Stephen Herr
AP Environmental Science
Section 1
stephen_herr@verizon.net
Lab 8 Measurement of Ozone
April, 2005
Surface level ozone measurement
0-3 Little of no change
4-6 Lavender hue
7-10 Blue or purple
0
5
Data from EPA ; Relative Humidity = 60%; April 9, 2005
Ozone strips when wet
dry
10
Ozone damage to pine needles
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Data Worksheet
Monitoring
Strip Color
Backyard
Brown with a
Hung under a pine tree in the
slight lavender
shade on a hill.
hue
Front yard
Brown with a
Hung from a gate in the shade
slight lavender
over grass.
hue
Freeway
Brown with a
In a dead oleander bush next to slight lavender
Monitoring
Location
1
2
3
Schoenbein
Number
≈ 4 when dry
Ozone conc.
ppb
≈ 90 ppb
≈ 5 when dry
≈ 115 ppb
≈ 4 when dry
≈ 90 ppb
4
the 210 freeway onramp in the
shade
Garage
hue
Brown with a
slight lavender
hue
≈ 4 when dry
≈ 90 ppb
AB REPORT/ ANALYSIS QUESTIONS
1. Compare the ozone concentrations at the three test sites. Were there differences
between sites? If so, can these differences be correlated to differences between the
measurement locations? Discuss thoroughly.
The test conducted in the front yard had a Schoenbein number of 5. The other three tests
all had Schoenbein numbers of 4. These sites probably had different humilities because
of their location. This would have affected their Schoenbein numbers (see question 7.)
These sites were differing distances from roads and traffic. The test in my back yard was
the farthest from a road, and the test conducted next to the freeway ramp was the closest.
My results did not seem to indicate that this made a substantial difference.
2. Identify and describe three sources of troposphere ozone.
Ozone naturally forms in the stratosphere through Hadley cells can bring this ozone down
to the troposphere. Ozone also can form in the troposphere through the interaction of
sunlight with hydrocarbons and nitrogen oxides in photochemical smog that occur in the
Chapman reactions. This smog is produces primarily by the burning of fossil fuels.
Electrical generators and motors also produce ozone.
3. Describe two ways that tropospheric ozone can affect living organisms?
Ozone is a strong oxidizer. It strips electrons from other chemicals. When ozone comes
in contact with the respiratory system, it can irritate it and cause breathing problems.
Ozone also adversely affects plants by damaging there leaves and needles which they
need to survive. The picture at the top of the report shows this.
4. How does relative humidity affect the ozone measurements?
The graph above shows the way humidity affected the ozone measurement. Greater
humidity causes the strips to develop faster. To compensate for this, corresponding
ozone level is reduced.
5. Would the ozone concentrations be the same for a Schoenbein number of 4 at
relative humidities of 30% and 70%? Explain.
No, the one with the relative humidity of 30% would have a ozone concentration of about
50 ppb where as the one with a relative humidity of 30% would have an ozone
concentration of 140 ppb.
6. The ozone concentration is given in ppb. What does ppb mean?
PPB is an acronym that stands for parts per billion.
7. What are some possible sources of error in this experiment?
Unfortunately, I was unable to obtain accurate humidity readings at each of the
locations. An accurate humidity reading is importunate to find the correct ozone level.
For example, if the relative humidity was 70% in the front yard, the ozone concentration
would have been about 70 ppb instead of 115 ppb. This is quite a disparity. Because of
this, I was unable to conclude whether or not the slightly darker colored strip from my
front yard could be attributed to an higher level of humidity or ozone. It is very probable
that it was more humid because it positioned over a lawn, but I cannot be entirely sure of
this.
It was very hard to match up the strips with the appropriate Schoenbein number.
This might have caused me to give some tests the wrong Schoenbein number. This
would result in an inaccurate Ozone concentration.
8. Write a comprehensive summary and conclusion for your results.
I used the following procedure to make the ozone detecting strips.
1. Measure 100 mL of distilled water in a graduated cylinder and pour it into the 250 Ml
beaker. 2. Weigh 5 g of cornstarch using the balance. Add this to the beaker of distilled
water and stir. 3. Place the beaker on the hot plate and heat the mixture over medium
heat. Stir the mixture constantly until it gels. The mixture will thick and translucent. 4.
Weigh 1 g of KI using the balance. 5. Remove the beaker carefully from the hot plate
and add the KI to the beaker. Stir the mixture well. You should turn off the hotplate. 6.
Cool the mixture. 7. Brush the pasty mixture carefully onto the filter paper (10 cm x 10
cm) using a cotton swab. Lay the filter paper on the glass plate during the coating
operation so that it won’t stick to the table. Turn the paper over and coat the second side.
It is important that the mixture be applied evenly and uniformly. 8. Dry on the coated
filter paper. 9. Cut the coated filter paper into three separate strips (10 cm x 3 cm
each).
I then placed the strips in four different locations (see question #1) and waited eight hours
for them to be exposed. After eight hours I collected the strips and exposed them by
dipping them into distilled water.
Ozone in the air oxidized the potassium iodide on the test paper to produce iodine. The
iodine reacted with starch, staining the paper a shade of purple.
The chemical reaction for this process is:
2KI  O 3  H 2O 
 2KOH  O 2  I 2
I 2  starch 
 starch  iodine  complex (blue/purple)

A picture of the strips can be seen at the top of this report. The instructions were unclear
as whether or not I was supposed to wait until the strips were dry to compare the colors
with the Schoenbein color scale. I decided to wait until the strips were dry because I
though it would give me more accurate results.
My results can be seen in the table near the top of this report. They were higher than the
maximum ozone concentrations that the EPA reported for that day. This can be seen in
the ground level ozone map.