1
Intro u
•
CHAPTER!
INTRODUCTION
Air Pollution is a burgeoning problem in both developing and developed
countries. Ever increasing urbanization & industrialization have led to enormous
emissions of a variety of pollutant e.g. S02, NOx, hydrocarbons, SPM, etc. into the
atmosphere. The ill-effects of these pollutants are well known. In addition to their
adverse effects on human health & vegetation, they cause the acidification of the
environment and also play a key role in global warming.
Air is an important natural resource for the sustenance of life and other
activities in the biosphere. As atmosphere plays a vital role in the existence of life,
proper understanding of the atmosphere, viz. its properties, behaviour and its effects
on human beings and the effect of human activities on it are very essential. But
various factors such as population boom, rapid industrialization and urbanization have
resulted in the deterioration of the air quality. Another important cause of
deterioration of the air quality is vehicular traffic, which is increasing day by day.
Atmospheric pollution is principally caused by man himself through modem life style.
1.1 Air Pollution :
Air pollution may be defined as
"any atmospheric condition in which
substances are present in concentrations high enough above their normal ambient
levels to produce a measurable effect on man, animals, vegetation or materials"
(Seinfeld, 1986). Substances mean any natural or man made chemical element or
compound capable of being air-borne. They may exist in the atmosphere as gases,
liquid drops or solid particles, which may range from carbonaceous soot to heavy
metals and complex organic compounds, leaving aside residues from nuclear fall out.
The effect may be felt over all life existing in the biosphere.
1.1.1 Sources of Air Pollutants
The sources of air pollutants are both natural and anthropogenic:
a) Natural sources : It consists of those substances which would be oresent even in
the absence of human activities. These are forest fires, volcanoes, dust storms,
sea-salt spray, pollen and spores released by plants and biological activities in the
soil.
b) Anthropogenic Sources : The pollutants are emitted due to the human activities. It
consists of gases and waste smoke formed by thermal power plants, industries,
house-holds, automobiles, rocket combustion processes, air crafts and certain
fluorocarbon compounds etc.
However the emissions from natural sources are comparatively higher in
amount than the anthropogenic emissions globally. But the latter does more harm
since the emissions are released into the atmosphere in a particular region in higher
concentration (Henderson-Sellers, 1984). Worldwide emissions of primary pollutants
are given in Table 1.1.
Table 1.1
Worldwide emissions (annual estimates) of primary pollutants.
Natural
Anthropogenic
Major sources
Pollutant
Major sources
Emission
Emission
( 106 tonnes)
(10 6 tonnes)
Sulphur dioxide
(S0 2)
Fossil fuel
combustion
196
Volcanoes
0(5)
Carbon
monoxide (CO)
Auto exhaust and
other incomplete
combustion
275
Forest fires
75
Carbon dioxide
Combustion
1.4 X 10
(C0 2)
4
Biological decay, release
from oceans
10 6
Combustion
53
Bacterial action in soil
430
Combustion
53
Bacterial action in soil
658
None
0
Biological action in soil
590
Hydrogen
sulphide (H 2S)
Sewage treatment
3
Volcanoes,
anaerobic
decomposition
100
Ammonia (NH 3)
Waste treatment
4
Biological decay
1160
Hydrocarbons
(HC)
Combustion,
chemical
processes
88
Biological processes
480
Particulates
Fossil fuel,
combustion, slash
and bum
agriculture
Nitric oxide
(NO)
.
Nitrogen dioxide
((NOz)
Nitrous
(N20)
oxide
690
Sea-salt spray, volcanoes
(Information compiled from various data sources; Henderson-Sellers, 1984 ).
2
1150-1500
1.1.2 Classification
Air pollutants are classified in three ways:
1.
According to chemical composition (Seinfeld, 1986)
a) Sulphur containing compounds
b) Nitrogen containing compounds
c) Carbon containing compounds
d) Halogen containing compounds
e) Toxic substances
f) Radioactive Substances
2.
According to physical state:
a) Particulates: These are solid or liquid particles in the a1r larger than single
molecules e.g. smoke, soot and fog etc.
b) Gaseous pollutants : These are present in the gaseous state in the air viz. S02 , CO,
NOxetc.
3.
According to chemical nature of origin :
a) Primary air pollutants: These are emitted directly into the atmosphere from
identifi~ble
sources. They pollute the air immediately upon bein.g emitted.
b) Secondary air pollutants: These are formed in the atmosphere when certain
chemical reactions take place among primary pollutants and normal atmospheric
constituents.
1.1.3 Effects of Air Pollution
Air is no where perfectly clean, even nature pollutes the atmosphere. The
importance of clean air can be understood from the fact that an average adult male
inhales about 15kg of air in a day compared to 1.2kg of food and 2.5kg of water for
drinking (Gupta, 1991 ). Thus, of the body's intake, 8% consists of food, 12% of water
and 80% of air. The presence of air pollutants adversely affect health of human
beings, animals and plants.
3
The hazardous effects of air pollutants may be grouped under the following
categories.
1.
Meteorological effects:
a) Reduction of Visibility
b) Formation of Acid Rain
c) Changes in rainfall pattern
d) Long term effects on climate
2
Material damage:
a) Corrosion of historical and religious monuments
b) Corrosion of metals
3
Plant damages:
a) Damage to agriculture
b) Damage to plants and trees
4
Physiological damage
a) Affecting human health
b) Increasing prevalence of bronchitis, respiratory infections and coronary heart
disease, skin and liver cancer, dermatitis.
---~-~-.
--- ...
Apart from direct effects on human health, material damage, ecological
damage and meteorological changes, a group of new problems have also emerged due
to air pollution over the past two decades. They are acidic deposition (Acid Rain),
global warming due to increased C0 2, Indoor pollution, lead deposition, long range
transport of pollutants, radioactivity, non-ionizing radiation, stratospheric ozone hole,
environmental toxicity and visibility reduction (Stem, 1986). The consequences of
increasing concentration of C0 2 world-wide may lead to the green house effect,
global warming, increase in mean sea level, submergence of coastal regions, melting
of polar ice, shift in the monsoon period etc.
The common air pollutants are suspended particulate matter (SPM), oxides of
nitrogen (NOx), sulfur dioxide (S02), hydrogen sulphide, ozone, fluorine compounds,
ammonia, hydrocarbons, various metallic dusts, carcinogenic agents etc.
4
1.2 Particulates and Gases
Particulate Matter: It is the solid and liquid aerosol suspended in the
atmosphere. It results both from direct emissions of particulates and from secondary
formations. These are emitted into the atmosphere from power plants, different kinds
of industries, motor vehicles, construction activities, natural wind blown dusts,
volcanic action, sea-salt spray and forest fires etc. Smoke, soot, dust, ash, pollen,
spores and many other materials are included in particulates.
Particulates are frequently the most obvious form of air pollution because they
reduce visibility. The visual range is inversely proportional to the concentration of
particulate matter. Reduced visibility is dangerous for air crafts and motor vehicles.
Emphasis has been placed on PM 10 (particles smaller than 10 !J.m in diameter) because
they are responsible for adverse health effects caused by particulates. These tiny
particles are drawn into the lungs and damage respiratory tissues.
