EE-II Unit - I
-
Upload
achyutha-anil -
Category
Documents
-
view
216 -
download
0
Transcript of EE-II Unit - I
-
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.