Tropopause

Ozone

Ozone is O3 formed from O + O2

Found in the lower Stratosphere as the ozone layer – good protective qualities

Found in the Troposphere as a result of human pollution – bad qualities photochemical oxidant

Ozone Formation

O3 + UV O + O2

O + O O2

O + O2 O3

It’s Replenishable

Ozone absorbs UV radiation

When UV strikes O3 it is absorbed and its energy used to break the chemical bond

O3 + UV O + O2

So UV doesn’t make it to the earth’s surface

Ozone Layer Layer in the lower stratosphere Keeps 95% of harmful UV radiation away Seasonal depletion of ozone layer above

Arctic & Antarctic, overall thinning everywhere but tropics

Depletion is serious long term threat to (1) humans, (2) other animals, (3) sun driven producers (plants) supporting food webs

CFC’s (Freons)

1. Discovered in 19302. Chemically stable, odorless, nonflamable,

nontoxic, noncorrosive dream chemical in the troposphere

3. Coolants, Propellants, Sterilants, Fumigants

4. 1974 discovered to be lowering concentrations of stratospheric ozone

5. Immediate ban called for

CFC’s II Large quantities being released – use, leaks,

production of plastics Remain in troposphere – unreactive, insoluble

very stable 11-20 years to rise to stratosphere Release high energy Cl atoms when exposed

to UV which speed up breakdown of ozone Each CFC lasts 65-385 years in stratosphere Can break down up to 100,000 molecules of

ozone

Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breakingoff a chlorine atom and leaving CFCl2.

UV radiation

Sun

Once free, the chlorine atom is off to attack another ozone moleculeand 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).

The chlorine atom attacksan ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2).

Cl

Cl

ClC

F

Cl

Cl

OO

Cl

OO

O

ClO

OO

ClO

O

Summary of ReactionsCCl3F + UV Cl + CCl2FCl + O3 ClO + O2

Cl + O Cl + O2

Repeated many times

Summary of Reactions

1. CCl3F + UV Cl + CCl2F

2. Cl + O3 ClO + O2

3. ClO + O Cl + O2

Steps 2 + 3 are repeated many times causing massive destruction of ozone

Methyl Bromide

Other major ODC Used as a pesticide and fumigant on crops Kills nematodes, fungi, weeds

Remember that ozone breaks down naturally when it absorbs UV

This speeds up that process and limits the regeneration of O3

Pollutants enhance O3 destruction disturbing the equilibrium of the O3 production system

Year

1970 1975 1990 2000 200519851955 1960 1965 1980 1995

400

350

300

250

200

150

100

Tota

l ozo

ne (D

obso

n un

its)

October monthly means

Decreasing ozone volume in fall over the poles

Seasonal Polar Thinning Seasonal loss of ozone in summers over poles Ozone hole is actually ozone thinning Sunless winters, polar vortex causes swirling

winds isolated from rest of atmosphere Ice crystals in clouds collect CFC’s and speed

release of Cl Sun returns in spring / summer and frees large

volumes of free Cl Ozone thinning travels north to effect Aus, NZ,

S. Am., S. Af.

August 7, 2001

October 10, 2001

35

30

25

20

15

10

5

0 5 10 15Ozone partial pressure (milipascals)

Alti

tude

(kilo

met

ers)

Year1979 1982 1985 1988 1991 1994 1997 2000 2003 2006

0

5

10

15

20

25

30M

illio

n sq

uare

kilo

met

ers

Figure 18-29Page 474Area of North America

Size of Ozone thinning

Antarctic

SeptOzoneLoss

Arctic

MarchOzoneLoss

Human Health

• Worse sunburn

• More eye cataracts

• More skin cancers

• Immune system suppression

Food and Forests

• Reduced yields for some crops

• Reduced seafood supplies from reduced phytoplankton

• Decreased forest productivity for UV-sensitive tree species

Wildlife

• 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 phytoplankton

Air Pollution and Materials• Increased acid deposition• Increased photochemical smog• Degradation of outdoor paints and plastics

Global Warming

• Accelerated warming because of decreased ocean uptake of CO2 from atmosphere by phytoplankton and CFCs acting as greenhouse gases

What are the effects?

Effects on Humans, Plants, Animals & Global climate

A 1% loss of stratospheric ozone equals a 2% increase in skin cancers & 1% increase in cataracts worldwide.

Humans make cultural changes, others cannot

Ultraviolet A Ultraviolet B

Thin layer ofdead cells

Squamouscells

Basallayer

Melanocytecells

Basalmembrane

Bloodvessels

HairEpidermis

Sweatgland

Dermis

Squamous Cell Carcinoma Basal Cell Carcinoma Melanoma

Solutions & Protection

Must immediately stop using ozone depleting chemicals

Long recovery time afterwards due to persistence in the atmosphere

Substitutes are available for most CFC uses Hydrocarbons seem to be best for future

How can the manufacture and release of ODC be reduced?

Refrigerants can be recycled Alternatives to gas blown plastics can be

used Alternative propellents – hydroflourocarbons

– better but a potent greenhouse gas Alternatives to methyl bromide can be used

for fumigation and pesticides

Problems Existing stockpiles were ok to use after the

phase out Old CFCs continue to leak out of junked cars

and fridges Black market trade in CFCs increasing because

they are not made but still useful China, India, Mexico have increased use and

production of CFCs Full recovery expected by 2050 if current

decline continues

Montreal Protocol 1987, 36 nations in Montreal Cut emissions of CFCs by 30% between 1989 and

2000 After 1989 ozone thinning info new meetings in 1990,

1992 formed new Copenhagen protocol, 177 nations more stringent reductions required

UNEP involved in these agreements as well as an accelerated phase out for Korea, China, India

Montreal Multilateral Fund est’d for aiding transition Also studying the relative effectiveness of the

measures being taken

Year1950 1975 2000 2025 2050 2075 2100

3,000

0

6,000

9,000

12,000

15,000A

bund

ance

(par

ts p

er tr

illio

n) No protocol

1987MontrealProtocol

1992CopenhagenProtocol

Ozone depleting chemical concentration Predictions in stratosphere

In the US

Government ratified Montreal Protocol agreeing stop production of CFC propellents

Taxes levied on CFC production and use Corporations changing their ways McDonalds (1987) – stopped use of

styrofoam packaging Caused foam packaging industry to stop

use of all CFCs by 1988

Next…

Return to 1980 levels by 2050 Assume countries follow agreement and

don’t produce new ODC Ozone loss has been cooling troposphere

masking global warming’s real effects Good precedent for global cooperation