Bryson and Baerries (1967) from aerial photographs noticed the occurrence of
deep, dense dust over the Rajasthan which diminished southward and eastward. The
top of the dust cover was found around 25,000 ft over north eastern part of the
Arabian sea to 30,000 ft and more over Rajputana Desert thinning to 17,000 ft over
the lower Gangetic valley. They also noticed that the cloud of dust sweeping out of
the desert was the major source of dust for the Indian area.
The particulate matter in the mining area are minerals, rock dust, fly ash, sand
dust from tailing dump, cement dust, smoke , soot aerosol particles, mist, fog and
fumes. The main source of SPM is the open cast mining. Because of the obvious
advantages, the open cast mining has gone up (in%) from 14 in 1951 to 35 in 198081, 48 by 1984-85, 59 currently and is expected to reach 65 by the year 2000-01 A.D.
(Banerjee, 1988). Besides these activities, point sources such as chimnies of the
power stations, cement plants and smelters etc. also contribute SPM in this area.
The important non-point sources of SPM in the mining area are the following:
1. Operation of various coal I mineral winning
2. Haul roads both of the paved and unpaved types.
3. Wind erosion from coal/ mineral
5
4. Blasting operation
5. Tailing dumps
(Banerjee, 1988).
Mining activity, which is a vital sector of economy in any country, is a dirty
and dusty operation. The main cause of pollution in the mining area is due to
suspended particulate matter (SPM).
Kumar (1990) pointed out the seasons and diurnal pollution potential in the
region of the vast industries oriented mining areas around Dhanbad. Minimum
concentration of SPM has been observed in monsoon periods( due to more favourable
dispersion and scavenging of air pollutants) in comparison to other months.
Gases:
S0 2 and NOx are the two major gaseous air pollutants whereas
hydrocarbons, CO and H2S etc. are also quite harmful.
Sulphur dioxide (S0 2): It is noxious, smog forming and the worst "problem" gas in
the atmosphere. It is colourless but corrosive gas which originates from the
combustion of sulfur-containing fuels, primarily coal and oil. It is also emitted by
industrial processes that consume sulfur containing raw materials. Fuel combustion
accounts for roughly 75% of all S02 produced. The major industrial sources are
smelting of metallic ores, refining oil, pulp paper mills, power plants. H 2S is largely
converted to so2 by burning in air.
.... (1)
Since the reaction is exothermic it can occur without photochemical action.
Once S02 is in the air, it is frequently oxidised into sulfur trioxide (S03) which
reacts with water vapor to form sulfuric acid (H2S04).
The possible S02 reactions in air are;
I) Reaction with atmospheric water:
S02 + H20
~
H2S03 + 18K. Cal (0.78ev)
.... (2)
II) Oxidation by atmospheric 0 2:
S02 + Yz 02
~
S03 + 22 K. Cal. (0.95ev)
.... (3)
Both reactions are possible but slow. The H2S0 3 produced in reaction (2) is
unstable and changes spontaneously in air to H2S04 • The S03 produced by reaction
(3) is extremely hygroscopic, the reaction involved being.
6
.... (4)
This is a large amount of heat for a hydration process. The resulting H2S04 is
itself strongly hygroscopic, and the molecule rapidly grows into a droplet. Hence in
the atmosphere, it is one of the constituents of smog.
When N0 2 and water are present, there is a reaction.
.... (5)
Very tiny particles act as a medium on which acidic sulfate ion (S0 4 -2) is carried over
long distances in the atmosphere. When it is "washed" out by rain, it contributes to a
serious environmental problem known as acid rain. It damages materials and
adversely affects plants. It effects breathing and respiratory system, damages lungs
tissue, causes premature death as it is highly irritating to mucous tissues.
Oxides of Nitrogen (NOx):
The major sources of NOx include fossil fuel burning, lightning, emissions from the
biosphere, stratospheric injections and biomass burning. NOx also forms naturally
when certain bacteria oxidise N-containing compounds. The initial product formed is
nitric oxide (NO). N0 2 is formed in the atmosphere by oxidation of NO. The sum of
both NO and N02 is designated as NOx. Both are formed by combustion at high
temperatures.
The basic reactions and resulting oxides of interest in pollution concerns are:
Yz N2 + Y2 02
Yz N2 + 02
~
~NO-
21.6 K.Cal (0.935 ev)
N02- 8.3K.Cal (0.36 ev)
NO+ Yz 02 ~N02 + 14.2K.Cal (0.62 ev)
.... (6)
..... (7)
.... (8)
It is to be noted that neither reactions (6) nor (7) occur spontaneously at room
temperature, but that reaction (8) does.
N02 has a distinctive reddish brown colour that frequently tints polluted city air and
reduces visibility. When air is humid, N0 2 reacts with water to form nitric acid
(HN03)
7
.... (9)
2N02 + H20 ---+ HN02 + HN03
Nitrous acid is unstable with respect to decomposition by the reaction
.... (10)
3HN02 ~ HN03 + 2NO + H20
Reaction (1 0) is both slow and readily reversible. The net result of these two reaction
IS
.... (11)
This reaction (Cadle and Allen, 1970) acts in humid air at room temperature to
convert about 5% of the N02 to HN03.
It also contributes to acid rain. Both these oxides play an important role in the
production of photochemical smog and causes corrosion of metals.
The period for which a pollutant remains in the atmosphere is also important
in the evaluation of atmospheric pollution.
The mean tropospheric residence time for gaseous NOx and HN03 is estimated
to be in the range of 1 to 4 days and that for N03- in the range of 3 to 9 days (Sienfeld
1986).
Because of these short atmospheric life times, the major effects of NOx are
expected to be in the order of local or regional scales only.
The fossil fuel sources of both NOx and S02 contribute largely to their
atmospheric budgets; over 90% of each gas being emitted in the northern hemisphere
is primarily from Europe and North America (Irwin and William 1988; Hameed and
Dignon 1988, Dignon 1992); on the other hand, throughout the southern hemisphere
the emissions from fossil fuel combustion account for 10% or less. These are
observed as soluble nitrogen at remote sites.
It has been quoted by Irwin and Williams (1988) that global natural emissions
of sulfur are in the range of 50 to 100 Tg S a- 1 while anthropogenic emissions are
about 80 Tg S a- 1 in 1979 and the anthropogenic contribution ofNOx is double that
of natural emissions (1 Tg = 10 12 g)
Hydrocarbons: Hydrocarbons are solid, liquid and gaseous compounds that are
composed only of hydrogen and carbon. In cities, the incomplete combustion of
8
gasoline in motor vehicles is the principal source of hydrocarbons, although some
hydrocarbons from other sources are carcinogenic. Gasoline is a complex mixture of
various hydrocarbons. When hydrocarbons react with certain other pollutants
(especially nitrogen oxides), noxious products result, which produces photochemical
smog. Hydrocarbons are of specific interest in air pollution studies as a result of the
worldwide use of hydrocarbons fuels in the internal combustion engine. Benzene
(C 6H6) and polycyclic aromatic hydrocarbons (PAH) are currently of great concern
arising from vehicular combustion.
