Title: Ozone and Greenhouse Effect-Getting It Straight!

Overview & Outcomes:

This lesson helps learners:

• confront major alternative conceptions commonly held about ozone layer depletion, ozone pollution and the greenhouse effect.

A concept map is not included for this lesson. Please refer to concept maps found in previous Investigations lessons.

Background Notes for the Teacher:

The following paragraphs include excepts taken from the paper. We begin with five quotations from student interviews conducted as part of the study.

Tammy: Yeah, I think it's basically, that everything works against the ozone and when the ozone breaks, that's when the global warming is going to come.

Candy: [We should] start buying things that like don't have those kind of gases in them. Like instead of buying hair spray with CFCs, you can buy some like in a pump or something.

Billy: CFCs cause destruction of the ozone layer to let the sun, the ultraviolet rays, get in and heat up the Earth.

Evert: And all those oil wells [on fire in the Middle East] gave off tons and tons of carbon dioxide, which made the ozone layer just come apart and that's where the biggest hole came from.

Sally: It [carbon dioxide] comes out of the exhaust. And as it goes up to the ozone past the stratosphere. Then after it hits the ozone it like eats it up and then UV come and hit Earth.

The above, which are transcript excerpts taken from interviews conducted with several students in the study, speak to the principal findings. They exemplify the five alternative conceptions found to be held by the students about GAC. These alternative conceptions all connected (Stratospheric) ozone layer depletion and GAC in some way and were as follows: (a) ozone layer depletion is a major cause of enhanced greenhouse effect (EGHE) (Tammy); (b) aerosol sprays contain CFCs and destroy the ozone layer (Candy); © CFCs cause EGHE exclusively through their role in destroying the ozone layer (Billy); (d) carbon dioxide destroys the ozone layer (Evert); and (e) carbon dioxide causes EGHE exclusively by destroying the ozone layer (Sally).

The percent of students in the study who provided evidence of these alternative conceptions are shown in a table presented on a following page.

Again, these alternative conceptions all connected (Stratospheric) ozone layer depletion and EGHE in some way and were as follows: (a) ozone layer depletion is a major cause of GW; (b) aerosol sprays contain CFCs and destroy the ozone layer; © CFCs cause GW exclusively through their role in destroying the ozone layer; (d) carbon dioxide destroys the ozone layer; and (e) carbon dioxide causes GW exclusively by destroying the ozone layer. The findings suggest that middle school students may possess specific alternative conceptions that limit and confound their understanding of the nature, causation, and resolution of GW. Additionally, the findings have implications for instruction on GW and connections students make with ozone layer depletion, that is, initial exposure to the concept of GW may evoke thoughts in students about the ozone layer. Concepts such as ozone hole, ultraviolet rays, CFCs, and greenhouse effect may be "loose" in many students' knowledge and connected inappropriately to make sense of formal instruction on GAC.

This lesson is an opportunity for students to confront major alternative conceptions commonly held about ozone depletion, ozone pollution and the greenhouse effect prior to formulating a response to the STS focusing question posed in the Foundations/Awareness Section, and proposing actions associated with that response in the Actions Section. It is a critical lesson.

*In this instance, exhaust, smoke, and car pollution were also accepted as the equivalent.

Materials:

For the class.

1. Large index cards or a substitute
2. Overhead film and projector (both optional)
3. Butcher paper and markers

Preparation:

Prior to day of lesson.

Instructional Procedures: (3 Days, 40 minutes each)

Day 1. (40 minutes)

1. Establish eight to ten cooperative learning groups. Give each group one of the statements written on a large index card (leave room on the card for students to re-write the statement). These are derived from alternative conceptions about ozone and EGHE that students are likely to hold. It is less critical that the last two statements on the list be used if only eight groups can be established.
   • The "greenhouse effect" is good; the "enhanced greenhouse effect" is a problem. (T)

   • Stratospheric ozone and Tropospheric ozone are different gases. (F)

   • Ozone is a greenhouse gas no matter where it is located. (T)

   • The carbon in CFCs destroys the ozone. (F)

   • CFCs do double damage: They destroy ozone and act as a greenhouse gas. (T)

   • Ozone in the Troposphere is both a greenhouse gas and it damages plants. (T)

   • Ozone depletion is major cause of EGHE. (F)

   • Most of the aerosol sprays we use contain CFCs. (F)

   • Few of today's expandable polystyrene (insulated foam) products contain CFCs. (T)

   • HCFCs and HFCs are safe to the environment. (F)

2. Ask each group to discuss its statement to decide whether it is True or False. If the statement is False, the group should rewrite it so it is true on the front of the index card. In addition the group is to compose a supporting argument for the True version of the statement, placing it on the back of the index card. "T" and "F" follow each statement above for the teacher's reference in checking students' ideas. It might be helpful to set a time limit for discussion of the statement (e.g., 5 minutes) and development of the argument (e.g., 10 minutes).

3. Each group should identify up to 10 concepts in the statement and their supporting argument, and concept map them. After the concepts have been identified, a suggested intermediate step would be to have each group member construct a propostional relationship, using two concepts from those that were identified, that might be included on the group c-map -- 2-3 minutes might be allotted for this. Each group should be prepared to argue for the validity of the propositional connections in their map (that opportunity will come the next period). The concept maps are to be submitted to the teacher for examination and photocopying before the next class session.

Day 2. (40 minutes)

Day 3. (40 minutes)

Assessment/Portfolio Items:

Journal Entry.

Project.

Other.

Click Here to go to Investigations Lesson 10: Carbon Dioxide Detection and Analysis