Air pollution is a problem for humans, animals, ecosystems and the built environment. The average adult breathes about 3,000 gallons of air every day. Children breath twice as much per pound of body weight and are therefore, more susceptible to the effects of air pollutants.
Therefore, it is necessary to control air pollution by applying some remedial measures. There are different remedial measures for different pollutants, which are as follows:
i) Mechanical collectors (dust cyclones, multicyclones)
Minimization of emission of particulate matter from point sources can be done by this method. The polluted air allowed passing to metallic cylinder at high speed. The particulates strike the walls of the cylinder and fall at the bottom.
This technique removes 50-90 per cent of large particulate matter along with a few medium and small particulates.
ii) Electrostatic precipitators
This technique also removes the particulate matter but these are 90 percent efficient. The particulates become electrically charged when passed through the precipitators.
The particulates attach themselves to the wall of device which has the opposite charge. By frequently tuning off the current, the particulates are allowed to fall to the bottom.
iii) Particulate scrubbers
Particulate matter and sulphur dioxide gases can be removed by this method. The polluted air passes through a fine mist of water which traps about 99 per cent particulate matter and approximately 80-90 percent sulphur dioxide.
The filters depurate out particulate matter from the stack gases in electric power plants. The smoke passes through a series of cloth bags trap the particulate matter.
At fixed temperature, hydrocarbons and organic substances can be controlled by the condensation of gaseous vapour.
vi) Catalytic converters
This is a device which runs exhaust gasses of automobiles through a bed of alumina pellets coated with platinum catalyst. This device is attached to the exhaust system of a vehicle and converts carbon monoxide and hydrocarbons into carbon dioxide and water and nitrogen oxides into nitrogen gases.
The particles of gas like C02, H20, H2S and S02 allow passing through high temperature for combustion.
Adsorption is a physical process that occurs when a gas or liquid accumulates on the surface of a solid or a liquid (adsorbent). Good adsorbents are silica gel, zeolites and activated carbon.
Some air pollution incidents
i) TCDD accident at Seveso , Italy (July, 1976)
A pollutant 2,3,7,8 tetrachlorobenzenzo-10-dioxin came out in the white cloud of poisonous gas during explosion in a herbicide manufacturing plant at Italy. About 200 people including children suffered from skin diseases. About 1% of the new born babies were premature.
ii) Methyl isocyanate (MIC) Bhopal gas tragedy (3rd December 1984)
Methyl isocyanate, CH3NCO (MIC) is generally used in the manufacturing of carbonate pesticide. It is a volatile liquid (B.P. 43-45eC). A Union Carbide Subsidiary Pesticide Plant released 40 tones of MIC gas, killed between 2500 and 5000 people.
The threshold limiting value (TLV) for MIC has been reported to be 0.02 ppm and for COCl9, 0.1 ppm. MIC occurs in association with COCl2, the combined effect gets fatal within 24 hours.
iii) Chernobyl disaster
An explosion as a result of nuclear reaction took place at Chernobyl, Ukraine, formerly USSR (now CIS). The reactor core temperature was found to be more than 2000QC.
The accident killed at least two thousand people. Soil, water and vegetation over 60 sq.km area around Chernobyl were highly damaged. The main cause of disaster is the long-lived radioactive isotope Cs-137.