THE DUAL NATURE OF OZONE
Stratospheric and Tropospheric Ozone
by: Daniel Cohan Ph.D. and Remelia Arpino
June, 2012
INTRODUCTION
This lesson packet contains two lessons on ozone: Stratospheric Ozone and Tropospheric Ozone.
This is the high school version of the Rice Air Curriculum, originally developed by Dr. Daniel Cohan and
Kavita Venkateswar in 2009. Its primary objectives are to provide high school teachers of Environmental
Systems or similar courses with curricular materials for engaging students in interactive and inquirybased learning about ozone in both the stratosphere and troposphere.
Each lesson is divided into two sections. The first section is the teaching guide that utilizes the
5E lesson plan format and the second section is the reproducible student materials. The suggested
activities include collaboration among students, use of technologies like computers for research, use of
apparatuses to measure weather conditions and ozone on school campuses, and a chance to develop
and apply their critical thinking skills in designing their own experiment in the second lesson.
Since the Houston region has long struggled to meet the federal air quality standards for
ground-level tropospheric ozone, it is hoped that at the end of the lessons, students will actively
participate in considering how they can reduce emissions that cause the formation of tropospheric
ozone.
Teaching The Dual Nature of Ozone:
Guide STRATOSPHERIC OZONE
Adapted by Remelia Arpino from the Rice Air
Curriculum by Daniel Cohan and Kavita Venkateswar
OBJECTIVE
This lesson focuses on stratospheric (high-level) ozone, which protects us from the harmful
radiation of the sun. The lesson explains how ozone naturally forms from oxygen and sunlight in the
stratosphere, and distinguishes between the protective stratospheric ozone layer and the tropospheric
ozone pollution that forms near the ground (covered in more detail in the Tropospheric Ozone Lesson).
Students will look at how certain chemicals can damage stratospheric ozone and how the Montreal
Protocol and the efforts of some companies and agencies are helping to protect the ozone layer.
Students will be active participants throughout the whole lesson and it is hoped that at the end of the
lesson, they will gain a deeper understanding of the stratospheric ozone.
In preparation for the subsequent lesson about tropospheric ozone, students in the Explore
activity will begin to measure ground-level ozone and meteorological factors that are related to
tropospheric ozone formation. Their skills in this investigation will be used in the next lesson for the
inquiry lab.
Figure 1. Stratospheric ozone forms naturally and protects us from ultraviolet radiation. Tropospheric ozone forms
from air pollutant emissions and harms human health. Credit: US Nuclear Regulatory Commission: Ozone: Good Up High, Bad
Nearby.
BACKGROUND INFORMATION
Most of the oxygen in the atmosphere, and the type that we need to sustain life, has two atoms
per molecule (O2). Ozone, by contrast, has three oxygen atoms (O3). Ozone forms naturally in the
stratosphere when intense ultraviolet radiation (UV-C) from the Sun splits an oxygen molecule (O2) into
two O atoms. Each O can then combine with another O2 to form O3.
About 90 percent of the ozone in the Earth’s atmosphere is found in what is known as the ozone
layer in the stratosphere (about 10-30 miles above Earth’s surface). The ozone layer absorbs most of the
Sun’s ultraviolet radiation to shield us from these damaging rays. Ultraviolet rays can cause a range of
negative effects: they can cause cancer, burn skin, damage eyes, weaken the human immune system,
and harm both plants and animals. In fact, estimates show that a one percent reduction in the ozone
layer results in a two to five percent increase in the number of cases of cancer!
Certain air pollutants can damage the ozone layer. The most dramatic depletion of the ozone
layer is the Antarctic ozone hole. In the early 1980s, scientists discovered major thinning of the ozone
layer above Antarctica during springtime1. In fact, they observed nearly 70% less ozone than had been
found there previously! Scientists realized that the depletion of the ozone layer is caused by the release
of certain chemicals such as chlorofluorocarbons (CFCs) into the atmosphere. Just a few decades ago,
CFCs were used in air conditioners, aerosol sprays, and cleaning products. When CFCs reach the
stratosphere, they react with the sunlight to release chlorine atoms, which can destroy ozone
molecules. In 1989, an international agreement known as the Montreal Protocol was signed to ban the
most destructive ozone-depleting gases and preserve the ozone layer. If the agreement is adhered to, it
is hoped that the ozone layer will completely recover by 2050.
