Aerosol, AIR uh sahl, is a mixture of extremely small particles in gas. The particles may consist of liquid droplets or bits of solid material suspended (distributed) throughout the gas. Aerosol particles vary in size, from about 10 nanometers to 100 micrometers (.004 inch) in diameter. One nanometer equals one billionth of a meter, or 1/25,400,000 inch. Smaller particles, like those that make up smoke, can remain suspended for days or weeks. Larger particles, such as rain, may stay suspended for only minutes. Aerosols in the air can affect health, visibility, and climate. Clouds and fog are aerosols that occur naturally. Cans of deodorant and devices called inhalers for treating asthma produce aerosols when used.