Dust suspensions generally

The proper management of dust collection follows a basic rule of any pollution control technology, namely that it is best to deal with a dust suspension as near to its source as possible, rather than after it has been diluted with gas from other sources. Thus, fume from a smelter should be treated in hoods immediately over the smelter, rather than in the general exhaust from the smelter building. 

Gases are generally the easiest type of media to use because the contaminants in the test atmosphere are in the gaseous phase. Technically, aerosols include any liquid- or solid-phase material that forms a stable suspension in air. Dusts are solid-phase (contaminant) particles suspended into a gaseous (atmosphere) phase. They are generally the most difficult to use when conducting a study. 

Particles in the atmosphere arise from natural sources, such as windborne dust, sea spray, and volcanoes, and from anthropogenic activities, such as combustion of fuels. Whereas an aerosol is technically defined as a suspension of fine solid or liquid particles in a gas, common usage refers to the aerosol as the particulate component only (Table 2.17). Emitted directly as particles (primary aerosol) or formed in the atmosphere by gas-to-particle conversion processes (secondary aerosol), atmospheric aerosols are generally considered to be the particles that range in size from a few nanometers (nm) to tens of micrometers... 

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