(a) Source Correction Methods:

Industries make a major contribution towards causing air pollution. Formation of pollutants can be prevented and their emission can be minimised at the source itself.

By carefully investigating the early stages of design and development in industrial processes e.g., those methods which have minimum air pollution po?ential can be selected to accomplish air-pollution control at source itself.

(b) Pollution Control Equipment:

Sometimes pollution control at source is not possible by preventing the emis?ion of pollutants. Then it becomes necessary to install pollution control equip?ent to remove the gaseous pollutants from the main gas stream.

The pollutants are present in high concentration at the source and as their distance from the source increases they become diluted by diffusing with envi?onmental air.

(c) Diffusion of Pollutants in Air:

Dilution of the contaminants in the atmosphere is another approach to the con?rol of air pollution. If the pollution source releases only a small quantity of the contaminants then pollution is not noticeable as these pollutants easily diffuse into the atmos?here but if the quantity of air contaminants is beyond the limited capacity of the environment to absorb the contaminants then pollution is caused.

However, dilution of the contaminants in the atmosphere can be accomplished through the use of tall stacks which penetrate the upper atmospheric layers and disperse the contaminants so that the ground level pollution is greatly re?uced. The height of the stacks is usually kept 2 to 21/2 times the height of nearby structures.

Dilution of pollutants in air depend on atmospheric temperature, speed and direction of the wind. The disadvantage of the method is that it is a short term contact measure which in reality brings about highly undesirable long range effects.

This is so because dilution only dilutes the contaminants to levels at which their harmful effects are less noticeable near their original source whereas at a considerable distance from the source these very contaminants eventually come down in some form or another.

(d) Vegetation:

Plants contribute towards controlling air-pollution by utilizing carbon dioxide and releasing oxygen in the process of photosynthesis. This purifies the air (re?oval of gaseous pollutant—CO2) for the respiration of men and animals.

Gas?ous pollutants like carbon monoxide are fixed by some plants, namely, Coleus Blumeri, Ficus variegata and Phascolus Vulgaris. Species of Pinus, Quercus, Pyrus, Juniperus and Vitis depollute the air by metabolising nitrogen oxides. Plenty of trees should be planted especially around those areas which are de?lared as high-risk areas of pollution.

(e) Zoning:

This method of controlling air pollution can be adopted at the planning stages of the city. Zoning advocates setting aside of separate areas for industries so that they are far removed from the residential areas. The heavy industries should not be located too close to each other.

New industries, as far as possible, should be established away from larger cities (this will also keep a check on increasing concentration of urban population in a few larger cities only) and the locational decisions of large industries should be guided by regional planning. The industrial estate of Bangalore is divided into three zones namely light, medium and large industries. In Bangalore and Delhi very large industries are not permitted.