Classification of air pollutants
Urbanization and industrialization are the main sources of air pollution and population explosion is responsible for urban growth, growth of industries & automobile revolution. Lots of toxic gases and particles got dissolved in the environment especially in the air. These gases and particles have disturbed the natural state of air which are very harmful to humans, animals, plants & other microorganisms. Based on the origin, classification of air pollutants has been done in two categories i.e. Primary and secondary air pollutants.
The disturbance in the quality of air by the foreign substance (gases & particle) which has a harmful effect on human & other living organisms is known as air pollution.
We can understand air pollution easily if we know the composition and components of the atmosphere. The clean air has the following gases:-
- Nitrogen 78%
- Oxygen 23%
- Argon 0.93%
- Carbon dioxide 0.032%
- Neon 0.0018%
- Helium 0.00052%
- Methane 0.00015%
- Krypton 0.0001%
- Hydrogen 0.00005%
- Dinitrogen Oxide 0.00002%
- Carbon monoxide 0.00001%
- Zenon 0.000008%
- Ozone 0.000002%
Sources of air pollution
There are two main sources of air pollution:-
Natural sources of air pollution:
Natural sources of air pollution are beyond human, these sources are naturally occurring by the physical and biological means. The natural pollutants are mainly pollen grains, fungal spores, cysts, microbes, and other marsh gases. Marsh gas, it is also known as methane (CH4), is produced by the anaerobic bacteria during digestion of organic matters in marshy places. Carbon monoxide is another gas which is formed intermediately during anaerobic digestion. The volcanoes are also a natural source of air pollution, during the eruption of volcanoes huge quantities of numerous gases with ash (particulate matters) get released into the atmosphere. A Forest fire releases smoke & harmful trace gas which leads to pollution, salt spray from oceans & dust storm is also a big source of air pollution.
Anthropogenic or Man-Made Sources of air pollution:
These sources cause maximum air pollution, industries, automobiles, advance agriculture activities, construction activities are the anthropogenic sources. Industries are the main consumer of fossil fuels like coal, & petroleum. Industrial emission contains a variety of harmful gases and particulate matters due to the combustion of fuel. Automobiles exhaust also contains gases, hydrocarbons & particulate materials.
Farmers are using lots of pesticides & herbicide to control harmful pests & herbs. They apply these chemicals to plants by using the spray technique. Excessive use of these chemicals releases so many harmful substances like hydrocarbons, chlorinated hydrocarbons, organic phosphate, arsenic & lead.
Classification of Anthropogenic sources of air pollution:
We can categories the anthropogenic air pollution sources into three-
Industries are the best examples of point sources, emission from the industrial stack.
Mobile sources of air pollution are automobile/vehicles.
Communities living in cities & towns add a verity of gases over a wide area.
Classification of air pollutants based on origin & state of matter:-
Primary and secondary air pollutants
According to their origin air pollutants are categorized into two forms i.e. Primary and secondary air pollutants.
Primary air pollutants:
The pollutants that are emitted directly from the source and are found in the atmosphere in the form in which they were emitted are known as primary pollutants. The sulfur dioxide, nitrogen oxides, hydrocarbons, ash, smoke, dust, mist & fumes are examples of primary pollutants.
Secondary air pollutants:
The pollutants that are formed in the atmosphere by chemical interactions between primary pollutants and atmospheric constituents are called secondary pollutants. These are usually formed by photochemical reaction or by a photochemical reaction or by hydrolysis or oxidation reactions in the atmosphere. Ozone, sulfur trioxide, peroxyacetyl nitrate, aldehyde & ketones, etc. are examples of secondary pollutants.