8/10/2019 EE-II Unit - I

1/37

Page 1of 37

ENVIRONMENTAL ENGINEERING II

UnitI: Air Pollution sources of pollution classification - effects on human beings Global

effects of Air pollution

1.1 AIR POLLUTION:

Air pollution is basically the presence of foreign substances in air in excessive

concentration which adversely affects the well being of the individual or cause damage to

property and environment.

Definitions

Air pollution may be described as the imbalance in quality of air so as to cause adverse

effects on the living organisms existing on earth.

According to World Health Organizations, air pollution is defined as, substances put into

air by the activity of mankind into concentration sufficient to cause harmful effect to his health,

vegetables, property or to interfere with the enjoyment of his property.

Indian Standards Institute define air pollution as, Air pollution is the presence in

ambient atmosphere or substances, generally resulting from the activity of man, in sufficient

concentration, present for a sufficient time and under circumstances which interfere significantly

with the comfort, health or welfare of persons or with the full use or enjoyment of property.

Structure of Atmosphere:

8/10/2019 EE-II Unit - I

2/37

Page 2of 37

Chemical composition of atmospheric air:

Average composition of clean dry air near sea level (PPM by volume)

Components Concentration in Estimated residencetime

Average conc. ppm Volume present

Major

Nitrogen N2 78.09 x 104 78.09 Continuous

Oxygen O2 20.94 x 104 20.94 Continuous

Minor

Argon Ar 93 x 102 0.93 Continuous

Carbon dioxide CO2 32 x 102 0.0318 2 to 4 years

Trace

Neon Ne 18 0.0018 Continuous

Helium He 5.2 0.00052 ~ 2 million years

Methane CH4 1.3 0.00013 4 to 7 years

Kyrpton Kr 1.0 0.0001 Continuous

Hydrogen H2 0.5 0.00005 Little is known aboutresidence time

Carbon monoxide CO 0.1 0.00001 0.5 year

Ozone O3 0.02 0.000002 ~ 60 days

Ammonia NH3 0.01 0.000001 7 days

Nitrogen Dioxide NO2 0.001 0.0000001 5 days

Slufur Dioxide SO2 0.0002 0.0000002 4 days

Hydrogen Sulfide H2S 0.002 0.0000002 2 days

Xenon Xe 0.081 - Continuous

Historical Overview:

The first incidence of air pollution gets lost in unrecorded history, but it certainly goes back

to the discovery of fire. However, notable air pollution episodes are:

(i) London Smog:In 1661 John Evelyn in his famous pamphlet Fumifugium, recommended

the removal of all smoke producing plants from London. But London did little about it, until

the famous London Smog of Dec. 1952, truly a major air pollution disaster, occurred. Coal

induced smog is formed by interaction of sulphur dioxide, smoke and water to form

sulphuric acid mist. It lasted for five days and caused 4000 deaths. Thereafter, London

experienced many air pollution disasters causing many excess deaths;

In January 1956 - 1000 deaths

December 1957 - 700 deaths

January 1959 - 200 deaths

December 1962 - 700 deaths

January 1963 - 700 deaths

(ii) Meuse Valley Belgium:A strong atmospheric inversion got settled over the Meuse

Valley on Dec. 1, 1930. Effluents from several factories in the valley, like So x and

soot were trapped in the stable atmosphere, 63 persons died and several hundred

others became ill.

8/10/2019 EE-II Unit - I

3/37

Page 3of 37

(iii)

Donora, Pennsylvania (USA):In October 1948, similar conditions led to one of the

first major air pollution disasters in USA. Seventeen people died and 43% of the

population became ill.

(iv) Pittsburgh: Prior to 1948 the nickname of Pittsburgh was Smokey City, and it

seemed to be appropriate as a black pall of smoke and soot often turned day into

night, and blackened the brightest buildings in a few months.

(v)

Los Angeles, California: In early 1950s due to large volume of traffic on Los

Angeles streets, photochemical smog is formed by the interaction of HCs and

oxidants (like NOx, CO, O3) in the presence of sunlight to form toxic PAN and ozone,

causing eye irritation, visibility reduction and damage to crops and rubber cracking.

(vi)

Bhopal Gas Tragedy:The methyl isocynate (MIC) gas leak in Bhopal in December,

1984 has been regarded as the worst industrial accident related to air pollution. At

least 5000 people were killed and some 50,000 people have been seriously affected

by the leak of poisonous MIC gas from the Union Carbide Pesticide Plant.

1.2 Sources of Air Pollutants:

The sources may be natural or anthropogenic (man-made). Natural Sources include

volcanic eruptions, forest fires, cosmic dust, pollen grains.

Emission Sources of Air Pollutants

Natural Sources

Volcanoes

Forest fires

Sulphur springs

Spray from the oceans

Natural geysers

Dispersion of sands and dust

Natural organic & inorganic decays

Vegetative decays

Marsh gases

Extra-terrestrial bodies

Cosmic dust

Pollen grains of flowers

Soil debris

Fungal spores

Photochemical reactions

Domestic burning of wood

Burning of fossil fuels

Industrialization

Agricultural activities

Vehicular emissions

Aircraft

Wars

Nuclear tests

Deforestation

Incineration

Power generation

Mining

Metallurgy

Waste treatment plants

Refrigeration industries

Man-Made Sources

8/10/2019 EE-II Unit - I

4/37

Page 4of 37

Anthropogenic or man-made air pollution sources

Source type Category Important Sources Typical pollutants

Combustion Stationary Power plants, industrialboilers, diesel generators,municipal or industrialincineration

SOx, NOx, CO, smoke, flyash

Roasting andheatingprocesses

Refuse burning Trace metal oxides

Mobile Motor, vehicles, aircraft CO, HC, NOx, SOx,particulates

Non-ferrousmetallurgical

Roasting, smelting andrefining operations

Dust, smoke, metal fumes(Cu, Zn, and Pb), oxides ofsulphur

Ferrousmetallurgical

Material handling, oresintering, and pelletising,coke ovens, blast furnaces,steel furnaces

Smoke, fumes, CO, odours,H2S, organic vapour,fluorides

Non-metallicminerals

Crushed stone, cementglass, refractories, ceramicmanufacture, coal cleaning

Mineral and organicparticulates

Food andagriculture

Food processing

Crop spraying anddusting

Field burning

Drying, preserving,packaging

Pest and Weed control

Refuse burning

Vapour, odour and dustorganic phosphates,chlorinated HC, organic,lead

Smoke, fly ash and soot

Petroleumindustries

Petroleum refining Boilers, process heaters,catalyst regenerators, flares,storage tanks, compressor

engines

SOX, HC, NOx particulatematter, CO, aldehyde,ammonia, odours

Inorganicchemicalindustries

Inorganic chemicals Sulphuric acid plants,fertilizer manufacture, nitricacid and ammonia plants,phosphoric acid manufacture

SOx, HF, H2S, NOx, NH3,particulate matter, H3PO4,etc

Chemicalindustries

Organic chemicals Plastics, paint and varnishmanufacture, syntheticrubbers, rayon, insecticides,soap and detergentmanufacture, Methanol,

phenol, etc

Particulate matter, odours,SO2, CO, organicintermediates, solventvapours

Paper

industries

Pulp manufacture Digester blow oxidation

towers

Mercaptans, dimethyl

sulphide, SO2

Among the emission sources, some are stationary point sources while others are moving

point sources. The pollution from industries is almost continuous. The vehicular pollution waxes

and wanes according to the peak hour traffic during the day and night.

The common air pollutants, their sources and pathogenic effects are given in table below.

Common air pollutants, their sources and pathological effects on man

Pollutant Source Pathological effects on man

Sulphur dioxide Colourless gas produced by coal and Respiratory irritant, aggravate

8/10/2019 EE-II Unit - I

5/37

Page 5of 37

oil combustion and certain industrialsources

asthma and other lung and heartdiseases, reduces lung function

Nitrogen oxides Brownish orange gas produced bymotor vehicles and combustion atmajor industrial sources

Inhibits cilia action so that sootand dust penetrate far into thelungs

Hydrogen sulphide Refineries, chemical industries andbituminous fuels

Causes nausea, irritates eyes andthroat

Carbon monoxide Burning of coal, gasoline, motorexhausts

Reduces oxygen carrying capacityof blood

Hydrogen cyanide Blast furnace, fumigation, chemical

manufacturing, metal plating, etc

Interferes with nerve cells,

produces dry throat, indistinctvision, headache, etc.

Ammonia Explosives, dye making, fertilizer

plants and lacquers

Inflames upper respiratory

passages

Phosgene orcarbonyl chloride

Chemical and dye making Induces coughing, irritation andfatal pulmonary edema

Aldehydes Thermal decomposition of oils, fats,or gylcerols

Irritate nasal and respiratorytracts

Arsines Processes involving metal or acids

containing arseic, soldering

Damage red cells in blood,

kidneys and cause jaundiceSuspended particles(ash, soot, smoke,

etc)

Solid or liquid particles produced bycombustion and other processes at

major industrial sources (e.g. steelmills, power plants, chemical plants,incinerators and almost every

manufacturing process)

Respiratory irritants, aggravateasthma and other ling and heart

diseases (especially incombination with sulphurdioxide); many are known as

carcinogens. Toxic gases andheavy metals absorb onto theseparticulates and are commonlycarried deep into the lungs.Cause emphysema, eye irritationand possibly cancer

Lead Very small particles emitted frommotor vehicles and smelters

Toxic to nervous and blood-forming systems. in highconcentrations can cause brainand organ damage

Ozone A colourless gas formed fromreactions between motor vehicleemissions and sunlight. It is the

major component of smog.

