II. The Ozone Layer and the Ozone Hole

Objectives:1. know the location and function of the ozone layer.2. know that the ozone hole is caused by a category of gases

called CFC’s sometimes referred to as freons.3. write balanced chemical equations for the production and

destruction of ozone.

II. The Ozone Layer and the Ozone Hole

• 90 % of ozone exists in the upper earth’s atmosphere called the stratosphere.

• A small percentage of ozone exists at ground level mostly in the form of smog.

II. The Ozone Layer and the Ozone Hole

• The ozone layer acts as a shield (or natural sunscreen) to protect the earth’s surface from harmful ultraviolet (uv) radiation.

– More O3 in the upper atmosphere results in less uv radiation that reaching the earth’s surface.

– Less O3 in the upper atmosphere results in more uv radiation reaching the earth’s surface.

II. The Ozone Layer and the Ozone Hole

• Chlorofluorocarbons (CFC’s) have been found to be a serious threat to the ozone layer.

• CFC – compound composed of carbon, fluorine, chlorine and hydrogen

• freon – trade name for CFC’s (du Pont)

II. The Ozone Layer and the Ozone Hole(don’t copy)

Example CFC Compounds

• CH4 – methane

• CH3Cl - chloromethane

• CH2Cl2 - dichloromethane

• CHCl3 - trichloromethane

Molecular Models

II. The Ozone Layer and the Ozone Hole(don’t copy)

Example CFC Compounds

• CH4 – methane

• CH3F - fluoromethane

• CH2F2 - difluoromethane

• CHF3 - trifluoromethane

Molecular Models

II. The Ozone Layer and the Ozone Hole(don’t copy)

• CFC compounds are nontoxic, nonflammable, inexpensive, and readily convert between the gaseous and liquid states.

• CFC’s have been widely used for 1. Aerosol-spray propellants

2. Refrigerant

3. Solvents

4. Foam blowing agents

II. The Ozone Layer and the Ozone Hole(don’t copy)

• Example aerosols:

II. The Ozone Layer and the Ozone Hole(don’t copy)

Aerosol Can Operation• Aerosol cans contain a

compressed gas over a liquid product to be dispensed (hair spray, deodorant, paint, oil, etc.)

• CFC gases were commonly used as propellants within aerosol cans.

• A variety of non CFC compounds are currently used (N2, CO2, etc.) depending on the application.

II. The Ozone Layer and the Ozone Hole(don’t copy)

• Because of growing concern over ozone depletion, most industrialized nations have banned the production and use of CFC compounds.

II. The Ozone Layer and the Ozone Hole(don’t copy)

Graph of Worldwide CFC Production

Worldwide CFC Production vs. YearOzone Hole Area Size vs. Year

1985 1990 1995 2000 2005 20100

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1975 1980 1985 1990 1995 2000 2005 20100

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II. The Ozone Layer and the Ozone Hole(don’t copy)

• Ozone is produced by uv radiation from the sun.

O2 + energy → 2O

O + O2 → O3

• Ozone is destroyed by uv radiation from the sun.

O3 + energy → O2 + O

II. The Ozone Layer and the Ozone Hole(don’t copy)

• Molecules of CFC compounds break down when they encounter ultraviolet (uv) radiation from the sun in the earth’s upper atmosphere.

CH3Cl + energy → CH3 + Cl

• Chlorine atoms react with ozone to yield chlorine monoxide and oxygen.

Cl + O3 → ClO + O2

• One CFC molecule can result in the destruction of 100,000 O3 molecules.

II. The Ozone Layer and the Ozone Hole

Example Ozone Hole Images

Where is the ozone hole within the ozone layer?

Oct. 19803.27 million sq. mi.

Oct. 198518.79 million sq. mi.

Sept. 1990 21.05 million sq. mi.

Sept. 199626.96 million sq. mi.

Sept. 200030.31 million sq. mi

Sept. 200526.77 million sq. mi.

II. The Ozone Layer and the Ozone Hole(don’t copy)

Graph of Ozone Hole Area vs. Time - Mr. Banner

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What would happen if the ozone hold would continued to grow?

Ex. 1 – Effects on Humans

Ex. 2 – Effects on Ecosystems

II. The Ozone Layer and the Ozone Hole(don’t copy)

• A decrease in ozone leads to an increase in exposure to harmful ultraviolet (uv) radiation from the sun.

II. The Ozone Layer and the Ozone Hole(don’t copy)

Example 1

• Increased exposure to harmful uv radiation from the sun to result in (but not limited to):– increased rates of sunburn– Increased rate of skin

cancers– cataracts– premature aging of skin

(wrinkled, leathery appearance

Example Skin Cancer Images

II. The Ozone Layer and the Ozone Hole(don’t copy)

Example 2

• An increase in harmful uv-radiation could kill microscopic algae called phytoplankton within the earth’s oceans.

• Example effect:

phytoplankton←krill←fish←humans

Food Chain Diagram