Something in the Air
By John Cowens

Online Extra: Here are some additional quick and easy science activities. Twinkle, Twinkle Little Star?

I love being outdoors in the autumn. During the day the air quality seems to be clean, crisp and clear. In the evening, the stars and planets twinkle and remind me of the song "Twinkle, Twinkle Little Star," which I sang and played on a recorder during a school carnival as a child. I'll save the story about my singing debut for another time – for now, check out these lessons on the air we breathe.

Particulate pollution
Dust and dirt in the atmosphere darken the sky during the daytime. These particulates come from both human and natural activities. Exhaust from internal combustion engines makes carbon monoxide gas, nitrogen oxide gas and carbon (soot) particles. Industrial, home-heating and forest fires also contribute to the dust and dirt in the sky. Natural processes, like lightning-caused forest fires and volcanic eruptions, also add large amounts of dust and ash to the air. These extra particles in the air not only filter out sunlight, causing redder sunsets and sunrises, but also increase "light pollution."

Street, residential and industrial lighting reflect off particles and water vapor in the atmosphere to prevent the night sky from being really dark. However, many urban areas have begun to choose street lighting that interferes less with astronomical observations. Because of light pollution, observatories are usually located as far from urban areas as possible. Survey teams spend several months on candidate mountain summits observing weather patterns. They study particulates, wind, humidity and temperature extensively before committing to the construction of an observatory.

Materials:

• a box or book of matches


• two dusty chalk erasers


• a flashlight


• a projector


• a projection screen


• a dark room

Procedure:

1. Darken your classroom and turn on the projector.
2. While standing in the projector beam, strike a match. Observe the shadows on the screen that are created by the smoke released by the combustion process.
3. Hit two chalk erasers together and observe the shadow caused by the dust.
4. Turn off the projector and turn on the flashlight. Stand against a dark background and stir up more chalk dust by slapping erasers together. Shine the flashlight's beam on the dust before it settles. Observe the brightness of the dust particles that are in the beam.

Particulate sampler
Even on a clear night, many small particles are present in the atmosphere. Dust particles are lifted into the air by the wind. Other particles are produced as combustion products from cars, fireplaces, industry, volcanic eruptions and a variety of other sources, including meteorites and comets. Every day about 100 tons of meteorite and comet dust fall to Earth from space. Overall, dust particles scatter some of the light that comes through the atmosphere from space.
Due to wide variations in air quality, pre-test this experiment in your school's neighborhood to learn how long to expose the sampler. The time period may have to be extended to several days to show measurable results.

Materials

• clear contact paper (14 cm square)


• graph paper – each square is 2 cm on a side


• cardboard or 1/4-inch plywood (40 cm square)


• cellophane tape


• a magnifying glass


• a pair of dice

Procedure:

1. Tape the graph paper to the center of the cardboard. Then tape the contact paper on the top of the graph paper with the sticky side up. Keep the protective backing on the contact paper.
2. Place the pollution sampler outdoors on a flat surface, preferably a meter or two above the ground. You may have to anchor the sampler if the air is windy. Remove the protective backing. Make sure the contact paper is firmly taped down on the cardboard.
3. After exposing the sampler outdoors for 24 hours (a longer sampling period may be required), turn the graph paper over onto the collecting surface, grid side down and return the sampler to school.
4. Remove sampler from the cardboard and observe the particulates from the back side of the contact paper. Using the magnifier, count the number of particles found in 10 randomly selected squares on the graph paper grid. Select the squares by tossing the dice. If the numbers come up two and five, the square is found in the second column, fifth row. Divide the total number of particles by 10 to get an average number per square.
5. Compare the average particle counts to the locations where the collectors were placed (proximity to farms, factories, freeways, etc.). Add the average particle count for all samplers together and divide by the total number of collectors to obtain a regional average for the 2 cm square. Using this average, calculate the total number of particles for one square kilometer of area centering on the school. What would the count be for 10 square kilometers?

I hope your students enjoy these experiments as much as mine do!

Online Extra: Here are some additional quick and easy science activities. Twinkle, Twinkle Little Star?

John Cowens teaches sixth grade at Fleming Middle School in Grants Pass, OR.