Unit2_Air pollution.pdf

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Dr. R.Saravanathamizhan Chemical Engineering Department

GE 2021 Environmental Science and

Engineering

Unit-2

Environmental Pollution


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Pollution

Pollution may be defined as an undesirable change in the

physical, chemical or biological characteristics of air, water

and land that may be harmful to human life and other animals,living conditions, industrial processes and cultural assets.

Pollution can be natural or manmade. The agents that pollute

are called pollutants.


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On the basis of natural disposal, pollutants are of two types:

Non-degradable pollutantsThese are the pollutants, which degrade at a very slow pace by

the natural biological processes. These are inorganic

compounds such as salts (chlorides), metallic oxides waste

producing materials and materials like, aluminium cans,

mercuric salts and even DDT. These continue to accumulate in

the environment.

Classification of Pollutants


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Biodegradable pollutants

These include domestic sewage that easily decomposes under

natural processes and can be rapidly decomposed by natural/

artificial methods. These cause serious problems whenaccumulated in large amounts as the pace of deposition exceeds

the pace of decomposition of disposal.

On the basis of the form in which they persist after their releaseinto the environment, pollutants can be categorized under two

types:


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Types of environmental pollution

Types of environmental pollution:

a) Air pollution

b) Water pollutionc) Soil pollution

d) Marine pollution

e) Noise pollution

f) Thermal pollution

g) Nuclear hazards


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Air Pollution


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Air Pollution

The WHO defines air pollution as the presence of materials inthe air in such concentration which are harmful to man and his

environment. A number of ingredients find their way in the air

and these are mostly gases, which rapidly spread over wide

areas.


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Air pollution


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Classification of Air Pollutants


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Primary and secondary pollutants



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These include those substances, which are emitted directly fromsome identifiable sources. This include-

(a) Sulphur compounds: SO2, SO3, H2S produced by the

oxidation of fuel.(b) Carbon compounds: Oxides of carbon (CO+CO2) and

hydrocarbons.

(c) Nitrogen compounds: NO2 and NH3.

(d) Halogen compounds: Hydrogen fluoride (HF) andhydrochloric acid (HCl).

(e) Particles of different size and substances: These are foundsuspended in air.

The fine particles below the diameter of 100 micron aremore abundant and include particles of metals, carbon, tar,fungi, bacteria, silicates and others.

Primary pollutants



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Secondary pollutants

The secondary pollutants are produced by the

combination of primary emitted pollutants in theatmosphere. In bright sunlight, a photochemicalreaction occurs between nitrogen oxides; oxygen andwaste hydrocarbons from gasoline that forms

peroxyacetyle nitrate (PAN) and ozone (O3), Both ofthem are toxic components of smog and causesmarting eyes and lung damage.


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Smog. The fog deposited with smoke and chemical

fumes forms a dark and thick covering, the smog.

Smog is very common in almost all the industrial

areas as the smog is trapped for many days by the

stagnant air. It is harmful both for animals and plants.


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Burning Fossil Fuels

Burning of wood, charcoal and other fossil fuels causes air

pollution by the release of carbon dioxide, sulphur dioxide etc.

Petroleum consists mainly of hydrocarbons, sulphur and nitrogen.Emissions from Automobiles

Vehicles are mainly responsible for more than 80% of

total air pollution. The major pollutants released fromautomobiles, locomotives, aircraft etc., include CO, unburnt

hydrocarbons and nitrogen oxide.

Sources of Air Pollution


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IndustriesPaper and pulp factories, petroleum refineries, fertilizer plants,

and steel industries, thermal power plants are the main sources ofair pollution. They add various harmful gases like CO, SO3, NO,Hydrocarbons etc., to the atmosphere.

Textile factories release cotton dust into the air. Citiesexperiencing this type of pollution are Kanpur, Surat andAhmedabad.

The pesticide and insecticide industries are posing serious threatto the environment.Food processing industries and tanneries emitoffensive odors. Release of poisonous gases from accidents alsoposes serious threats.

e.g. Bhopal Gas Tragedy in which methyl isocynate (MIC) gas

leakage killed several people.In Tokyo, about 34 tones of carbon particles mixed with other

suspended particles settle per square kilometer every day.


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Agricultural ActivitiesSpraying of insecticides and weedicides also cause airpollution. These, when inhaled create severe problems to bothanimals and man.

WarsVarious forms of explosives used in war pollute the air byreleasing poisonous gases. This greatly disturbs the ecology ofthe area. Nuclear explosions pollute air by radioactive rays.The effects of nuclear explosions on Hiroshima and Nagasakiare well-known examples.

Natural Causes

Gas emissions from active volcanoes, marsh gas, spores offungi and pollens are the natural causes of air pollution.


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Common Air Pollutants

Air pollutants are of two main types ~gaseous andparticulate.

Oxides of carbon. Nitrogen and sulphur are gaseouspollutants.

Particulate pollutants may be solid or liquid particles,larger particles settle down quickly viz., sand and

water droplets whereas small dust particles remainsuspended in air for a long time. These are added intothe atmosphere by the processes of blasting, drilling,crushing, grinding and mixing.