Respiratory irritant, aggravatesasthma and other lung and heartdiseases, impairs lung functions.

Ozone is toxic to plants andcorrodes materials.

1.3 Classifications of Air pollutants:

Air pollutants may be classified according to origin, chemical composition and state ofmatter.

1. According to Origin:

On the basis of origin, air pollutants can be divided into two categories Primary

and Secondary air pollutants.

Primary air pollutants are those which are emitted directly to the atmosphere and

found there in the form in which they are emitted. For example, particulates, carbon

monoxide (CO), oxides of sulphur (Sox), oxides of nitrogen (NOx), hydrocarbons (HCs),

radioactive compounds, particles of metal, pollen, bacteria, etc. The five main primary

8/10/2019 EE-II Unit - I

6/37

Page 6of 37

air pollutants (viz particulates CO, SOx, NOx and HCs) contribute more than 90% of

global air pollution.

Secondary air pollutants are those which are produced in the air by the

interaction among two or more primary air pollutants, or by reaction with normal

atmospheric constituents, with or without photoactivation. For example, ozone (O3),

peroxyacetyl nitrate (PAN), formaldehyde, formation of acid mists, smog (coal induced

and photochemical smog), etc.

2. According to Chemical Composition

On the basis of chemical composition, air pollutants can be divided as organic

and inorganic air pollutants. Organic compounds contain carbon and hydrogen, and

many also contain certain elements such as oxygen, nitrogen, sulphur and phosphorous.

Examples of organic air pollutants are hydrocarbons, aldehydes, ketones, carboxylic

acids, organic sulphur compounds, etc. Inorganic air pollutants include compounds, such

as CO, CO2, SOx, NOx, O3, NH3, CL2, HF, H2S etc.

3.

According to State of Matter:

On this basis, air pollutants are classified as particulate and gaseous air

pollutants. particulate air pollutants include finely divided solids and liquids dispersed in

gaseous media. Dust, smoke, fly ash, flumes, etc., are examples of solid particulates;

while mist, spray, fog etc., are liquid particulate air pollutants. Gaseous air pollutants areorganic gases like benzene, methane, butane, aldehydes, ketones, etc. as well as

inorganic gases like CO2, SOx, CO, NH3, H2S, NOx etc. Aerosols which may be solid

particles (dust, smoke) and liquid particles (fumes, oil mists, polymeric reaction

products)

4. According to Mobility:

Stationary Sources

Point Sources

These are large stationary sources, such as,

industries, power plants, municipal

incinerators, etc.

Area Sources

These are small stationary sources and

mobiles sources with indefinite routes. Such

as, residential heating, commercial and

institutional heating, open burning city traffic,

etc.

Mobile Sources

Line SourcesThese are highways, railway tracks,

navigation routes, etc.

Area SourcesThese are airports, railway stations, ports,

etc.

8/10/2019 EE-II Unit - I

7/37

Page 7of 37

1.4 Effects of Air pollution on Human Health

The air we breathe has not only life sustaining properties, but also life damaging

properties. An average man breathes 22,000 times a day and takes in 16kg of air each day. The

impurities in the inhaled air can affect human health in a number of ways, depending upon the

nature and concentration of the pollutants, duration of exposure, and age group of the receptor.

Depending upon the chemical nature of the pollutants, some pollutants may be harmful when

present in small concentrations and others only if they are present in high concentrations. The

duration of exposure to polluted air is also an important factor. The infants, elders and those

with chronic diseases of the lungs or heart are more susceptible to the effects of air pollution. It

has also been observed that the effect of air pollution on human health is worst or maximum

during winter season, when pollution levels reach a climax. The various health effects are as

under:

i) Eye irritation can be caused by many air pollutants such as NO x, O3, PAN, smog,

particulates.

ii) Nose and throat irritation can be caused by SOx, NOx insecticides, pesticides etc.

iii) Gaseous pollutants like H2S, SO2, NO2 and hydrocarbons can cause odour nuisance

even at low concentrations.

iv)

Irritation of the respiratory tract can be caused by SOx, NOx, O3, CO, etc.

v) Increase in mortality and morbidity rate.

vi) A variety of particulates, particularly pollens, can initiate asthmatic attacks.

vii)High concentrations of SO2, NO2, SPM (suspended particulates matter) and

photochemical smog can aggravate chronic pulmonary diseases like bronchitis andasthma.

viii)Carbon monoxide, which is two hundred times more reactive than oxygen, combines

with haemoglobin in the blood and consequently increases stress on those suffering from

cardiovascular and pulmonary diseases. Similarly, nitric oxide (NO) can react with

haemoglobin and reduce the oxygen carrying capacity of the blood.

ix) Hydrogen fluoride can cause flurosis and mottling of teeth.

x) Air pollutants such as polycyclic organic compounds, aliphatic hydrocarbons, etc. can

cause cancer.xi) Dust particles can cause dust specific respiratory diseases, such as, silicosis (associated

with silica dust), asbestos (associated with asbestos dust), etc.

xii)Heavy metals, like lead (emitted from vehicles), may enter the body through the lungs

and can cause poisoning. Its high concentration can damage liver and kidney, and can

cause abnormality in fertility and pregnancy, and mental development of children gets

affected.

xiii)Exposure to radioactive isotopes like Iodine 131, Phosphorous 32, cobalt 60, Radium

226, etc can cause anaemia (iron deficiency, Ieukaemia (RBC deficiency), cancer and

genetic defects.

8/10/2019 EE-II Unit - I

8/37

Page 8of 37

1.5 Effects of Air Pollution on Plants:

The primary factor that governs the gas absorption by the plant leaves is the degree of

opening of the stomata. The stomata are the openings in the leaf, generally in the bottom of the

leaf, through which CO2enters to play its role in photosynthesis. When the stomata are wide

open (day time), the absorption is maximum and vice-versa. As a result, the same conditions

that enhance the absorption of CO2, also expose the plant to injury by absorbing a pollutant

gas. Most of the plants close their stomata during night and are, therefore, much more resistant

at night. The effects of some of the important air pollutants on plants are given in table 1.2. The

air pollutants that affect plants include SO2, O3, fluorides, NOx, Pan, ethylene, NH3, mercury,

smog, herbicides, etc.

Effects of Air Pollutants on Plants

S. No Pollutant Effects on plants

1. SO2 Bleaching of leaves, necrosis (killing of tissues)

2. O3 Premature aging, suppressed growth, necrosis, bleaching, collapse of

leaf

3. NO2 Suppressed growth, bleaching

4. Fluorides Necrosis at leaf tip.

5. Ethylene Leaf abscission (dropping of leaves), leaf epinasty (downward curvature

of leaf)

6. PAN Suppressed growth, silvering of lower leaf surface.

These pollutants interfere with plant growth / yield, and the phenomenon of

photosynthesis. dust, smog, etc. reduce the amount of light reaching the leaf, and also by

clogging the stomata may reduce the intake of carbon dioxide. Plant response to air pollutants

varies from species to species, for example, some plants are sensitive to fluoride but resistant

to sulphur dioxide. The sensitivity of plants to air pollutants depends on many factors, such as,

climatic conditions (that include duration of light, temperature, humidity, and light intensity),

soil, water and fertility.

1.6 Effects of Air pollution on Animals:

The process by which the animals get poisoned is entirely different from that by which

human beings exposed to air pollutants are poisoned. In case of animals, it is a two-setp

process:

(i) Accumulation of air pollutants in the vegetation and forage; and

(ii) Subsequent poisoning of the animals, when they eat the contaminated vegetation /

forage.

8/10/2019 EE-II Unit - I

9/37

Page 9of 37

The pollutants mainly responsible for most livestock damage are:

Fluorine: Of all the farm animals, cattle and sheep are the most susceptible to fluorine

toxicity. Horses are quite resistant, while poultry are probably the most resistant to fluorine

of all the farm animals. Fluorine is a cumulative poison under conditions of continuous

exposure to subacute doses. Its effects are lack of appetite, rapid loss of weight lameness,

periodic diarrhoea, muscular weakness, wearing of teeth, and death.

Lead: chronic lead poisoning has been observed frequently in animals that have been

grazing near smelters and lead mines. It causes paralysis and difficulty in breathing. In case

of acute lead poisoning, the onset is sudden and the course is relatively short. There is

complete loss of appetite, paralysis and diarrhea.

Arsenic: In acute cases, it can cause severe salivation, thirst, vomiting, irregular pulse and

respiration, abnormal body temperature, and death in few hours. Chronic arsenic poisoning

causes cough, diarrhea, anaemia, abortion, paralysis and death.

