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Investigatory Project on Air Pollution


Investigatory Project on Study of Pollutants in Air (Class 12)


Atmosphere acts as an insulating blanket around the earth. It is the source of essential gases, and it keeps day and night temperatures. It becomes a shield and protects the earth from UV radiations and meteors. Normal composition of clean air in the atmosphere is as follows.






Carbon Dioxide



Other gases









But, due to pollution, the concentrations of the different gases show variations. Besides, a number of harmful gases are also added into the atmosphere. These affect air quality adversely and make it unfit for the survival of organisms. Air pollution results from gaseous emissions from industries, thermal power stations, automobiles, domestic combustion, etc. Undesirable substances are added into the atmosphere through human activities also. Besides, volcanic eruptions, forest fires and natural decays give out large quantities of harmful dust and sulphur compounds into the air.

Pollutants are the substances which cause adverse effect on the natural quality of any component of the environment. Air pollutants can be conveniently classified into two main groups. They are Gaseous pollutants and Particulate matter.

Gaseous pollutants: They are pollutants which are usually gaseous in nature under normal temperature and pressure. They may be primary or secondary in nature. Primary pollutants enter the atmosphere directly from various sources (carbon monoxide, hydrocarbon, sulphur dioxide etc.). Secondary pollutants are formed during chemical reactions between primary air pollutant and other atmospheric constituents like water vapour, light (eg: photochemical smog and PAN – Peroxy Acetyl Nitrate). Gaseous pollutants includes oxides of carbon, oxides of sulphur, hydrogen sulphide, hydrocarbons, oxides of nitrogen, ozone and other oxidants.

Particulate pollutants: Particulate matter includes solid particles or liquid droplets which remain suspended in the air. Smoke, photochemical smog, dust, soot, asbestos fibres, radioactive elements, aerosols, etc. are the particulate air pollutants. The sources of particulate pollutants are fuel combustion and industrial operations, handling, loading and transfer of industrial materials agricultural operations and construction works and automobile exhaust. Besides, many kinds of biological particulate matter also remain suspended in air. They include pollen grains, spores, bacterial cells, fungal spores etc.


To examine the process of particulate matter in the air

Materials and methods

A leaf of a plant growing in the open area, a leaf from a plant growing in a glass house, slides, cover slips, white handkerchief/cotton wool, brush, microscope etc.

Procedure 1

Pluck a leaf from a plant growing in the open area. Pour a few drops of glycerine over it and rub it with a clean brush. Take a drop of glycerine from the leaf over a clean slide and cover it with the cover slip. Observe it under the microscope. Repeat the experiment by taking a leaf from the plant growing in a glass house.

Observation: The slide prepared from the leaf of a plant growing in the open area shows the presence of number of pollutants such as dust, pollen grains and spores etc.

Procedure 2

See a beam of light entering inside a dark room through a window.

Observation: A number of dust particles and other particulate pollutants are seen moving here and there in the beam of light.

Procedure 3

When you come back from the school or from any other busy places, wipe your face with a clean handkerchief or cotton wool.

Observation: A large amount of pollutants get collected on the hand kerchief or cotton wool.

Procedure 4

Apply some glycerine on a clean slide. Keep the slide outside for the whole day. Now examine the slide under the microscope.

Observation: A number of types of pollen grains, spores of number of fungi, dust particles, soot etc. are seen sticking on the slide.


The air contains a number of particulate pollutants. The concentration of pollutants is variable in different localities.

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