THE IMPORTANCE OF DUST • Moisture in the atmosphere condenses as it cools. However, the water must condense upon something that it can cling to. Dust serves that purpose. In air that contains absolutely no dust, droplets would simply bounce off each other and would not condense until the atmosphere reached an incredible 300% humidity. Every single drop of rain and snow that falls contains a piece of dust, so precipitation really does “clean” the air. • If there’s too much dust in the atmosphere, water droplets are divided between so many particles that none of the drops ever gets big enough to fall to the earth. A super dusty cloud can hold up to twice as much actual water as a normal cloud, but each droplet is half the normal size and no rain falls. • Huge fires such as those that sometimes burn in the tropics produce gigantic smoke plumes. Studies done by NASA showed that clouds that pass through this smoke will become super-saturated in dust and will subsequently drop far less rain than clouds that skirt the edges of the smoke. A similar study showed that when volcanoes exploded upwind of the island of Taiwan, the rainfall amounts on Taiwan dropped. This is why cloud seeding is such a tricky business. In cloud seeding, either solid particles of carbon dioxide dry ice or a fine mist of silver iodide are spread through clouds. Too much and the cloud dissipates. Just the right amount, and rain falls.
NASA'S DUST COLLECTION • NASA actually keeps a Dust Library. There’s a collection of about 100,000 specks of space dust on file at the Johnson Space Center in Houston. Scientists collect space dust from places such as trapped in the Antarctic ice, in the mud at the bottom of the ocean, collected by weather balloons, or gathered by spacecraft in orbit. Space dust generally clings to a magnet whereas earth dust does not, making it easy to separate and identify.