Carbon monoxide (CO): It 1s a colourless, odourless and pmsonous gas
produced by incomplete burning of carbon in fuels. CO is the most abundant primary
pollutant and that about two-thirds of the nation wide emissions are from vehicular
sources, mainly highway vehicles. Because it can not be seen, smelt, or tasted, CO
can have an effect on people without realizing it. In small amounts it causes
drowsiness, slows reflexes and impairs judgement. At high concentrations, CO can
cause death by not allowing the blood to transport adequate oxygen. It poses a serious
health hazard in poorly ventilated tunnels and underground parking facilities.
1.3 Atmospheric chemistry
The atmosphere is an oxidative medium. The primary pollutants are oxidised
through photochemical and chemical reactions as they are dispersed into it.
Hydrocarbons react to form aldehydes, then to acids and finally to C02 . Sulfur
containing compounds pass through the chain starting with reduced sulfur compounds
and oxidized to S02 and then to H2S0 4 • In the degradation cycle of nitrogen
containing species, ammonia is oxidized to NO then NO to N02 and finally N0 2 to
HN03.
Nitrogen dioxide is the most important radiation absorbing air pollutant. It
absorbs over the entire visible and u.v. range of the solar spectrum in the lower
atmosphere.
In air pollution chemistry photochemical dissociation reactions have their own
importance. Because the end products (mainly free radicals) that result from them.
These products then initiate or participate in a large number of other reactions
9
responsible for the conversion of primary pollutants into secondary ones.
Primary pollutants (S0 2, NO, CO and organics except aldehydes) as such are
not important absorbers of radiation at the wavelengths prevalent in the lower
atmosphere.
Even small amounts ofN02 present in the atmosphere are sufficient to trigger
a complex series of photochemical reactions. In the presence of sunlight ozone
formation occurs as a result of the photolysis ofNOz (Seinfeld, 1986):
.... (1)
NO+O
.... (2)
Where M is a third species (such as NOz, metalic oxide) which acts as a catalyst.
M absorbs the excess vibrational energy and thereby stabilizes the 03
molecules formed. Once formed 03 reacts with NO to regenerate NOz.
.... (3)
Ozone photolyses to produce both ground state (0) and excited singlet (OeD))
oxygen atoms
03 + hv
~
.... (4)
0 + Oz
~ oeD)+Oz
.... (5)
The ground state 0 atom combines rapidly with 0 2 by reaction (2) to reform
03. However, when oeD) is produced, since the oeD) ~ 0 transition is forbidden, it
must react with another atmospheric species. Most often oeD) collides with N 2 or 0 2
removing the excess energy and quenching oen) to its ground state.
oeD)+M~O+M
.... (6)
1
Occasionally, however, 0( D) collides with H20 and produces two hydroxyl radicals,
.... (7)
This radical is non-reactive with oxygen, and it reacts with most atmospheric
species, such as hydrocarbons, aldehydes and carbon monoxide.
When this radical reacts with carbon monoxide, it ultimately produces
hydroperoxyl radical
10
CO+OH·~
.... (8)
COz + HOz"
The hydroperoxyl radical then reacts with NO to form NOz and to regenerate
the OH" radical.
HO"z +NO
~
.... (9)
NOz + OH"
Finally OH" and N0 2 may react to form nitric acid.
OH" + NOz ~ HN03
.... (10)
The final products may be either nitric acid or PAN and photochemical smog.
From a thermodynamic point of view, SOz has a strong tendency to react with
oxygen m mr
S0 2 +
1120z~
.... (11)
S03 + 18K.Cal (0.78ev)
If formed, S0 3 reacts very rapidly with water vapor to form sulfuric acid
S03 + HzO
~
HzS04 (aq) + 38 K Cal (1.65ev)
.... (12)
In the atmosphere, it may well be one of the constituents of smog.
So far, the gas-phase oxidation of NOx and S02 have been discussed. Another
most important oxidation of S0 2 is through aqueous phase reaction.
Absorption of SOz in water results in
SOz(g) + HzO ~ SOz• HzO
.... (13)
SPz•HzO ~ H++ HSo3-
.... (14)
HSo3- ~ H+ +
so3-z
..... (15)
However, this reaction is dependent on the pH of solution.
When SOz dissolves in aqueous solution, the three S(IV) result, SOz•H20,
HS0 3- and S0 3-2 . The conversion of dissolved S(IV) to sulfate S04-2 (also referred to
as S(VI) is an important route for forming atmospheric sulfate. Several oxidizing
species have been identified, including dissolved oxygen, ozone, and hydrogen
peroxide.
. ....... (16)
The reaction may be uncatalyzed or catalyzed by certain dissolved metal ions.
Saxena and Seigneur (1987) concluded from their simulation studies that gasII
phase oxidation pathway dominates sulfate formation for daytime conditions in
summer; at night atmospheric sulfate production is dominated by aqueous-phase
pathways which depend strongly on Fe and Mn concentration and on the liquid water
content of aerosols which in tum is dependent on relative humidity.
The NO-N0 2 system also undergoes transformation through aqueous phase
reactions. The reactions are the following:
2N02 (g)+ H20 ~ 2H+ + N02- + N03-
.... (17)
NO (g)+ N02 (g) + H20 ~ 2H+ + 2N02-
.... (18)
However, N0 2 and S0 2 were found to be the dominant nitrogenous and sulfurous
compounds in the atmosphere (Cadle eta!., 1985).
The acids formed in the above reaction, are neutralized partially or fully in the
atmosphere by the presence of alkaline fly ash, alkaline particles and /or gases and
ultimately removed from the atmosphere either by wet or dry deposition or both.
1.4 Ambient Air Quality:The ambient air quality is a complex and dynamic environmental
phenomenon. It exhibits
larg~
temporal and spatial variations due to the changes in
the rate of emissions from anthropogenic and natural sources as well as due to
changes in meteorological and topographic conditions. The monitoring of ambient air
quality in an area is imminent to provide data to allow a resolution of the dynamic
nature of air quality in terms of temporal and spatial variations. The monitoring data
so generated may be compared with the prescribed permissible air quality standards
and their violations may suggest the bias and gravity of air pollution problems
prevailing in an area.
The air pollution in urban areas arises from a multiple of sources including
natural as well as anthrogpogenic sources viz. industrial processes, automobiles,
vehicular traffic, power plants as well as domestic sources. The concentration of air
pollutants can vary considerably from one location to another as they depend not only
on the quantities that are emitted but also on the ability of atmosphere to disperse the
pollutants. Dispersal, in tum, is related to the stability of the atmosphere. Hence air
pollution conc~ntrations vary temporally, causing the air pollution pattern to change
with different locations and time. Hence air quality is not just a function of the
12
quantity and types of pollutants emitted into the air, but it is also closely linked to the
at~osphere's ability to disperse these noxious substances. Dispersal in turn depends
on the stability ofthe atmosphere.
The national ambient air quality standards for sulfur dioxide, nitrogen dioxide
and suspended particulate matter are given in Table 1.2.
