Aerosol << AIR uh sahl >> is a mixture of extremely small particles in gas. The particles, also called particulates, 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.
Fine particles and vapor constantly enter Earth’s atmosphere, producing atmospheric aerosols. Natural particles, such as pollen, volcanic ash, and dust, stimulate the formation of clouds. Human activities release additional dust, soil, smoke, other particles, and vapors into the air. These particles and vapors form additional atmospheric aerosols that contribute to air pollution.
Light scattered by atmospheric aerosols produces the sky’s red glow at sunset. Particles also reflect some solar radiation back into space, slightly lowering Earth’s surface temperature. In heavily polluted areas, sunlight reacts with atmospheric aerosols to produce smog. Heavy concentrations of smog reduce visibility and affect human health by damaging lung tissue.
Manufacturers package aerosol products in containers called aerosol cans. Within such cans, the product remains dissolved in a propellant, usually a liquefied gas. The contents of the can are sealed under pressure. Opening a release valve ejects the pressurized solution. The released propellant vaporizes while the product suspended in it condenses to form an aerosol. Inhalers convert medicine into aerosols that can be breathed into the lungs. These pharmaceutical aerosols are used to treat asthma and other respiratory problems. Some products in pressurized cans, such as whipped cream, are not aerosols because they are gases suspended in a liquid rather than solids or liquids suspended in gas.