As we have seen, the ozone layer in the stratosphere is a vital layer of protection for the Earth.
This layer that contains most of the atmosphere’s ozone is far above the air that we breathe every day,
and even above the altitude where most airplanes fly. However, when ozone forms near the surface in
the troposphere, where humans breathe, it is an air pollutant that can harm our lungs and the natural
environment. This tropospheric ozone is the same molecule as in the stratosphere. However, in the
troposphere, ozone forms in very different ways than in the stratosphere. We’ll learn more about
tropospheric ozone in a separate lesson.
1
The dramatic thinning of ozone over the South Pole does not last for the entire year. Instead, it usually
occurs in September or October (Antarctic springtime) and “fills in” or disappears by December. Special
conditions in the Antarctic winter make its stratospheric ozone especially sensitive to depletion by
chlorine when the sun returns in the early spring. Outside of Antarctica, slight reductions in
stratospheric ozone have also been observed over most of the planet.
TEXAS STANDARDS
TEXAS ESSENTIAL KNOWLEDGE AND SKILLS (TEKS)
Environmental Systems TEKS 9: The student knows the impact of human activities on the environment.
The student is expected to:
A. Identify causes of air, soil, and water pollution, including point and nonpoint sources;
B. Investigate the types of air, soil, and water pollution such as chlorofluorocarbons, carbon
dioxide, pH, pesticide runoff, thermal variations, metallic ions, heavy metals, and nuclear
waste;
C. Examine the concentrations of air, soil, and water pollutants using appropriate units;
D. Describe the effect of pollution on global warming, glacial and ice cap melting, greenhouse
effect, ozone layer, and aquatic viability;
E. Analyze past and present international treaties and protocols such as the environmental
Antarctic Treaty System, Montreal Protocol, and Kyoto Protocol.
TEXAS COLLEGE AND CAREER READINESS PROGRAM (CCRS)
SCIENCE STANDARDS WITH PERFORMANCE INDICATORS
I.
Nature of Science
A.
Cognitive skills in science
1. Use creativity and insight to recognize and describe patterns in natural phenomena.
2. Rely on reproducible observations of empirical evidence when constructing,
analyzing, and evaluating explanations of natural events and processes.
B.
Collaborative and Safe working practices
1. Collaborate on joint projects.
2. Demonstrate skill in the safe use of a wide variety of apparatuses, equipment,
techniques, and procedures.
C.
Current scientific technology
1. Use computer models, applications, and simulations
D.
Effective communication of scientific information
1. Use several modes of expression to describe or characterize natural patterns and
phenomena. These modes of expression include narrative, numerical, graphical,
pictorial, symbolic and kinesthetic.
II.
Foundation Skills: Scientific Applications of Mathematics
A.
Understand the real number system and its properties
1. Calculate the sums, differences, products and quotients of real numbers.
III.
Foundation Skills: Scientific Applications of Communication
A.
Scientific Reading
1. Set up apparatuses, carry out procedures, and collect specified data from a given set
of appropriate instructions.
B.
Presentation of scientific /technical information in appropriate formats for various
audiences
1. Prepare and present scientific/technical information in appropriate formats for
various audiences.
C.
Research skills/information literacy
1. Use search engines, databases, and other digital electronic tools effectively to locate
information
IV.
Cross-Disciplinary Themes
A.
Change over time/equilibrium
1. Recognize patterns of change
V.
Environmental Science
A.
Earth systems
1. Know the major features of the atmosphere
B.
Human practices and their impacts
1. Understand how human practices affect air, water and soil quality.
ENGAGE
Option 1: Brainpop Video - Ozone Layer (Use this option if you have access to Brainpop.com otherwise,
use option 2.)
Materials: (for Option 1 and 2)
For each group:
Labels and diagram of the three layers namely: troposphere, ozone layer and stratosphere
(SM-1)
Procedure:
1. Before showing the video, have students identify the three layers namely; troposphere,
ozone layer and stratosphere by placing the correct labels in the diagram. Use SM-1
material for this preliminary activity.
2. Have students watch the short video on ozone layer.
3. At the end of the video, ask students the following questions:
a. How many oxygen atoms are there in an ozone molecule?
b. What is the role of the ozone layer?
c. What chemicals damage the ozone in the stratosphere?
d. What government agency oversees programs designed to help the ozone layer?
