Harmful effects of particulates
(i) Effect on human beings
The particulates seriously affect the human respiratory system & cause several respiratory illnesses. The particles with small size are more harmful in this context. The particulates in fact, become the carriers of the toxic substances from the atmosphere to the human & cause big health hazards.
(ii) Effect on visibility
Particulates in the atmosphere cause scattering & absorption of sunlight & reduce the visibility.
(iii) Effect on Materials
The adverse effect of particulates on materials include corrosion of metals (when the atmosphere is humid), erosion & soiling of building, sculptures & painted surfaces & soiling of clothes & draperies.
CONTROL OF AIR POLLUTION
Air pollution can be checked either at source or at the dispersal stage of various pollutants. Although the Prob. of controlling air pollution at source is not easy, yet it can be reduced to some extent by taking steps such as,
Use of appropriate raw materials, selection of proper sites for industrial units & use of modern techniques for efficient reduction of emission & effluents.
Different methods for the control of various air pollutants are as follows:
1. Control of CO
Some of the measures which can be adopted for control of CO pollution are:
(a) Use of anti pollution exhaust catalyst.
(b) Modification & improvement in internal combustion engine.
(c) Use of other fuels such as CNG, LPG & LHG.
2. Control of CO2
CO2 level can be maintained by reducing its release from industrial units & controlling vehicular exhaust etc. Hydrogen is being looked upon as pollution less future fuel.
3. Control of NOx Pollution
(i) Power plants & industrial units emit large amounts of NOx. Such emission can be reduced by almost 90% with the help of two step combustion.
(a) In the first step, the fuel is burnt at high temperature in a limited supply of air.
(b) In the second step, the unburnt fuel is burnt at lower temperature in excess of air.
(ii) Acidic scrubbing of fuel gases: The large amounts of nitrogen oxides emitted form power plants & industrial units can also be removed by scrubbing the fuel gases with sulphuric acid.
(iii) NOx in vehicular exhaust is converted into N2 & trace amount of NH3 with the help of anti-pollution exhaust catalyst.
4. Control of SO2 pollution
The process of removal of SO2 is known as flue as flue gas desulphurisation (FGD). Sulphuridioxide from flue gases is commonly removed by using chemical scrubbers consisting of a slurry of CaCO3 where SO2 is absorbed forming CaSO3.
Smog & its ill effects
Smog is a mixture of smoke & fog. The principal source of classical smog is the combustion of industrial household fuels. Because of the presence of SO2 & carbon (soot particles), classical smog has a reducing character.
Photo Chemical Smog
This is another type of smog which is distinctly different from the classical smog.
The principal constituents of the photo chemical smog are ozone & oxides of nitrogen.
It causes irritation in eyes due to the presence of ozone. This type of smog is formed through photo chemical reactions involving solar radiations, hence is named as photo chemical smog.
Harmful effects of smog
(i) Smog causes respiratory Problems
(ii) It reduces visibility
(iii) It damages plants & other material like electronic & electrical equipment.
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