An aerosol is a system of liquid or solid particles small enough to have low settling velocity and therefore capable of stability when suspended in air.
We are continuously inhaling particles that are suspended in the air, and when these aerosols are visible they are called dust, fog, mist, fume, smog, smoke, and soot. Such aerosols are the subject of the paper, "Aerosols in Nature," in the first part of this symposium. Obviously inhalation of particles is not new, but the increase in air pollution in an industrialized society, and the awareness of dangers caused by pollutants, has given new importance to the study of aerosols.
In the last decade, there has been an extraordinary increment in the use of artificial aerosols in many types of industry, in cosmetics, household products, insecticides, and in other areas. These constitute another category of aerosols that are possible offenders of the human lungs.
Lourenço RV. Inhaled Aerosols. Arch Intern Med. 1973;131(1):21-22. doi:10.1001/archinte.1973.00320070023002