demonstrate how pollutants can be trapped near the ground because
of atmospheric conditions.
- 4 identical small, clear glass jars (baby food
jars work well)
- Very hot tap water
- Ice water
- Index cards large enough to cover the mouth of
- Red food coloring
- Shallow pans or baking dishes (for spillage)
temperature can play an important role in the buildup or dispersion
of surface air pollution. In general air temperature decreases as
you move upward in the atmosphere. Under most circumstances the
air close to the earth warms as it absorbs surface heat, and begins
to rise. Winds occur when cool air rushes in to take the place of
the rising warm air. The wind causes "mixing" in the atmosphere
and can carry away or dilute pollution.
can play a different role if air movement is influenced by topography
or by air pressure (density). Cold air is generally "heavy"
because low temperature causes slower molecular motion, contraction,
and increased density. Gravity causes denser, heavier air to sink
below lighter, less dense air. Warm air is "light"; higher
temperature leads to faster molecular motion, expansion, and a decrease
The cold dense
air close to the ground does not readily circulate and mix. Pollutants
such as carbon monoxide and particulate matter are "trapped"
below the "lid" of warm air. The quantity of pollution
tends to increase until the lid is lifted or a wind occurs. Using
hot and cold water, you can simulate normal atmospheric conditions
and a cold weather temperature inversion.
normal conditions, place both jars in a shallow pan or baking
dish to catch any spills.
jar with hot water and one jar with ice water (no ice). Fill
the jars to the brim. Put several drops of red food coloring
in the jar with the hot water, to represents pollutants in the
air near the earth.
index card over the top of the jar with the cold (clear) water
and quickly flip the jar on top of the jar with hot, polluted
(red) water. Make sure the openings of the two jars are perfectly
aligned and hold them in that position while you quickly but
carefully pull the index card out. Let the Jars stand.
conditions: Repeat the above procedure, except in this case
place the red food coloring in the jar of cold water. Then place
the index card over the top of the jar with the hot (clear)
water and invert it over the jar full of cold, polluted (red)
water. Let the jars stand.
in the first instance? The hot (red) and cold (clear) water
mix immediately, moving some of the red food coloring (pollutant)
into the upper jar, which becomes red. At the same time the
red (pollution) in the lower jar is diluted. This mixing of
the warmer, colored water shows how warm air near the earth
can move upward into the colder upper atmosphere and disperse
In the second instance, the cold (red) water is trapped and
can't escape upward. The jar of hot water on top (clear) has
“trapped” the dirty (red) cold air, just as warm air can trap
a layer of cold, polluted air and create unhealthful air quality
students to identify sources of pollution which might particularly
contribute to cold air (wintertime) inversions.