Air pollution and its control
- It is the occurrence or addition of foreign particles or gases or pollutants is the air in that much concentration which have an adverse effect on man, animals and vegetation
- The combustion of fossil fuels, automobile exhausts, industries and mining are mainly responsible for 60-80% of air pollution.
- More than 50% of air pollution is caused by CO, 18% by SO2, 12% by hydrocarbons, 10-15% by particulates, 6% by nitrogen oxides and 2% by the remaining.
- Air pollutants are either gaseous (or) particulate.
- Air pollutants are primary if they remain in the air in the same from in which they are released from the pollution source and if they are formed by the reaction between primary pollutants in the presence of sunlight, they are secondary air pollutants [Eg. Ozone, PAN, H2SO4, HNO3 etc].
- Particulate matter (PM) consists of soot, flyash, dust of various types, fun, hair, spores etc. It is differentiated into settleable and suspended.
- PM from processing industries causes pneumo coniosis, byssinosis, Emphysema, siderosis, asbestosis, blacklung, silicosis.
- Carbon monoxide accounts for 50% of atmospheric pollution which is produced due to incomplete combustion of fossil fuel in automobile engines, forest fire.
- Carbon monoxide has a strong (200 times more than O2) affinity for Hb in blood to produce a stable carboxy Hb (or) CoHb. It impairs O2 transport resulting in asphyxia.
- CO2 is a green house gas, produced from combustion of fuels, volcanic eruptions which causes headache and nausea. In general it is not a air pollutant but in very high concentration it traps UV rays and causes rise in temperature on earth.
- H2S is a product of putrefaction, treatment of 'S' containing ores and bituminous fuels which causes mottled chlorosis and defoliation in plants, decolourises paints, produces eye irritation, throat irritation and nausea.
- Hydrocarbons (HC) (or) Volatile Organic Carbons (VOC's) are produced naturally from paddy fields, cattles, marshy areas and certain plant like pine trees.
- HC especially polynuclear aromatic HC (or) are formablehyde are carcinogenic, causes eye-irritation and irritation of mucous membrane and bronchial constriction due to which there is increased muccus secretion and Alveoli tearing.
- Sulfur oxides are produced in large quantity during smelting of metallic ores containing sulfur, Petroleum refining, H2SO4 manufacturing, volcanic eruption.
- In the air, SO2 oxidises to SO3 and combines with H2O to form sulfurous acid H2SO3 and H2SO4 which is the cause of acid rain.
- Lichens, mosses and garden pea are SO2 pollution indicator.
- SO2 causes membrane damage, metabollic inhibition, growth and yield reduction.
- The important effect of nitrogen oxides are as follow.
→ They act on unsaturated 'HC' to form PAN (peroxyacylnitrate).
→ Nitrogen oxid give rise to photochemical smog.
→ They cause fading and deterioration of different types of textiles.
- Chlorofluorocarbons (CFS) (or) Freons are released as aerosols by jets flying at high attitudes. They are a group of highly stable, odourless, non toxic, chemically inert made up of e.f and cl.
- CFC's have a high residence time of our 100 years.
- Smog (smoke + fog) is opaque or dark fog having condensed water vapours, dust, smoke, gases which causes silvering and glazing and necrosis in plants, allergy in human
- Smog is of 2 types (i) classical / London smog and (ii) photochemical / Los angles smog which is caused due to primary and secondary pollutant respectively.
- Classical smog is dark brown and opaque, whereas photochemical smog is grey / yellowish brown.
- Arresters, cyclone separators, Gravity settling chamber, filters, Electrostatic, Precipitators, scrubbers could be used to control particulate matter (pm).
- Gaseous pollutants are removed from emissions by three methods (i) combustion, (ii) absorption and (iii) adsorption.
- Compulsory use of unleaded petrol, enforcement of euro II norms, Fitting vehicles with catalytic converters could be few measures adopted for reducing automobile pollution.
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