Air pollution

  AIR POLLUTION AND ITS CAUSE AND SOLUTIONS

 The air pollution is caused due to addition of unwanted substances or gases. The atmospheric pollution is mainly

caused by the activities of man and concentrated to the inhabited and the industrial complexes in cities.

There are two main categories of air pollutants

(i) Gases (ii) Particulates

Gases :

The gaseous materials include various gases and vapours of volatile substances or the compound with a boiling point below 200°C.

Particulate matter :

Particulate matter consist of solid particles or liquid droplets (aerosols) small enough to remain suspended in air

e.g. soot, smoke, dust, asbestos, fibres, pesticides, some metals (including Hg, Pb, Cu and Fe) and also biological agent like tiny dust mites and flower pollen.

MAJOR AIR POLLUTANTS AND THEIR EFFECTS

    1.Carbon monoxide (CO) -

Source - It is the main air pollutant released from smoke of automobile.

Effect - Carbon monoxide is highly toxic gas, it combines with haemoglobin of the blood and blocks the

transportation of oxygen. Thus, it impairs respiration and it cuases death due to asphyxiation when inhaled in large amount.

     2. Un burn Hydrocarbons - (3,4 Benzopyrine, CH⁴ Benzene)

Source - These are mainly released from automobiles and burning of fossil fuel (petrol, diesel). Methane(CH⁴) is the most abundant hydrocarbon in atmosphere and its main source is marshy area and paddy field.

Effect - Hydrocarbons causes lungs cancer.

Note : Poly nuclear aromatic hydrocarbons - It is an important hydrocarbons and it also causes lungs canceri.e. This is carcinogenic.

   3. Ethylene -

Source - Ethylene released in air during fruits ripening.

Effect - Falling of leaves without particular regason, falling of flowering bud before time.

   4.Nitrogen oxide-(NO, NO,)

Source - Burning (combustion) of fossil fuel in automobiles.

Effect - These nitrogen oxide form photochemical smog in atmosphere and release ozone. Nitrogen oxide also responsible for acid rain. Entry of these nitrogen oxide causes respiratory trouble such as emphysema, bronchitis, swelling of lungs and lungs cancer etc.

      5. Sulphur oxide - (SO², SO³)

Source - These are most harmful gaseous pollutants, main source of sulphur oxides are coal burning, smelters, oil refineries.

Effect - Lichen and mosses do not grow in So, polluted areas. Lichen and mosses are indicator of So,

pollution. Sulphur oxides causes chlorophyll destruction. Taj Mahal also get effected.

    6.Smoke - (SO² SO³, NO², NO, CO, CO²,)

SECONDARY POLLUTANTS

   A. Smog (Smoke + Fog) -

This word was given by Desvoeux. Smog/Smoke is measured by Ringlmann method.

Smog is two types

(a) Los Angeles Smog or Photo Chemical smog -

It was first observed in Los Angeles. In this process smoke, log, nitrogenoxide, hydrocarbons, oxygen. UV

light and high temperature are essential. These components react with each other and form reddish

brown smog (PAN+O+ Nitrogen oxides) or brown haze/brown air. Los angles smog is light induced

smog

Effect -

Photochemical smog causes irritation in eyes and harms the lungs. Due to smog elastic substances (rubber/tyers) also affected. Smog causes damage in rubbers.

  * Ozone causes harm to mucous membrane.

   * During smog peroxyacetyl nitrate (PAN) is formed. PAN stops or inhibits the photolysis of water in hill reaction of photosynthesis and affect or inhibit the photosystem -II. PAN also inhibit the chlorophyll formation in plants.

(b)  London smog or sulphur smog -

It was first observed in London. In this process coal, smoke, fog, sulphur oxide and low temperature ar

essential. These components react with each other and form vapour (fog) of H²SO⁴ which is known as London smog.

Effect -

Due to inhalation of H²SO⁴, vapour with fog 4000 people died in London in 1952.

B. Acid rain -

This word was given by Robert August. NO, and SO, released from different sources in form of smoke ane

dissolved in atmospheric water vapour to form sulphuric acid and nitric acid (H²SO⁴, + HNO³,). These acids come down on earth with rain water this is called acid rain.

