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Smell an Onion

To see how invisible substances can affect your body, and to learn how wind affects air pollution, try this:

Have three classmates volunteer to be scientists. Each of the remaining students will act as monitoring instruments in different parts of a city. Each "instrument" should raise a hand the instant he or she smells onion. One scientist should observe the "instruments" and be prepared to draw on the chalkboard a rough map of the smell's path through the "city." One scientist should measure the time between the first and last hand raised and how long it takes for the odor to disappear. The last scientist should count the number of people whose eyes water.

Turn on the fan and slice up an onion. How much time passed between the first and last "instrument" readings? How many students "cried" from the onion? By studying the map on the board, what conclusions can you make about the effect of wind on air pollution?

[Reprinted with permission of National Wildlife Federation from National Wildlife Week 198 Educator's Guide, We Care About Clean Air, ©1987]

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