Table 1.2
National Ambient Air Quality Standards
Concentration in Ambient Air
Parameter
Time
Sensitive
Industrial
Residential,
weighted
Area
Area
Rural
Method of Measurement
&
Other Areas
Average
Sulphur
Annual*
15!-lg/m'
80!-lg/m'
60!-lg/m'
-improved West and gaeke
Dioxide
24 hours*
30!-lg/m3
1201-1g/m 3
80jlg/m3
Method
-Ultraviolet Fluorescence
(SOz)
Oxides of
Annual*
15!-lg/m'
80!-lglm'
60!-lg/m'
-jacab
Nitrogen as
24 hours*
30!-lg/m 3
1201-1g/m 3
80!-lg/m 3
modified
&
Hochheiser
-(Na-Arsenite) Method
(N0 2)
Suspended
Annual*
70!-lg/m'
360!-lg/m'
140!-lg/m'
-High volume Sampling
Particulate
24hours**
100!-lg/m 3
500!-lg/m 3
2001-1g/m 3
- (Average flow rate not less
than 1.1 m3/minute)
matter
(SPM)
Respirable
Annual*
50!-lg/m'
120!-lg/m'
60 1-1g/m'
-Respirable particulate Matter
Particulate
24 hours**
75jlg/m 3
150 1-1g/m 3
100 1-1g/m 3
Sampler
Size Less
Annual*
0.50!-lg/m 3
1.0 1-1g/m'
0.75 1-1g/m3
-AAS Method after sampling
than
24 hours**
0.75!-lg/m 3
1.5 1-1g/m 3
1.00 1-1g/m 3
Matter
(RPM)
10!-lm
using
-EPM 2000 or equivalent
Lead (Pb)
filter
Carbon
8 hours**
l.Ojlg/m'
5.0jlg/m'
2.0jlg/m'
-Non-dispersive Infra red
Monoxide
I hours*
2.0 1-1g/m3
IO.Ojlg/m 3
4.0jlg/m 3
-Spectroscopy
(CO)
*
**
Annual arithmetic mean of minimum 104 measurements in a year taken
twice a week 24 hourly at uniform interval.
24 hourly I 8 hourly values should be met 98% of the time in a year.
However, 2% of the time, it may exceed but not on two consecutive
days.
(Source : CPCB, NAAQMS /611994-95)
13
1.5 Air Pollution In India :
Air pollution has become increasingly an important aspect of environment in
the fast developing country like India due to rapid industrialization and urbanization.
India accounts for 16% of the world's population but it has only 2.42% of the
total world area. The land area of India is only 3.28 million km
2
.
The density of
population continues to rise, and on an average it is 269 person/km2 . Increased
population demands more power; the generation of which is associated with
environmental pollution and consequent health effects. Population explosion leads to
air, water, soil, & noise pollution. In addition to various important industries, the other
important source of air pollution in the Indian environment is the domestic
consumption of low grade fuels, resulting in intensely smoky atmosphere affecting
visibility. Fine dust by the deserts and other fallow dry fields generate SPM. India has
.one of the largest network of roads in the world. Automobiles traffic adds
significantly to the air pollution in cities. These vehicles are powered by internal
combustion engines which can be grouped into three general classes (Pundir, et a!.,
1983) viz1. Passenger cars powered by four stroke gasoline engine.
2. Two and three wheelers powered by small crank case scavenged by two stroke
gasoline engine.
3. Buses and trucks equipped mostly with four stroke diesel engines.
Ninety percent (90%) of pollution in Indian cities is due to automobile
exhaust. The worst offenders are not the diesel power buses and trucks, but the two
stroke vehicles, viz; two and three wheelers which constitute three fourths of the
vehicle population (Mathur et al., 1983). Human's intervention with the atmospheric
environment is unprecedented. People are clearly altering the composition of the air.
Calcutta Municipality passed "Smoke Nuisance Act" in the beginning of the
20th century in their anxiety to clean the city (Gupta, 1991). Black smoke, mainly
from burning of coal in chimneys, was regarded as the main cause of air pollution.
Blackness of smoke was, however, determined by some arbitrary scale and action was
taken. Though the act did not cover most of the factors of pollution caused by smoke,
14
it served well for more than half a century.
Recently the Govt. of India passed the prevention and control of Air pollution
Act in 1981. Other statutory attempts ;to deal with pollution are already in vogue
through the above act. Besides this, a number of government agencies are formulating
standards and initiat.ing measures to Gontrol pollution.
At the centre of these effects is the Ministry of Environment and a full fledged
Department of Environment. In addition
to that, various State Pollution Control
Boards and Central Pollution Control Board have an extensive network of air quality
monitoring stations all over India.
To assess the air pollution m India, National Environmental Engineering
Research Institute (NEERI), Nagpur, is working as WHO collaborating centre and
carrying out the project (WHO, 1984). A network of air quality monitoring stations
has been initiated by NEERI in cities where its zonal laboratories are based. The ten
cities covered represent most of the major urban population concentration in India.
The population levels at each station alongwith wind roses prepared from wind data
collected by IMD are being documented by NEERI (1980, 1983, 1988). Several air
pollution studies have been carried out by individual workers in India:
Air quality of Madras was studied by Hussein (1971) and found that the Basin
Bridge area was the most polluted part in the ci_ty. He also concluded that SPM and
dust fall concentration in the city were found higher than cities like Chicago, London,
Tokyo, Los Angeles and San Francisco.
Ambalavanan (1981) studied air quality around Basin Bridge at House Madras
and found that the maximum concentrations of SPM, S0 2 and N0 2 were 178.03 llg
3
m- and 90.68 IJg m-3 respectively. He also found that the accumulation of pollutants
seemed to be higher during late evening and night.
Air pollution due to automobile emissions in the Madras city was studied by
Sankiliraj (1981) and it was found that the maximum value of S02 was well within
the safe limits.
Visakhaptanam is situated in a valley with some major industries established
15
in the south west at the foot of Y arada Hills. The ambient air quality data revealed
that due to typical topography of the city and wind pattern, the SOz levels increased to
some extent at the foot of Yarada Hills in the south during the winter months, creating
a sensitive zone requiring better air pollution control during the critical months
(Mundri et al., 1986).
Observations of gases viz. SOz, NH3, NOz, and 03 were made during 1981 to
1984 at six different locations representing urban-industrial, urban, non-urban,
thermal power plant and marine environment in India by Khemani et a!., (1987).
Except in the urban industry, the concentration of NOz, and 03 at different
environments were in the order of background values.
All these studies point out that the air quality at many urban areas in India is
deteriorating. Thus, it may be said that in India the problem of air pollution and its
subsequent consequences has been recognized and the nation as a whole is conscious
about it.
Now it is the time to think about the effective control measures both in short
and long terms. Hence, the study of air pollution climatology is one the steps in that
direction and it is also necessary to examine the carrying capacity of the atmosphere.
The
latter
attempts
have
been
made
to
develop
diffusion
models
by
.Padmanabhamurty and Gupta (1977, 1978, 1979, 1986), Gupta (1980,84) and Patil
and Patil (1990).
1.6. The Urban Problem:
Industrialization and urbanization injects foreign particles and gases into the
urban atmosphere, which modify climate and deteriorate the air quality. The rate at
which our cities are growing is faster. Urban areas swell not only with their own
people but also with influx of rural population. When cities grow rapidly, they
demand huge quantities of energy and raw materials for transport, communication,
construction, production and packaging. Urban areas generate large amounts of solid
waste, more of air, water and noise pollutants. In urban areas houses and roads are
made of concrete. Big cities of Bihar like Patna, Dhanbad, Ranchi, and Jamshedpur
etc. where most of the lanes and roads are narrow, impede wind flow. Hence cities
16
and town become concrete jungles with dense population and dwindling greenery.