Wet deposition :- If acid comes down on earth with rain, log and smog, it is known as wet deposition.

Dry depositon :- If acid settled on earth surface through solid dust particles with nitrate or sulphate, this called dry deposition.

Note:

The pll of acid rain is lesser than <5.6

In acid rain the ratio of H²SO⁴, and HNO³, is 7:3 (70% 11,50, +30% HNO³)

Effects -

(1) Due to acid rain acidity of soil and water increases.

(2) Acid rain also causes damages historical monuments. e... Taj Mahal, Red Fort.

GREEN HOUSE EFFECT

Usually carbon dioxide is not considered as pollutant, but its higher concentration forms a thick layer above the earth's surface, checks the radiation of the heat from the earth surface. Because of this, temperature of the earth's surface increases, this is called "green-house effect" or global warming

Green house gases contribution

Main green house gases are CO², CH⁴, CFC, N²O excluding this SO² , O³, water vapour are also released from industries and NO², released from agriculture which are responsible to increase the green house effect.

Mean increase in CO²  in atmosphere

In this phenomenon cover of CO², layer around the earth, allow the short wavelength incoming solar radiation to come in but does not allow the long wavelength of out going heat radiation from warm surface of earth and surface keep the earth warm. The consequent increase in the global mean temperature is referred to as global warming.

Note :

1. It has been observed that in the recent past, the level of Co, in the atmosphere has increased from 280 ppm to 368 ppm in 1956 to 2002. If present growth rate is continued then the amount of Co, will be doubled upto 2020 century. Even 2-3°C rise in temperature will lead to melting of glaciers and ice caps of polar region and consequently the floods in rivers, rise in sea level and changes in cycle of rain. Islands may be submerged in sea water.

2. Carbondioxide fertilisation effect - Due to increased CO², concentration the rate of photosynthesis will increase (up to a few year). The response of the plants to elevated concentration of CO², is known as the CO² fertilisation effect.

3. The global mean temperature has increased by 0.6°C in 20th century.

4. Sea level has been raised by 1 to 2 mm per year during 20th century.

5. Without greenhouse effect the averge temperature at surface of Earth would have been a chilly -18°C rather than the present average of 15°C.

6. Increase in the level of greenhouse gases has led to considerable heating of Earth leading to global warming. During the past century, the temperature of Earth has increased by 0.6°C, most of it during the last threebdecades.

CONTROL OF AIR POLLUTION

Control of particulate matter - Two devices are use to remove particulate air pollutants

(a) Arresters

(b) Scrubbers

ARRESTERS:

These are used to separate particulate matters from contaminated air.

Arresters are of different types :

(i) Cyclonic separators and Trajectory separators :- These are commonly used to separate out particulate matters from industrial emissions with minimum moisture content. These separators work on the principle of dust separation by centrifugal force.

(ii) Electrostatic precipitator :- It is the most efficient device to remove fine particulate pollutants.

Electrostatic precipitation device work on the principle of electrical charging of the dust particles and

collecting it on a differently charged platform.

There are several ways of removing particulate matter the most widely used of which is the electrostatic precipitator, which can remove over 99 per cent particulate matter present in the exhaust from a thermal power plant.

It has electrode wires that are maintained at several thousand volts, which produce a corona that releases  electrons. These electrons attach to dust particles giving them a net negative charge. The collecting plates attract the charged dust particles. The velocity of air between the plates must be low enough to allow the dust to fall.

SCRUBBERS :

These are used to clean air for both dust and gases. Wet and dry two types of scrubbers are used for dust separation. A scruber can remove gases like sulphurdioxide. In a scrubber, the exhaust is passed through a spray of water or lime.

2) Control of Gaseous pollutants - Combustion, absorption and adsorption technique are used to control gaseous pollutants.

    (a) Combustion - In combustion process, oxidisable gaseous pollutants are completely burnt at a high

temperature. Petrochemical, fertilizer, paints and varnish industries used combustion control of gaseous

pollutants.

    (b) Absorption :- In this technique, gaseous pollutants are absorbed in suitable (liquid) absorbent materials.

     (c) Adsorption :- This technique is applied to control toxic gases, vapours and inflammable compounds that

could not be efficiently removed or transferred by a fore said technique. Such air pollutants are adsorbed on large solid surface.