1.7 Effects of Air Pollution on Materials:

Air pollution damage to property / material is a very important economic aspect of

pollution, and it covers a wide range:

(i) Corrosion:Air pollution damages materials chiefly by corrosion of metals. The prime

air pollutant responsible for metallic corrosion is SO2. In the presence of oxygen andmoisture, it is converted to sulphuric acid. Deposition of this acid on metal parts of

building roofs, railway tracks, overhead wires, metal on bridges, and other structures

cause enormous loss due to corrosion.

(ii) Damage to building materials:The acid deposition reacts with lime stone, marble,

and other building materials to cause deterioration and disfigured the building

materials.

(iii) Damage to paints and protective covering: Pollutants like SO2, O3, H2S, and

aerosols damage protective coating and paints of the surface.(iv) Damage of textile dyes and textile fibres: The fading of textile dyes and

deterioration of natural and synthetic textile fibres is caused by SOx, NOx and O3.

(v) Rubber Cracking:Rubber cracking of tyres and various forms of electrical insulation

is caused by ozone and PAN.

(vi) Deterioration of leather and paper:Sulphur dioxide causes leather to lose much

of its strength and ultimately disintegrate; which has posed a serious problem of

storage of leather bound books in libraries. The impurities in paper absorb SO2 and

convert it into H2SO4 in the presence of moisture, which makes the paper extremely

brittle and decreases its folding resistance.

8/10/2019 EE-II Unit - I

10/37

Page 10of 37

(vii)

Effect on glasses and ceramics: Although glasses and ceramics are especially

resistant to the chemical action of air pollutants, but long exposure for years showed

a change in their surface appearance.

(viii) Damage to objects of art and architecture:Acid rains cause intangible loss to

objects to art and architecture throughout the world. For example, effects on the Taj

Mahal, Belur Temple, Cleopatras needle (a stone structure in London), Statue of

Liberty, and many more monuments, paintings (such as Ajanta frescos), antique

costumes and other art objects.

(ix) Increased transportation costs in period of smog.

(x) Loss due to reduction in tourists traffic due to effects to air pollutants on art

treasures and tourist centres.

(xi)

Expenditures due to the adoption of technical measures for the reduction of smoke or

other emission from factories.

(xii)

Expenditures in connection with the administrative organization of pollution control.

1.8 Primary air pollutants

1.8.1 Particulate pollutants

Airborne small, solid particles and liquid droplets are commonly known as particulates.

When present in air in excess, they pose a serious pollution threat. The life period of

particulates varies from a few seconds to several months; it depends on the settling rate, size,

and density of particles and turbulence.

Particulates can be inert or extremely reactive materials ranging in size from 100m

down to 0.1m and less. The inert materials do not react readily with the environment nor do

they exhibit any morphological changes as a result of combustion or any other process, whereas

reactive materials could be further oxidized or may react chemically with the environment.

Classification of Particulates:

Dust: Particulates of size 1-200m belong to this category and are formed by the natural

disintegration of rocks and soil or by mechanical processes like grinding and spraying.They are removed from the air by gravity and other inertial processes by large settling

velocities and also act as centres of catalysis for many of the chemical reactions taking place in

the atmosphere.

Smoke: Particles of size 0.01-1m constitute smoke which can be either in the liquid or solid

form and is formed by combustion or other chemical processes. Smoke may have different color

depending o the nature of materials burnt.

Fumes: Solid particles of size 0.1-1m which are normally released from chemical or

metallurgical processes belong to this category.

8/10/2019 EE-II Unit - I

11/37

Page 11of 37

Mists:Liquid droplets generally smaller than 10m which are formed by condensation un the

atmosphere or released from industrial operations represent mist.

Fog:It is the mist in which the liquid is water and is sufficiently dense to observe vision.

Aerosols:All airborne suspensions, either solid or liquid belong to this category and these are

generally smaller than 1m.

Particles of size 1-10m have measurable settling velocities but are readily stirred by air

movements, whereas particles of size 0.1-1m have small settling velocities. Particles below

0.1m, as submicroscopic size found in urban air, undergo random Brownian motion resulting

from collision among individual molecules.

Effects of particulate pollutants on human health:

The effects of particulate pollutants are largely dependent on the particle size. Airborne

particles, i.e. dust, soot, fumes, and mists are potentially dangerous to human health. The nasal

system prevents coarser particulates bigger than 5 microns from entering the respiratory

system. Soluble aerosols will be absorbed into the blood from the alveoli while the insoluble

aerosols are carried to the lymphatic stream and get deposited in pulmonary lymphatic depot

points or in the lymph glands, where they create toxicity in the respiratory system. Lead

interferes with the development and maturation of red blood cells. It is respond that a smoker

can easily develop symptoms of asthma which is also due to a concentration of lead greater

than in non-smokers.

Effects of particulate pollutants on materials:

Particulates affect a variety of materials in various ways. They cause damage to

buildings, paints, furniture, etc. Painted surfaces are very susceptible to damage in wet

conditions.

1.8.2 Sulphur oxides:

SO2is an unpleasant and highly irritating gas, when it is present in concentration greaterthan 1 ppm and adversely affects men, animals, plants and materials. It is perhaps the most

damaging among the various gaseous air pollutants. Along with SO2, SO3 is discharged, at

about 1-5 percent of the SO2 concentration, and it combines rapidly with moisture in the

atmosphere to form Sulphuric acid which has a low dew point. Both these oxides are rapidly

removed from the atmosphere by rain or settle out as aerosol due to which their concentration

is less compared to their emissions from human activities.

Sources of Emission of Sulphur oxides:

The global sulphur fluxes per year into the atmosphere by anthropogenic and natural

sources are shown in fig.

8/10/2019 EE-II Unit - I

12/37

Page 12of 37

Sulphur dioxide is one of the principal constituents of air pollutants. It is a colourless,

non-flammable and non-explosive gas with a suffocating pungent odour. It has an odour

threshold of 0.5ppm, and a taste threshold of 0.3ppm. It is highly soluble in water, and is about

twice as heavy as air. SO2 remains airborne for an average period of 2-4 days, during which

time it may be transported as far as 1000km. Therefore, the problem of SO2 pollution is an

international one. The background level for sulphur dioxide in ambient air ranges from 0 to

0.02ppm. It is produced from the combustion of sulphur-bearing materials.

S + O2 SO2

SO2Sinks:

Sulphur dioxide is relatively stable in atmosphere, and acts either as a reducing or an

oxidizing agent. Reacting photochemically or catalytically with other components in the

atmosphere, it produces sulphur trioxide (SO3), Sulphurous acid (H2SO3), Sulphuric Acid

(H2SO4).

The end product (i.e., H2SO4 or its salts) reaches the earths surface either as wet

deposits or dry deposits, and forms sulphates.

8/10/2019 EE-II Unit - I

13/37

Page 13of 37

Effects:

The oxides of sulphur have pronounced effects not only on human health but also on

plants and materials.

Sulphuric acid, Sulphur dioxide and sulphate slats tend to irritate the mucous

membranes of the respiratory tract and fasten the development of chronic respiratory diseases,

particularly bronchitis and pulmonary emphysema. The most widespread disaster due to SO2

occurs when it is

Concentration ppm Effects

0 to 1.0 No detectable response

1.0 to 2.0 Cardio respiratory response in healthy persons

2.0 to 5.0 Detectable responses, tightness in chest

5.0 to 10.0 Choking and increased lung resistance to air flow

10.0 to 20.0 Severe distress, some nose-bleeding

> 20.0 Digestive tract affected, eye irritation

400 to 500 Fatal

The effects of SO2concentration in ambient air depend on the exposure time, age group

and health of the receptor.

Accompanied by smoke, i.e. during smog formation with fine particulates. SO2 is

particularly harmful because both sulphur dioxide and sulphuric acid molecules paralyse the hair

like cilia which line the respiratory tract. Without the regular sweeping action of the cilia,

particulates are able to penetrate to the lungs and settle there. These particulates usually carry

with them concentrated amounts of sulphuric acid and SO2, thus bringing these irritants into

direct and prolonged contact with the delicate lung tissues. The SO2 particulate combination

(smog) has been cited as cause of death in several air pollution tragedies, like Meuse Valley

episode (1930), Donora Pennsylvania tragedy (1942), London episode (1952), and many more.

Effects on Plants or Vegetation:

Effects on plants can be classified as acute or chronic. The SO2 concentration in acute

exposure is high for a short period, resulting in the damage characterized by clearly marked

dead tissues between the veins or on the margins of the leaves (called leaf necrosis); chronic

injury comes from exposure to low concentration for long periods of time, which causes

brownish-red or bleached white areas on the blade of the leaf. The plant injury threshold for

SO2 is about 0.3 to 0.4 ppm exposure for eight hours. Plants are particularly sensitive to SO 2

during day periods of intense light, high relative humidity, adequate moisture and moderate

temperature. They are generally more sensitive during growing seasons, regardless of climate

conditions. Plants vary widely in their vegetables such as beans, spinach and lettuce, and trees

such as apple, mulberry and pine are particularly sensitive to sulphur dioxide. While potatoes,

onions and corn are more resistant to sulphur dioxide.

