environmental pollution notes

7/22/2019 Environmental pollution notes

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Environmental Pollution Control(ETZC362)

Dr. Jegatha Nambi Krishnan

Department of Chemical Engineering

11thJan. 2014

etzc362


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BITS Pilani, K K Birla Goa Campus11th Jan. 2014 (Course Code: etzc 362)

Air Pollution

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Air pollution:any atmospheric condition in which certain substances are present insuch concentrations that they can produce undesirable effects on manand environment

Gases - Sulphur oxides, nitrogen oxides, carbon monoxide,hydrocarbons etc.Particulate matter - smoke, dust, fumes, aerosols,Radioactive materials

Air pollutant is a particular substance -Its concentration is high

compared to the background value & cause adverse effects onhumans, animals, plants or property.

Ex. Sulphur dioxide - > 2 x 10 -4ppm


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BITS Pilani, K K Birla Goa Campus

1. Mass concentration, , defined as the ratio of the mass of

pollutant to the mass of air plus mass of pollutant

Where mp is the mass of pollutant and ma is the massof pure air in a given volume of air-pollutant mixture.

2. Volume concentration, , defined as the ratio of the volume

of pollutant to the volume of air plus volume of pollutant

11th Jan. 2014 (Course Code: etzc 362)

Scales of concentration

pa

p

p

mm

mw

pa

p

pvv

vy

3


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3. Volume concentration in parts per million (ppm),y ppm

4. Mass-Volume concentration, p (g of pollutant per cubicmetre of air), defined as the ratio of the mass of the

pollutant to the volume of air plus volume of pollutant

Assuming that perfect gas law hold for pollutants that areusually formed in the atmosphere



610 pppm yy

pa

p

p vv

m

4





The relation between p and yppm :

p - Concentration of a pollutant whether it be gaseousor particulate (g/m3)

yppm - Volume concentration in parts per million (ppm),

Mp - Molecular weight of the pollutant

45.24

103ppmpp

yM

5



The normal cubic meter is important if the emissiontemperature is greater than ambient as one mole of the

emission gas does not occupy 22.4 L.

At non standard temperatures and pressures, correctionshave to be made.

At STP ( 0C and 101.3 Kpa), 1 mole of an ideal gas

occupies 22.4 L.At non STP conditions,


L

P

kPa101*

K273

T*22.4mole1


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Classification Air Pollutants


Primary Pollutant (Directly emitted from source)- Ex. Particulatematter, inorganic gases and radioactive compounds.

Secondary Pollutant (Formed as a result of chemical andphotochemical reactions in the atmosphere)

Properties of Air Pollutants (particulate matter and gaseous pollutants)

The classification of various particulates may be made as follows:

Dust Particles of size ranging from 1 to 200m. These are formed by

natural disintegration of rock and soil or by mechanical processesof grinding and spraying.

Smoke Fine particles of size ranging from 0.01 to 1 m resultingwhich can be liquid or solid from combustion or other chemicalprocesses. Based on materials burnt it is of different colours. 7


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Fumes Particles of size ranging from 0.1 to 1m formed

by condensation, sublimation , or chemical reaction /

metallurgical processes.

Mist Liquid droplets generally smaller than 10m which are

formed by condensation in the atmosphere or released from

industrial operations.

Fog It is the mist in which the liquid is water and is sufficiently

dense to obscure vision.

Aerosol Air-borne suspensions either solid or liquid; these are

generally smaller than 1m. Dispersion of microscopic solid or liquid

particles in gaseous media.


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Particles- 1-10m

Particles of size ranging from 0.1 to 1m have smaller settling velocities readilystirred by air movements. Those below 0.1 m, a submicroscopic size found in

urban air, undergo random Brownian motion resulting from collisions among

individual molecules.

Most particles of size ranging from 0.1 to 10m in urban air cause significant

damage to health.

Hydrocarbons which can coalesce into aerosol droplets that constitute one kind of

particulate matter.

Most harmful components of incomplete combustion are generally

grouped as particulate polycyclic organic matter (PPOM). PPOMs are

derivatives of benz--pyrene, a potent carcinogen.


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Sizes of Atmospheric particulate matter

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Gaseous PollutantsOxides of Sulphur (SOx, H2SO3)

SO2 is the most important pollutant emitted and is oxidized slowly in clean air to sulphurtrioxide. SO3 with moisture in atmosphere to form sulphuric acid. Both SO2 and SO3are relatively quickly washed out of the atmosphere by rain or settle out as aerosols.Ex. Large SO2 from roasting and treatment of non-ferrous sulphide minerals,principally lead, zinc and copper ores. Metallic and non metallic industries,Petroleum refining operations.

