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Smog Convection Currents

In this demonstration, students observe the formation of smog by watching smoke (air particles) trapped in a layer of cold air under a layer of warm air. 

Convection is the transfer of heat by the movement of a gas or liquid from one position to another. The basic premise behind convection is that heated matter becomes more buoyant and "rises", while cooler material "sinks." These convection currents occur in atmospheres, oceans, the Earth’s mantle and in a bowl of hot soup. When they occur in our atmosphere, convection currents cause local breezes, winds, cyclones and thunderstorms.

The action of convection currents also result in smog.

When hot air rises and traps cool air below, it also traps the pollutants such as carbon monoxide and dust particles to cause the “brown cloud” effect. Wind or precipitation can reduce the brown cloud by stirring up and breaking up the warm layer of air that traps the cold air and pollution down near the surface of the earth.

Objectives

  • Describe and illustrate the water cycle and associate parts of the cycle with weather conditions.

  • Observe and describe changes to the properties of water when it is heated or cooled and associate these changes with weather conditions.

Materials

  • Per Demo or Group:
    large jar
    jar lid with small hole
    clear tape
    black paper
    ice pack (or sealable bag with 6 ice cubes)
    sealable bag
    475ml warm water
    duct tape
    matches

Key Questions

  • What is happening to the air when you wait for 2 minutes?
  • What are the relative temperatures of the air at the top of the jar and at the bottom?
  • How is the air moving within the jar?
  • How does this demonstration relate to smog?

What To Do

Preparation

  1. Punch a hole into the jar lid. The hole should be large enough for a match to pass through easily. Create a flap by covering the outside of the hole with a piece of tape that you can peel back. If your jar lid is too hard to punch a hole into, use a piece of wax paper and an elastic band instead, and punch a hole into the paper.
  2. Wrap black paper around one side of the jar. Secure with clear tape. It’s easier to see the smoke against a dark backdrop.
  3. Fill the sealable bag with 2 cups of warm water.
  4. OPTION: If you are not using an ice pack, fill another sealable bag with 6 ice cubes.

Demonstration

  1. Put the ice pack or bag of ice cubes in the bottom of the jar.
  2. Tape the warm water filled bag to the top of the jar using duct tape and suspend it so it hangs inside the jar near the top. Make sure the hole remains unobstructed.
  3. Put the lid on the jar and wait 2 minutes.
  4. Light a match and then blow it out so that it releases smoke. Open the tape flap on the jar lid, drop the unlit match into the jar and close the flap. The more quickly and smoothly you can do this step, the better the results will be. You’ll want to try to disturb the air inside as little as possible.
  5. Observe what happens to the smoke within the jar.

Extensions

  • Explore conduction, convection and radiation and how temperature influences weather.

Other Resources

Mrs. Simcox | Global Warming Lessons | Temperature Inversion