Dust is a collection of microscopic particles of material. Dust is heavy enough to see and light enough to be carried by the wind.

Dust can be made up of pollen, bacteria, smoke, ash, salt crystals from the ocean, and small bits of dirt or rock, including sand. Dust can also contain tiny fragments of human and animal skin cells, pollution, and hair.

When its windy outside, you can see dust particles blowing through the atmosphere. Large amounts of dust that are carried through the atmosphere by strong winds are called dust storms. Dust storms mostly occur in dry, open areas.

The Sahara Desert in Africa has many dust storms. Most Sahara dust is made of sand. Dust storms in the Sahara Desert can blow a wall of dust as high as one mile off the ground. Dust storms can make it very difficult to see and breathe.

In 1983, a dust storm covered the city of Melbourne, Australia. The deserts of Australia were experiencing drought, so sand and soil were loose. The dry conditions allowed about 50,000 tons of material to erode as dust. Melbourne had more than 1,000 tons of dust dumped on it. The dust caused so much damage that it took years of work and millions of dollars to repair.

Individual particles of dust are a major part of cloud condensation nuclei (CCN). Cloud condensation nuclei are made up of tiny pieces of solid material in clouds. CCN could be a dust storm drifting through a cloud, or an updraft with dust particles in it. Water vapor in the clouds condenses, or turns to liquid, around CCN. Invisible dust is often at the center of every raindrop.

In some areas, windblown dust settles into deposits called loess. Loess is a type of sediment that is loose and fragmented. It can be many meters deep. Loess often develops into fertile soil for agriculture because it retains water, allows many different plants to take root, and has abundant nutrients.