Oxides of Nitrogen (NOx = NO &NO2)

Among the seven oxides of nitrogen, N2O, NO and NO2 are formed in appreciablequantities in the atmosphere. NO2 major pollutant emitted by fuel combustion andnitric acid plants.

Carbon Monoxide (CO) and CO2CO -Single largest pollutant in urban atmosphere and has strong affinity towards

hemoglobin of blood stream and so dangerous asphyxiant. The rate of oxidation ofCO to CO2 is very slow. The main sources of CO in the urban air are smoke andexhaust fumes of burning gas, coal or oil.



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Lighter Hydrocarbons (HCs)

Gaseous and volatile liquid hydrocarbons.

CH4 is the abundant hydrocarbon constituting 40-80% of total

HCs. It has very low photochemical activity and so non-methaneHC concentration is of interest.

Among the alkenes, ethylene and propenes are prominentpollutants. Ex: toluene and m-xylene (urban atmosphere)

Terpenes-volatile HCs (pine tar and wood sources)

These are responsible for the production of secondarypollutants in the presence of sunlight and nitrogen oxides formingphotochemical oxidants Ozone.



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Emission sources- Source type

NaturalThe pollutant emission from natural sources is much greater thanthat from anthropogenic sources. Fortunately, natural pollutantsare distributed throughout the world and reach a sink such asocean or the soil. The atmosphere can cleanse itself from thepollutants given sufficient time. Ex. wind blown dust, pollen, sea

salt nuclei, volcanic ash and gases, smoke and trace gases fromforest fire.

AnthropogenicThe pollutants are concentrated in specific locations and reachhigh levels in atmosphere. The emission of these pollutants is atsuch massive rates that they overwhelm the capacity of theenvironment to cleanse itself. Ex. Combustion of fossil fuels Ex.SO2, NO2, CO & fly ash, trace metal oxides, Ex. mercury, lead andcadmium. Chemical and metallurgical industries, food andagriculture etc.


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Classification of Anthropogenic Airpollution sources

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Behavior and Fate of Air Pollutants

Natural Pathways (scavenging processes) of exchange ofpollutants from atmosphere to earth surface

Particulates:

Wet removal by precipitation. Dry removal by sedimentation, impaction and diffusion.

Gases:

Wet removal by precipitation.

Chemical reaction in the atmosphere to produce aerosols and /or absorption on aerosols with subsequent removal.

Absorption or reaction at land and ocean surfaces.


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Wet PrecipitationWet precipitation has two distinct mechanisms rainout andwashout

The rainout includes various processes taking place insideclouds, where the contaminants serve as condensation nuclei on whichdroplets condense. Ex. Particles less than 0.1m . These particlescaptured by cloud droplets (30 m).

The washout mechanism refers to the removal of pollutants below the

cloud level by falling rain. Ex. Particles larger than 2 m .

The wet precipitation is very effective in removing acid droplets andsulphate particles formed after chemical reactions.



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Dry DepositionParticulate matter smaller than 0.1m often coagulates through mutual collisions and formslarger aggregates which are effectively removed by gravitational settling. Brownian motion isthe major mechanism of coagulation, although atmospheric turbulence also enhances thediffusive motion of particles.

Atmospheric turbulence is particularly effective for coagulating larger particles whose

Brownian motion is less pronounced.

The rate of settling of the particles depends on their settling

velocities according to Stokes Law:

Where

vt = terminal settling velocity; dp = particle diameter;

p and a = density of particle and air, respectively;

a = viscosity of air; P = air pressure; C = constant


pd

Cgd

v papa

p

t

2

118

2


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Interaction at the earths surface

Gaseous pollutants can be transported to the earth surface byatmospheric turbulence where they interact with the oceansurface, vegetation and upper layers of the soil and are removed

by absorption or chemical reaction.

SO2 and CO are the 2 major pollutants formed.

SO2

- Ocean, vegetation and upper layers of the soil

Co converts to CO2 or CH4- Biological action by the bacteria inthe soil acts as a sink.



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Chemical reactions in the atmosphere

Many of the gaseous pollutants undergo chemical reactions within theatmosphere and form new compounds or aerosols.

Oxides of the sulphur is removed from the atmosphere primarily by wet

precipitation.

