This article throws light upon the twenty-eight main sources of air pollution by industries. Some of the sources are: 1. Fertilizer Complex 2. Cement Factories 3. Thermal Power Stations 4. Sulphuric Acid Industry and Other Industries 5. Aeroplanes 6. Fluoride Industry 7. Nitric Acid Plants 8. Chloralkali Plants 9. Iron and Steel Industry 10. Radioactive Natural Sources and Others.
Source # 1. Fertilizer Complex:
The fertilizer complex releases oxides of nitrogen and dust particles whose size ranges from submicron to 1000 microns. Dust particles may be evolved from the processes as drying, burning, calcining, grinding, screening, mixing, conveying or packaging. The major sources of dust emission can be listed in Table 7.
The recorded annual average dust fall at Sindri Township (Table 8).
The average dust fall in various cities of the world can be listed below:
Source # 2. Cement Factories:
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The cement dust is a common air pollution around cement factories and construction sites. Chemically it is mixture of oxides of aluminium, potassium, silica, calcium and sodium.
The experimental results have shown that this dust reduces the size and number of leaves in plants. Growth reduction by cement dust has been reported by Bohne, Darley and Lerman. It has been found that dust affected plants inspite of their reduced growth are able to survive and complete their life cycle.
The studies revealed that there was a definite reduction of 33.34 in the number of grains per spike of dusted plants. It was also noted that weight and volume of 10000 grains was reduced by 11.4 and 12.6% respectively. The researches have revealed that the reduction in grains per spike was due to partial failure of pollen grain germination on dust-laden stigmas and eventually lack of fertilization in the ovary.
Hence from above data, it can be concluded that in areas polluted with cement dust, cultivation of plants in general and wheat in particular will suffer a sizable loss in terms of biological and economic field.
Source # 3. Thermal Power Stations:
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These stations are the principal sources of SO2. It is best known and man-made pollutant. Fortunately because of its high reactivity and short life in atmosphere, no significant build up is reported. However, all industrialized areas suffer from SO2 fumes.
The recent data of SO2 concentration in some big industrialized cities of India is given below:
The table 10 indicates that the mentioned cities are polluted with SO2 and if the concentration of SO2 goes on increasing every year due to industrialisation then it will create problems for buildings, animals, human beings and plants.
Source # 4. Sulphuric Acid Industry and Other Industries:
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The industries producing sulphuric acid either by contact process or by Lead Chamber process discharge large quantities of SO2 in the air and pollute the atmosphere upto a few kilometer distances.
Many other industries also involve in one way or the other SO2 causing a big air pollution in the region. The stack gas analysis data is given in table 11.
Source # 5. Aeroplanes:
The fuel in aeroplanes on combustion produces SO2 as pollutant in the upper part of the atmosphere. This SO2 forms sulphurous (H2SO3) and sulphuric acids — which are poisonous and fall on the ground with the rain and pollute the soil and rivers. In general, sulphuric acid destroys plants, animals, water bodies and also the fertility of the soil completely.
The main reactions are as follows:
SO2 + H2O → H2SO3
H2SO3 + O (air) → H2SO4 Sulphuric acid
2SO2 + O2 = 2SO3
SO3+H2O = H2SO4
Source # 6. Fluoride Industry:
The industry produces fluoride compounds which have serious effects on plants, animals and human beings. The toxic effects of fluoride on liue-stock arise from ingesting contaminated forage on which fluoride dust has been settled.
Cattle and sheep are very much susceptible to fluorine poisoning. Horses and poultry develop fluorisis due to large increase in fluoride content in their bones and teeth acquiring a stiff posture and becoming lame. In cattle the milk production decrease and they lose their weight.
Hydrogen fluoride destroys the leaves and fruits in the plants.
The details of fluoride production and stack gas analysis data are presented in Tables 12 and 13. The effect of fluoride on jowar leaves has also been exhibited in Table 14.
Source # 7. Nitric Acid Plants:
Nitric acid plants generally release oxides of nitrogen in the atmosphere which are serious pollutants. There is an increasing concern over their levels in the atmosphere on account of their role in photo-chemical reactions which result in the formation of highly toxic substances in polluted environments.
These oxides of nitrogen also consume a lot of ozone of the above atmosphere.
The probable reactions are as follows:
NO + O3 → NO2 + O2
NO + O3 → NO2 + O2
NO2* → NO2 + Hv
Source # 8. Chloralkali Plants:
Emission from chloralkali plants includes:
(1) Chlorine gas
(2) Carbon monoxide
(3) Carbon dioxide and
(4) Hydrogen.
Source # 9. Iron and Steel Industry:
The emission from iron and steel industry includes:
(1) SO2
(2) Metal oxides and
(3) CO and CO2
Source # 10. Radioactive Natural Sources:
The radioactive elements which occur in igneous rocks and soils can be divided into three parts:
(1) Uranium series (U238)
(2) Thorium series (Th232) and
(3) Actinium (U235)
The gases such as radon and thoron which give rise to a series of radioactive decay products which get deposited on SPM in the atmosphere. So samples of suspended particulates collected by high volume samplers exhibit definite amounts of absorbed radioactivity.
