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Environmental Pollution
Environmental pollution can be defined as any undesirable change in the physical,
chemical or biological characteristics of any component of the environment ( air,
water, soil), which can cause harmful effects on various form of life or property.
Pollutant are defined as matter or energy which leads to undesirable changes in the
environment. Pollutants include solid, liquid or gaseous substances present in
greater than natural abundance produced due to human activity, which have a
detrimental effect on our environment. From an ecological perspective pollutants
can be classified as follows:
1) Degradable or non-persistent pollutants: These can be rapidly broken down by
natural processes. Eg: domestic sewage, discarded vegetables etc.
2) Slowly degradable or persistent pollutants: Pollutants that remain in the
environment for many years in an unchanged condition and take decades or longer
to degrade. Eg: DDT and most plastics.
3) Non-degradable pollutants: These cannot be degraded by natural processes.
Once they are released into the environment they are difficult to eradicate and
continue to accumulate. Eg: toxic elements like lead or mercury.
Environmental Pollution could be of various types:
1) Air Pollution: Air pollution occurs due to the presence of certain
substances (including the normal constituent in excess) in concentration
which can cause undesirable effects on human health, property and
structure. These substance include gases, particulate matter, radioactive
substances etc.
Classification of Air Pollutants: Based upon their origin air pollutant are
classified into two type:
a) Primary Pollutants: Pollutants that are emitted directly from identifiable
sources are produced both by natural events (for example, dust storms
and volcanic eruptions) and human activities (emission from vehicles,
industries, etc.). There are five primary pollutants that together contribute
about 90 percent of the global air pollution. These are carbon oxides (CO
and CO2), nitrogen oxides, sulfur oxides, volatile organic compounds
(mostly hydrocarbons) and suspended particulate matter.
Major primary pollutant:
1) Particulate matter: Particulates are small pieces of solid material (for
example, smoke particles from fires, bits of asbestos, dust particles and
ash from industries) dispersed into the atmosphere. The effects of
particulates range from soot to the carcinogenic (cancer causing) effects of
asbestos, dust particles and ash from industrial plants that are dispersed
into the atmosphere.
Some definition:
a) Aerosol : General term for particles suspended in air. Example: Sprays
from pressurized cans
b) Mist : Aerosol consisting of liquid droplets. Example: Sulfuric acid mist
c) Dust : Aerosol consisting of solid particles that are blown into the air or
are produced from larger particles by grinding them down. Example :Dust
storm
d ) Smoke: Aerosol consisting of solid particles or a mixture of solid and
liquid particles produced by chemical reaction such as fires. Example:
Cigarette smoke, smoke from burning garbage.
e) Fume : It applies specifically to aerosols produced by condensation of hot
vapors of metals. Example: Zinc/lead fumes
f) Plume : Geometrical shape or form of the smoke coming out of a chimney.
g) Fog : Aerosol consisting of water droplets.
h) Smog : Term used to describe a mixture of smoke and fog.
2) Hydrocarbon: Hydrocarbons are a group of compounds consisting of
carbon and hydrogen atoms. They either evaporate from fuel supplies or are
remnants of fuel that did not burn completely. They act as precursor for the
production of secondary pollutant.
3) Nitrogen oxides: Nitrogen oxides are found in vehicular exhausts. Nitrogen
oxides are significant, as they are involved in the production of secondary air
pollutants such as ozone. They are also important component of acid rain.
4) Sulfur oxides: are produced when sulfur containing fossil fuels are burnt.
They are major source of increase acidity in the atmospheric rain, a
phenomenon known as acid rain.
5) Carbon monoxide: is a colorless, odorless and toxic gas produced
when organic materials such as natural gas, coal or wood are incompletely
burnt. Vehicular exhausts are the single largest source of carbon monoxide.
Carbon monoxide is however not a persistent pollutant. Natural processes
can convert carbon monoxide to other compounds that are not harmful.
6) Carbon dioxide: It is a component of atmospheric system and currently
make 0.038 per cent of the atmosphere. It is important for maintaining the
biotic system as source of carbon. However during past decade its
concentration is increasing in atmosphere due to burning of fossils fuel and
land use changes. It shows property of green house gas, thereby results into a
phenomenon known as global warming.
Beside these primary pollutant there are certain pollutant
which are not a natural component of atmosphere, however it is introduced by
human activities, such as CFC, MIC (methyl isocyanate).
b) Secondary Pollutant: Pollutants that are produced in the atmosphere
when certain chemical reactions take place among the primary pollutants
are called secondary pollutants. Eg: sulfuric acid, nitric acid, carbonic acid,
etc.
Some more example of Secondary pollutant:
a) Tropospheric Ozone: The majority of tropospheric ozone formation occurs
when nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic
compounds (VOCs), such as xylene, react in the atmosphere in the
presence of sunlight. NOx, CO, and VOCs are called ozone precursors.
b) Peroxyacetyl nitrate (PAN): Acyl peroxy nitrates, or Peroxyacyl nitrates
(also known as APNs, or PANs), are powerful respiratory and eye irritants
present in photochemical smog.