Oxides of nitrogen are removed through their conversion process to formnitric acid.

CO is removed by the fast reaction with hydroxyl radicals present in theatmosphere. Another possible mechanism is the migration of CO into thestratosphere, where the oxidation to CO2 may subsequently take place bythe hydroxyl radicals. All these pollutants inter-reactby photochemicalprocesses in the phenomenon known as thephotochemical smog.



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Interaction at the Earths surfaceAbsorption

At the ocean surface SO2, first diffuses through the gas phase, crosses the

gas-liquid interface, and finally diffuses into the bulk of the ocean where

it is absorbed

NO2 also absorbed by ocean and other surface waters

ADSORPTION

SO2 first diffuses to the external surface of the solid, penetrates into the

pores of the solid,

and is subsequently adsorbed on the pore site


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BIOLOGICAL ACTION IN SOIL

Soil contains certain bacteria which can make use ofCO in their metabolism, producing either CO2 or CH4.

OHCHHCO

COOCO

242

22

3

22


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SO2 is oxidized to SO3 which combines with atmosphericmoisture to form H2SO4 mist(Slow process)

Metal salt particles serve as nucleation sites for droplet

formation and react with H2SO4 to produce sulphates,

which are also removed by wet precipitation

4232

322 22

SOHSOOH

SOOSO

HClSONaSOHNaCl 22 4242

Chemical reactions in atmosphere

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Direct conversion of NO2 to HNO3 in presence of moisture(slow process)

NOHNOOHNO 322 23

Chemical reactions in atmosphere

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Conditions for the formation of photochemical smog areAir

stagnation, sunlight, & high concentration of HCs & N oxide

in the atmosphere.

Smog arises from photochemical reactions in the loweratmosphere by the interaction of HCs & nitrogen oxidereleased by exhausts of automobiles & some stationarysources.

This interaction results in a series of complex reactionsproducing secondary pollutants like ozone, aldehydes,ketones, & PAN

Photochemical Smog

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smogNOHC atmloweratandhvx

)(PANsNitratesPeroxyacylKetones

Aldehydes

Ozone

Photochemical Reaction

Photochemical Smog

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Interaction at the Earths surface

ABSORPTION

At the ocean surface SO2, first diffuses through the gas phase,

crosses the gas-liquid interface, and finally diffuses into the bulk ofthe ocean where it is absorbed

NO2 also absorbed by ocean and other surface waters

ADSORPTION

SO2 first diffuses to the external surface of the solid, penetratesinto the pores of the solid,

and is subsequently adsorbed on the pore site



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Photochemical smogThe conditions for the formation of photochemical smog are air stagnation,

abundant sunlight, and high concentrations of hydrocarbon and nitrogen

oxides in the atmosphere.

Smog arises from photochemical reactions in the lower atmosphere by the

interaction of hydrocarbons and nitrogen oxide released by exhausts of

automobiles and some stationary sources.

This interaction results in a series of complex reactions producing secondary

pollutants such as ozone, aldehydes, ketones, and peroxyacyl nitrates.



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h d f A ll


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The starting mechanism is the absorption of ultraviolet lightfrom the Sun by NO2. This causes the nitrogen dioxide todecompose into nitric oxide and highly reactive atomicoxygen .

ONOhvNO 2

The atomic oxygen initiates oxidizing processes or quicklycombines with molecular oxygen to form ozone, whichitself is reactive and acts as an oxidant:

223

32

ONONOO

MOMOO



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B h i d F f Ai P ll


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M is an energy-absorbing molecule or particle is required tostabilize O3 or else it will rapidly decompose.

Under normal conditions, the ozone formed will be quicklyremoved by reaction with NO to provide NO2 and O2.

However, when hydrocarbons are present in the atmospherethis mechanism is partially eliminated as NO reacts with thehydrocarbon radical peroxyacyl (RCO.3) and as a result ozoneconcentration builds up to dangerous levels.

Hydrocarbons compete for free oxygen released by NO2decomposition to form oxygen-bearing free radicals such as theacyl radical.

( )H C O R C O a c y l r a d ic a l



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B h i d F f Ai P ll


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This radical takes part in a series of reactions involvingthe formation of still more reactive species, which in turnreact with O2, hydrocarbons and nitric oxide.

32.

23

22.

3.

