Landmark Lesson Plan: Chlorofluorocarbons and Ozone Depletion
Subject areas: Atmospheric chemistry, chemical reactions and history
Principal author: Erica K. Jacobsen
The following inquiry-based student activities are designed for use in high school lesson planning. The handout, activities, and videos will help students understand the timeline and reasons for the initial development and use of chlorofluorocarbons as refrigerants, but also their eventual banning due to their damaging effect on stratospheric ozone. Students will also explore the chemical reactions related to this damage and the challenges faced by atmospheric researchers.
The activities are designed as a ready-to-go lesson, easily implemented by a teacher or his/her substitute to supplement a unit of study. In atmospheric chemistry, the activities relate to the different regions of the atmosphere and the different roles that the same chemical can play depending on its location, and the work of atmospheric chemistry researchers to educate others about the harmful effects of chlorofluorocarbons (CFCs). In chemical reactions, the activities relate to CFCs and stratospheric ozone. In history, the activities highlight the process of change connected with the use of refrigerants throughout history. An additional science-related concept is the perception of chemicals as positive or negative.
- Teacher’s guide: Includes the handout, student activities and answer guide
- Handout: “Chlorofluorocarbons and Ozone Depletion”
- Student activities: Include the four activities described below.
While these activities are thematically linked, each is designed to stand alone as an accompaniment for the handout. Teachers may choose activities based on curricular needs and time considerations.
- History Exercise: Chronology of Chlorofluorocarbons and Ozone Using the handout, students place major events from the development and use ofrefrigerants from the 1920s to the 1980s, along with their associated environmental effectsand a worldwide decision made to limit chlorofluorocarbon use. They also consider thetiming of some of the events, such as why it took quite some time to limit CFCs once it wasknown they were harmful, and how quickly a limit on their use would affect theenvironment. (15–20 min.)
- Perceptions of Chemicals Students recognize that our perception of a chemical as positive or negative is not aclear-cut decision. They describe how ozone can have either a positive or a negativeeffect depending on its location in the atmosphere, then discuss how the perception ofchlorofluorocarbons changed over several decades. (15–20 min.)
- Chlorofluorocarbon Debate Students outline the responses of various stakeholders to F. Sherwood Rowland andMario J. Molina’s 1974 argument regarding CFCs and ozone. They also describechallenges then faced by atmospheric chemistry researchers in obtaining convincingdata. Finally, they consider possible causes of a real world 2018 CFC situation. (15–20 min.)
- Atmospheric Reactions Students explore the reactions that take place between CFCs and ultraviolet light in thestratosphere, and the resulting reactions this triggers with ozone. They also compare thesedamaging reactions to a similar ozone reaction that is viewed as a positive one. (15–20 min.)