8/10/2019 EE-II Unit - I

14/37

Page 14of 37

Effects on Materials:

Sulphur dioxides effect on materials is quite significant. Paper absorbs SO2, the sulphur

dioxide is oxidized to H2SO4, and the paper yellows and becomes brittle. Similarly, leather also

weakens and disintegrates in the present of SO2. Due to these reasons, libraries store leather

bound books and historical documents in carefully controlled environments. Excess exposure to

SO2 accelerates corrosion rates of many metals (such as iron, steel, zinc, copper and nickel) at

higher relative humidities. The accelerated corrosion is particularly noticeable in winters when

more fuel is burned. Corrosion rates are about 1.5 to 5.0 times more in polluted urban areas

than in clean air areas. Sulphuric acid aerosols readily attack building materials, especially those

containing carbonates (such as marble, limestone, slate and mortar).

The carbonates are replaced by sulphates which are water soluble.

1.8.3 Oxides of Nitrogen (NOx):

On the seven oxides of nitrogen, viz, nitrous oxide (N2O), nitric oxide (NO), nitrogen

dioxide(NO2), nitrogen trioxide (NO3), nitrogen sesquioxide (N2O3), nitrogen tetraoxide (N2O4)

and nitrogen pentaoxide (N2O5), that exist in ambient air, only two oxides of nitrogen (NO and

NO2) are primarily involved in air pollution. Nitric oxide (NO) is a colourless and odourless gas;

while nitrogen dioxide is a reddish-brown gas having a pungent suffocating odour. Nitric oxide is

emitted to the atmosphere in much larger quantities than nitrogen dioxide, Typical background

levels of NO are about 2 to 3 ppb, and for NO 2about 4.0 to 5.0 ppb. Nitric oxide is formed in

high temperature combustion processes when atmospheric oxygen and nitrogen combine

according to the following reaction.

The major process by which NO2is formed in the atmosphere is

NO + O3 NO2+ O2

Nitric oxide and nitrogen dioxide remain airborne for average residence period of about 4

days and 3 days respectively.

Sources and sinks:

Some oxides of nitrogen are produced naturally, while others are anthropogenically

produced. Bacterial decomposition of organic matter releases NOxinto the atmosphere, mainly

in the form of nitric oxide. Small concentrations on NO xproduced in the upper atmosphere by

solar radiation reach the lower atmosphere through downward diffusion. NOxare also produced

by lightning and forest fires. In fact, naturally occurring sources of NOx produce about ten times

as much of NOxas do the anthropogenic sources. The natural sources of NOx are more or lessuniformly distributed on global basis, while anthropogenic sources are concentrated in urban

8/10/2019 EE-II Unit - I

15/37

Page 15of 37

areas. Primary origins of human induced NOxare from fuel combustion in transportation and in

stationary sources (power and heating), industrial processes in which nitric acid is used,

emissions from electric utilities, mining and electric arc welding.

Nitrogen dioxide, which is heavier than air, is readily soluble in water forming nitrous or

nitric acid. There are various photochemical reactions which take care of NOxand give nitric acidas the end product as indicated in the following reactions:

2NO2+ H2O HNO3+ HNO2

3NO2+ H2O 2HNO3+ NO

2NO + O2 2NO2

NO2+ O3 NO3+ O2

NO3+ NO2 N2O5

N2O5+ H2O 2HNO3

Both nitrous and nitric acid will fall out in the rain or combine with ammonia (NH3) in theatmosphere to form ammonium nitrate (NH4NO3). In this instance, the nitrogen oxides will

produce a plant nutrient.

Health effects of NO2on humans

Concentration ppm Effect

0.12 Odour threshold

0.7 to 2.0 Increased resistance of the lungs airways

5 to 20 Eye and nasal irritation

20 to 50 Pulmonary discomfort

50 to 100 Inflammation of lung tissues100 to 150 Bronchiolitis fibrosa obligerans

>150 Fatal

Effects:

Oxides of nitrogen are the second most abundant (next to SOx) air pollutants in many

cities. Like SOxthey too have effects on human health, plants and materials.

Nitrogen dioxide has more harmful effects in human health as compared to nitric oxide.

Table () indicates the health effects of NO2 on humans. Exposure to NO2, even at low

concentrations, can lead to increased resistance of the lungs airways to air movement,

increased frequency of acute bronchitis among infants and older persons, increased incidence of

respiratory illness, and irritation to the alveoli of the lungs.

Nitric oxide (NO) is a relatively inert gas and moderately toxic. Nitric oxide, like carbon

monoxide, can combine with hemoglobin to reduce oxygen carrying capacity of the blood. NO

concentrations are generally less than 1.0 ppm in the ambient air and are, thus, not considered

health hazards.

8/10/2019 EE-II Unit - I

16/37

Page 16of 37

There is no evidence that NO cause damaging effects on plants while NO2 can cause

some injury to vegetation. Infact, secondary pollutants produced during photochemical

reactions involving NOx, such as PAN and O3, are far more likely to be damaging to plants.

Effect on materials includes fading of textile dyes, yellowing of white fabric and oxidation

of metals when exposed to high levels of NO2.

Nitrous oxide (N2O) or laughing gas, which is often used as a dental anesthetic, is an

important greenhouse gas. It is not believed to have any harmful effects as an air pollutant

except in its role as a greenhouse gas (refer Art.6.7) One N2O molecule is about 200 times as

effective as one CO2molecule, as a greenhouse gas.

1.8.4 Carbon Monoxide (CO):

It is a colourless, tasteless and odourless gas. It is slightly lighter than air (0.965 times as

heavy as air) and is insoluble in water. It is chemically inert under normal conditions and has an

estimated atmospheric life of about two and a half months. It is a poisonous gas and is

generally classified as an asphyxiant. The atmospheric background of CO is 0.1 ppm. It is

produced by

(i) Incomplete burning of the carbon in fossil fuels

2C + O2 2CO

(ii) Reaction between carbon dioxide and carbon containing materials at very high

temperatures in industrial processes, such as in electric and blast furnaces.CO2+ C 2CO

(iii) And by dissociation of carbon dioxide at higher temperatures

Sources and Sinks:

Carbon monoxide sources are both natural and anthropogenic. The natural sources are

volcanic eruptions, natural gas emissions, forest fires, oxidation of methane gas from decaying

vegetation, electrical discharge during storms, etc. The anthropogenic sources are motorvehicles, aircrafts, railways, industries (such as iron and steel, petroleum and paper industries,

electrical and blast furnaces, etc.), fuel combustion in stationary sources for power and heating,

agricultural burning, solid waste disposal, etc.

The major carbon monoxide sink is some soil micro organisms. These soil sinks can take

care of atmospheric carbon monoxide, but neither CO nor the sinks are distributed uniformly. In

fact, the highly populated urban areas having the highest ambient CO concentration often have

the least amount of available soil sinks.

8/10/2019 EE-II Unit - I

17/37

Page 17of 37

Health effects of COHb at various levels in the blood

COHb level % CO level ppm Effects

302 Cardiac and pulmonary functional changes

10 to 25 30 to 200 Headaches and dizziness

25 to 40 200 400 Loss of consciousness

40 to 60 400 750 Respiratory failure, coma, death after several hours

>65 >1000 Rapid death

Effects:

At present ambient levels, carbon monoxide has little, if any, effect on property,

vegetation or materials. But it can seriously affect human aerobic metabolism, due to its high

affinity for hemoglobin (Hb). It reacts with the hemoglobin of blood and displaces oxygen to

form carboxy hemoglobin (COHb), thus, reducing the capability of the blood to carry oxygen.

Since the affinity of hemoglobin for CO is about 200 times more than for oxygen,

therefore carbon monoxide can seriously impair the transport of oxygen even when present at

low concentrations. The health effects observed in persons exposed to CO are indicated in Table

(). As COHb levels increase, effects become more and more severe. It must be kept in mind

that the absorption of CO by the body increases with the performed. Carbon monoxide is

believed to impose an extra burden on those already suffering from anemia, disease of heart

and blood vessels, chronic lung disease, overactive thyroid or even fever. It also affects central

nervous system, and is responsible for heart attack and high mortality rate.

However, the carbon monoxide poisoning can be cured by exposing the effete person to

fresh oxygen. The following reverse reaction takes place:

1.8.5 Ozone (O3):

Ozone is a bluish gas with a pungent odour. It can be created by passing a high voltage

through dry atmospheric air between two stationary electrodes. It is unstable and breaks down

to normal oxygen and nascent oxygen (which is a powerful oxidizing agent).

Natural ozone mainly occurs in the stratosphere (between 16 to 40km), where it serves

a vital biological role in absorbing high energy photons of ultraviolet radiation from sun and

hazardous effects of UV-B radiations*. Natural ozone is also present in troposphere, where ithas a background concentration of about 0.02ppm. Some of this tropospheric ozone has

8/10/2019 EE-II Unit - I

18/37

Page 18of 37

diffused down from stratosphere, while the remainder is formed photochemically from the

action of UV photons on natural NOx. Though only about 10% of atmospheric ozone occurs in

the troposphere (remaining 90% occurs in the stratosphere), but due to its strong oxidizing

nature it has harmful effects on plants, animals, human beings and materials.

