Air Pollution: Tropospheric Ozone, Particulates, and Indoor Carbon Dioxide

Anne Soos
AP Consultant in Biology and Environmental Science
The Hun School of Princeton, Princeton, NJ

In this series of field tests students will measure ozone, particulates, and indoor CO₂ concentrations.

Ozone

While ozone is definitely "good" in the stratosphere, it is regarded as "bad" in the troposphere. Students will use commercially prepared ozone measuring paper to determine tropospheric ozone concentrations at 2 different locations in and around your school.

Particulates

These fine particles can be easily inhaled, and the smaller they are, the more dangerous they are in terms of lung damage. Students will use a simple particulate collector to measure the number of particulates deposited in 2 different locations in and around your school over a period of a few days.

Indoor CO₂

The concentration of CO₂ can build up significantly in poorly ventilated indoor spaces. Students will use a CO₂ sensor to take measurements in selected spaces in your school to investigate ventilation and to see how the CO₂ concentration varies with the time of day.

Teacher preparation

1. Have the class work in teams of 3 to 6 students.
2. Direct each team to choose 2 locations to test: 1 indoors and 1 outdoors. Each team should test separate locations.
3. Have each team make 2 signs to place with its test equipment. Signs must be placed at each location advising that this is a science experiment and should not be removed or disturbed.
4. Have each team develop a data table on which to record results.
5. Make sure that each team member has been assigned a specific job, and have each team submit a job list to you on Day 1 of the lab, along with a list of locations they will be testing. Make sure they head their lists with their team name.

Activities

Activity 1: Particulates

Procedure and calculations

Note: This part of the lab may be started before the other sections.

1. Obtain the particulate collectors. Put your team name on the collectors.
2. Research the amount of time you should leave them in place to collect particles. Also research whether they should be hung vertically or placed horizontally, sticky side up, or both.
3. Put the collectors in position, along with the science experiment signs.
4. Retrieve the collectors at the time agreed on by the team and bring them back to the lab.
5. Use a dissecting microscope to count the particulates per unit area. Try to identify some of the particulates (pollen, dust, plant debris, etc.).
6. Calculate the rate of deposition, in terms of particulates per hour, by dividing the number of particulates by the number of hours the collector remained in place.
7. Calculate the number of particles deposited per hour per square meter. (Your particulate collector may come with a convenient counting grid.)
8. Share your calculations with your team.

Activity 2: Ozone

Procedure and calculations

Note: For each location, you will need either a 1-hour and 8-hour test paper (they come as a unit) or a 10-minute test paper.

1. Decide as a team whether you will use a 10-minute test paper, or the 1- and 8-hour test papers.
2. In pencil, write your initials in small letters in 1 corner of the prepared paper.
3. Place the ozone collectors in the same locations as the particulate collectors.
4. Read and record the ozone concentrations at the end of the appropriate time period.

Activity 3: Indoor carbon dioxide

Procedure and calculations

1. Follow the procedures for using the CO₂ probes supplied by the manufacturer.
2. You will standardize your probes in the classroom to make sure they show similar readings. Then your team will decide how long to run the experiment (at least 24 hours is suggested) and program the interface appropriately. (CO₂ probes use a lot of power, so the probe and interface must be plugged in.)
3. Place the probes in the same indoor location as the ozone and particulate collectors.
4. At the end of the agreed-upon time, collect the probes and download the data.

Comments

Team reports

I usually ask the teams to present their data either in the form of a series of posters or a short oral report. I look for complete data tables and graphical representations of the data. I also expect each team to discuss the air pollutants in some detail: source, effects, and analysis of their data in terms of what they found and how they explain it. Finally, I ask them to draw a conclusion as to air quality at the school, and support their conclusions by referring to their data.

Helpful equipment for this series

• CO₂ Probes
• 1- and 8-Hour Ozone Paper
• 10-Minute Ozone Paper (item #653105) (this requires making a conversion to ppb, but that is easily done via an online converter)
• Particulate Collectors with White, Transparent, and Ruled Sections (item #653044)(to make counting the particulates easier)
• Dissecting Microscopes (required for accurate particulate counting)

If you can leave your CO₂ probes outside in a secure location for 24 hours, you can get some very interesting results, especially in the Northeast in late spring or early fall, when the trees are still photosynthesizing. You can usually collect a lot of particulates in the form of pollen in spring. Also, depending on the amount of time you have, this lab could be done several times during the school year to compare results at different seasons. Data analysis, especially counting particulates, is time consuming, and you should be prepared to spend several days doing the lab if you want your students to be successful.

Note: http://www.airnow.gov/ is a good resource for air pollution topics.