2021-06-08 11:30:44
Notes on Environmental Chemistry:
Components of Environment:
Atmosphere: This comprises a blanket of gaseous layer around earth.
Hydrosphere: This comprises about 96% of earth’s surface & includes all sources of water like oceans rivers lakes, glaciers, ground water etc.
Lithosphere: It refers to earth’s solid crust containing the outer mineral cover. It comprises soil, minerals, organic matter etc.
Biosphere: It refers to the domain of living organism in covalent with atmosphere hydrosphere as well as lithosphere.
Environmental Pollution :
Process of contamination of the environment with harmful wastes arising mainly from human activities.
Pollutant: Any substance or species produced either by a natural source or by human activity, which produces adverse effect on the environment.
Contaminant: A substance which does not occurs in nature but is introduced by human activity into the atmosphere affecting its composition.
Source: The site from which the pollution or contaminants originate.
Sink: The material or medium which consumes or interacts with a long lived pollutant is called sink.
Receptor : Anything that is affected by the pollutants.
Threshold limit value (TLV) : This indicates the permissible limit of a pollutant in atmosphere to which a healthy worker is exposed during hours a day or 40 hours a week for life time without any adverse effects. TLV are determined by experimentation on animals, by use of medical knowledge, epidemiology surveys & environmental studies.
Tropospheric pollution or Air pollution:
It is the atmosphere condition in which the presence of certain concentration produce harmful effects on man and his environment. These substances include:
(i) Gases such as oxides of sulphur, CO, oxide of N2 and hydrocarbons
(ii) Particulate matter such as dust, smoke, fumes etc.
(iii) Radioactive material & many others.
Primary pollutants : These are the pollutants which are emitted directly from the sources. Some examples are:
Particulate Matter : Such as ash, smoke, dust, fumes etc.
Inorganic gases : Such as sulphur dioxide, carbon monoxide etc.
Particulate matter:
Soot: produced by incomplete combustion of carbonaceous fossils fuels such as coal, fuel oil, natural gas, wood etc in insufficient supply of oxygen.
Metal particles: These are released by various metal finishing operation. The micro particles of toxic metal & SO2 gas present in the polluted atmosphere get absorbed on the particles rendering them highly toxic.
Metal oxides : They are generated by combustion of fuels containing metallic compounds.
Lead salts: Their source is lead tetraethyl (Pb(C2H5)4) which is added to gasoline to improve its antiknock property. In order to avoid deposition of PbO suitable amounts of C2H4Cl2 & C2H4Br2 are added to gasoline along with Pb(C2H5)4.
Fly ash: It originates from the combustion of high ash fossil. It contains partially burnt particles of the fuels.
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.
Solid Hydrocarbons: These are emitted from petroleum refineries & comprise of paraffins, olefins & aromatics.
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.
Acid mist : Sulphuric acid mist is produced when SO3 present in the atmosphere comes in contact with moisture. Nitric acid mist is produced when oxides of nitrogen, viz, NO & NO2, undergo the series of reactions in the atmosphere.
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