These conditions are conducive for deteriorating air pollution levels.
Urbanization inadvertently modifies the local climate. It rmses urban
temperature compared to rural areas- a phenomenon known as "Heat Island Effect".
The head island, a zone of excess temperature in urban centres in comparison with
surrounding rural areas, is in some cases has an entirely favorable effect, especially
for locations in high latitudes (Landsberg, 1972). Urban temperatures in winter nights
are high compared to their rural counterparts.
Other effects of urbanization are increased surface humidity, air temperature,
slowing of wind, decrease of solar radiation, visibility evaporation, sunshine duration,
simulation of rainfall etc. Increased pollution changes the precipitation to become
acidic.
1. 7 Air Pollution Control :
There are various devices now developed to mitigate particulate material and
harmful gases from being discharged into the atmosphere. Bag filters, cyclone
collectors, and industrial electrostatic precipitators, and scrubbers are devices to filter
industrial fumes. It can also be controlled by using less polluting fuels or by adopting
suitable processes which cause less pollution. It can also be minimized by proper
emission scheduling. The polluting activity through the knowledge of existing air
quality and meteorological conditions which either disperse or accumulate the
pollutants can also be adopted.
Some suggestions regarding control of urban air pollution are given below:
1. While the industrial growth of cities can not be stopped, it is necessary to run
industries with greater control of emissions.
2. Where industries are concentrated, residential colonies have to be distant.
3. Cooking fuel (LPG, CNG) should be made available on priority basis in urban
areas to reduce indoor pollution.
4. Vehicles with old technology should be barred from plying in big cities.
17
5. Three I two- wheelers should be upgraded to four stroke engines.
6. Heavy duty vehicles should not be allowed to inner city roads at peak hours (8AM
to 12 PM and 4PM to 8PM) so as to reduce traffic stagnation.
7. To encourage the introduction of modem technology in vehicles, the pnce
differential between diesel and petrol should be minimized as diesel is a greater
source of pollutant release.
8. Catalytic converters should be made compulsory far all petrol driven vehicles and
dieselised vehicles must have a particle trap.
9. We should manage traffic better by allowing wide roads and spacmg of bus
terminii and bus stops should be located away from crowded junctions. At present
in many cities, bus stops are located next to traffic signals thus blocking the flow
of vehicles.
10. At railway stations, we need to regulate pedestrian and vehicular traffic
movement.
1.8 Role of Meteorology In Air Pollution:
Meteorology plays a significant role in air pollution. Even in our most polluted
cities
~here
there are heavy industries, there are
freque~t
periods when the
atmospheric air is quite, clear and transparent. These frequent fluctuations are not
caused by gross changes in the emission of local pollutants rather they are a function
of variations in the meteorological conditions.
The solution to pollution is dilution. If the air into which pollutants are
released is not dispersed, the air will become more toxic. Two most important
atmospheric conditions affecting the dispersion of pollutants are
1.
The strength of the wind
2.
The stability of atmosphere.
These factors are critical because they determine how rapidly pollutants are
diluted by mixing with the surrounding air after leaving the source. The study of air
pollution can not be complete unless the meteorology is considered as both are
18
complimentary to each other. When the contaminants are emitted into the atmosphere
they are at the mercy of weather. They are transported, diffused (thus diluted),
transformed into secondary pollutants and /or removed from the atmosphere through
wet/dry deposition or accumulated in the atmosphere depending upon the existing
meteorological conditions, such as wind, stability, temperature, humidity, intensity
and duration of solar radiation and presence of other chemical species in the
atmosphere.
Therefore, the pollution level at any place and time represents a balance
between the rate of emission from their sources and the rate at which they are
dispersed in the atmosphere. (Hewson, 1950, 1952, 1955 and 1956; Pack, 1964;
lglaur, 1968; McCormick, 1969; Winthrop, 1971; Middleton, 1971; Shaw and Munn,
1971; Munn, 1976; Raymound and Lowry, 1976; Stom1, 1976; Wark and Warner,
1976; Padmanabhamurty, 1980).
The climatological and air quality observation obtained for the periods 197490 and 1983-90 in the Greater Athens Area were analyzed by (Kassomenos et al.,
1995). Their results showed that the air quality in the Athens Basin is strongly
affected by the meteorological conditions especially those which are in favor of local
circulations. The worst air pollution episodes were associated with anticyclonic
conditions or advection of warm air masses. The physiographic characteristics of the
GAA induced mesoscale circulation's in .the area, and the interaction
between
synoptic, regional and meso-scale flows play an important role in the formation of the
appropriate atmospheric conditions which are in favour of air pollution episodes.
Hence meteorological parameters influence the concentration of pollutants in
the atmosphere always. Atmospheric pollution does have a substantial influence in
social life and its various activities. It is, therefore necessary to assess the capacity of
the atmosphere to dilute the pollutants and carry them away. For this purpose a study
of air pollution climatology of a particular place is necessary.
19
1.9 Air Pollution Climatology:
Air pollution climatolgy is mainly concerned with aggregate of weather
elements that influence the fate of air-borne effluents of both anthropogenic and
natural origin. It is based on meteorological elements and air quality. For air pollution
purposes, the location and time periods are very important since climate varies from
place to place and periodically. Air pollution climatology is usually described in terms
of relevant elements; wind, temperature, stability, sunshine, stagnation, diffusion
parameters, atmospheric composition etc.
Air pollution climatology is mainly concerned with urban climatology because
most sources of air pollution are located in the urban areas. The meteorological
parameters which affect the atmospheric pollution can be classified into two groups:
I. Primary and
2. Secondary
Wind speed/direction and atmospheric turbulence are placed under primary
category. The secondary factors include temperature, humidity, precipitation, solar
radiation, pressure and visibility. The primary factors are responsible for dispersion
and dilution whereas, secondary factors affect the primary parameters.
Different meteorological parameters affect the pollutants in different ways.
Hence it is necessary to understand the role of each parameter in the dispersal and
transport of pollutants.
1.9.1 Wind:
Air motion relative to the earth's surface is called wind. Wind direction is the
direction from which the wind blows. Wind direction indicates the path in which the
pollutants are transported. Wind speed determines the travel time of pollutants from
the source to the receptors. It specifies how rapidly the contaminants advance
forward. The concentration of air pollutants is inversely proportional to the wind
speed.
As the effluents from industrial stacks are released at various height and
hence transported and diffused through various layers of the atmosphere, it is
20
appropriate to take into account of average winds in the convective mixed layer of the
atmosphere. There are deviations from mean speed and direction of wind. Due to
variation of velocity component in all directions random motion is produced which is
responsible for the movement and diffusion of pollutants about the mean wind path.
This type of motion is called atmospheric turbulence.
Pioneering work in India was done by Mukherjee (1959) who pointed out that
the winds at Alipore were the determining factors in transporting pollutants from city
and other industrial areas towards Dum and Barrackpore and resulting in fog at those
places.
A preliminary study of meteorological conditions in relation to irritating
pollution effects experienced by the residents of Viskhapatnam on 30 & 31 October
1974 was done by Satyanarayana and Subramanyam (1975). Gentle winds from the
source region towards the residential areas augmented the effect and caused irritation
l
to the residents.
