Title: The Impact of Tropospheric Ozone Pollution on Plants

Overview & Outcomes:

Investigations Lesson 3 linked the atmospheric composition concepts from Investigations Lesson 1 and the electromagnetic energy concepts from Investigations Lesson 2 with depletion of the ozone layer. This lesson will help to illustrate the distinction between good (stratospheric) ozone and bad (tropospheric) ozone and that ozone gas has more than one role in the earth's atmosphere. Investigations Lesson 5 is intended to link the electromagnetic energy concepts discussed in Investigations Lesson 2 with the upcoming lessons dealing with the greenhouse effect (Investigations Lesson 6, 8 and 9). Again, the three faces of ozone are presented across Investigations Lessons 3, 4 and 7 -- ozone as a protector (Investigations Lesson 3), ozone as a poison or toxin (Investigations Lesson 4), and ozone as a greenhouse gas (Investigations Lesson 7).

This lesson helps learners:

• recognize the various roles of ozone gas in the earth's atmosphere.
• explain the damaging effects of ozone pollution on life.
• graph data on ozone pollution.

The concept map shows model relationships among concepts this lesson seeks to develop. Concepts introduced in this lesson are bolded on that concept map and concepts from other lessons are in plain text (not bolded).

Background notes for teacher:

The ozone layer, located high above the earth in the stratosphere, protects the earth from damaging ultraviolet waves from the sun. This stratospheric ozone is often referred to as "good ozone" because of its life saving function. Tropospheric ozone is less familiar to students. Tropospheric ozone is a greenhouse gas that absorbs and emits infrared energy. In addition, tropospheric ozone is a deadly air pollutant at ground level. Ground level "ozone pollution" is harmful to both plants and animals. This ozone is understandably referred to as "bad ozone".

The lower atmosphere or troposphere ozone is created through a photochemical reaction when sunlight reacts with the emissions (i.e., fumes and gases) from motor vehicles, dry cleaners, gas stations, and many industrial processes. The sun's energy activates a chemical reaction between hydrocarbons and nitrogen oxides which produces this "bad ozone." (Nitrogen oxides + volatile organics + sunlight = ozone pollution.) This reaction is known as a "photochemical" reaction, due to the involvement of the sun's energy. Tropospheric ozone is a main component of smog. Anyone who breathes smog or ozone polluted air may experience coughing and congestion. Ozone is damaging to the lungs and can cause or increase the severity of existing respiratory problems. Therefore, ozone pollution should be of significant concern to those at higher risk such as joggers, smokers, asthma sufferers, the elderly and infants.

Tropospheric ozone also is one of the most significant and damaging airborne pollutants to plant life. Therefore, it is known as a powerful "phytotoxin." Symptoms of plant damage can appear as early as one day after high exposure of several hours. Noticeable effects to the leaves of crops include changes in shape, discoloration and necrosis (i.e., cell death). More subtle effects include reductions in plant size and weight, due to the fact that ozone pollution can decrease a plant's ability to perfom photosynthesis. Ozone pollution also takes its toll on forests. Increased concentrations of ozone pollution are the primary cause of the decline in pines in southern California and the eastern United States. Ozone pollution has also been considered as the primary cause of many declining European forests.

Finally, ozone can adversly affect materials. For example, it can crack and age rubber and other similar materials, and speed up oxidations processes such as rusting.

Additional Teacher References:

1. James J. MacKenzie and Mohammed T. El-Ashry, Ill winds: Airborne Pollution's toll on trees and crops. World Resources Institute, September, 1988.
2. American Phytopathological Society. Phone: 612-454-7250. E-mail: ZZZ6882@VZ.cis.umn.edu.
3. Vistanomics, Inc. markets a device that can be used by students to measure ground level ozone pollution. The device is called an ECO-Badge. The ECO-Badge is a credit card sized device that holds a chemically treated paper test card that changes color according to the level of ozone in the air. The introductory ECO-Badge kit contains 2 clip-on monitoring badges, 60 chemically treated filter paper test cards, an ozone fact sheet, a colormetric chart, and a lesson plan of student activities written by a teacher. For more information on these ozone measuring devices contact: Vistanomics, Inc., 230 North Maryland Avenue, Suite 310, Glendale, CA 91206-4261; Telephone (818) 409-9157; Fax (818) 409-9334.

Materials needed:

For the class:

1. The video Ozone: The Hole Story available from S. C. Johnson Wax, Modern Talking Picture Service, 5000 Park Street North, St. Petersburg, FL 33709 (Phone (800) 243-6877).
2. Introductory ECO-Badge kit (optional).

For each student:

1. copy of the data on levels and effects of ozone pollution
2. graph paper

Preparation:

Prior to lesson:

1. If you plan to use ECO-Badges they should be ordered two months in advance.
2. Copy handouts for students.

Instructional Procedures: (2 Days 40 minutes each)

Day 1. (40 minutes)

1. To facilitate integration of this new information on tropospheric ozone with the student's exisiting knowledge of ozone, begin this lesson by constructing with the class a concept map of the following concepts, most of which were introduced in previous lessons: ozone, atmosphere, stratospheric ozone, good ozone, tropospheric ozone, bad ozone, enhanced greenhouse effect, UV rays, infrared rays, life (and others as the teacher sees appropriate). These concepts are found in the top four horizontal levels of the concept map shown under the "overview and outcomes" section in this lesson.

2. The concept map constructed in step 1 should be expanded as the teacher introduces concepts new to this lesson (those in bold print in concept map shown within "overview and outcomes" section).

3. Show the last/third section of the video Ozone: The Hole Story , and hold a brief discussion of the main points.

Day 2. (40 minutes)

1. Have students construct a multi-line graph from the data provided on the effects of ozone pollution on various crops. Students should write a few statements that reflect their interpretation of the graph. If desired, the teacher can provide some questions to guide the student's interpretation and conduct a class discussion of the students' interpretations.

2. Have students construct an ascending bar graph from the data provided of lower atmospheric ozone pollution levels across various US cities.

3. End the lesson by asking students to individually construct a concept map of the concepts used in a similar activity the previous day: ozone, atmosphere, stratospheric ozone, good ozone, tropospheric ozone, bad ozone, enhanced greenhouse effect, UV rays, infrared rays, life (and others as the teacher sees appropriate).

Optional: Using ozone detection device

Assessment/Portfolio Items:

You may wish to collect graphs and individual concept maps and use them to generate a grade. Students should include these in their portfolios.

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