CH3C(O)OO· + NO2 → CH3C(O)OONO2
General equation:
Hydrocarbons + O2 + light → CxHyC(O)OO·
CxHyC(O)OO· + NO2 → CxHyC(O)OONO2
Sources of Air Pollutants: It is mainly divided into two types:
a) Natural sources: The natural sources of air pollution are volcanic eruption,
forest fire, sea salt sprays, biological decay, pollen grains of flowers, spore
etc. Radioactive material present in earth crust are the sources of
radioactivity in the atmosphere.
b) Man-made (Anthropogenic sources): it include thermal power plant,
industrial units, vehicular emissions, fossil fuel burning, agricultural
activities etc.
Human can be affected by both indoor or outdoor air pollution. The most
important indoor air pollutant is radon gas ( causing lung cancer) a
radioactive atomic gas that results from the radioactive decay of radium, which
may be found in rock formations beneath buildings or in certain building
materials (bricks, concrete, tiles etc) themselves. Beside radon carbon
monoxide, sulphur dioxide and hydrocarbon released due to incomplete
combustion of fossil fuel, wood for cooking purpose are other major air
pollutant.
Fate of pollutant in the atmosphere:
•Once pollutants enter the troposphere they are transported downwind,
diluted by the large volume of air, transformed through either physical or
chemical changes or are removed from the atmosphere by rain during which
they are attached to water vapor that subsequently forms rain or snow that falls
to the earth’s surface.
• However this transportation and dilution of air pollutant depend strongly upon
the metrological condition prevailing in that area. In an unstable atmosphere
with high wind speed dispersion and dilution rate of pollutant are much
higher compare to a stable atmosphere.
Stable atmosphere:
If we (somehow) lift the parcel: It will cool at the dry adiabatic lapse rate.
The parcel will find itself cooler than the environmental (sounding) temperature.
At the same pressure, a cooler parcel will be more dense than the environment.
Being denser, the parcel will descend back to where it came from.
STABLE!
Unstable atmosphere:
If we (somehow) lift the parcel: It will cool at the dry adiabatic lapse rate. The parcel will
find itself warmer than the environmental (sounding) temperature. At the same
pressure, a warmer parcel will be less dense than the environment. Being less
dense, the parcel will ascend and move farther from where it came from. UNSTABLE!
Temperature Inversion:
• Although the temperature of air relatively near the earth’s surface normally
decreases with increasing altitude, certain atmospheric conditions can
result in the opposite condition—increasing temperature with increasing
altitude. Such conditions are characterized by high atmospheric stability and
are known as temperature inversions. Because they limit the vertical
circulation of air, temperature inversions result in air stagnation and the
trapping of air pollutants in localized areas.
Frontal inversion: An inversion can form from the collision of a warm air mass
(warm front) with a cold air mass (cold front). The warm air mass overrides the
cold air mass in the frontal area, producing the inversion.
Radiation inversions: It is the most common form of surface inversion and
occurs when the earth's surface cools rapidly. As the earth cools, so does the
layer of air close to the surface. If this air cools to a temperature below that of
the air above, it becomes very stable, and the layer of warmer air impedes any
vertical motion. Radiation inversions usually occur in the late evening through
the early morning under clear skies with calm winds, when the cooling effect is
greatest.
Subsidence inversions: It takes place in hill area, where cooler surface air
tends to flow into valleys at night, where it is overlain by warmer, less dense
air., often accompanied by radiation inversions, can become very widespread.
marine inversion is produced during the summer months when cool air laden
with moisture from the ocean blows onshore and under warm, dry inland air.
Illustration of pollutants trapped in a temperature inversion.
Impact of Temperature Inversion: Due to temperature inversion condition,
environment become more stable thereby prevent dispersal and dilution of
air pollutant from localized areas. One major air pollution scenario due to
temperature inversion condition is London Smog (winter of 1952).
The weather in Greater London had been unusually cold for several weeks
leading up to the event. Because of the cold weather, households were
burning more coal than usual to keep warm. The smoke from approximately
one million coal-fired stoves, in addition to the emissions from local
industry, was released into the atmosphere.
Thousands of tons of black soot, tar particles, and sulfur dioxide had
accumulated in the air from the heavy coal combustion. Estimates of PM10
concentrations during December, 1952, range between 3,000 and 14,000
μg/m³ with the high range being approximately 50 times higher than normal
levels at the time. PM10 is particulate matter less than 10 micrometers in
diameter. Due to temperature inversion condition the thick, smoke-polluted
air to be trapped under the inversion. The following 114 hours in London
experienced visibility less than 500 meters with 48 hours below 50 meters
visibility. The smog-related deaths were primarily attributed to pneumonia,
bronchitis, tuberculosis, and heart failure.
Effect of air pollution: Air pollution has adverse effects on living
organisms and materials.
1) Effects on human health:
•
Air pollutants especially particulate matter( PM) is related to respiratory
disease in human being. Particles come in a wide range of sizes. Those
less than 10 micrometers in diameter (PM10) are so small that they can
get into the lungs, potentially causing serious health problems. Suspended
particulates can cause damage to lung tissues and diseases like asthma,
chronic bronchitis and emphysema( damage of air sacs leading to loss
of lung elasticity and acute shortness of breath. Metal in form of PM like
lead, Asbestos etc also cause cancer or affect vital organs like kidney, liver,
spleen etc.