Option 2: You Tube Video: NASA: Exploring Ozone
Procedure:
1. Before showing the video, have students identify the three layers namely; troposphere,
ozone layer and stratosphere by placing the correct labels in the diagram. Use SM-1
material for this preliminary activity.
2. Go to http://www.youtube.com/watch?v=qUfVMogIdr8 and have students watch the
short video from NASA.
3. At the end of the video, ask students the following questions:
Facilitation Questions:
1.
2.
3.
How does stratospheric ozone protect life on earth?
What chemicals do you know that could damage the stratospheric ozone?
In addition to those chemicals, what are the other ingredients or factors known to
deplete the ozone?
EXPLORE PART I
Teacher notes: The first explore activity will introduce students to the equipment that is used to
monitor ground-level ozone. It is important that they will develop the skills of using all the equipment
listed below since they will be doing an inquiry lab in the next lesson. Do not forget to emphasize in this
activity that they are measuring ground-level (tropospheric) ozone, not stratospheric ozone.
Teacher Preparation: Print the SM-2 (Rice Air Curriculum: Ozone and Meteorology Data Sheet)
and SM-3 (Cloud Guide) for each group of students.
Materials (one for each group):
 Rice Air Curriculum: Ozone and
Meteorology Data Sheet (SM-2)
 Cloud Guide (SM-3)
 Ozone strips
 Ozone scanner




Hygro-thermometer
Infrared Thermometer
Wind vane
Thermal glove
Procedure:
1. Take your students outside the classroom and have them measure the different parameters
listed in the Ozone and Meteorology Data Sheet.
Note: Be sure to review the GLOBE Protocol for Ozone. It is important that the ozone strip
must be exposed for at least an hour. Make the necessary adjustments according to your
class time.
2. Ask your students to record the beginning of class data in their data sheet.
3. Repeat the procedure after an hour and have your students record the end of class data in
their data sheet.
Facilitation Questions:
1. What is the difference between the beginning and end of class data?
2. How do you account for the difference of the data?
EXPLORE PART II
Teacher Preparation: Make copies of the Introduction to Ozone Cards for your student groups.
Procedure:
1. Divide the class into seven (7) groups.
2. Assign one ozone card (SM-4) to each group of students.
3. Instruct the students to read, brainstorm and discuss the information in the card for 15
minutes.
4. Remind them that after the activity, they are going to present it to the class for discussion.
Give them an additional 10 minutes to prepare visual materials that would help them in the
delivery of the information.
EXPLAIN
Teacher Preparation: Make copies of SM-5 (Note-taking worksheet) for individual student. This
will keep each student focused during the presentation.
Vocabulary




Ozone
Oxygen molecule
Oxygen atoms
Ozone layer




Stratospheric ozone
Ultraviolet rays
Electromagnetic spectrum
Chlorofluorocarbon
 Montreal Protocol
 Antarctic ozone hole
Procedure
1. Give students 5 minutes to prepare for their presentation.
2. Distribute SM-5 to individual student for note-taking during presentation.
3. Each group of students will explain the information in the card to the class.
Note: Be sure to clarify things before proceeding to the next group. Facilitate the
discussion by asking questions.
ELABORATE
Teacher Notes: The elaborate or extension activity is an online research activity. Students are
going to read the ‘Achievements in Stratospheric Ozone Protection Progress Report’ by the US
Environmental Protection Agency. The information that they will gather from this report will enhance
their understanding on the cause of stratospheric ozone depletion as well as the efforts of companies
and agencies back then and now to save the ozone layer. This task can be given as a homework or inclass assignment.
Teacher Preparation: If your access to computers is through the computer lab, be sure to
reserve it in advance for this lesson. Make copies of SM-6 for individual student.
Materials:
 Computers
 Achievements in Stratospheric Ozone Protection Worksheet (SM-6)
 Pens/pencils
Procedure:
1. Distribute the SM-6 to individual student.
2. Ask them to type ‘http://www.epa.gov/ozone/downloads/spd-annual-report_final.pdf’ into
their internet browser. The first page of the document should be: ‘Stratospheric Ozone
Protection Progress Report.’
3. Instruct the class that they are going to read the whole document and answer the questions
in the worksheet.
EVALUATE
Teacher Preparation: Print copies of the Summative Assessment (SM-7).
Procedure:
1. Distribute the SM-7 to each student.
2. Assess the students by giving the 5-question summative assessment.
Answer Key
1. D
2. D
3. A
4. B
5. C