What is ozone? Is it harmful or beneficial? Is there really an "ozone hole" in the atmosphere? Can it be repaired?

Insights

Ozone is a gas, a form of oxygen, that is found in the layers of the atmosphere, most predominantly in the stratosphere. Here, 90% of the atmosphere's ozone is distributed in a ratio of five ozone molecules to every million molecules of other gases. This minute distribution serves as a shield that helps screen the sun's rays by absorbing some of the ultraviolet(UV-B)radiation.

Depletion of the ozone in the atmosphere can have severe consequences on earth. Plants, animals, and humans all suffer when exposed to higher levels of ultraviolet rays. Food crops have stunted growth; marine phytoplankton can die off; and humans are more vulnerable to skin cancer.

Atmospheric research in the mid-1980s indicated a serious thinning of the ozone shield, upsetting a natural balance between oxygen and ozone in the stratosphere. This thinning was evident from satellite pictures and showed up as a dark area; thus the term "ozone hole" was coined. It was apparent to scientists studying the ozone depletion that chemicals called chloroflourocarbons (CFCs), used in spray cans, refrigerators and air conditioners, foam, plastics, and cleaning solvents, might be contributing to the problem. After being released, either during the manufacturing process or from consumer use, CFCs reach the stratosphere. There, chemical reactions break apart the CFCs. The chlorine then breaks down the ozone. A single chlorine atom can destroy 100 thousand molecules of ozone.

The degree of ozone depletion has followed an annual cycle that corresponds to the amount of sunlight that reaches the Antarctic. The cycle begins every year around June when the vortex winds develop in the Antarctic. Cold temperatures produced by these winds create polar stratospheric clouds that capture the floating CFCs. For the next two months, a reaction occurs on the cloud surface that frees the chlorine in the CFCs but keeps the chlorine contained within the vortex area. In September, sunlight returns to the Antarctic and triggers a chemical reaction, causing chlorine to convert ozone to normal oxygen.

Measured ozone levels usually are lowest in October. November brings a breakdown in the vortex that allows the ozone-rich air to combine with the thinning ozone. Wind currents carry this mixture over the southern hemisphere and carry the "hole" over other areas of the earth.

Connections

1. What can we do to help "close" the ozone hole?
2. In 1992, representatives of countries from around the world gathered in Rio de Janeiro for what was called the Earth Summit. What resolutions concerning ozone depletion came out of this meeting?

Vocabulary

chlorine a chemical element important in the destruction of ozone
chlorofluorocarbons (CFCs) chemical compounds made up of carbon, fluorine, and chlorine
ozone a molecule made up of three atoms of oxygen
stratosphere the layer of the earth's atmosphere just above the troposphere; extends from 15km to about 50km above the earth
total ozone mapping spectrometer (TOMS) an instrument flown aboard the NIMBUS-7 spacecraft that provides high-resolution mapping information about atmospheric ozone content
ultraviolet radiation (UV-B) high energy electromagnetic waves that lie beyond the purple end of the visible spectrum

Resources

Aeronomy Laboratory/NOAA
325 Broadway
Boulder, CO 80303
(303) 497-5785

Climate Protection Institute
5833 Balmoral Drive
Oakland, CA 94619
(newsletter)

NASA
Education Division
Mail Code F
Washington, DC 20546
(Atlas 1 Teacher's Guide: Earth's Mysterious Atmosphere)

NASA CORE
Larain County, JVS
15181 Route 58 S
Oberlin, OH 44074
(216) 774-1051 Ext. 293
(videotapes from shuttle missions during which Blue Planet was filmed)

National Air and Space Museum
Office of Education
Washington, DC 20560
(202) 357-3133
(Blue Planet educational booklet)

PBS Environmental Resource Compendium
1320 Braddock Place
Alexandria, VA 22314
(703) 739-5402

Main Activity

Before information about ozone is released to the general public, scientists spend many hours analyzing ozone data from earth and space. Here's your chance to be an ozone-research analyst.

Materials

• NIMBUS-7 TOMS Images: The Twelve Octobers. Order one for each two students by lithograph name and number (HqL-308) from:
  NASA Goddard Space Flight Center
  Greenbelt, MD 20771
  (301) 286-8955
  
• paper
  
• pencil
  

Note: Instructor may wish to make photocopies of the TOMS lithographs so that the information on the back is not available until students have interpreted the data.

1. Divide students into research-analyst pairs.
2. Discuss why the Dobson Unit key will be important and note the range of the value for each color. (If paper copies have been made, allow time for the students to color in the key.)
3. Use the questions below to analyze this data and to formulate predictions.

Questions

1. Which year had the lowest ozone concentration? Which had the highest? Did the level always drop from year to year? Explain possible reasons for this.

2. What is the geographic location of the thinnest concentration? The thickest? Why might this be? Have maps or globes available to aid in answering these questions, or superimpose lines of longitude and latitude on the TOMS maps.

3. Why were the images taken in October? What differences would you expect in images taken during November, December, and January?

4. How important is the use of color in these images?

5. Based on the October images, what predictions can you make for ozone levels in 1995? Justify your predictions.

6. What information might appear in a news article reporting this data? How could it be presented to help the general public understand its importance?

Invite a dermatologist to speak to your class. Ask for information about the effects of exposure to ultraviolet radiation. What is the meaning of SPF on sun-lotion packaging? Is there a time when exposure to ultraviolet radiation is helpful? What about tanning salons?

Contact Goddard Space Flight Center in Greenbelt, Maryland and the Aeronomy Laboratory in Boulder, Colorado. Find out about the different methods of gathering data for ozone research. What types of spacecraft are used? What types of airplanes? How often are expeditions sent to the pole? How do they gather data? What are plans for future expeditions?

Create on videotape or audiotape a "news program" about the ozone situation. Be as factual as possible. Include information about what the ozone layer is, its importance, materials and actions that are believed to contribute to ozone depletion, and actions students could take to help improve the situation. Share this with your science class or ask permission to air it as a public service on school-wide television.

Newton's Apple is a production of KTCA Twin Cities Public Television.
Made possible by a grant from 3M.
Educational materials developed with the National Science Teachers Association.