Exercise 22
To determine the amount of Suspended Particulate Matter (SPM) in air at different sites in a city
To determine the amount of Suspended Particulate Matter (SPM) in air at different sites in a city
Principle: Environmental pollution is the unfavourable alteration of our surroundings wholly or
largely as a by-product of man's action through direct or indirect effects of changes in energy
patterns, radiation levels, chemical and physical constitutions of environment and abundance of
organisms. Substances that cause pollution to the environment are called pollutants. They are the residues of things that man makes, uses and throws away. These residues pollute soil, water and air.
The atmosphere in highly populated area is very rich in dust, smoke and SPM all due to vehicular
exhausts and industrial emission.
Requirement: A few freshly cut broad leaves, Vaseline, laboratory balance, weights, brush,
paper clips and twine thread
Procedure:
This experiment is an outdoor activity and may be conducted by assigning 2–3 students into a group.
Collect a few locally available broad leaves from a nearby tree plant (Canna, Peepal, etc.).
Wash the leaves gently in running water to remove any dust settled on their surfaces.
Blot dry the surface area of the leaves. To calculate the area of the leaf, trace the outline of the leaf on graph paper (Fig 22.1). Within the traced area calculate the total number of full squares, 1/2, 1/3 and 2/3 squares and individual small squares. Add all the squares to get the total leaf area. Multiply their value with two to obtain total area of both the surfaces.
Take 8–10 feet long twine thread and tie five leaves leaving a foot distance in between. Apply an extremely thin layer of Vaseline on both surfaces of each leaf. Make a bundle of these leaves and pack them in polythene bags. Ensure that the outer surface of polythene bag does not have any Vaseline sticking on it.
Make three such bundles of smeared leaves, each bundle containing 5 leaves.
Mark bundles as A, B and C and carefully weigh each bundle of leaves along with the polythene bags.
Select three spots (X, Y and Z) near by your school. Spots selected should be in a manner that spot 'X' has very heavy vehicular traffic, the spot Y has moderate traffic and spot 'Z' has little or no vehicular traffic. At spot 'X' expose each leaf of bundle 'A' by stretching the attached thread and tie the two ends to two poles or branches of trees preferably at 10 feet height above ground. Keep leaves exposed for about two hours.
After exposure at spot 'X', collect the leaves and carefully re-bundle exposed leaves and place them along with the string in the polythene cover 'A'.
Repeat the same process at spot 'Y' and 'Z' exposing leaves of 'B' and 'C' bundles respectively.
At the end of the experiment, return back to the laboratory. Reweigh each bundle of exposed leaves along with their respective polythene cover.
- Calculate the amount of suspended particles deposited in mg cm2 of leaf at each spot.
- Compare the results of three different spots and interpret.
Since the weight of suspended particles will be in milligrams or even less it is advised to use a very sensitive laboratory balance.