;!::
~
Hence, wind is one of the most indispensable parameters in the dispersion of
atmospheric pollutants. It carries the pollutants to long distances and associated
turbulence dilutes them. The higher the wind speed, the greater the volume of air that
passes over the top of chimney or over any source at unit time, and greater the
dilution of the effluent.
1.9.2
Stability
One of the important characteristics of the atmosphere is its stability- i.e. its
tendency to resist vertical motion or to suppress existing turbulence. This tendency
directly influences the ability of the atmosphere to disperse pollutants emitted into it
from natural and man-made sources. Stability depends on the vertical distribution of
the temperature. Normally, temperature decreases with height in troposphere. The rate
of decrease of temperature is called lapse rate. The lapse rate of the environment is
called "Environmental lapse rate" (ELR). Lapse rate of a parcel of air which moves
adiabatically in the vertical is called "Adiabatic lapse rate" (ALR). The adiabatic
lapse rate of dry air is called "Dry adiabatic lapse rate" (DALR) is about 0.98 degree
Celsius per 100 metre.
21
Stability is classified as unstable, neutral and stable based on environmental
lapse rate (ELR) vis-a-vis dry adiabatic lapse rate (DALR). When the ELR is equal to
DALR, the atmosphere is said to be neutral. When the ELR is greater than DALR, the
atmosphere is said to be unstable. A rising air parcel cooling at the adiabatic rate
becomes warmer and less dense than its surrounding air in unstable atmosphere.
When the ELR is less than DALR, the atmosphere is said to be stable. In this
condition, a rising parcel of air becomes cooler. and more dense than its surroundings
and tends to return to its original position.
Thus, stability is expressed in terms of lapse rate of air parcel and that of
environment based on the following criteria of buoyancy of the air parcel;
(i)
Unstable when ELR > DALR
(ii)
Neutral when ELR
(iii)
Stable
=
DALR
when ELR < DALR
When temperature increases with height, it is called inversion. Stable
conditions occur in the night and are unfavorable for atmospheric diffusion due to
inhibition of turbulence within the layer. Unstable conditions occur during day time
and is characterized by strong solar heating which promotes turbulence, and is
considered most favorable for atmospheric diffusion of pollutants.
Hence unstable conqitions are favorable for the diffusion of pollutants whi}e
stable and inversion conditions are not. During unstable conditions, the plume from
the source loops due to intense turbulence; during neutral condition, the plume
assumes a
cone shape; during stable condition especially during inversion, the
diffusion of plume in the vertical is restricted and hence the dense plume with slight
horizontal meandering travels.
1.9.3
Inversion
The extreme case, which is called "Inversion" occurs when the temperature
instead of decreasing, increases with height forming a very stable atmosphere. From
the view point of air pollution such a situation inhibits mixing of pollutants often
raising their concentration to dangerous levels.
22
Temperature inversion represents a situation in which the atmosphere is very
stable and the mixing depth is significantly restricted. Cold air prevents upwards
movement, leaving the pollutants trapped in a relatively narrow zone near the ground.
Most of the air pollution episodes cited earlier were linked to the occurrence of
temperature inversions.
Many extensive and long-lived air pollution episodes are linked to temperature
inversions that develop in association with the sinking air that characterizes slow
moving centres of high pressure (anticyclones). As the air sinks to lower heights, it is
compressed and so its temperature rises. Because turbulence is always present near
the ground, this lowermost portion of the atmosphere is generally prevented from
participating in the general subsidence. Thus an inversion develops aloft between the
lower turbulent zone and the subsiding warmers layers.
1.9.4
Temperature:
Temperature plays a significant role in affecting the concentration of
pollutants through chemical/photochemical reactions and it also influences the
turbulence and stability which are primary agents of diffusion. Further the fall
velocities for the different precipitating elements are also influenced by temperature,
because this velocity depends on the shape of falling element and the shape in tum of
falling element depends on ambient temperature.
The ambient temperature affects air pollution as:
(i)
It afiects plume rise. The rise of plume above the stack is directly proportional
to the difference between the stack gas temperature and the ambient air
temperature.
(ii)
It also affects the rate of chemical reactions.
High environmental temperature is obviously deleterious to health and
comfort and prolonged exposure can be instrumental in the incidence of strokes, heart
disease and pulmonary disorders (Schuman eta/., 1964).
Using synoptic and climatological data
~(1951-77)
of 16 stations of
Bangladesh, temporal and spatial variations of the absolute maximum temperature
23
have been studied. Empirical probabilities for the interval 35.1°- 40.0°c and 40.145.00c of absolute temperature have been examined (Ahmed and Mobassher, 1991).
Decadal variations of meteorological parameters viz. temperature, pressure
and seasonal and annual rainfall were studied for the period 1901 to 1986. The
temperatures are showing a decreasing trend in almost all the northern parts of the
country (north of 23 °N) and a rising trend in Southern parts (South of 23 °N). There is
G'--
a small warming trend for country as whole (Srivastava eta!., 1992).
~
1.9.5
Humidity
Humidity is the general term used to describe the amount of water vapor in the
air. The most familiar term used to describe the moisture content of air is relative
humidity. Relative humidity is the ratio of the actual mixing ratio to the saturation
mixing ratio ie. it is a ratio of the air's actual water vapor content compared to the
amount of water vapor required for saturation at that temperature. Thus, it indicates
how near the air is to saturation rather than indicating the actual quality of water
vapor in the air. Because relative humidity is based on the atmospheric water vapor
content and the amount of moisture required for saturation is temperature dependent,
it can be changed in either of two ways. First, if moisture is added to or removed from
air, its relative humidity will change. The second condition that affects relative
humidity is air temperature. When the water vapor content remains constant, a
decrease in temperature results in an increase in relative humidity.
Water vapor interacts with air pollutants significantly. The atmospheric
moisture accumulates over the pollutant molecules and forms aerosols. The water
vapor also absorbs the pollutants. This water vapor condenses over pollutants which
act as nuclei to form cloud droplets and precipitate as rain. In addition to this, local
and regional water budgets change because of terrestrial temperatures. Water changes
easily from vapor to the liquid and solid phases with large release or absorption of
heat.
Quantitative effects of the three major meteorological parameters viz., relative
humidity, solar radiation and wind speed on the level of SPM were studied by
Mukherjee and Ray (1991). They observed that apart from solar radiation and wind
speed, the relative humidity was a significant parameter in the dispersion and
modeling studies. Analysis of macro-level monthly data of SPM and relative humidity
24
for Calcutta, Bombay, Delhi and Hyderabad revealed negative correlation between
SPM and humidity.
Other important facets of atmospheric humidity involve the formation of dew
which is generally expressed in terms of dew point. Dew point is defined as the
temperature to which a given parcel of air must be cooled at constant pressure and
constant water vapor content in order for saturation to occur (Rosenberg eta!., 1983).
1.9.6
Precipitation:
Water drops fall from atmosphere to the earth's surface in a number of forms such
as drizzle, rain, freezing, snow, sleet, graupel and hail which in general is termed as
precipitation. This process requires:1. supply of water (vapor or liquid),
2. microscopic particles for condensation called nuclei and
3. updraft of proper magnitude and persistence.