Thus we can say that Ozone is a life savior, if present in stratosphere; but a pollutant, if present

in troposphere.

Sources and Sinks:

Ozone is a major concern in air pollution. Mainly it is produced in the stratosphere, but a

small concentration diffused downwards. Also small amount is produced by lighting and forest

fires. The emission of precursors hydrocarbons, CO and NOx, mainly from vehicles, is

responsible for higher ozone concentrations in the troposphere.

Nitric oxide (NO) present in atmosphere reacts with ozone and is thus, responsible for

the elimination of ozone.

Effects:

Ozone is a smelly and poisonous (at higher concentration) gas. Ozone, which is a major

component of photochemical smog along with PAN, has an irritant action in the respiratory track

reaching much deeper into lungs than oxides of sulphur. It can cause coughing, shortness of

breath, air-way constriction, headache, chest tightness, altered red blood cells and eye, noseand throat irritation.

The effects of ozone on plants include premature aging, suppressed growth, necrosis

(killing of tissues), bleaching and collapse of leaf.

Being an extremely active compound, ozone readily oxidizes paints, textile fibres, dye

and elastomers (such as rubber). In fact, the cracking of tyres has become a serious economic

problem. Though, technology is available to protect elastomers but only at significantly highcost.

1.8.6 Fluorides:

HF is a highly corrosive and irritant gas. A typical fluoride concentration in the

atmosphere is 0.05mg/m3. Because of its extreme toxicity, HF is a problem wherever processed

involving fluorides take place, such as in the production of phosphate fertilizers, smelting of

certain iron ores, and manufacturing of aluminium.

8/10/2019 EE-II Unit - I

19/37

Page 19of 37

Emission sources:

Fluorine is a gas so reactive that it does not occur naturally in elemental form. However,

many fluoride-containing minerals such as fluorspar, cyrolite, and certain appetites and used by

industry. Some industries also produce HF either as a byproduct or to form various useful fluoro

derivatives.

Industrial and commercial processes involving fluorine compounds which may release

fluoride and HF

Emission processes Processes using large amounts of

fluorine-derivates

Aluminium smelting Clouding of electric bulbs

Steel production Cut glass finishing

Phosphate fertilizers Aviation fuel production

Enamel and pottery manufacture Insecticides and rodenticides

Brick making Separation of uranium isotopes

Missile Propulsion Synthesis of plasticsBeryllium, zirconium, tantalum and niobiumpurification

Aerosol, refrigerant and lubricantmanufacture

Cleanings of castings Wood preservation

Welding Cement reinforcing

Sandstone and marble cleaning Furniture cane bleaching

Crolite, fluorspar and apatite mining Water supplementation

Industrial emissions are superimposed upon significant natural background sources.

Consequently, levels in both air and water supplies vary widely. The majority or rural and urban

air monitoring sites record very low levels of atmospheric fluoride measured as total dissolved

fluoride. Near phosphate fertilizer plants, aluminium smelters, or volcanoes, however levels may

rise above 200 ppm. Water supplies around these areas may also show elevated levels, well

above the 1 ppm recommended as an optimum to provide an acceptable incidence of dental

cares and at the same time allow for the correct bone growth of children.

Hydrogen fluoride and fluoride ions effects on animals and human ubiquitous

by product:

Food and drinks are the most important sources of human fluoride intake. Normally,

these contain below 1 mg 1-1 of fluoride. Tea, fish and other sea foods are heavily laden

exceptions. Other vegetables and cereals grown in areas subjected to high fluoride emissions

may also be enriched in fluoride. The various physiological effects of fluoride in animals and

humans are shown in table below.

Physiological effects of fluoride in animals and humans

Process Disturbance

Carbohydrate metabolism Glycogen levels depleted glycogen turnover depressed

phosphorylase activity reduced

Lipid metabolism Activation of acetate inhibited liver lipases activated certainesterases inhibited

8/10/2019 EE-II Unit - I

20/37

Page 20of 37

Mineral metabolism Interference in iron uptake sulphite and phosphate counteractthe inhibiting effect of Ca2+upon intestinal absorption

Hormonal balances Effect on parathyroid function a

* Calcium levels are influenced by parathyroid hormone produced by the parathyroid and a

hormonal derivative of vitamin D (called 1,25 dihydroxyl cholecacalciferol) found in the liver

and kidneys both of which raise blood serum levels of calcium. Release of calcitonin from the

thyroid, however, causes enhanced calcification of the bone tissues which then reduces blood

calcium levels again.

Effects on plants

Fluoride deposition on plants not only causes them damage but may result in a second

untoward effect. Grazing animals may accumulate an excess of fluoride, which mottles their

teeth and ultimately causes to fall out.

Problems associated with fluoride in plants are well known in relationship to fluorosis in

farm animals. Animals grazing on pasture very close to brick works, smelters and phosphate

fertilizer factories, or fed forage gathered from such area, may shoe fluorosis, a condition also

occasionally found in humans. The major recommendation has been to ensure that the yearly

average fluoride content of herbage does not exceed 40 mg 1-1a-1.

Application of lime to crops and herbage has long been known to be a practical means of

reducing the effects of fluoride injury. Originally, it was thought the lime caused the

immobilization of the fluoride on the surfaces of the leaves as insoluble calcium fluoride.

However, calcium chloride spraying has a similar alleviating effect to lime and recent studies

have shown that the remedy actually relies upon additional calcium entering the leaves to

interact with the fluoride inside and redress any calcium imbalances in the regulatory processes.

Accumulation by plants:

Crop less in the USA due to fluoride is ranked fourth in importance after O 3, SO2 and

nitrogen based air pollutants. However, on a weight for weight basis, fluoride is the most

phytotoxid of all atmospheric pollutants. Injuries to the most susceptible plants occur atconcentrations between 10 and 1000 times lower than those of other air pollutants. Rates of

uptake of fluoride into leaves are also faster than those of any other pollutant and go on to

cause problems to animals feeding upon these plants.

Both gaseous and particulate fluorides are deposited on plant surfaces and some

penetrate directly if the leaf is old or weathered. Nevertheless, the main access into a plant is

by HF entering through the stomata. An important feature of fluoride uptake and transport in

plants is that it is later carried in the transpiration stream towards the leaf tips or margins

where it accumulates and phytotoxid effects usually develop. Plant species show wide ranges of

susceptibilities to fluoride but environmental factors, such as light, temperature, humidity,

8/10/2019 EE-II Unit - I

21/37

Page 21of 37

water stress, etc., all influence plant response. Young conifers, gladioli, peaches and vines are

especially sensitive while tea and cotton are very resistant.

There are several mechanisms, which reduce fluoride levels in plants. These include

shedding of individual leaves or surface waxes, leaching by rain, or voltalization. Fluoride levels

are often lowest during summer months because of more favourable meteorological conditions

for better dispersal of fluoride pollution and greater turnover of leaves in grass swards during

summer.

There are many reports of changes in photosynthesis, respiration or metabolism of

amino acids, proteins, fatty acids, lipids and carbohydrates in plants due to fluoride. Certain

enzymes are modulated by the presence or absence of fluoride but these do not explain the

wide range of metabolic changes known to occur. These are due to interactions between

fluoride and calcium or magnesium. Calcium and fluoride together for example, stimulate

phosphate uptake which means that calcium adsorption sites on cell membranes are involved in

response to fluoride. Cytoplasmic calcium is a ubiquitous regulator of cell metabolism and

many, but not all, of its effects ae mediated by a calcium-binding protein calmodulin, which in

turn stimulates a variety or enzymes. Moreover, calcium ions are known to affect the transport

selectivity of membranes with respect to other substances. Because of this, fluoride exerts an

effect in various regulatory activities (table ()) and this probably explains why it is so phytotoxic

at such low concentration.

Fluoride also forms magnesium-fluorophosphate complexes and, consequently

manyenzyme pathways are adversely affected by fluoride. Most reactions involving ATP, for

example, require additional magnesium complexes to function correctly. If these natural

complexes are also disturbed by the presence of additional fluoride then key reactions are

inhibited.

Normally, soils contain between 20 and 500mgg-1 fluoride but, because it has limited

solubility in soil water, uptake by roots is relatively low, and there is little relationship between

soil fluoride and total plant fluoride content. Consequently, atmosphere sources of fluoride are

more important than fluoride in groundwater in determining the amount of fluoride in or on a

crop.

