1AIR POLLUTION & CONTROL

MD MOUDUD HASAN LECTURER

DEPARTMENT OF AGRICULTURAL AND INDUSTRIAL ENGINEERINGFACULTY OF ENGINEERING

HAJEE MOHAMMAD DANESH SCIENCE AND TECHNOLOGY UNIVERSITYDINAJPUR

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3Definition Air pollution means any solid, liquid or gaseous substances

present in the atmosphere in such concentrations that may tend to be injurious to human beings or other living creatures or plants or property or enjoyment.

Perkins (1974) defined air pollution as “air pollution means the presence in the outdoor atmosphere of one or more contaminants such as dust, fumes, gas, mist, odour, smoke or vapour in quantities or characteristics and of duration such as to be injurious to human, plant or animal life or to property or which unreasonably interferes with the comfortable enjoyment of life and property.”

4Sources of Air Pollution (a) Point sources: These are the sources which cause direct

release of air pollutants. Example The emission of gases from an industry through a chimney.

(b) Non-point sources: These are the sources which release some substances which are capable of undergoing chemical reactions in the atmosphere to generate air pollutants. Example Photochemical smog.

(c) Man-made or Anthropogenic sources: These are the sources which generate air pollutants by human activities. Example Vehicular discharges, burning of fossil fuels, population explosion etc.

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6Sources of Air Pollution (i) Vehicular discharges: A mixture of CO, CO2, and NOx are

emitted as exhaust gases from automobiles. They cause air pollution as such. Moreover, they also react with oxides of nitrogen in the presence of sunlight to produce highly toxic photochemical smog.

(ii) Burning of conventional fossil fuels: Burning of coal, lignite, natural gas and combustion of petrol/diesel/CNG produces gaseous by-products like CO, SO2 NOx which are toxic. They pollute the air and make it unfit for breathing.

(iii) Population explosion: It creates the emission of Greenhouse gases, global warming, destruction and loss of forest cover and wildlife etc.

7The Natural and Man-made (Synthetic) Air Polutants and Their Consequences (i) Carbon monoxide (CO) Sources: Forest fires, agricultural burning, incomplete

combustion of fuels, tobacco smoking, automobile exhausts, etc.

Effects: Toxicity, blood poisoning leading to death, increased proneness to accidents.

(ii) Sulphur dioxide (SO2) Sources: Combustion of coal and petroleum products,

sulphuric acid plants, power houses. Effects: Irritation of throat and eyes, suffocation, aggravation

of asthma and chronic bronchitis.

8The Natural and Man-made (Synthetic) Air Pollutants and Their Consequences

(iii) Oxides of Nitrogen (NOx) Sources: Nitric acid plants, automobile exhausts, explosives and

fertilizer industries, power stations. Effects: Headache, respiratory irritation, impairment of lung

defenses, corrosion of teeth, loss of appetite. (iv) Mercury (Hg) Sources: Mining and refining of Hg, industries linked with

manufacture of medicinal products, pesticides which use organic mercurials.

Effects: Inhalation of Hg vapours cause toxic effects, highly toxic organo-mercurials may cause irreversible damage to brain and nervous system.

9The Natural and Man-made (Synthetic) Air Polutants and Their Consequences (v) Lead (Pb) Sources: Automobile emissions, electroplating waste, plumbing,

lead paint industry, printing etc. Effects: Cause liver and kidney damages, mental retardation in

children, abnormalities in fertility and pregnancy, gastro intestinal damage.

10HARMFUL EFFECTS OF AIR POLLUTION ON MATERIALS

The air pollution affects the materials in following ways:- (i) Abrasion (loss of material by wind with coarser particles). (ii) Corrosion ( acidic effect of rain water). (iii) Deposition and removal (adhering substances and removal

of material by rusting.) (iv) Direct chemical attack (effect of gases like SO2). (v) Indirect chemical attack (action of acid or its fumes on

stones like marble, corrosion of reinforcement due to diffusion of gases in RCC).

11The Measures Used for Controlling Air Pollution The most effective method to control air pollution is to prevent

the formation of pollutants or to reduce their emission at the source itself.

(i) Source correction methods: In case of industrial pollutants, the designing and development of plants may be so selected so as to have minimum emission of air pollutants. Examples (a) By suitable design modification of the tanks, evaporation from

petroleum refineries can be minimized. (b) Use of correct grade of raw material like low-sulphur oil and

coal is recommended.

12The Measures Used for Controlling Air Pollution (ii) Cleaning of gaseous effluents: These techniques control pollution by the

removal of pollutants from the exhaust. These methods are used in combination with source correction methods.

(a) For gaseous pollutants: The gaseous pollutants are removed by absorption in a liquid, or adsorption on a solid. Catalytic converters are also used as they convert gaseous air pollutants into harmless gases.

(b) For particulates: Following techniques are generally used for control of particulate emissions:

Gravitational settling chambers, Cyclone separators, Fabric Filters, Electrostatic precipitators, Wet scrubber etc.

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