Precipitation scavenges the gaseous and particulate pollutants. The intensity of
precipitation, the solubility and size spectrum of the falling particles and the fall
velocities of the individual particles are important for precipitation scavenging
studies. The intensity of precipitation is the amount of precipitation per unit time
(Drake eta!., 1979).
Precipitation scavenges the gaseous and particulate pollutants from the
atmosphere in two ways;
(i)
Wash-out
(ii)
Rain-out
Wash-out is the interaction and subsequent removal of gaseous and particulate
pollutants by falling rain drops. Rain-out is the collection and subsequent removal
from the atmosphere of gases and particulates by cloud particles prior to their growth
to and descent as rain drops.
Kellogg eta!. (1972) estimated that 86% of the atmospheric sulfur is deposited
at the earth surface by precipitation. Sulfur and other pollutants are captured by
precipitation in two ways, namely, rain-out and wash-out.
Thus, rain-out is removal within the clouds, whereas, wash-out is removal by
25
precipitation below the clouds. Hence, precipitation plays vital role in reducing the
concentration of air pollutants in the atmosphere.
1. 9. 7 Visibility
Visibility constitutes an important meteorological parameter for the safe and
efficient conduct of aircraft operations, particularly during their landing and take off
phases.
Visibility is defined as the greatest distance at which a black object of suitable
dimensions can be seen and recognized against the horizon sky, or, in the case of
night observations, could be seen and recognized if the general illumination were
raised to the normal daylight level (W.M.O., 1966).
Dayakishan and Ganda (1988) observed a definite trend of deterioration of
visibility at IGI Airport (Palam) during the last 13 years. This deteriorating trend is
due to increased load of air pollutants i.e. aerosols over Delhi.
Summer visibility data from a rural site in southern England were analyzed in
different wind directions and related to possible air pollution source areas. Climate
change was not the major cause of visibility improvement .S02 emissions are more
. important for visibility improvement than changes in. long distance transport of air
pollution from continental Europe (Lee, 1990).
The variability
of visibility as a function of selected meteorological and
chemical variables suggested that scattering of light in Hong Kong was mainly related
to NH/, S0 "2, N0 - and trace element. Mixing height is the most important
4
3
meteorological factor involved in visibility reduction (Sequeira et al., 1998).
In fact, visibility is affected by air pollutants and it provides insight into air
quality trends. The reduction of visibility is one of the most common effects of air
pollution resulting from the absorption/scattering of light by airborne liquid and solid
materials. Absorption of certain wavelengths of light by gas molecules and particles is
sometimes responsible for atmospheric coloration's. However, light scattering is the
most important phenomenon responsible for impairment of visibility. Light scattering
26
refers to the deflection of the direction of travel of light by airborne material.
Visibility is reduced when there is significant scattering because particles in the
atmosphere between the observer and the object scatter light from the sun and other
parts of the sky through the line of sight of the observer. The light decreases the
contrast between the object and the background sky, thereby reducing visibility.
Hence, there is decrease in visibility due to increase in air pollution and vice versa.
1.10 Air Pollution Potential
Air pollution potential may be thought of as a measure of inability of the
atmosphere to adequately dilute and disperse pollutants vertically and horizontally
emitted into it, based on the values of specific meteorological parameters of the
microscale features (Gross, 1970). Hence, condition in which dispersal of pollutants
can occur denote low pollution potential, whereas, conditions which allow for
accumulation of pollutants denote high pollution potential.
Occurrences of meteorological conditions associated with extensive and
persistent areas of high air pollution potential over the western United States were
found. The most likely large scale synoptic feature conducive to poor air quality is
found to be the quasi-stationary anticyclone. A typical episode of high pollution
potential was described by Holzworth, (1962).
Munn and Hirt (1969) presented the classical problem of diffusion from a
point source, plume rise, the meso-scale problem urban meteorology, and forecasting
air pollution potential.
Effective pollution potential indices of ten stations in India are obtained for
each month, season and year by Reddy (1974) who concluded that high pollution
potential exists over the stations in different months.
Viswanadtham and Santosh (1989) have estimated the air pollution potential
by computing isothermals, inversions, lapse conditions, mixing heights and
ventilation coefficients over South India for the months of January, April, July and
October.
High pollution potential is defined as "a meteorological
27
condition which
given the existence of emissions, would be conducive to the occurrence of poor air
quality (Gross, 1970)". For deciding the location of any new industry or any pollutant
releasing source at any place; a thorough study of air pollution potential is essential.
For assessing the pollution potential, two important parameters are required viz.,
(i).
Mixing height
(ii)
Ventilation coefficient
1.10.1 Mixing height
It is defined as the height up to which air pollutants mixup primarily through
the action of atmospheric turbulence.
The vertical extent to which this turbulent
mixing takes place varies diurnally from season to season and is also affected by
topographical features.
Under convective conditions, the m1xmg layer may extend upto several
kilometers above the surface but under stable conditions its height may reduce to
zero. In the absence of temperature differences, between the air and the surface,
mixing is brought about solely by mechanical turbulence and the depth of the mixing
height separates polluted surface air from clear air aloft. It is expressed in meters.
Mixing height and wind speed data are derived for mornings and afternoons
from five years of surface and upper air measurements at 62
National Weather
Service stations through out the Unites States. These calculations illustrate the typical
large diurnal variation in atmosphere dispersion (Holzworth, 1970, 1972).
Miller ( 1967) presented a method to estimate the vertical extent of
atmospheric mixing during the afternoon and the average transport wind speed.
Afternoon mixing depth is assumed to be dependent upon the observed difference
between the maximum afternoon surface temperature and the mean virtual
temperature of the atmospheric layer containing the top of the mixing depth.
The variation of mixing height in the Toronto area was investigated using rawinsonde data by
Padmanabhamurty and Munn (1973). According to them, the height of the surface mixed layer is of
considerable importance in the prediction of pollution potential and of pollution concentrations.
McCaldin and Sholter, (1970) have shown that the turbulence registered by an aircraft flying
within the mixing layer decreases significantly over about two to three hours in late afternoon. Thus, in
a fair weather situation, the mixing height increases during the day with rising surface temperature and
28
attains maximum around the time of maximum temperature ·epoch and later decreases as the surface of
the earth cools slowly.
In India, Raman and Kelkar (1972) have made daily estimates of morning and
afternoon mixing height for Bombay based on 530 hr.;I.S.T. rawinsonde observations
and daily maximum and minimum surface temperatures. They found that the average
value of heat island (based on minimum temperature) was 2.5°C for Bombay and then
used this value in calculating morning mixing height.
Surface meteorological data were analyzed and mixing depths and stabilities
were worked out in order to evaluate the carrying capacity of the atmosphere over
Delhi. Based on the above analysis an emission schedule was suggested for the four
seasons (Padmanabhamurty and Tangirala, 1990).
The mixing heights, wind speeds and ventilation coefficients at the selected
sites in Egypt were calculated by Salem et al., (1993 ). The analysis of mixing height,
ventilation coefficients indicate that meteorological conditions during afternoon are
most favourable for rapid dispersion of pollutants.
