We recommend measuring ozone during
a warm time of the year when the levels are higher, and encourage
you to do it again later when it is cooler. Ozone levels are highest
in temperate regions during hot weather in the summer. These are
the month of June, July, and August in the northern hemisphere.
Of course in the southern hemisphere the summer occurs in December,
January, and February. In warmer climates nearer to the equator
high levels of ozone can occur at any time of the year.
Your students have three [four, if you include tobacco leaves]
methods for measuring ozone. By using more than one method your
students will learn about the larger lessons of instrumental range
and reliability. Two of the methods, the TERC Rubber-Thread Ozonometer
and ECO Badges, require about seventy minutes. Since this time
exceeds the length of an average class period, we suggest you
ask several students to place these tools in their measuring locations
before the start of class. The third method, gas-sampling tubes,
take only about 10 minutes for a measurement.
The three methods of measurement will give differing results.
This is an opportunity to discuss with your students the various
factors involved in instrumental accuracy and the importance of
calibration to a known standard. If the instructions are followed
carefully, the gas sampling tube will be the most accurate. The
values recorded by this method can be used to check the calibration
of the other methods.
1. Refer to the Toolkit section
for detailed information about assembling, calibrating, and using
the TERC Rubber-Thread Ozonometer, the EcoBadges, and the gas-sampling
tubes.
2. Read the background piece on Tropospheric Ozone.
1. There are two main research questions
your students can investigate:
a. What is the level of ozone in the air we breathe and how does
the presence of vegetation and climate affect the levels?
b. How well do the two experimental methods for measuring ozone
work when compared to the gas-sampling tube method? Remind your
students that their data are needed by other members of the larger
community to evaluate and calibrate the operation of the TERC
rubber thread ozonometer against the gas sampling tube system.
Explain that it is important to compare ozone levels in vegetation-rich
areas with levels in areas that are barren of vegetation. Ask
them to think if any factors should be constant in this comparison
(distance from road, time of day, cloudiness, etc.). Ask them
to consider how vegetation could affect gas levels.
2. Explain that we are also curious about indoor levels of tropospheric
ozone. Some people report high levels around certain office copiers.
3. Hand out the ozone student worksheets. Explain to your students
the different characteristics of the two desired measuring-site
locations:
FIELD Ð an outdoors area with a high vegetation density, such
as a grassy field or forest.
BARE Ð an outdoors area without vegetation, such as a parking
lot or rooftop.
It is important to measure at both these locations so you, and
your colleagues will have results to compare and discuss.
4. Explain to your students that they should follow the directions
for its construction carefully, and make sure that the needle
is not too tight and is free to move. In cases where ozone levels
are as lower than 50 ppb, the ozonometer will need to be left
out longer to obtain an accurate reading. (See Note on the back
of the Student Field Worksheet-Ozonometer.)
Enter your data in a shared data
base.
Ask your students to write a letter
to a local regulatory agency asking about the monitoring and regulation
of tropospheric ozone levels. Evaluate the letter for their grasp
of tropospheric ozone issues and the thoroughness of their research.
Place the letter in their portfolio.
Ask students to present their project to other classrooms in the
school. Ask other teachers to evaluate their work.
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