Overview:
In this lesson, students will explore how aerosols absorb and scatter light energy. The video for this lesson is a demonstration by Bill Nye. This demo can also be done in the classroom with a large water container, air pump, and a match. Bill Nye shows how, with soot, clouds are whiter and easier to see. With soot particles, there are more surfaces for water to condense on. These particles are called cloud condensation nuclei (CCN). White objects scatter and reflect light energy which leads to cooling of the atmosphere. Other aerosols could be darker in color and therefore absorb light energy. This causes warming of the atmosphere. In general, aerosols tend to have a cooling effect.
The experiment in this lesson can be done several ways. If students are familiar and experienced with inquiry, a list of materials can be given and then students would write their own procedures and carry out the experiment. For classrooms that do not have experience with inquiry, the materials and procedures can be provided for the experiment.
Any degree of inquiry could be done with this experiment.
The Lesson:
To start the day’s lesson, use the provided PowerPoint:
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Slide 1 – Photo of pollution layer just above the clouds at sunset
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Slides 2-4 – Students take notes on scattering, absorption, albedo and light energy
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Slide 5 – Questions for Bill Nye video
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Slide 6 – Link to Bill Nye video
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Slide 7 – Intro to experiment (students will most likely answer by saying a white shirt either by experience or knowing that white reflects and black absorbs)
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Slide 8 – Basic overview of experiment
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Slide 9 – Alternate experiment (open inquiry)
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Slide 10 – Lab report assignment
If students are following a set of procedures, allow them to start on the experiment once they understand the directions and have materials. If students are designing their own experiment, have them write up their procedures first before they conduct the experiment. Check to make sure their experiment will test the difference between pure snow or ice and snow or ice with soot. Students should see that the snow or ice with soot warms faster and therefore melts quicker.
This is due to the dark color soot absorbing the light energy and transferring that heat to the snow or ice.
Materials Needed:
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Snow or crushed ice
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Soot
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Thermometers (2 per group)
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Light source (lamp or bright window)
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Tray to hold snow (2 per group)
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Scale
Example Procedure:
1.
Place snow or crushed ice in trays (equal amount in each tray)
2.
In one tray, mix in soot
3.
Place trays under light source (equal distance from light)
4.
Take beginning temperature and record in data table
5.
Turn on light source and begin taking temperature measurements every 2 minutes and record in data table
6.
Continue for 30 minutes
7.
Make observations between temperature readings and record on lab handout
L. Harkness 2013