Physiological effects on fluoride on plants

Process Disturbance Likely cationinteraction

Respiration and Glycolysis inhibited Mg2+

Carbohydrate Pentose phosphate pathway

Metabolism Enhanced Mg2+

Unusual mitochondrial swelling Mg2+

Oxidative phosphorylation reduced Mg2+

Photosynthesis Unusual chloroplast structure Mg2+

Inhibited pigment synthesis Mg2+

Increased PEPCa activity Mg2+

8/10/2019 EE-II Unit - I

22/37

Page 22of 37

Reduce electron flow Ca2+

Amino acid and Increases in free amino acids

Protein metabolism And asparagines Ca2+/Mg2+

Decrease in ribosome sizes Ca2+/Mg2+

Nucleic acid Changes in transportation and

Metabolism Translation Ca2+/Mg2+

Fatty acid and lipid Increased esterase activities Ca2+/Mg2+

Metabolism Decreased unsaturated /saturated ratios Ca2+/Mg2+

Other metabolic a Increase in peroxidase activities Ca2+/Mg2+

Changes Decrease in acid phosphatase

Activity Ca2+/Mg2+

Transport and Altered plasma membrane Ca2+

Translocation ATPases

Fruit development Poor fertilization and seed

Germination Ca2+

Reduced pollen tube growth Ca2+

Reduced seed number and fruit size Ca2+

1.8.7 Hydrocarbons (HCs):

Hydrocarbons are those organic compounds which contain only carbon and hydrogen.

Like CO, they represent unburned and wasted fuel. Most of the major chemicals in gasoline and

other petroleum products are hydrocarbons, which are divided into two categories aliphatic and

aromatic.

Aliphatic hydrocarbons group contains alkanes, alkenes and alkynes. The alkane are

saturated bydrocarbons (i.e., methane) and are fairly inert, and generally not active in

atmospheric photochemical reactions. The alkenes, generally called olefins, are unsaturated and

highly reactive in atmosphere, The alkenes (such as ethylene), in the presence of sunlight,

react with nitrogen dioxide at high concentrations to form secondary pollutants such as PAN

(peroxyxcetyl nitrate) and ozone, The alkynes, through highly reactive, are relatively rare and

thus not of major concern in air pollution.

Aromatic hydrocarbons are biochemically and biologically active, and some are

potentially carcinogenic. They are derived from or related to benzene. Though aromatics do not

display the reactivity characteristics of unsaturated aliphatic hydrocarbons, but the polynuclear

group of aromatic hydrocarbons is carcinogenic.

Sources and sinks:

Hydro carbons present in the atmosphere are from both natural and anthropogenic

sources. Most of the natural hydrocarbons are from biological sources, though some amounts

come from geothermal areas, coal fields, natural gas from petroleum fields and natural fires.

The more complex naturally produced HCs found in the atmosphere (such as volatile terpenes

and isoprene) are produced by plants and trees. The terpene molecules combine to form

aerosols that produce the blue-haze over forested areas. The estimated natural emission of

8/10/2019 EE-II Unit - I

23/37

Page 23of 37

hydrocarbons in atmosphere is about 7.4 x 108 tons per year, which is about 85% of the total

estimated emissions of HCs. Methane (CH4) is the major naturally occurring hydrocarbons

emitted in the atmosphere. It is produced in the anaerobic decomposition of organic matter in

water or soil. Natural background levels of methane in the atmosphere range from 1.2 to 1.5

ppm on global basis. The average residence time of CH 4 is about 3 to 7 years in the

atmosphere.

The anthropogenic sources contribute about 15% of the total estimated emission of HCs

in the atmosphere. The major anthropogenic sources of hydrocarbons are industrial sources

(notably refineries) and transportation (particularly automobiles). The maximum concentration

as well as emissions of hydrocarbons from human activities are generally found in areas of high

population density (due to high traffic density). Some of the important HCs emitted from these

sources are ethane, propane, n-butane, isopentane, n-pentane, isobutene, ethylene, acetylene,

toluene, xylene, etc. Hydrocarbon emissions from solid waste disposal agricultural burning andcoal waste fires also contribute to anthropogenic sources.

Several chemicals and photochemical reactions are responsible for the removal of HCs

from the atmosphere. As they are thermodynamically unstable towards oxidation, therefore,

they tend to be oxidized through a series of steps. The end products of oxidation are CO2, solid

organic particulate matter or water soluble products, which are removed from atmosphere by

dry or wet deposition.

Effects:Hydrocarbons are generally not toxic at concentrations normally found in the

atmosphere, but they are major pollutants because of their role in the formation of

photochemical smog.

Experimental tests on humans and animals with aliphatic hydrocarbon concentrations of

500 ppm produce no harmful effects. But plynuclear group of aromatic hydrocarbons from

automotive exhaust emissions are carcinogenic in nature.

Ethylene, produced in automobile exhaust, is one of the very few hydrocarbons that can

cause plant damage even at low concentrations. Tomato and pepper plants and orchids can be

severely damaged if they are exposed to ethylene (0.01 to 0.3 ppm) for longer duration.

1.8.8 Ammonia:

Ammonia (NH3), which is a pungent gas, is used as a raw material in large quantities

used by industries for the synthesis of ammonium nitrate, plastics, explosives, dyes and drugs.

Further it is also used as a refrigerant.

8/10/2019 EE-II Unit - I

24/37

Page 24of 37

Emission sources:

Emission of NH3from the biological degradation of proteins on soil surfaces into the atmosphere

occurs in a very large scale which is known as NH3 volatilization and compared to this the

industrial contribution is negligible. Atmospheric concentrations of NH3 in temperate rural

regions range from 5 to 10 ppm but are much higher near the equator. In urban regions, higher

levels of NH3 upto 280ppm are recorded which may be found in increasing levels close to

industrial and intensive agricultural sources. In some developed countries, atmospheric levels of

NH3are still rising with accelerated use of artificial fertilizers and higher stocking rates of farm

animals.

NH3 readily forms cations or complexes of varying stability which effects the rate of

volatilization. Most important among these is the affinity of NH3with H2O to from ammonium

ions which is strongly enhanced by increased alkalinity (as shown below). This means that

there is an increased likelihood of NH3volatilization at high pH.

Variation of CO2level or changes in temperature will have a marked influence on the NH3

NH4+ relationship as both ionization of H2O and the dissociation of NH3 are temperature

dependent. Furthermore, exchange of NH3between solution and the air above varies markedly

with temperature.

In soils, NH3 may be either adsorbed onto clay or organic particles and react with

carbonyl and other acidic groups to from exchangeable salts, or it may combine with other

organic components to form non-exchangeable products. In view of this different soils have

different rates of NH3volatilization and these, inturn, are affected by their water contents. As

OH- ions are removed in process of conversion on NH4+to NH3

-. As NH3is volatilized from the

soil surface to the atmosphere, the soil solution becomes acidified at rates which depend on the

soil buffer capacity. In view of this volatilization of NH3 is more likely from soils where the

acidity produced can be neutralized by high levels of carbonate or other forms of alkalinity

which explains why larger emissions of NH3occur from natural calcareous soils or after liming.

The anions present in applied fertilizers also effect the rate of NH3 volatilization from

soils. Urea is frequently uses as an alternative fertilizer because the enzyme urease, which is

widely distributed in plants, microbes and soils, catalyses the hydrolysis of urea to bicarbonate

and NH4+. As urease activity tends to be greater in soils with large organic contents and rather

less in calcareous soils, the usual increase of NH3volatilization form alkaline soils and decrease

from acid soils is reversed when urea is used as fertilizer.

8/10/2019 EE-II Unit - I

25/37

Page 25of 37

NH3volatilization also takes place with the higher rate from stored animal manures in

stock-yards or from sewage works. The factors involved are similar to those of applied slurries

on fields. Periodic addition of fresh material to the tops of piles of manure or the agitation of

sewage ponds, therefore, greatly accelerates rates of NH3 volatilization. Most NH3 in the

atmosphere arises from the directly hydrolysis of the urea in animal urine, other contributions

being of less importance.

In Europe, as much as 10% of useful N is lost directly by NH3 volatilization and, in

warmer climates, this can rise to as much as 30%. The amounts of N released into the

atmosphere globally by NH3volatilization are very large-between 115 and 245 millions of tons

of nitrogen oxide. Background atmospheric levels of NH3 over Belgium, Denmark, and the

Netherlands, which are intensive arable and livestock-raising countries, are often around 25ppm

with peaks up to 75ppm NH3. Estimates of total N released into the atmosphere from these

countries are especially high.

The large releases of NH3 to the atmosphere over the last three decreases are due to (a)

increased animal stocking levels, (b) increased human population, (c) increased use of artificial

fertilizers, in the form of either NH4+nitrate or urea, and (d) decreased, sinks for NH3or NH4

+

uptake. The first three go hand in hand. As material standards improve, humans move from

plant-orientated to animal-based diets. This means more food has to be grown to feed animals

and this can only be done by using more artificial fertilizer.

Much could be done to reduce N losses associated with applications of N fertilizers due to

NH3volatilization and run-off of excess nitrate into ground waters. Direct injection of anhydrous

NH3or urea at the right depth into soil has not yet been extensively exploited. Even substituting

urea for NH4+in irrigation waters will reduce losses due to NH3volatilization below 2% in poorer

regions where N is unduly expensive, and losses by this route tend to be greater because of

higher temperatures.

Removal of ammonia from the atmosphere:Once in the atmosphere, NH3 neutralizes sulphuric or nitric acids and, by decreasing

acidity, promotes the oxidation of SO2 to sulphate by O3. Normally, atmospheric NH3 has an

average lifetime of 0.5h before conversion to NH4+. At wind speeds of 10ms-1, therefore, a

molecule of NH3travels about 18km before it turns into NH4+.

