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Student Worksheet:
Ozone Testing Tools
Name: _________________________________
Group: _______________
Note: Milkweed is only available in the late summer and is not found in every region of the U.S.
Bioindicators are biotic species, (plants, animals, etc.), that display noticeable changes
if surrounding environmental conditions change. Scientists have found that certain
organisms can be correlated with certain pollutants. The changes displayed by the
organism are measurable through various methods, therefore can offer quantitative
information on ecological resources.
Common Milkweed is considered to be a bioindicator of ozone. Milkweed shows signs
of damage from ozone by showing stiples, or dark polka dots, all over the leaves, losing
leaves, turning strange colors, or not growing very big. Photographs of injured plants
can be viewed on the Forest Health Monitoring Program's web site:
Common milkweed (Asclepias syriaca) usually has a solitary, simple stem (1.5-6 feet
tall) though clumps of multiple stems can be found. Leaves are opposite, oval, and 2-10
inches long. The surface of the leaf is hairy beneath and smooth above. The leaf stem
is short and thick. Milkweed exudes a thick white sap from any cut or broken surface.
Milkweed is common in fields, meadows, and along roadsides from New Brunswick to
Saskatchewan, south to Georgia and Tennessee and west to Iowa and Kansas.
Milkweed flowers from June to August. The flower actually consists of many flowers in a
large cluster on a stalk. A flower stalk may originate from the tip of a branch or stem or
at the junction of a leaf with the stem. The flowers are usually pollinated by insects
because the pollen is lumped in waxy masses not conducive to wind fertilization. Very
few of the flowers produce large, healthy pods. The distinctive seeds of the milkweed
are dispersed by the wind catching the long silky hairs. Studies of seed dispersal
indicate seeds typically drift 25 to 100 feet before settling to earth.
There are many other plants that serve as bioindicators for ozone if milkweed is not
found in your area. A brief list includes: Blackberry, Huckleberry, Spreading Dogbane,
Black Cherry, Choke Cherry, and Sassafras. Please consult the following USDA Forest Service's Forest Inventory and Analysis (FIA)’s web site for more bioindicators
and information:
Copyright © 2005 Stevens Institute of Technology,
Center for Innovation in Engineering and Science Education (CIESE) All Rights Reserved.
 locally harvested or observed milkweed leaves
 milkweed leaf/Plant Injury Index
 optional: list of species effected by ozone:
1. Define a sampling objective, or the scientific question (hypothesis) you will address.
2. Methods of Data Collection: Fill in the table below for each day data is collected
(how long you will perform sampling)
Date(s) of
Speed &
rain, fog, etc.
3. In late August through mid September, select a study area with these
** Remember, if the area is on private land, get permission from the landowner to
conduct research at that location. **
Plants are at least 50 feet from the road to avoid the direct effects of vehicle
exhaust, road salts, and road site mowing. Abandoned fields, remote, unmowed areas in parks or prairies are ideal sites.
Have students select a study area that has at least 20 milkweed stems located
close together.
Copyright © 2005 Stevens Institute of Technology,
Center for Innovation in Engineering and Science Education (CIESE) All Rights Reserved.
4. Choose 10 stems at random for the study. Each plant must have a stem with 10 or
more leaves on it. Mature leaves measure 2 – 4 inches in length. Avoid plants that
are diseased or have insect chewing marks on them.
5. Record findings on the chart. Select first milkweed stem. Measure and record the
height of the stem, base to the top. Use inches for measurement and record.
a. Count and record the total number of mature leaves on the plant. Mature
leaves measure 2 – 4 inches in length.
b. Count and record the number of leaves showing ozone injury on the plant.
c. Estimate the percentage of leaf area injured.
d. Repeat steps for nine more plants.
Height of the stem,
base to the top
Total # of mature
# of leaves with
ozone injury
Estimate % of
leaf area injured
Copyright © 2005 Stevens Institute of Technology,
Center for Innovation in Engineering and Science Education (CIESE) All Rights Reserved.
6. Draw a map showing the location of the study area. The map should show features
near the site like roads, trails, signs and buildings that would allow another person to
easily find the site.
1. Access the AIRNow web site ( and obtain
near real-time data for the area (if available).
2. How does the Ozone data you collected compare with the AIRNow data for your
region? For example, is it similar or different? Be sure to include any reasons you
think might influence this and identify possible sources of NOx and VOCs leading to
the production of ground level ozone
3. As a concluding activity, each group will create and deliver a 5 minute presentation
about the investigation they created and the data collected. Each presentation
should contain the following information:
 The sampling objective (hypothesis) for the investigation;
 A description of the method of data collection, including the frequency,
duration, and location of monitoring;
 How did the different measurement tools compare?
 How did the data compare with the AIRNow data? and
 What are possible sources of ozone?
Copyright © 2005 Stevens Institute of Technology,
Center for Innovation in Engineering and Science Education (CIESE) All Rights Reserved.