Classification of Pollutants
Classification of Pollutants:
The classification of pollutants is done from different points of view:
(i) Depending upon their existence in nature pollutants are of two types, namely quantitative and qualitative pollutants.
(a) Quantitative Pollutants:
These are those substances normally occurring in the environment, who acquire the status of a pollutant when their concentration gets increased due to the unmindful activities of man. For example, carbon dioxide, if present in the atmosphere in concentration greater than normal due to automobiles and industries, causes measurable effects on humans, animals, plants or property, then it is classified as a quantitative pollutant.
(b) Qualitative Pollutant:
| Effects of Pollution | |
| Atmosphere and Air pollution |
These are those substances which do not normally occur in nature but are added by man, for example, insecticides, Pesticides.
(ii) Depending upon the form in which they persist after being released into the environment, the pollutants are categorized into two types, namely primary and secondary pollutants.
(a) Primary Pollutants:
These are those which are emitted directly from the source and persist in the form in which they were added to the environment. Typical examples of pollutants included under this category are ash, smoke, fumes, dust, nitric oxide, sulphur dioxide, hydrocarbons etc.
(b) Secondary Pollutants:
These are those which are formed from the primary pollutants by chemical interaction with some constituent present in the atmosphere. Examples are: Sulphur trioxide, nitrogen dioxide, aldehydes, ketones, ozone etc.
Nitrogen oxides and hydrocarbons are two primary pollutants released from automobiles but in the presence of sunlight, they react to form peroxyacyl nitrate (PAN) and ozone, two secondary pollutants which are far more toxic than the primary pollutants from which they are derived. This phenomenon of increased toxicity by chemical interaction among the pollutants is known as Synergism.
Primary Pollutant:
- They are pollutants which are passed into environment in the form they are produced.
- They belong to various categories like particulate, aerosol, reduced, oxidized.
- They are less toxic.
- They do not show synergism
- Primary pollutants persist in the form they are released in the environment.
Secondary Pollutants:
- The pollutants develop as a result of interaction of primary pollutants and environmental constituents.
- They are more toxic.
- Secondary pollutants show synergism.
- They are modified products
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