Measurement of rates of NH3deposition is complicated because some intensively farmed

lands give off more NH3 than they receive. On the other hand, fluxes towards damp acidic

ecosystems are considerable and cannot be accounted for by stomatal uptake alone as they

from perfect sinks for NH3. For example, the uptake rate of wet health land in the Netherlands

may be as high as 100 kg N ha-1a-1.

8/10/2019 EE-II Unit - I

26/37

8/10/2019 EE-II Unit - I

27/37

Page 27of 37

may contain considerably higher concentration under pressure commonly found in deep

aquifers. It imparts an unpleasant taste and odour to water even in small concentrations. It is

not toxic in low concentrations that normally exist in the atmosphere (0.002ppm), but is toxic in

high concentrations. The threshold limit value (TLV) of hydrogen sulphide is 10ppm.

Sources and Sinks:Hydrogen Sulphide is a biological waste product from anaerobic bacteria decomposition

of organic matter in the soil, or a by-product of reduction of sulphur from mineral deposits. It

may be present in appreciable quantity in ground waters. In atmosphere, H2S and SO2coexist.

Hydrogen sulphide is produced by the reduction of sulphate and organosulphur compounds by

the bacterium Desulphovibrio desulphuricans and associated with methane thial (CH 3.S.H.).

dimethyl sulphide (CH3.S.CH3) and carboxyl sulphide (C.O.S). All these species have

objectionable odour, even at low concentrations. Hydrogen Sulphide is not so stable, and is

readily oxidized in air.

Effects:

Exposure to hydrogen sulphide for short periods can result in fatigue. But high

concentrations of H2S due to accidental release often cause fatalities. This occurs in the

production and processing of sour gas and oil, which contain hydrogen sulphide. There are

many incidences of leakages if H2S from natural gas processing plans killing hundreds of people.

1.9 Secondary air Pollutants

Secondary air pollutants are chemical products that are formed from the reactions ofvarious primary air pollutants with one another; some of the important secondary pollutants are

products of photochemical reactions;

8/10/2019 EE-II Unit - I

28/37

8/10/2019 EE-II Unit - I

29/37

Page 29of 37

concentrations of the species are low). However, human activities emit not only Nox to the

atmosphere but also carbon monoxide hydrocarbons and carboxyl compounds. By their

reactions with hydroxyl radicals, they disturb the NO2 photolytic cycle and, thus, not only

prevent the reaction of ozone with NO but also cause the accumulation of ozone,

peroxyacylnitrates (PAN), and other constituents of photochemical smog. In addition, the

photolytic decomposition of carbonyl compounds also disturbs this cycle. Some of the important

photochemical smog reactions that take place in the atmosphere are as under:

Normal NO2photolytic cycle:

8/10/2019 EE-II Unit - I

30/37

Page 30of 37

Production of hydroxyl radical:

O3+ hv O++ O2

O++ H2O 2OH(Hydroxyl radical)

Chain and disturbance reactions:

CO + OH CO2+ H

H+ O2 HO2(hydroperoxyl radical)

HO2 + NO NO2+ OH

RCHO + OH RC(O)+ H2O

(Aldehydes) Acetylradical

RC(O) + O2 RC(O)O2(Acetyl peroxy radical)

RC(O)O2+ NO2 RC(O)O2NO2

(PAN)

RC(O)O2+ NO NO2+ RC(O)O

RC(O)O+ O2 RO2+ CO2

RO2+ NO RNO3

(Alkyl nitrate)

RO2

+ NO NO2+ RO

RO+ O2 RCHO + HO2

(Stable aldehyde)

HO2+ NO NO2+ OH

RH + OH R+ H2O

R+ O2 RO2

RCHO + hv R

+ HCO

HCO+ O2 CO + HO2

(Carbon Monoxide)

Terminating Reactions:

OH+ NO2 HNO3

RO2+ NO RNO3

RC(O)O2+ NO2 RC(O)O2NO2

The end product of these photochemical reactions is photochemical smog consisting of

air contaminants such as ozone, PAN, aldehyde, ketones, alky nitrates and carbon monoxide.

8/10/2019 EE-II Unit - I

31/37

Page 31of 37

1.10 Global effects of air pollution:

Air pollution problems are not necessarily confined to a local or regional scale. atmospheric

circulation can transport certain pollutants far away from their point of origin, expanding air

pollution to continental or global scales. It can be truly be said that air quality problems know

no international boundaries. Scales of pollutant transport in the atmosphere can be described as

i)

Local, ii) Regional, iii) Continental and iv) Global. The global effects of air pollution may

be i) Global Warming (green house effect), ii) Ozone layer depletion (ozone hole), and

iii) Acid rain

1.10.1 Global Warming (Green House Effect)

Incident solar energy as short-wave radiations, mostly in the form of visible light, is

absorbed by the earths surface and emitted into space as long-wave infrared (heat) radiations.

There are several gases in the earths atmosphere, primarily water vapour and CO2 that are

transparent to the incoming short-wave radiations but are nearly opaque to the reflected long-

wave radiations. Thus much of the earths heat is retained, which causes a warming effect. This

phenomenon is known as green house effect, and the gases that have the ability to absorb

reflected long-wave radiations and produce this effect are called green-house gases. it is due to

the natural occurrence of the green-house effect (i.e. presence of water vapour and CO2) that

there is a higher atmosphere equilibrium temperature; otherwise the earths mean surface

temperature would have been 180C instead of the present +170C. There is concern that

increasing concentrations of carbon dioxide and other trace greenhouse gases due to human

activities will enhance the green-house effect and causes global warming.

The greenhouse gases which cause greenhouse warming of the global climate (excluding

water vapour) are carbon dioxide, methane and a number of other trace gases like nitrous oxide

(N2O), tropospheric ozone, chloro-fluoro carbons (CFCs), hydro-chloro-fluoro carbons (HCFCs),

methychloroform (CH3CCL3), carbon tetrachloride (CCL4), sulphurdioxide, fluorine, bromine,

iodine, and compounds of nitrogen and sulphur. The principal sources of green house gases are

summarized. While Fig shows the estimated contributions of greenhouse gases to global

warming.

Estimated contributing of greenhouse gases to global warming in 1980s

8/10/2019 EE-II Unit - I

32/37

Page 32of 37

Major sources of greenhouse gases

S. No Gases Major Sources

1. CO2 Fossil fuel combustion, deforestation, respiration

2. CH4 Wetlands, anaerobic decomposition of organic wastes, termites

3. N2O Natural soils, fertilizers, fossil fuel combustion

4. CFC 11 Photochemical reactions in troposphere, transport (diffusion) from

stratosphere

5. O3 Manufacturing of foams, aerosol propellant

6. CFC 12 Refrigerant, aerosol propellant, manufacturing of foams

7. CFC 113 Electronics solvent

8. HCFC 22 Refrigerant, production of fluoropolymers

9. CH3CCL3 Industrial degreasing solvent

10. CCL4 Intermediate in production of CFC 11, CFC 12, solvent

The greenhouse effect at its natural level is very essential for life to exist on this planet

(earth); but its increase (i.e. enhanced greenhouse effect), as is actually taking place, is feared

to cause global climate changes of irreversible and highly destructive type. The concentrations

of CO2and other greenhouse gases in the atmosphere are rising alarmingly, and making it clear

that we are going to experience a general warming-up of the atmosphere. In fact, some

warming-up from 0.3 to 0.70C has already taken place during the last one century.

Effects

Speculated scenarios based on global warmings include the following

i. Increase in global mean temperature at about 0.30C per decade.

ii. There may be more warming-up in higher latitudes during late autumn and winter, than

in tropics. In tropics, the expected rise would be less than the global average; and in

temperature regions, more than the global average.

iii. Flooding of many coastal areas (lands and islands) due to rising sea levels resulting from

the thermal expansion of the oceans, the melting of glaciers and ice sheet, and probably,

from the melting of polar ice caps. One set of response predicted for average global

temperature and sea-level rise is shown in table 2. Rises in sea-level of this magnitude

would be disastrous for low-lying areas of Netherlands, Maldives, and other such area.

Prediction of a sea-level rise

Year 1990 2030 2060 2100

CO2conc. (ppm) 354 470 600 850

Temp. rise (0C) 1.1 2.0 3.3

Sea-level rise (cm) 18 38 65

8/10/2019 EE-II Unit - I

33/37

Page 33of 37

iv.

An increase in global average temperature is predicted to increase the amount of water

vapour in the atmosphere (because saturated vapour pressure increases with

temperature), thereby increasing the long-wave optical depth, trapping more long-wave

radiation and increasing the temperature further.

v. Increase in global average temperature will lead to dislocation of suitable land for

agriculture, and thus may adversely affect the world food production. For instance, the

wheat growing areas in the northern latitude will shift towards poles, i.e. from fertile

lands (in USA, Canada and Russia) to poor soils (in the north pole). In case of India, it is

predicted that the wheat production will drop in the fertile northern belt.

vi. The dislocation and possible extinction of certain biological species and ecosystems

cannot be ruled out.

vii.

