Aerosol - (n.)

Any small particle, solid or fluid, that is suspended in air. Abundance values typically range from 100 to 10,000 particles per cubic centimeter for air over land with higher values found in cities. Sizes vary greatly, but typically are near 0.1 μm or less. The particles originate from wind-blown sea-salt or dust, volcanic eruptions, burning of vegetation, combustion of coal and petroleum products, and other natural and anthropogenic processes. Aerosol particles serve as nuclei for condensation of water droplets and for growth of ice crystals and also influence the radiation balance directly. In the lower stratosphere, concentrations are extremely low; much of the aerosol here consists of droplets of sulfuric acid.