BioEd Online

Teacher Background

Indoor air pollution can occur in many ways. Some indoor pollutants are produced when something burns. These include gases, such as carbon monoxide, as well as particles, like those in soot. Tobacco smoke introduces these pollutants and many other chemicals into the air. Other indoor pollutants, such as pollen, spores, insect parts and droppings, and dust mites come from biological sources. Formaldehyde, a poisonous chemical, can be given off by particle board, carpeting, insulating foam, some cleaners, permanent-press fabrics, and tobacco smoke. These and many other sources (such as solvents and cleaners, paints, glues, and dry-cleaning fluids) add potentially harmful chemicals to the air.

The concentration of such compounds is much higher indoors than outdoors, in part because many modern, energy-efficient buildings are designed to prevent air leaks or the introduction of outside air into heating or cooling systems. With inadequate ventilation, chemicals and other substances become concentrated in these closed environments.

To reduce indoor air contamination, heating and cooling systems should by serviced regularly. Humidifiers and air conditioners should be cleaned frequently to reduce places where molds and bacteria can multiply. New buildings should be ventilated thoroughly before being occupied. Other measures that can reduce the buildup of harmful indoor pollutants are given on page 3 of the Air unit's Explorations magazine.

Objectives and Standards

Concepts

• Many kinds of gases and particles travel through, and become dispersed in, air.

• Substances in air become concentrated in enclosed spaces.

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Science, Health, and Math Skills

• Observing

• Measuring

• Comparing data

• Drawing conclusions

Materials and Setup

Teacher Materials (see Setup)

• 48 meters of string or heavy yarn (6-meter length piece per group of 3 students)

• 3/4-in. roll of masking tape

• marker

• orange

• stopwatch with a second hand (or wristwatch or classroom clock)

Optional Materials

• 8 metric tape measures or meter sticks

• sharp knife

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Setup

1. Before conducting the activity, measure and cut string or yarn into eight 6-meter pieces (one piece per group).

2. With a marker or pieces of tape, make lines at 2-meter, 4-meter and 6-meter points (adjust distances depending on the size of your classroom) on each piece of yarn. Older students can mark their own string segments.

3. This is a whole-class activity that can be carried out as a discovery lesson without prior introduction.

Procedure and Extensions

Time

Preparation: 20 minutes

Class: 15 minutes indoors; 15 minutes outdoors; 20 minutes to compare results

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Part 1: Indoors

1. Arrange the pieces of string on the floor like spokes of a wheel around a central point in the room (see PDF for illustration). Divide the class into three groups. Tell the members of one group to sit on the 2-meter marks on the various pieces of yarn. Tell the second group to sit on the 4-meter marks, and the third group to sit on the 6-meter marks.

2. Stand in the center of the “wheel” holding the orange. Before you proceed, tell the students that they should raise their hands as soon as they smell the scent from the orange.

3. Begin to peel the orange, hold it in your hand and turn around slowly. Record (or have one or more students observe and record) the times when approximately three-fourths of the students at each distance have raised their hands.

4. On the board, create a graph showing the time it took for the group at each distance to smell the orange. (Leave the graph on the board until after you have conducted the outdoor portion of the activity.)

5. Use the graph to talk about odors traveling through the air. Ask questions such as, Which group smelled the orange first? Which one smelled it last? Why do you think that happened?

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Part 2: Outdoors

1. Ask students, What do you think will happen if we peel the orange outside? Will you smell it more quickly or more slowly? Have students record their predictions.

2. Repeat steps 1 through 3 from Part 1 in an outdoor location.

3. After returning to the classroom, make a second graph, using the same scale as on the first, to show the time required for odors to travel outdoors. Compare the two graphs, and discuss differences. Ask, In which environment did you smell the odor more quickly? Was the odor stronger in either place? Could everyone smell the scent in both locations? Why do you think that happened? (In most cases, the scent will be noticed more quickly indoors. However, air currents indoors and breezes outdoors may affect the results. Discuss these variations with the class.)

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Part 3: Compare and contrast

1. In a class discussion, relate this experiment to the movement of particles through air (see the activity “Moving Air”), and lead students to understand how pollutants can become concentrated in indoor environments. Ask, What do you think an odor is? (It can be a gas or tiny particles of liquid floating in the air. Explain that many gases and particles float in air all the time.) Ask, What happens when things floating in air get trapped inside a room? What if it were a harmful gas? How could pollutants in air enter our bodies?

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Extensions

• About 30 minutes after finishing this activity, have students return to the outside location where they conducted their test. Ask, Can you still smell the orange? What about inside the classroom? Is the orange scent still detectable?

• Stand in front of a fan or other source of moving air while peeling the orange. Have students predict whether and how this will affect the distribution of orange scent in the room.

• Try this activity with different scents, such as those from perfumes, air fresheners, and vinegar.

Handouts and Downloads