Young children know about dust. They know it accumulates on desk tops, shelves and TV and computer screens. They have probably seen dust kicked into the air during outdoor sports and swept into the air by brooms and street sweepers. They may not know that dust can travel across continents and oceans.

Dust is pieces of matter so small that they tend to float in the air for a while before falling to the floor or the ground. The smaller the dust particle, the longer it stays in the air.

Dust particles can be so small that they are nearly invisible. How small is small? Let's compare dust with a human hair.

A hair on your head is between 50 and 80 millionths of a meter across (a meter is about 39 inches). Light colored hair tends to be thinner than dark hair. Some dust particles are so small that you could place a hundred or more across a human hair! These dust particles can stay in the air for hours or even days. Others are much larger, and giant dust particles may be half a millimeter across. A strong wind can blow particles this size and larger into the air, but they soon fall to the ground.

We usually think of dust as tiny particles of soil. But dust can be many other things. Have you ever heard of dust mites? These tiny creatures feed on tiny particles of dried skin that our bodies shed. Yes, our bodies are dust factories! So are dogs and cats, which are constantly shedding tiny bits of dead skin known as dander. The feathers of birds may shed tiny particles known as feather dust. Pollen, tiny bits of plants, lint and pieces of dead insects can be considered dust, especially when they accumulate inside your house. Lint and tiny bits of thread from clothing and fabrics is much more common than you might expect.

But this is only the beginning. If you collect some dust from a busy street and look at it through a microscope, you will find tiny bits of rubber from tires and tiny particles from brakes. If you saw a piece of wood, you will make saw dust. If you smooth wood or plastic with sand paper or file your finger nails, you will also produce dust.

People react to dust in different ways. If dust enters your eyes, it may causes redness and even tears. People with allergies may react to dust by sneezing and by becoming congested. People with asthma can be especially sensitive to dust, which can trigger asthma attacks. Sneezing is the body's way of expelling dust, so, If you inhale some dust, you will need to reach for a tissue. But watch out! The tissue you use to expel the dust from your nose is itself a dust factory! You can prove this for yourself in a simple experiment we'll do later.

It's best to avoid inhaling dust. Large particles of dust become trapped by your nose and are eventually expelled. But very small dust particles can travel deep into your lungs and remain there.

House dust can cause sneezing or an allergic reaction. Outdoors, strong winds can cause major dust storms. These can also be a health hazard, especially when the blowing dust includes mold spores and pesticides. Blowing dust can sting your skin, irritate your eyes and lungs and cause respiratory infections and asthma attacks. Sometimes dust storms can reduce how far you can see on a road. When this happens, cars and trucks must drive slowly or not at all. Wind storms blow soil away from farms and ranches. Wind storms in East Asia and North Africa can send giant clouds of dust across the Pacific and Atlantic Oceans!

• See how dust can reach deep inside your lungs

• Dust Imagery from the MODIS Rapid Response System

• Aerosol data from the Live Access Server

• The GLOBE Program


• Elementary GLOBE

Project ideas contributed by Forrest M. Mims III, Geronimo Creek Observatory, Texas