]> Aerosol having its origin over the continents with industrial, urban, agricultural, forest, and desert sources, with potential for high concentrations of hygroscopic aerosol. A maximum in large-particle concentrations observed in the lower stratosphere between 15 and 25 km. 1 2.5 10. 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.