These are suspended droplets, solid particles or mixture of two. So all the atmospheric substances that are not gases are called particulates.
A number of terms are used to categorize particulate depending on their size, mode of formation and physical state, some of these are:
Aerosol: aerosol is any tiny particle of liquid or solid dispersed in atmosphere.
Dust: small solid particle formed by breaking of soil or rock.
Fumes: these are fine solid particles formed by condensation of vapours of solid materials released by chemical or metallurgical operations.
Mist: liquid droplets formed by condensation of vapours in the atmosphere eg. H2SO4 mist.
Fog: if mist is made up of water droplets of size (1 to 40 u) and reduces visibility it is called fog.
Smoke or soot: these are the terms used to describe particles primarily composed of carbon that results from incomplete combustion.
Fly ash: these are smaller ash particles coming along with the furnace flue gases and are basically composed of inorganic mineral.
1. Volcanic eruption, wind and dust storm etc.
2. Burning of wood, coal, oil and gaseous fuels.
3. Industrial processes such as smelting and mining operations.
Aerosols (CFC's, (NO)x, (SO)x) are released as emissions from jet aero planes and supersonic aero planes deplete the ozone layer.
Harmful effects on human life: the smaller particles (less than 10 um) capable of reaching lungs and becomes site for adsorption of carcinogenic compounds and may cause cancer. The health effects caused by different of particulate is summarized in table.
Fumes, dust, soot, mists and aerosols can bring severe damage to soil, building, sculpture and monuments.
Particulate play important role in radiation and heat balance of earth.
Particulate can absorb free radicals thus acts inhibitors of free radical chain reactions.
Control: it can be controlled by using equipments like filters, gravity settling chamber, cyclone collectors, wet scrubbers and electrostatic precipitators etc.