Cloud in a Bottle: Particulates are the Problem

Subject Area

Weather

Age or Grade

7th-8th

Estimated Length

30 min

Prerequisite knowledge/skills

Basic Knowledge of Atmosphere and phases, Works well in weather unit.

Description of New Content

Particulates cause increased cloud formation

Particulates are from combustion

If applicable to class, the idea of negative feedback loop

Goals

Produce a cloud of water vapor in the bottle with smoke, while non is produced in the bottle without smoke.

Materials Needed

Two 2-liter bottles with caps

Small amount of water

Matches (safety googles)

Procedure

Opener.

Clouds require small liquid or solid particles around which to form, otherwise water vapor will stay in the form of a gas, rather than condensing to form a cloud. One of the things that clouds often form around is particulates, small particles, which naturally occur in the atmosphere, from a variety of sources ranging from Saharan desert sand to particles from the eruption of volcanoes.

Development

Produce two capped identical 2-liter bottles with labels removed. Have students measure 200ml of water in a graduated cylinder, and direct them to pour it into one of the two bottles, repeat for the second bottle. Have the students cap each bottle and return to their seats. The teacher should don safety goggles, and remove the cap from one of the bottles, and lay it on its side. Next strike a match very near the bottle, allowing as much of the match to ignite as quickly as possible, then extinguish the match by blowing it out, and quickly place the smoking match into the open bottle. When smoking begins to cease, remove the match and cap the second bottle. Emphasis that the bottles are nearly identical at this point, the only variable in the experiment is the presence or absence of smoke in the bottle. Ask for a volunteer and have the class gather around the bottles. The teacher and volunteer should shake both bottles vigorously for 20 seconds. Then the teacher should demonstrate squeezing and releasing the smoke free bottle to the students, what do they observe? Next have the volunteer squeeze and release the bottle with the “invisible” smoke particles. A puffy cloud will appear. Allow students to try squeezing both bottles, the effect will work for a few minutes, with the cloud appearing for a few seconds after each squeeze and release, it is important to shake the bottles to increase the amount of water vapor between each squeeze.

Closure

One of the goals of the 1970 Clean Air Act was to reduce the amount of particulates produced from many combustion products like coal, gasoline and diesel, either by actually changing the fuel, or introducing some kind of collector or scrubbed in the exhaust system. Of particular interest was the reduction of sulfates in exhaust. This reduction, however, had an unintended consequence, the reduction in these particles lead to an increase in mean global temperatures in the mid-north latitudes, as the particles had been scattering sunlight and cooling the air, often through the creation of clouds. While well intentioned, and much needed, this negative feedback loop from burning fossil fuels was broken, and lead to a sharp increase in mean global and arctic temperatures from the late 1970s until present. This can also be a very good time to indicate that even the best scientists at NOAA and NASA are often learning new and exciting things, sometimes having unexpected results.

Evaluation

Extensions

References

EPA Clean Air Act http://www.epa.gov/air/caa/