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Home >> Biology >> Environmental Pollution >>Air Pollutants and Their Effects
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Air Pollutants and Their Effects
1.Particulate matter.
It is of two types -settleable and suspended settleable dusts have a particle longer than 10µm. Smaller particles are able to remain in air for long periods. Their types are :
(i) Aerosol - less than 1 µm
(ii) Dust-more than 1 µm
(iii) Mis-more than 1 µm.
(a)Dust and smoke cause irritation of respiratory tract and produce bronchitis, asthma and lung disease.
(b) Smog is dark fog formed by duct and smoke particles causing condensation of water vapours around them and attracting other chemicals like SO2, H2S, NO2 etc. Smog harms plant through silvering, glazing and necrosis besides reducing availability of light. It causes a number of accidents e.g. a 5 day smog in London (1952) killed about 4000 persons.
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(c) Particulate matters scatters and partly absorbs light. In industrial areas sunlight is reduced to 1/3 in summer and 2/3 in winter. It is hazardous to vehicles.
| Some diseases |
Cause |
| (i) Pneumoconiosis or lung fibrosis called byssinosis |
Cotton dust |
| (ii) Asbestosis |
Asbestos industry |
| (iii) Silicosis |
Stone grinders |
| (iv) Siderosis |
Iron mill |
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2. Carbon monoxide
(a) Formed by incomplete combustion of fuels.
(b) It combines with haemoglobin of blood and impairs oxygen carrying capacity.
(c) At 100 ppm CO causes giddiness and headache.
(d) Other harmful symptoms are -exhaustion, decreased vision, cardiovascular malfunction etc.
3. Sulphur oxides
(a) Compound has mutagenic properties
(b) It corrodes metals like Zn and Fe.
(c) It results in discolouration and deterioration of buildings, sculptures, leather, paper etc. Reported threat to Taj Mahal of Agra from Mathura refinery is an account of it.
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(d) Above 1 ppam it affects human-beings, causes eye irritation, injury to respiratory tract.
(e) It causes chlorosis (destruction of chlorophyll changed to phaeophytin) and necrosis of vegetation even in low concentration. Leaves assumes water-soaked appearance. Monocots are most sensitive.
4. Nitrogen oxides.
They are produced both from biological and non-biological activities as well as human activities like combustion in industries and automobiles.
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(a)They are formed in stratosphere due to solar flares. Large flares shall form enough oxides to destroy the protective ozone layer.
(b)Oxides posses mutagenic properties
(c ) They cause eye irritation, lung edema, blood congestion, and dilation of arteries. At a concentration of 15-50 ppm they cause injury to lungs, liver and kidneys.
(d)They produce lesions,necrosis,defoliation,die back and death of many plants
(e) In presence of moisture they have a corrosive effect on metals.
(f) Nitrogen oxides give rise to photochemical smog.
(g) They act on unsaturated hydrocarbons to form peroxy acyl nitrates or PAN.
5. Carbon dioxide.
Earlier an atmospheric balance of CO2 was attained through plants by photosynthesis. But now -a-days excessive combustion activity has increased CO2 level leading to greenhouse effect(discussed in previous chapter). Melting polar ice caps and glaciers could cause sea levels to rise.
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6.Benzpyrene.
Carcinogen produced in tobacco smoke, automobile exhausts and industrial effluences.
7. Phosgene and methyl isocyanate.
Phosgene (COCl2) is a poisonous and suffocating liquid used in dye industry and synthesis of organic compounds. Release of phosgene and MIC in industrial accident of Bhopal is an living havoc.
8. Aerosols.
Commonly famous as jet affluents they are also used as disinfectants. Chlorofluorocarbons (CCl3F1,CCl2F2) are also used in refrigeration and formation of plastic foams.CCl4 is produced naturally as well as human activity. Chlorofluorocarbons released by jet flying at higher altitude react with ozone and deplete it.
9. Ozone.
Ozone protects earth from high energy UV rays. Ozone is trosposphere has a warming effect. It has toxic effects also:
(a)At conc. of only 0.02 ppm ozone destroys chlorenchyma and produce necrotic areas.
(b) Ozone hardens rubber
(c) It discolours and damage textiles.
(d) At less than 1 ppm, ozone injures mucous membrane.
10. Pollen and microbes.
They are normal constituents of air. Microbes directly damage vegetation, food articles and cause disease in plants, animals and humans as well. Excess of pollen cause allergic reactions in several human beings commonly called hay fever.
11. Automobile exhausts.
90% of lead pollution is caused by gasoline combustion which contains (CH34) Pb (TEL-Tetraethyl lead) used as an antiknock. Lead is emitted as aerosol which pass into lungs and hence blood. Bombay residents have a lead content of 16-18 µg/100ml of blood while lead shows toxic effect beyond 20µ/100 ml. Larger lead particles settle down on soil and pass into food chain.
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