Air Pollution

Module 3 - POLLUTION

46. Define pollution

Contamination of our surrounding air, water, land etc. with undesirable or harmful substances are called pollution. The pollutants may be in the form of solid, liquid or gas.

47.Over exploitation of natural resource

Over use of natural resources for economical gain without taking care of environmental degradation is called as over exploitation. As the mankind changed their life from forest wilderness to agriculturist, began to change the environment. Forests were being converted into agricultural lands and then to concrete buildings. Natural water resources like rivers are built with huge dams for irrigation. Industrialization, Urbanization, population growth etc. increased the use of consumer goods which lead to over exploitation of natural resources. 

48. Air pollution

Contamination of atmosphere or air with undesirable substances are called air pollution.
Various air pollutants are:

1.    Carbon monoxide
2.    Oxides of sulphur
3.    Oxides of nitrogen
4.    Particulate matters
5.    Dust
6.    Smoke
7.    Fly ash
8.    Smog

Causes of air pollution

The causes of air pollution may be classified as natural and man made.

    -Forest fire

    -Domestic burning of wood

Natural causes

    -Volcanic eruption
    -Blowing wind carrying sand and dust
    -Vegetable decays
    -Natural organic and inorganic decays

Man made causes

    -Burning of fossil fuels
    -Industrial emissions
    -Vehicular emission
    -Agricultural activities
    -Incineration sites
    -Power generation
    -Waste treatment plants
    -Solid waste dumping sites

49. Causes of air pollution

50. Sources of air pollution

51. Effects of air pollution

Atmospheric pollution can affect the human health, plants, birds, animals and materials on earth. Air pollution is the reason for acid rain and smog. It is also one of the reason for green house effect and ozone layer depletion.

Effects on human health

    - Air pollution is one of the reason for a number of diseases like Bronchitis, Asthma, Silicosis,  Asbestosis etc.

    - Lead emission from vehicles cause diseases for liver, kidney and abnormality in fertility and pregnancy.
    - Smog causes eye irritation, nasal and throat irritation etc.

Effects on plants

    - The pollutants in the air interfere with plant growth and photosynthesis.
    - The various diseases found in plants are: Bleaching of leaves, Necrosis, Premature aging and Leaf abscission.

Effects on animals

    - Air pollutants accumulate in the vegetations and subsequently reach into the animals as they eat it and causes various diseases.

Effects on materials

    - Presence of sulphur dioxide (SO2) in the air cause corrosion of metal parts, degrade or disfigure the marble and other building materials.

52. Control measures of air pollution

The following are the approaches generally followed to control the emissions discharged into the atmosphere.

1. Proper planning and zoning of industrial and housing areas.

2. By using tall stacks (chimneys), the pollutants can be discharged at a sufficient height from the ground where air flow is more and thus help in the dispersion of the pollutants over a large area and dilute the concentration.
3. Reduction at source by process changing. This can be achieved            by 
i) Substitution of raw material. E.g. use of low volatile coal in place of high volatile coal to eliminate smoke and dust.
ii) Substitution of fuel. E.g. Compressed Natural Gas can be use in place of coal and oil to eliminate emission.
iii)    Modification of the process equipment or repair and maintenance of the existing equipment, help to reduce the emission.
iv)Reduction at source by using control devices like-
                     Gravitational settling
                     Cyclone separator
                     Fabric or bag filters
                     Electro static precipitator
                     Wet collector ( scrubber )

53. Control devices for air pollution

 Air pollution control devices are categorized as:

    a) Control devices for particulate matter

    b) Control devices for gaseous contaminants

Control devices for particulate contaminants

Based on physical principles, they are divided into five major group. They are:

    1.    Gravitational settling

    2.    Cyclone separator

    3.    Fabric or bag filters

    4.    Electrostatic precipitator

      5.    Wet collector (scrubber)

Control devices for gaseous contaminants

The treatment process for the control of gaseous emissions include:

       1. Absorption
       2. Adsorption
       3. Condensation
       4. Combustion

Absorption
In this method, contaminant gas is brought in contact with a liquid absorbent.
Adsorption
In this method, steam of effluent gas is passed through a porous solid material.
Condensation
In this method, gas is converted into liquid by process of condensation.
Combustion
In this method, more toxic gas forms are converted into less toxic gas like CO2 and water by burning.

54. Acid rain

Acid rain is an after effect of air pollution. When sulphur dioxide and nitrogen oxides formed with pollutant smoke from burning coal, industries, power plants etc. are being transported by prevailing wind, they form secondary pollutants such as nitric acid vapour, droplets of sulphuric acid and particles of sulphates. These chemicals descent on earth in two forms- 1. Wet as acid rain and 2. Dry as acid particles.

Acid rain has many harmful effect on environment and human health. It causes respiratory diseases like bronchitis, asthma etc. It also damages statues and buildings, metal surfaces, automobile finishes etc. It also damage tree foliage and deplete the calcium and magnesium in the soil which in turn reduce the tree growth. 

55. Smog

Smog is an after effect of air pollution. The mixture of smoke and fog of dense structure build up over the polluted cities and it last for several hours or days which causes serious health problems like bronchitis, asthma, nasal discharge, soar throat, vomiting, burning sensation, eye irritation etc. This pollutant smoke may be from vehicle emission, burning of coal, burning of agricultural waste and fire crackers.

56. Ozone layer depletion

The upper stratosphere consist of considerable amount of ozone which work as an effective screen for the harmful uv radiation reaching to the earth surface. The CFC and Halons migrate into the upper atmosphere and slowly diffuse into the stratosphere. This is a slow process and may take 5-15 years.
This change in ozone layer causes the harmful uv radiation reach into the earth surface which has serious implications for mankind.
    -This uv radiation affect the human health like sunburn, aging of         the skin, chicken pox etc. 
    -It also affect the ability of the plants to capture light energy                 during the process of photosynthesis. 
    -This reduce the nutrient content and growth of the plant. 
    -It also affect the phytoplankton and zooplankton thereby                     adversely affect marine ecosystem.

In the stratosphere, unfiltered uv radiation severs the chemical bonds releasing chlorine rom the rest of the CFC. This attack the ozone molecule resulting into splitting it into an oxygen molecule and an oxygen atom. This way the ozone layer is being damaged.