•
Carbon monoxides combine with hemoglobin of blood to form
carboxyhaemoglobin, due to which oxygen carrying capacity to various
part of the body decrease which may results into suffocation, dizziness,
unconsciousness and even death.
• Hydrocarbon emission from vehicle or industrial units ( benzene,
formaldehyde etc.) may results into mutation, reproductive problem or even
cancer.
2) Effects on Plant: Air pollution affects plant by entering through stomata
(leaf pores through which gases diffuse), destroy chlorophyll and affect
photosynthesis. Gaseous pollutant like SO2, ozone etc can leads to necrosis(
dead areas of leaf), chlorosis( yellowing of leaf due to reduction of
chlorophyll), abscission ( dropping of leaves).
3) Effects on aquatic life: Air pollutants (SOx and NOx) when mix up with
rain can results into acid rain which reduces the pH of fresh water lakes
especially in the higher latitude. This reduction in pH has adverse effect on
aquatic biotic life.
4) Effects on materials: Metal parts of building, vehicle, bridges, wires and
railway tracks are affected due to corrosion by particulate matter which further
get accerlated in presence of SO2 and moisture. Acid rain also affect the
structure made up of marble and limestone. Example: Yellowing of Tajmahal in
Agra. Ozone in the atmosphere can cause cracking of rubber tyres.
Beside these effect, air pollutants also leads to stratospheric
Ozone depletion which results into increase UV-rays exposure on earth
surface and Global warming due to green house gases are major
environmental problem .
Control of Air Pollution: Air pollution can be controlled by applying
various measures such as:
1) Zonation in landuse pattern: Industries should be set up far away from
the residential areas and Industries should be located in places so as to minimize
the effects of pollution after considering the topography and the wind directions.
2) Dilution of emission: It can be done by increasing stack height, beyond
inversion layer. Wind current will disperse the pollutant.
3) Low Sulphur coal in industries to reduce emission of SOx from coal
burning.
4) Installment of pollutant control equipment such as cyclones, bag house filters etc
to reduce pollutant emission from industry.
5) Establish vehicular emission norm to reduce emission from vehicles, regular
tuning of engines, installing catalytic converters, engine modification to have fuel
efficient (lean) mixture to reduce CO and hydrocarbon emission, slow and cooler
burning of fuels to reduce NOx emission( Honda Technology).
6) Using mass transport system, bicycles etc.
Bharat stage emission standards are emission standards instituted by
Government of India to regulate the output of air pollutants from internal
combustion engine equipments, including motor vehicles. The standards
and the timeline for implementation are set by the Central Pollution Control
Board under the Ministry of Environment & Forests.
Air Pollution control through pollution control equipment:
1) Particulate matter: Many devices are available for removal of particulate matter
and choice of which depend upon characteristics of particulate matter, flow rate,
collection efficiency, costs etc.
a) Cyclone: These are employed for large size particle. The gas with particle in it
enters tangentially at the top of cylinder and spin forming a vortex. Due to
centrifugal force, particle strike the wall of cylinder.
b) Bag house filter: It contain large number of filter bags made of fabric. Dirty gas is
passed through the filter bags which leaves the bags through their pores. The dust
particle get deposited on the inner surface of the bag filters and may form a cake which
can be removed by shaking.
c) Wet scrubber: Dirty gas is passed through
water in the chamber or water is sprayed on the
gas. Particles are made wet and are removed
from the gas stream which leaves from the
top of scrubber.
d) Electrostatic precipitator: It can be plate type or cylinder type. Vertical wires are
placed between the parallel plates or wires is hung along the axis of the cylinder. Higher
negative voltage is applied to the wire. Dust particle while passing from the lower end
get negatively charged and are collected on the positively charges surface.
Electrostatic precipitators utilize electric energy and can efficiently remove even
submicroscopic particles.
2) Gaseous pollutant: Gaseous pollutant can be reduced by physical
absorption on porous solid materials like activated charcoal, silica gel etc.
Effluent gases can be absorbed in liquid absorbent, example: SO2 absorbed in
ammonia solution.
Air quality monitoring:
The Central Pollution Control Board (CPCB) initiated its own national Ambient Air
Quality Monitoring (NAAQM) program in 1985.
Ambient air quality standards in India developed by the Central Pollution Control Board
Legal aspects of air pollution control in India:
The Air (Prevention and Control of Pollution) Act was legislated in 1981. The Act
provided for prevention, control and abatement of air pollution. In areas notified
under this Act no industrial pollution causing activity could come up without the
permission of the concerned State Pollution Control Board.
To regulate vehicular pollution the Central Motor Vehicles Act of 1939 was amended in
1989. Following this amendment the exhaust emission rules for vehicle owners were
notified in 1990 and the mass emission standards for vehicle manufacturers were
enforced in 1991 for the first time. The mass emission norms have been further revised
for 2000.