What is Air Pollution?

Class 11 Chemistry Chapter 14 Enviromental Chemistry


Air pollution is the addition of unwanted component in air that causes harm to living organisms. Air pollution is nothing but atmospheric pollution. Atmospheric pollution is generally studied as tropospheric pollution and stratospheric pollution. Tropospheric pollution occurs due to undesirable solid or gaseous particle in the air. It is classified into gaseous air pollutant and particulate pollutant. In this article, let’s talk about various pollutants causing air pollution.

Gaseous air pollutant

Gaseous air pollutant consist of oxides of sulphur, oxides of nitrogen, hydrocarbons, carbon dioxide and carbon monoxide.

Oxides of sulphur

Oxides of sulphur are formed when fossil fuel having sulphur is burnt. However, sulphur dioxide is a poisonous gas, which is harmful for both plants and animals. Even low concentration of sulphur dioxide causes respiratory disease like asthma, bronchitis, emphysema in human beings. Moreover it causes irritation to eye. High concentration of SO2 leads to stiffness of flower buds. Uncatalysed oxidation of sulphur dioxide is slow. However, in presence of other air pollutants, it facilitates speedy oxidation of sulphur dioxide to trioxide
2SO2(g) + O2(g) → 2SO3(g)
The reaction can also takes place in presence of ozone and hydrogen peroxide.
SO2(g) + O3(g) → SO3(g) + O2(g)
SO2(g) + H2O2(l) → H2SO4(aq)

Oxides of Nitrogen

Dinitrogen and dioxygen are main constituents of air. These gases don’t react with each other under normal temperature. However, at high altitudes, when lightning strikes, they combine to form oxides of nitrogen. One of the oxide, NO2 is oxidised to nitrate ion, NO3 which is washed into soil where it act as fertilizer. Also, in an automobile engine, when fossil fuel is burnt, dinitrogen and dioxygen combine to yield quantities of nitric oxide(NO) and nitrogen dioxide(NO2):

                         1483K
N2(g) + O2(g)    →    2NO(g)
NO reacts instantly with oxygen to give NO2
2NO(g) + O2(g) → 2NO2(g)
Rate of production of NO2 is faster when nitric oxides reacts with ozone in the stratosphere.
2NO(g) + O3(g) → 2NO2(g) + O2(g)
red haze in traffic is due to oxides of nitrogen.
Higher concentration of NO2 damage the leaves and plants and retard rate of photosynthesis
Nitrogen dioxide is a lung irritant that can lead to acute respiratory disease in children. It is toxic to living tissues also. It is also, harmful to various textiles fibres and metals.


Hydrocarbons

Hydrocarbons are composed of hydrogen and carbon and are formed by incomplete combustion of fuel in automobile. Also, hydrocarbons are carcinogenic. Moreover, they harm plants by causing ageing, breakdown of tissues and shedding of leaves, flowers and twigs.

Carbon Monoxide

It is colorless and odourless gas, however it is highly poisonous in nature. It blocks delivery of oxygen to organs and tissues. Carbon monoxide is generated from incomplete combustion of coal, firewood, petrol , etc. Carbon monoxide when enter in human body, it combines with haemoglobin to form carboxyhemoglobin. Moreover, carboxyhemoglobin is 300 time stable than oxygen hemoglobin complex. Thus it prevents transfer of oxygen to body organs. This also, decreases oxygen carrying capacity of blood. It results in headache, weak eyesight, nervousness and cardiovascular disorder.

Carbon dioxide

It is released in atmosphere by burning of fossil fuels and decomposition of limestone during the manufacture of cement. Carbon dioxide gas forms 0.03% of atmosphere. With increase in use of fossil fuel large amount of carbon dioxide is released in the atmosphere. Carbon dioxide is used by green plants to prepare their food.


Particulate air pollutant

Other than gaseous air pollutant, particulate air pollutant also cause air pollution. This includes smoke particulate, dust particulate, mist particulate and fumes.

Smoke particulate

It contains solid, or, mixture of solid and liquid particles formed during combustion of organic matter. Some examples are: cigarette smoke, smoke from burning of fossil fuels, garbage, dry leaves, oil smoke etc.

Dust particulate

Dust is made of fine solid particle, over 1µm. It is mainly produced during crushing, grinding and attribution of solid materials. Some examples of particulate emissions are sand, sawdust, pulverised coal, cement, fly ash from factories, etc.

Mist particulate

It is produced by particles of spray liquids and by condensation of vapors in air. Some examples of this type are: sulphuric acid mist and herbicides and insecticides that miss target and travel through air and forms mists.

Fumes particulate

Fumes are formed by condensation of vapors during sublimation, distillation, boiling and several other chemical reaction. Organic solvents, metals and metallic oxides mostly forms fume particles.
Keywords: Air pollutants, Pulverised coal, Carboxyhemoglobin

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