David Brooks, September, 2006
Are your students discouraged about sun photometer measurements because it is hard to find days with unobstructed views of the sun? This is often a problem, and in some locations it is possible to go for days and even weeks without finding suitable conditions for using a sun photometer. You can supplement this measurement with your own air sampler. This can give some interesting results, and can be done even when it's raining if the collector is protected from the rain.
A basic particle collector can consist of something no more sophisticated than a piece of clear transparent tape or a small piece of transparent contact paper, mounted on a piece of cardboard, sticky side up. You can even just smear some petroleum jelly on an index card. If you have access to even a basic low-power microscope, use a microscope slide so you can examine what you have collected. You should be able to find pollen grains, carbon particles, dust or sand, and organic matter, including small insect parts. If you have polarizing filters, it may be interesting to use them when you view these particles.
With only a little work, you can make a slightly more sophisticated version of this experiment. Buy a small "muffin" fan from an electronics surplus supplier such as All Electronics. You can get such fans as small as 1" square. Depending on the fan, you may also need to get a wall transformer power supply, or use a rechargeable battery. Mount the fan on one end of a cardboard or PVC tube, so that the fan blows air through the tube (as opposed to sucking air through the tube. The tube should be several inches long. At the other end of the tube, mount a piece of stiff cardboard or corrugated cardboard at an angle of about 45° to the end, so air flow is not blocked, but air blows across the collector. Mount your sticky collector in the center of this piece of cardboard. Then hang your collector outside. If you make two collectors, you can hang one inside and one outside. If you are using a wall transformer for power, of course you will need to hang it where you have access to an outlet.
Your students should develop their own data collection protocol. How long? Where? At the end of the collection period, cover the collector surface with a piece of transparent sticky paper to preserve the sample. Be sure your students understand the importance of permanently marking the date and data collection times (start/stop) on the collector sample, along with other relevant information: Windy? Cloudy? Hazy? Humid? High/low Air Quality Index? Upon what pollutant is the Air Quality Index based for the collection date? etc.
This device should collect many more particles than a collector that is just exposed to ambient air. This simple piece of equipment can be used by young students, and can also be the basis for science fair projects even at the high school level.