]> Air Mass A widespread body of air, the properties of which can be identified as 1) having been established while that air was situated over a particular region of the earth's surface (airmass source region), and 2) undergoing specific modifications while in transit away from the source region. The presence of substances in the atmosphere, particularly those that do not occur naturally Air Pollution Phenomenon particularly associated with smog episodes in cities such as Denver, Colorado. Aerosol having its origin over the continents with industrial, urban, agricultural, forest, and desert sources, with potential for high concentrations of hygroscopic aerosol. Particles suspended, reducing visibility by scattering light; often a mixture of aerosols and photochemical smog. A maximum in large-particle concentrations observed in the lower stratosphere between 15 and 25 km. The term for solid or liquid particles found in a gas. Some particles are large or dark enough to be seen as soot or smoke. Type of air pollution, such as Los Angeles smog, associated with the buildup of oxidation products formed from the degradation of hydrocarbons, etc. A haze created by the presence of finely divided particles of sea salt in the air, usually derived from the evaporation of sea spray. Reduced visibility in the atmospheric boundary layer caused by suspended particles of soil, mixed into the air during strong winds. A natural fog contaminated by industrial pollutants, a mixture of smoke and fog.