02/23

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““The World We Create”The World We Create”NATS 101NATS 101Section 6Section 6

Project 1

Mean 88.4%SD 10%

86.6%87.5%87.7%87.7%88.2%89.2%89.5%89.9%90.1%

UNIT 1

UNIT 2: Environmental changes, Natural or Man-Made?

UNDERSTANDING OZONE

DEPLETION

Ozone Layer

Last class we talked about

the importance of

the Ozone Layer for life in our planet.

95% penetrates

5% penetrates

0% penetrates

Ozone Cycle Recap.

2 O3 3 O2

UVB

Natural destruction of Ozone: UVB absorbed!

3 O2 2 O3

Natural formation of Ozone: UVC absorbed!

UVC

Let’s analyze what you understood!

Each small group will need 1 bag that includes:

Marsh mellows Gumdrops Tooth picks

1 white board per letter team.

GOAL:To Model the Cycle of

destruction an formation of O3.

2 O3 3 O2

3 O2 2 O3

UVB

UVC

If marsh mellows represent oxygen molecules, and tooth picks are chemical bonds:

Use these materials to model the cycle of destruction and formation of O3. You need to build a sequence of at least five 3D-frames (a single one of a series of still models) that shows the whole process.

After your group is finished, let your TAs know. They will select a group that will draw the set of frames on a whiteboard to show to the rest of the class.

You 5 minutes

2 O3 3 O2

3 O2 2 O3

UVB

UVC

You need at least 5 frames! One group will write it on a white board

for your team.

Destruction

Formation

The Natural Cycle

There is evidence that shows that pollutants released by humans are interfering with

this cycle.

An ozone hole?Concern about thinning of the ozone layer over

Antarctica arose in the 1970’s but it was not monitored until in the 1980s

We know the amount of O3 is changing

1 Dobson Unit = 0.01 mm at 0o C, 1 atm

The Evidence

The presence of chlorine atoms

Cl and ClO molecules is

inversely correlated with

O3 concentration.

Cl

Sources of chlorine

Where are CFC’s found? Foaming agents for plastics Solvents for cleaning Aerosol propellants Refrigerants Fire extinguishers

Main sourceCFC’s: chlorofluorocarbons

CFCs are handy Nontoxic; Not flammable; Stable in the Troposphere unreactive; Many different forms so they have many

different applications.

UVC

Cl Action

UVC produces very reactive Cl atoms that affect the natural cycle of O3

formation-destruction.

ClRadical

Cl + 2 O3 3 O2 + Cl

If marsh mellows represent O, Gumdrops represent Cl, and toothpicks represent Chemical bonds:

Model how Cl atoms may be affecting the cycle of formation and destruction of O3. You need to build a sequence of four 3D-frames that show the effect of Cl atoms. Discuss why the action of Cl is SO problematic.

Cl Action

After your group is finished, let your TAs know. They will select a group that will draw the set of frames on a whiteboard to show to the rest of the class.

You 10 minutes

Cl + 2 O3 3 O2 + Cl

Cl 2 O3

Cl 3 O2

Hint: ClO is formed in the process Discuss why the action of Cl is SO problematic.

The sequence should have at least 4 frames (Including beginning and end)

CFCs in the Stratosphere

CFCs take on average fifteen years to reach the stratosphere, and they can remain in the atmosphere for up to

one hundred years.

However, once there, one single

Cl. radical can destroy over

100,000 ozone molecules!

Cl Action

The Effects

The largest area of diminishing ozone

has been documented in the stratosphere over Antarctica since

the 1980s.

Here is a NASA movie of the ozone “hole” over Antarctica from July through December:

What is happening in Antarctica?

Average Size

Size and Seasons

This graph shows the area of ozone depletion in Antarctica.

What is it telling us about the time of year when the area of ozone depletion is greatest?

Artic vs. Antartic

Why the Antarctic?

What are these data telling us

about the relationship

between: temperatures, seasons, and sunlight in the

Arctic and Antarctica?

Your Ideas• In your groups discuss the relationships that

you see among temperature, seasons, sunlight, and area of ozone depletion.

How has the area of the ozone hole over Antarctica changed in the past 25 years?

How does it change with seasons? How do you explain it?

What differences do you observe between Antarctic ozone and Artic ozone?

What may explain the difference?

Discussion

What has been done?Ozone can be rebuilt if active pollutant agents are

eliminated from the atmosphereLegislation

1980s: US banned the use of CFCs in aerosol cans

1987: Montreal Protocol many nations agreed to stop use of CFCs and replace them with alternatives such as HCFCs

Clean Air Act: Amended to include “Ozone Protection Program”

Recovery?

• Estimated ozone recovery: Up to 100 years from 2006

2045-2060

• Estimate of the amount of ozone remaining: ~58% +/- 5%

Beginning of Ozone Recovery:

• ~15 years after decrease in CFC production:

2005-2010

Wrap-up: How are they related?

Build as many connections between these concepts. CLEARLY STATE THE CONNECTION USING A VERB

OR PHRASE.

OZONE

UVA

UVB

UVC

CFC

STRATOSPHERE

OZONE DEPLETION

SKIN CANCER

OZONE

UVC

blocks