Source # 11. Incineration of Refuse or Solid Waste:
The refuse or solid wastes contain the following pollutants:
(1) Benzo (a) pyrene
(2) Organic acids
(3) Particulate
(4) Ammonia
(5) Oxides of sulphur
(6) Hydrocarbons
(7) Aldehydes
(8) Carbon monoxide and
(9) Oxides of nitrogen.
Source # 12. Industrial Sources of Odour Pollution:
Offensive smell is the most strident kind of pollution and its reduction involves not only chemical, physical and engineering problems but also social, physiological and psychological.
Generally tanneries, meat and fish processing, tallow melting and refining and gut cleaners create odour pollution in the area in which they are located. Tallow is the term, which describes animal fat from all sources. Its main constituents are palmitates, C15H31COOR and sterates C17H35COOR of glycol, C3H8O3 with some oleatets, C17H33COOR of glycerol.
The melting point of tallow is about 45°C. Below 45°C, there is hardly any smell. The blue fumes which come out due to heating of fat above 45°C are due to formation of acrolein and other burnt and carbonized products which are irritant and offensive.
In guts, the gaseous decomposition products are released producing a serious pollution of air.
Cooking smells, the gases from sewage and domestic refuse, maggot (worm like larva) breeding and catering industry also cause air pollution.
The main pollutants from kitchens are:
(1) Aldehydes
(2) Hydro-carbons
(3) Carbon monoxide
(4) Carbon dioxide and
(5) Obnoxious gases.
Source # 13. Emissions:
The coarse particles of solid particulate matter which settle out of the atmosphere by gravity are called emissions. These emissions pollute the atmosphere.
Source # 14. SPM (Suspended Particulate Matter):
These are particles, either liquid or solid dispersed in gaseous medium. The solid particles may be irregular may be irregular in shapes but liquid particles are sphericity in shape. Particles larger than 100 µm tend to settle out of the air by gravity. They cause air pollution.
Source # 15. Sulphur Dioxide:
The coal burning power plants release 41% of the total emission of SO2. The combustion of coal and petroleum products together liberates about 18 million tons of S02 to the atmosphere from vehicles.
Source # 16. Nitrogen Oxides:
The fuel combustion sources produce 10 million tons of nitrogen oxides, with about 25% from electricity generation, 17% from industrial, 9% from residential, 46% from transportation sources and 3% from commercial operations.
Source # 17. Carbon Monoxide:
99% CO comes from vehicles. In 1984, 213 million tons was discharged into the atmosphere.
Source # 18. Viable Particles:
A large number of viable particles are found in the atmosphere over land during the growing season. These consist of pollens, microorganisms and insects. In fact, the pollens are aeroallergens and are found in the atmosphere due to grasses, trees, plants, bushes and weeds. The pollen grains produce hay fever and various types of allergic reactions in human beings.
The most important viable particles are yeasts, algae, fungi, spores, bacteria, rusts and moulds etc. Except algae, all other microorganisms can be transported by wind. They are generally responsible for infection in animals, plants and human beings.
The bacteria are found in air, water, soil, vegetation, food, dust particles and in the bodies of human beings and animals. They are always present in the atmosphere irrespective of climate cold, hot or rainy season.
Source # 19. Atmospheric Reactions:
The oxides of nitrogen discharged into the atmosphere from combustion of fuels and industries are highly reactive.
They react with moisture or water and from various acids as follows:
2NO2 + H2O → HNO2 + HNO3
3HNO2 2NO + HNO3 + H2O
Similarly, the SO2, which is discharged into the atmosphere from iron works, factories etc. produces the following products with H2O and fall on the earth:
2SO2 + O2 → 2SO3
SO3 + H2O → H2SO4
2SO2 + 2H2O + O2 → 2H2SO4
About 80 million tons SO2 is released into atmosphere per year. The rate of H2S formation is about 300 million tons per year.
Now take the case of CO2. It is released by all forms of life during respiration and is assimilated by green plants during photosynthesis.
CO2 which is released by carbonaceous fuels etc., has increased its concentration in the atmosphere. Emission of CO to the atmosphere is more than 200 million tons per year.
In fact, the chemical reactions occurring in the atmosphere convert gases or vapours into solid and liquid products by oxidation, reduction, condensation, polymerization, combination and other mechanisms. The photochemical reactions in the upper atmosphere convert complex molecules into simple molecules due to solar radiation.
Source # 20. Man-Made Sources of Air Pollution:
Man is the main culprit for producing pollution in the air through use of coal, oil and natural gas as fuel and exhaust gases from automatic vehicles. Besides this, the industrial activities such as oil refining, iron and steel manufacturing, non-ferrous manufacture of rubber tyres, tubes and pulp and paper and other processes, industries have added new dimensions to the field of air pollution.
