ozone depletion in the stratosphere the other story ch. 19

Ozone Depletion in the Stratosphere

The other storyCh. 19

APES

• Everything away except a writing utensil

Alt

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Ozone concentration (ppm)

Alt

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(m

iles)Stratospheric ozone

Stratosphere

Troposphere

40

35

30

25

20

15

10

5

00 5 10 15 20

0

5

10

15

20

25

Photochemical ozone

Beneficial Ozone

Harmful Ozone

*

What does the ozone layer do?

Protects Earth from dangerous UV

What does the ozone layer do?

• Protects Earth from dangerous UV – Cause mutations

• Higher rate skin cancer, cataracts, and immune system problems

– Essential for life: affect plants & marine ecosystems in unknown ways

– Prevents tropospheric ozone

Stratospheric Ozone Absorbs: • ALL UV-C radiation (most energetic – most lethal)• MOST UV-B radiation, but NO UV-A radiation

Consequence: Increase UV (UVB) reaching Earth’s surface

Human – Sunburn– Skin Cancer– Cataracts– Efficiency in immune

system

Ecosystem– Reducing of primary

productivity in oceans– Disrupt food chains– Damage

fish/amphibians/mammals

– Widespread effects on major food crops

– Decrease plant productivity

– Impair/destroy phytoplankton

Class of Chemicals Primarily Responsible for Thinning of Stratospheric Ozone Layer

Class of Chemicals Primarily Responsible for Thinning of Stratospheric Ozone Layer

• Chlorofluorocarbons (CFCs)– Coolant/refrigerant/air conditioner– Aerosol or propellant– Foam-blowing plastics/insulation (styrofoam)– Solvent/Cleaners

• Halocarbons– Fire retardants (fire extinguishers)– Soil fumigant/pesticide– Solvents– Foam blowing insulation

Class of Chemicals Primarily Responsible for Thinning of Stratospheric Ozone Layer

• Chlorofluorocarbons (CFCs) – AKA Freons– Wonder Chemical – Inexpensive– Stable in troposphere

• Chemically unreactive• odorless• nonflamable• nontoxic,• non corrosive

Class of Chemicals Primarily Responsible for Thinning of Stratospheric Ozone Layer

• Others– Hydrobromoflurocarbons (HBFCs)

• Fire extinguishers

– Methyl bromide • fumigant

– Hydrogen chloride • Emitted by space shuttles

– Carbon tetrachloride, methyl chloroform, n-propyl bromide, hexachlorobutadiene

• Cleaning solvents

HOW do CFCs Break Down Ozone?*

1. CFCs & others released into troposphere

2. CFCs move/drift upward into stratosphere

3. UV radiation breaks apart CFCs releasing Chlorine (bromine/fluorine)

4. Sunlight causes chemical reaction allowing Cl to attack O3 creating O2

THUS reducing O3 levels

HOW do CFCs Break Down Ozone?*

CCl3F+UV Cl+CCl2F

Cl + O3 ClO + O2

ClO + O CL + O2

SunOnce 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).

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

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How Do We Know This is Happening?

Predicted by Mario Molina & Sherwood Rowland

How Do We Know This is Happening?

• James Lovelock predicted haze came from human sources

• Presented at conference with meteorologists & chemists

Original Hypothesis

Nitrogen Dioxide Neutralizes Some Chlorine

Still Significant (though lower) levels of ozone depletion

Hypothesis Changes

Seasonal Thinning of Ozone at the Poles

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.

Seasonal Thinning of Ozone at the Poles

• Polar stratospheric clouds - high-altitude clouds of ice particles in ozone layer

• Ice particles provide solid surface for reactions

Seasonal Thinning at the Poles

Ozone thinning (hole)

Polar vortex

Seasonal Thinning of Ozone at the Poles

Final Hypothesis

Additional Evidence

• Airplane flew through ozone hole

Ozone Depletion Occurs Worldwide

Montreal Protocol• 1987• 36 nations• 50% reduction in CFC (not

others) production by 1998• Phase out CFCs in developed

countries by 1996• Phase out use of CFCs in

developing countries by 2005

Copenhagen Protocol• Montreal Protocol Amendment• 1992• 93 countries • Accelerated phase out – by 1996

PREVENTION!!

International Cooperation

• Reach 1980 levels by 2068• 1950 levels by 2108

Ozone Depletion

Projected worse over Antarctic and Arctic between 2010 & 2019

Need Help?

• Good Ozone Link

Characteristics of Global Warming and Ozone Depletion

Global Warming

CO2, CH4, NOx (greenhouse gases)

Absorbs infrared (IR) radiation

Raising the earth’s surface temperature

Decrease burning of fossil fuels

Ozone Depletion

O3, O2, and CFCs

Absorbs ultraviolet (UV) radiation

Decreasing O3 concentration in the stratosphere

Eliminate CFCs