L10.2 Ventilation Coefficient
The product of mixing height and wind speed averaged through the surface
mixed layer is called ventilation coefficient. It is expressed in m 2s- 1•
The. criteria adopted by US National Meteorological Centre and Atmospheric
Environment Service, Canada, for assessing/ forecasting high pollution potential are
that the morning mixing heights should be:::;; 500 m and transport wind speed:::;; 4 m s· 1
and the afternoon ventilation coefficient should be :::;; 6000 m2s- 1 and transport wind
1
speed :::;; 4 m s- (Gross, 1970). Hence, the lower the mixing height, adverse is the
condition for dispersion of air pollutants.
At Delhi and Mathura, the morning and afternoon mixing depths and average
wind speeds through mixing layer and ventilation coefficients and inversions were
calculated. More intense inversions occurs at Mathura than at Delhi. Low mixing
depth, low wind speed and intense ground inversion lead to high pollution potential at
Mathura (Padmanabhamurty and Mandai, 1979).
At Visakhapatnam, the morning mixing depth and transport wind speed and
29
the afternoon ventilation coefficient and transport wind speed which satisfy the
stipulated criteria for high pollution potential point out that control measures to
alleviate the pollution problems are to be taken between December and February
(Padmanabhamurty and Mandai, 1980).
1.11 Significance of Air Pollution Climatology:
Air pollution climatology is significantly important because it explains the
ability of the atmosphere to dilute or stagnate pollutants over a region at any time. It
provides primary assessment of the variation in the dispersion ability of the
atmosphere, both diurnally and seasonally. It also helps to compare dispersal
capacities of different regions. It deals with the climatological parameters which are
responsible for diffusion of air pollutants.
The important uses of air pollution climatology are urban planning and
planning of the location of pollution sources in relation to sensitive areas and air
quality management programmes. Some predictive studies may be made regarding
pollution potential and suggestions can also be made pertaining to emission
scheduling, siting new industries as well as town and country planning. Therefore,
knowledge of air pollution climatology is inevitable in air pollution studies and in
urban planning.
Wind roses, stability classification and visibility wind roses at three stations
viz. Dehradoon (valley), Mussoorie' (hill slope) and Roorkee (plains) were presented
and discussed in connection with Doon valley pollution (Padmanabhamurty et al.,
1987).
Ravichandran (1989) studied the diffusion climatology of Delhi. He analyzed
different meteorological data and concluded that pre-monsoon and monsoon months
have high carrying capacity of pollutants whereas winter and post-monsoon months
have lesser dispersal capacity of pollutants.
For Delhi, day time is suitable for good dispersion in all months but the setting
up of any industry in the region of W to NNW is not advisable. In the case of existing
industries, emissions must be lessened during night time and particularly in the winter
months (Padmanabhamurty and Ravichandran, 1991 ).
30
The seasonal and diurnal pollution potential around Patna, the capital region
of Bihar, and Gaya was studied by Rai and Padmanabhamurty (1993). It was
concluded that pre-monsoon and monsoon months have a high carrying capacity of
pollutants whereas winter and post-monsoon months have less dispersal capacity.
Night and early mornings hours have less dispersal capacity of pollutants due to stable
atmosphere accompanied by light or no winds.
Ravichandran (1994) studied some meteorological aspects of air pollution at
Delhi. He found that good dispersal of pollutants will generally be in warmer months
especially during day time than in winter. The high pollution in Delhi is due to
increasing urbanization and industrialization. The assimilative capacity of the urban
atmosphere may not meet the demands of pollution due to anthropogenic sources.
Nandankar (1994) studied the diffusion climatology of Uttar Pradesh taking
meteorological data of various stations. He suggested that morning hours have high
pollution potential and low in the afternoon. Better dispersal of pollutants can be
expected in summer followed by monsoon and poor in winter and post-monsoon
season. Area near the foot hills of the Himalayas have high pollution potential and the
area in the central parts of the state and the southern districts have respectively
moderate and low pollution potential.
The important parameters in Air pollution climatology are the temporal and
spatial variation of wind, stability, mixing height, Ventilation coefficient etc. In the
past, several studies have been made in India and abroad taking different aspects
in the air pollution climatology. (De Mairrs, 1961; Hosler, 1961; Holzworth, 1962,
1964, 1967, 1970, 1972, 1974, Williams, 1964; Miller, 1967; Gross, 1970;
Padmanabhamurty and Munn, 1973; Ramesh, 1976; Padmanabhamurty and Mandai,
1979, 1980, 1981; Vittalmurty et.al.; 1980 a & b; Padmanabhamurty 1984; Gmo,
1985;
Kumari,
1985;
IMD,
1985;
Sadhuram
and
Vittalmurty,
1986;
Padmanabhamurty et.al., 1987; Pierce, 1988; Padmanabhamurty and Tangirala, 1988;
Ravichandran, 1989, Kumar 1990, Rai and Padmanabhamurty, 1993, Nandankar,
1994; Kassomenos et.al; 1995).
31
1.12
Objectives of the Present Study:
Several industries (Iron & Steel, mining, fertilizer, oil refinery, cement, coal
washeries, lead smelter, sugarcane, alcohol, fire bricks, foundry, industrial gases,
leather etc.) have been/are being set up in Bihar due to abundance of fuel and
minerals. Urbanization has also been on the increase ever since. This has led to an
increase in emission of a variety of air pollutants in major cities across the state.
Unfortunately, the lack of concern for environment by the government authorities and
a relatively lesser environmental awareness among people of the state, have created a
situation where not much attention is paid to the control of these air pollutants coming
out of industries, households, vehicles etc. As a result of which air pollution levels
have been increasing alarmingly in almost all major cities of Bihar. Hence these
activities deteriorate the air quality of the state of Bihar. Thus, a need is felt to make a
comprehensive assessment of the air pollution climatology of Bihar which deals with
the meteorological parameters responsible for dispersal of air pollutants in order to
suggest precautionary measures to control pollution in the state.
It is our prime concern to protect our air environment. But, it is not possible to
stop the ever increasing number of vehicles or industries. However, we can control
the air pollution in such a way that concentration of pollutants does not interfere much
with the human activities. It can be minimized by adopting a highly developed
technology in industries or automotive _mechanism, installing controlling equipment.
In addition to that, knowledge of meteorological conditions is also very
essential like source strength, types of pollutants, their fate in the atmosphere, their
chemical behavior etc. Meteorological parameters play an important role in
determining the concentration of air pollutants.
In the present study the dispersal capacity of some areas in Bihar in the four
different seasons viz., winter (January), pre-monsoon (April), Monsoon (August) and
post-monsoon (October) has been assessed. No such study has been made earlier for
the state of Bihar. The present study would thus be very useful in understanding the
diurnal and seasonal variation of the diffusion parameters and their impact on the
concentration of the air pollutants.
32
The main objectives of the study are:
1. To study the temporal and spatial variation of temperature, humidity, stability,
wind, inversion, mixing height, ventilation co-efficient.
2. To study the effects of increasing industrialization on visibility and
3. To identify areas of high and low pollution potential and to suggest prospective
industrial locations or mitigation of pollution at the existing industrial locations
i.e. in urban planning and locating new industrial areas in relation to sensitive
areas.
4. To study air quality management.
5. To prepare emission schedule for certain locations in Bihar.
Hence, this study is more beneficial in scheduling the pollution activities and
proper planning. In the second chapter, brief description of the study area along with
different stations studied are presented.
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