Ask students the following question: How does weather
affect air pollution?
Lead them toward the next question if they don’t
bring this up themselves:
How do convection currents and temperature inversions
influence air pollution?
By the end of the lesson students will hopefully
be able to explain the following: Polluted air will
be moved and diluted by convection currents, but
will remain stagnant during a temperature inversion.
1. Divide your students into small groups and see
if they can suggest methods to show how convection
currents and temperature inversions influence air
pollution. Perhaps their ideas will illustrate this
point just as clearly as the following experiments,
and the lesson will stick with them longer if they
do the brainstorming. In case there are few reasonable
suggestions, here’s an activity to help you
Take the top off the shoe box and lay the box on its
side. Cut two holes in the topside of the box (one at
end), just large enough for two paper towel tubes. Push
the tubes into the holes and seal the openings with tape
in order to ensure an airtight seal. You have just made
two paper towel tube chimneys.
3. Set a candle in a clay base under one of the paper
towel tube chimneys, pressing the clay firmly into place
to hold it tight. The candle should be at least 2 inches
lower than the chimney. (Make sure the wick is exposed
4. Cover the open side of the box with clear plastic wrap.
Tape the plastic wrap to the front of the box, forming
an airtight seal.
5. Very CAREFULLY, using a long match, (or a match taped
to a pencil) light the candle by putting it down the chimney.
Once the candle is lit, allow the box to warm up for approximately
6. Take a tightly wadded up paper towel and light it with
a match. Let it burn for a few seconds, and then blow it
out. It should be smoking profusely. Note that the smoke
rises (warm air). Now hold the smoking paper down over
the second chimney (without the candle). Record your observations:
The cold (heavier) air above the smoking paper will push
the smoke down through the chimney. The smoke will then
warm, rise toward the candle, and exit the convection box
via the opposite chimney. This demonstrates the cyclic
nature of convection and how warm air rises and cold air
7. Now, to simulate a temperature inversion, blow out
the candle, place the ice cubes down both chimneys and
let the box cool down for five minutes.
8. While the box is cooling down, put the heat lamp directly
over one chimney, not blocking it, but making sure the
heat is funneled down into the box.
Drop a smoking wad of paper down the other chimney, and
then place a
piece of paper over this chimney. A temperature
inversion prevents normal convection. The warmer air mass
moves over the cooler ground air and traps it. Compare
the heated chimney with the unheated one. After 30 seconds
of viewing the trapped smoke, lift the unheated chimney’s
cover and watch the smoke escape. Record your observations.
on your observations, does this demonstration support
or reject your hypothesis? Why or why not?
1. What, in nature, warms the air like the candle did in
How does Tucson’s geography and weather make
it a prime candidate for temperature inversions?
3. What human activity is most responsible for air pollution
in our community?
4. Recall that pollution lingers during a temperature
inversion, when cool polluted air is trapped under a lid
of warm air. At what time of day or night are these conditions
most likely to occur?
5. What human activity occurs at this time of day or night
that contributes to air pollution?
6. What would cause cold, polluted air to rise and be
diluted? At what time of day or night would you expect
this to happen?
7. If the sun rose later in the day, what effect would
this have on lingering air pollution?
8. At what time of the year would you expect this to happen?