Increase in the severity of storms

viii. Other effects include more evapotranspiration in tropics, alternation in existing

precipitation patterns, effect on hydrological cycle, effect on human health (like heat

strokes), etc.

Control

Since, Co2 accounts for about half of the greenhouse gases and there is a strong

evidence linking temperature and CO2changes, therefore, the nest way to solve this problem of

global warming due to increasing concentration of CO2is to use sources of energy that do not

produce carbon dioxide such as wind, hydroelectric, geothermal, solar, tidal and nuclear

energy. Similarly, the emissions of other greenhouse gases in the atmosphere should also bestopped to prevent the enhanced greenhouse effect.

1.10.2 Ozone Layer Depletion (Ozone Hole):

In stratosphere, ozone is found in a concentrated thick layer at varying heights from

16km to about 40km at different latitudes. Its concentration, in ppmv (parts per million by

volume), at tropopause is less than 1.0 and then starts increasing to reach a maximum value of

about 8.0 at about 30km, and then again starts decreasing to a value of 2.0 at 40km. Its valuereaches to zero at about 100km. In the stratosphere, O3 is formed naturally when oxygen is

dissociated by ultraviolet solar radiations in the wave-lengthe region of 80 to 240nm.

Where M is any third body molecule (mostly likely N2 or O2 in the atmosphere) that

remains unchanged in the reaction. The ultraviolet radiations in the region of 200 to 300 nm

can also dissociate the ozone:

8/10/2019 EE-II Unit - I

34/37

Page 34of 37

In this (above) reaction, ozone portrays the absorption of ultraviolet-B radiations and

hence is responsible for the removal of UV-B radiations (= 280 to 320 nm) that would

otherwise reach the earths surface. The concern is that, any process that depletes stratospheric

ozone will increase the UV-B radiations reaching the earths surface. Increased UV-B will be lead

to increased incidence of skin cancer and could have deleterious effects on certain ecosystems.

The three important areas, where human activity can influence the ozone cycle, have been the

direct emission of NOxby supersonic transport flying above the tropopause, additional transport

of nitrous oxide (N2O) as a result of increased use of nitrogenous fertilizers, and the formation

of atomic chlorine in the stratosphere from chloro-fluoro carbons (CFCs) (used as refrigerant,

aerosol propellant and industrial solvent) released in the troposphere. Another class of

compounds, halons, are also ozone depleting compounds. Halons are bromo-chloro-

fluorocarbons or bromo-flurocarbons that are widely used in fire extinguishers. Although the

emissions of halons and thus their atmospheric concentrations are much lower than the most

common chloro-flurocarbons (CFCs), but they are 3 to 10 times more destructive than the

CFCs.

The Nox emission from supersonic transport in stratosphere or the diffusion of NO x in

stratosphere from the lower atmosphere, cause ozone depletion in the following way:

The net effect on this sequence is the destruction of two molecules of ozone, since the oxygen

atom (O) would have combined with oxygen molecule (O2) to form ozone. Most significantly,

the NO acts as a catalyst because it is not consumed, and therefore can participate in the

reaction sequence many times.

The CFCs (like chloro-fluoro methane or Freon) are inert in normal and physical reactions, but

they get accumulated in greater amounts at high altitudes, and there in stratosphere, they

release chlorine atoms under the influence of UV radiations (

8/10/2019 EE-II Unit - I

35/37

Page 35of 37

In this sequence the chlorine atom acts as a catalyst, and two O3 molecules are

destroyed. Before the CL is finally removed from the atmosphere (in 1-2 years) by precipitation,

each CL atom will have destroyed thousands of ozone molecules.

The first evidence that stratospheric ozone depletion is occurring comes from the

discovery of the Antarctic ozone hole that could have been caused by human produced

pollutants. This hole formation or the level of ozone depletion is increasing yearly. In the

vertical profile, the most affected zones are around 40 to 50 km and the lower stratosphere

below 20 km. The various studies carried out show that globally, stratospheric ozone

concentrations have declined during the winter, spring and summer in both the northern and

southern hemisphere at middle and high latitudes. The declines are most evident during winter

months. In north Europe and America, during late winter and early spring, ozone is getting

depleted and it is feared that in near future more ozone holes may develop. The studies carried

out in India show that a good part of the country has low ozone belt, and further depletion

could cause serious problems.

Effects

The thick shield (layer) of ozone present in the stratosphere is extremely useful as is

prevents the UV-B radiations coming from sun to reach the earths surface; and thus the plants,

animals and human beings escape from the hazardous UV-B radiations. Increase in UV-B

radiations have damaging effects on the DNA of exposed cells of organisms and can cause

mutation and skin cancer. Other effects are climate changes due to global warming, non-formation of stratospheric winds, and deleterious effect on certain ecosystems.

Control

The only practical warming solution to this problem is to accelerate the phaseout and

complete elimination of the production of CFCs halons, carbon tetrachloride and

methychloroform. Though such steps will stop the increase of CFCs in the atmosphere; but,

because of their long life-times, the already emitted CFCs will remain in the atmosphere for

centuries.

1.10.3 Acid Rain

The term acid rain was first used by Robern A. Smith in 1872. Since then numerous

western investigators added insight to this emerging environmental challenge.

The term acid rain is used to describe all precipitation and / or deposition, which is more

acidic than normal. It results, when gaseous emissions of particularly Sox and NOx interact with

water vapour and sunlight, and are chemically converted to strong acidic compounds such as

sulphuric, sulhurous, nitric and nitrous acids. When these compounds (acid gases or their

precursors or acid particles) along with other organic and inorganic chemicals are deposited on

8/10/2019 EE-II Unit - I

36/37

Page 36of 37

the earth as aerosols and particulate, the deposition is called as Dry deposition; and when these

are carried to the earths surface by precipitation. However, dry deposition is estimated to be a

small fraction of total acid deposition.

Generally, clean rain is slightly acidic as it dissolves varying amounts of naturally

occurring carbon dioxide from the atmosphere. The lowest pH level which can be produced by

carbonic acid (orCO2) is 5.6. Therefore, the precipitation or rain is said to be clean rain upto a

pH of 5.6, which is the natural background pH of rain water.

Hence, acid rain, on precipitation, is defined as the one which has a pH less than 5.6.

The principal species associated with dry-acid deposition are SO2(g), acid sulphate

particles (H2SO4and NH4HSO4), and HNO3(g), while the principal dissolved acids are H2SO4and

HNO3. Other acids, such as hydrochloric acid (HCL) and organic acids, usually account for only a

minor part of the acidity. Although organic acids can be significant contributions in remote

areas.

Both acid particles and gases can be incorporated into cloud droplets. Particles are

incorporated into droplets by nucleation, impaction, Brownian movement, diffusiophroesis

(transport into the droplet induced by the flux of water vapour to the same surface),

thermophoresis (thermally induced transport to a cooler surface), and electrostatic transport.

Advective and diffusive attachment dominate all other mechanisms for pollutant gas uptake by

cloud droplets. Most of the H2SO4 in precipitation is due to the diffusion of SO2 into the cloud

droplets, where it is oxidized to H2SO4by one of the several mechanisms; while most of the

NHO3 in precipitation is due to the diffusion of HNO 3(g) into the droplets. The following

equations summarize the reactions for sulphuric acid and nitric acid formation:

Effect:

The ecological impact of acid rain is quite serious. It is likely to produce irreversible

changes. The acidification of streams and lakes affects aquatic animals and plants. High acidity

results in reduced fish population. Green algae and many forms of bacteria, which are essential

to aquatic systems, will be killed due to acidity. Also at low pH the rate of decomposition of

8/10/2019 EE-II Unit - I

37/37

organic matter in water bodies is reduced, which increases the degree of water pollution. Acid

rains can affect vegetation and soil in many ways. It adversely affects the growth of trees, and

hence affects the forests that results in consequent vanishing of greenery. Due to acid rains, the

plant nutrients, such as potassium, are gradually leached out of the soil; and the population of

earth worms is reduced, thus affecting the fertility of soil. Acidic air pollutants have also been

responsible for many other damaging effects like corrosion of metals weakening or

disintegration of textiles, paper and marble, and works of art and architecture. The building and

sculptural materials (e.g. marble, limestone, etc.) become pitted and weakened mechanically as

a soluble sulphates are leached out by acid rain.

Acid deposition, in fact, shows a correlation with the prior movement of the air mass

over major sources of Sox and NOx emissions. The acidity in Swedish lakes and rivers is due to

emissions from highly industrialized areas of UK and central Europe. The British parliament

building has suffered serious damage from the presence of sulphuric acid in rainfalls. The Taj

Mahal is seriously affected due to pollutants released, particularly, from Mathura refinery.

Similarly, in Canada trees and aquatic life in lakes are being killed by acid rain, 60% of which

originates from USA.

Control:

One of the simplest solutions to the problem is to neutralize the acid with lime. But it is

quite expensive, especially when large areas of water-bodies have to be limed. Further, large

scale liming may create its own ecological problems. probably, the best way to overcome this

problem is reduced emissions of Sox and Nox from anthropogenic sources. Effective air

pollution prevention and control measures are required for both stationary and mobile sources

of air pollution.