The man-made pollutants are listed in Table 15.
Source # 21. Mineral Acids:
(i) Nitric acid manufacture:
It has been estimated that for the production of 1 ton of acid, about 30-100 pound of nitrogen oxides is produced, out of which about 70-80% of brown coloured nitrogen dioxide (NO2) can be reduced to colourless nitric oxide (NO) by a catalytic reaction unit. Because of extra fuel requirement, about 25% of total nitrogen oxide is reduced to nitrogen and oxygen by catalytic reduction.
(ii) Sulphuric acid manufacture:
In this plant the main emissions are (SO2) and sulphuric acid (H2SO4).It has been estimated that for the production of 1 ton of acid, the emissions of SO2 range from about 25-70 pounds. Without acid must eliminators can reduce SO2 to 0.02 from 0.2 pounds of acid must/ton of acid produced.
Emissions:
(1) SO2 and (2) SO3
(iii) Hydrochloric acid manufacture:
The principal emissions are:
(1) HCl,
(2) Chlorinated products,
(3) Unreacted hydrocarbons and
(4) Chlorine.
The contaminants can be minimized if the effective absorption tower or scrubbing system is used to remove residual HCl.
(iv) Phosphoric and manufacture:
In the electric furnace process- phosphate rock siliceous flux and coke are heated in an electric furnace to produce phosphorus. The principal emissions are (1) Phosphoric acid and (2) Phosphorous Penta oxide (P2O5). Emissions of P2O5 are in the range of 3.6 to 5 pounds of elemental phosphorous (P4) burnt.
In the wet process:
H2SO4 and phosphate rock are reacted to form phosphoric acid and gypsum. Main emissions are (a) gaseous fluorides with Some H, (b) P2O5 along with phosphoric acid.
Source # 22. Petrochemical Refineries:
An oil refinery consists of:
(i) Distillation towers,
(ii) cracking towers
(iii) pressure vessels
(iv) heat exchangers
(v) valves
(vi) pumps and
(vii) storage tanks.
From the refineries, we get the following emissions:
(i) Particulate
(ii) CO
(iii) HCHO
(iv) NH3
(v) NO2
(vi) Gasoline
(vii) Kerosene and
(viii) Fuel oil etc.
Source # 23. Emissions from Fuels, Incinerators and Internal Combustion Engine:
When coal is used as a fuel, we get the following emissions:
(i) Particulate matter — 30-150 lbs/ton of fuel.
(ii) SO2 -60-120 lbs/ton of fuel.
(iii) Other organics—20-30 lbs/ton of fuel.
The contaminants discharged to the atmosphere from fuel burning, incineration of refuse and internal combustion engine are as follows:
(i) Particulate matter (Soot and fly ash)
(ii) Sulphur dioxide and
(iii) Natural gas
(iv) Exhausts from engine include:
(1) CO,
(2) Oxides of nitrogen,
(3) Hydrocarbons
(4) Oxygenates of hydrocarbons,
(5) Lead compounds,
(6) Carbon particles,
(7) Motor oil
(8) Non-volatile reaction products formed from motor oil in the combustion zone. High molecular weight olefins and carbonyl compounds are produced in the reaction.
The amount of above products depends upon the composition of fuel, method of firing and other factors.
Source # 24. Natural Gas:
The emissions from natural gas combustion are given in the following tables.
Source # 25. Combustion of Coal:
In the combustion of coal, we get the following products:
(i) Carbon monoxide (CO)
(ii) Oxides of nitrogen (NOx)
(iii) Sulphur dioxide (SO2)
(iv) Aldehydes (RCHO) and
(v) Hydro-carbons (CxHy).
The quantities of these pollutants depend on the composition of Coal, method of firing, the size of unit, atmospheric conditions, etc.
The burning of coal also produces:
(i) Fly ash emission and
(ii) Particulate emission: The important constituent of particulate emission is benzo (a) pyrene which has been found to be carcinogenic to animals.
Source # 26. Combustion of Fuel Oil:
The main pollutants are:
(i) Particulate emissions and
(ii) Oxides of sulphur.
Source # 27. Kraft Pulp Manufacture:
From the Kraft pulp industry, we get the following gaseous pollutants.
(i) H2S (2) Marcaptans and (3) Various other sulphides.
The main pollutants and their major sources of generation are presented in Table 20.
Source # 28. Noxious or Offensive Gases:
The requirement of the 1906 Act of U.S.A is that the best practicable means shall be used to prevent the escape of noxious or offensive gases, whether directly or indirectly, into the atmosphere and for expression ‘noxious or offensive gas’ includes the list of gases and fumes given in section 27 (1) of the act of U.S.A. as extended by the 1966 and 1971 orders, and as effectively extended by section 11 (2) of the Clean Air Act 1958, it also includes smoke, grit and dust. The list now includes all listed in Table 21.
In India we have also adopted the U.S.A. pattern and so the above gases have also been listed as offensive gases.