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Carbon DioxideCO2 content of air has increased by 20% during the last

century. CO2 causes nausea and headache. Its increase in the

air may cause green house effect, rise in the atmospheric

temperature. This may melt the polar ice resulting in rise in

level of oceans and flooding of coastal regions.

Carbon Monoxide

It is a very poisonous gas and is produced by incompletecombustion of fuel. If inhaled it combines with hemoglobin

and reduces its oxygen-carrying capacity. This leads to

laziness, reduced vision and death.


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Oxides of Nitrogen

These include NO and NO2, which are released byautomobiles and chemical industries as waste gases and alsoby burning of materials. These are harmful and lower theoxygen carrying capacity of blood.

Oxides of Sulphur

SO2 and SO3 are produced by burning of coal and petroleumand are harmful to buildings, clothing, plants and animals.

High concentration of SO2 causes chlorosis (yellowing ofleaves), plasmolysis, damage to mucous membrane andmetabolic inhibition. SO2 and SO3 react with water to formSulphuric and sulphurous acids. These may precipitate as rainor snow producing acid rain or acid precipitation.


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Photochemical Oxidants

Formed by the photochemical reactions between primary

pollutants, viz. oxides of nitrogen and hydrocarbons. Nitrogen

oxides in the presence of sunlight react with unburnthydrocarbons to form peroxyacyl nitrate (PAN), Ozone,

aldehydes and some other complex organic compounds in the

air.

Hydrocarbons

These are unburnt discharges from incomplete combustion of

fuel in automobiles. These form PAN with nitrogen oxides,

which is highly toxic.


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Particulate MatterIndustries and automobiles release fine solid and liquidparticles into the air. Fly ash and soot from burning of coal,metal dust containing lead, chromium, nickel, cadmium, zincand mercury from metallurgical processes; cotton dust fromtextile mills; and pesticides sprayed on crops are examples ofparticulate pollutants in the air. These are injurious torespiratory tract.

Aerosols

Aerosols are chemicals released in the air in vapour form.These include fluorocarbon (carbon compound havingfluorine) present in emissions from the Jet aeroplanes.Aerosols deplete the ozone layer. Thinning of ozone layerresults in more harmful ultraviolet rays reaching the earth,which are harmful to skin, and can lead to skin cancer also.


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Radioactive Substances

These are released by nuclear explosions and explosives.These are extremely harmful for health.

FluoridesRocks, soils and. minerals containing fluorides release anextremely toxic gas called hydrogen fluoride on heating. Thisgas is highly injurious to livestock and cattle.


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Effects of Air Pollution

Effect on Plants

(i) SO2 causes chlorosis and also results in the death of cellsand tissues.

(ii) Fluorides and PAN damage leafy vegetables such aslettuce and spinach.

(iii) Oxides of nitrogen and fluorides reduce crop yield.

(iv) Smog bleaches and blaze foliage of important leafy plants.

(v) Hydrocarbons cause premature yellowing, fall of leave andflower buds, discoloration and curling of sepals and petals.

(vi) Smoke and dust cover the leaf surface and reducephotosynthetic capacity of plants.

(vii) Ozone damages cereals, fruits, and cotton crop.


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Effect on Man

The effect of pollutants on animals and man are as follows-

(i) Ozone causes dryness of mucous membranes, changes eyevision, causes headache, pulmonary congestion and produce

chromosomal aberrations.

(ii) SO2 causes drying of mouth, scratchy throat, smartingeyes and disorders of respiratory tract.

(iii) SO3, CO and NO2 diffuse into blood stream and reduceoxygen transport. CO damages cardiovascular system.

(iv) Cotton dust leads to respiratory disorders e.g. bronchitisand asthma.


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Effect of Air pollution



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Mathura oil refineries lies only 40 km away from Taj-Mahal-

The oil refineries emits 25-30 tones of SO2 daily in spite ofusing low sulphur fuel.

This results in acid rain the sulphuric acid could react with

calcium carbonate and form soluble calcium sulphate whichwould cause pitting in Taj Mahal.

Steps have been taken to save Taj Mahal.

Establishing of pollution monitoring stations inside Taj Mahal.

Cleaning the effluents emitted by chimney of the oil refinery.

Closing down two thermal power station at Agra.

Developing of green belt of 1 to 5km around the monument.



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Bhopal Gas Tragedy

1984 December 3rd union carbide industry MIC released.2000 people were killed around 30,000 propel were injured.

Do some case study on air pollutant?


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Control of Air Pollution

Gravity settling chambers (GSC)

Cyclones

Electrostatic precipitators (ESP)

Filtration units bag house filters

Wet scrubbers


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Gravity settling chamber


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Cyclone Separator


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Electrostatic precipitator


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Filtration unit


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Wet scrubber


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SO2 pollution can be controlled by extracting sulphurfrom the fuel before use.

Desulphurization process.

Gaseous pollutant


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Summary

Air pollution

Air pollution sources

Air pollution effectsAir pollution case study

Air pollution controlling methods

Gaseous pollution controlling methods

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