Enviromental Chemistry
4.0 Particulates
4.0 Particulates
Particulates refer to finely divided solid or liquid particles suspended in air. The particulates, usually present in atmosphere are soot, water particles, metal oxides & metal salts, fly ash, asbestos powder, dust, solid hydrocarbons etc. Liquid aerosols include sulphuric acid & nitric acid mists.
Some common particulates & their sources
(i) Soot
The most common particulate injected into the atmosphere through human activity is soot which is produced by incomplete combustion of carbonaceous fossils fuels such as coal, fuel oil, natural gas, wood etc in insufficient supply of oxygen.
(ii) Metal particles
These are released by various metal finishing operation. The micro particles of toxic metal & $S{O_2}$ gas present in the polluted atmosphere get absorbed on the particles rendering them highly toxic.
(iii) Metal oxides
They are generated by combustion of fuels containing metallic compounds.
(iv) Lead salts
Their source is lead tetraethyl $\left( {Pb{{\left( {{C_2}{H_5}} \right)}_4}} \right)$ which is added to gasoline to improve its antiknock property. In order to avoid deposition of PbO suitable amounts of ${C_2}{H_4}C{l_2}\& {\text{ }}{C_2}{H_4}B{r_2}$ are added to gasoline along with $Pb{\left( {{C_2}{H_5}} \right)_4}.$
(v) Fly ash
It originates from the combustion of high ash fossil. It contains partially burnt particles of the fuels.
(vi) Asbestos dust
It originates from industrial units manufacturing asbestos sheets, gaskets ropes etc. Asbestos flowing & asbestos insulations also contribute towards asbestos dust in the atmosphere.
(vii) Solid Hydrocarbons
These are emitted from petroleum refineries & comprise of paraffins, olefins & aromatics.
(viii) Dust Particulates
Dust particulates originate from natural, domestic, industrial or agricultural sources. These are thrown into atmosphere by volcanic eruptions, blowing of dust by wind, mining operations etc.
(ix) Acid mist
Sulphuric acid mist is produced when $S{O_3}.$ present in the atmosphere comes in contact with moisture. Similarly nitric acid mist is produced when oxides of nitrogen, viz, $NO$ & $N{O_2}$ undergo the series of reactions in the atmosphere.
Harmful effects of particulates
(i) Effect on human beings
The particulates seriously affect the human respiratory system & cause several respiratory illnesses. The particles with small size are more harmful in this context. The particulates in fact, become the carriers of the toxic substances from the atmosphere to the human & cause big health hazards.
(ii) Effect on visibility
Particulates in the atmosphere cause scattering & absorption of sunlight & reduce the visibility.
(iii) Effect on Materials
The adverse effect of particulates on materials include corrosion of metals (when the atmosphere is humid), erosion & soiling of building, sculptures & painted surfaces & soiling of clothes & draperies.