2

3

32

)(

ORCOORCO

NORCONORCO

ketonesCOR

aldehydesRCHOHCRCOradicalperoxyacylRCOORCO



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B h i d F t f Ai P ll t t


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The typical smog episode occurs in hot, sunny weather

under low humidity conditions. The characteristics

symptoms of the smog are the brown haze in the

atmosphere, reduced visibility, eye irritation, respiratory

diseases and plant damage.



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E A


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Effects of Air Pollution


Human healthAdverse effects may be divided into acute and chroniceffects.

Acute: High concentration for shorter duration.

Chronic: lower concentration for higher durations(prolonged periods).

Particular attention to six pollutants:Particulates, sulphur oxides, carbon monoxide, nitrogenoxides, hydrocarbons and photochemical oxidants.

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Eff f Ai P ll i


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Pollutants may Enter into body by 4 ways:

Ingestion: by means of swallow

Inhalation: by means of respiration inhaled intolungs

Absorption: by means of absorption in skin or eye

Injection: by means of external injection


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Respiratory Effects:

Pollutants may enter the body by a number of ways but primarily

through respiration.

Causes skin irritation.

The major organs of the respiratory system are nose, pharynx, larynx,

trachea, bronchi and lungs. The first four of the above is called

as upper respiratory tract (URT) where as the last 2 are called

as Lower respiratory tract (LRT).

Particulate matter inhaled may be deposited in various regions of the

respiratory system depending on the particle size.


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Particles above 10m are almost retained in the nose itselfand smaller than this may escape the entrapment and

passes through the URT.

Fine particle in the size range from 0.5 to 5m are

deposited in LRT.

This results in the damaging the respiratory organs.



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The Respiratory and the Alveoli


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The Respiratory and the Alveoli.

the pulmonary alveoli are the terminal ends of the respiratory tree, which outcropfrom either alveolar sacs or alveolar ducts, which are both sites of gas exchangewith theblood as well. Carbon dioxide rich blood is pumped from the rest of thebody into the alveolar blood vessels where it through diffusion releases its carbondioxide and absorbs oxygen.

Source: Wikipedia 38

http://en.wikipedia.org/wiki/Respiratory_treehttp://en.wikipedia.org/wiki/Alveolar_ductshttp://en.wikipedia.org/wiki/Bloodhttp://en.wikipedia.org/wiki/Capillarieshttp://en.wikipedia.org/wiki/Diffusionhttp://upload.wikimedia.org/wikipedia/commons/9/9f/Illu_conducting_passages.svghttp://en.wikipedia.org/wiki/Diffusionhttp://en.wikipedia.org/wiki/Capillarieshttp://en.wikipedia.org/wiki/Bloodhttp://en.wikipedia.org/wiki/Alveolar_ductshttp://en.wikipedia.org/wiki/Respiratory_treehttp://en.wikipedia.org/wiki/File:Alveolus_diagram.svg


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Particulate Matter:

Interference of inert particles with the clearing

mechanisms of the respiratory tract.

Particles act as carriers of adsorbed toxic gases

such as SO2 and produce synergetic effects.

Particles may be intrinsically toxic because of their

physical or chemical characteristics.



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Lead

Lead is neurotoxin whose poisoning results in convulsions, delirium,coma,severe and irreversible brain damage and death.

Cadmium

Cigarette smoking constitutes a major source for cadmium accumulation in the

body. It inhibits the performance of certain enzymes thereby producinghypertension in humans. Also causes cardiovascular diseases when exposed tofumes or oxides of cadmium.

Mercury ( Hg present as gas due to high Vap pressure)

Effects of mercury poisoning include neurological damage, chromosomal

aberrations and even death. It penetrates through membranes separatingbloodstream from brain causing injury to cerebellum and cortex.

Higher levels of mercury can build up in the fetus without the mothershowing any signs of illness. The effects are congenital birth defects or thedeath of the fetus.



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Gaseous Pollutants

Sulphur Dioxide

Leads to broncho-constriction when exposed for a few minutes

to levels of 1.6 ppm. Chronic effects are the infection of the

respiratory system in children.Primary threat of SO2 is the formation of H2SO4 and sulphate aerosols.

Carbon Monoxide

When inhaled, passes through the lungs and diffuses directly

into the blood stream to form carboxyhemoglobin, because of itsaffinity, 210 times greater than that of oxygen. This results in

limiting the availability of hemoglobin to carry the oxygen

resulting in asphyxiation.



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Oxides of Nitrogen NO is not irritant and does not show any adverse health effects at the

concentrations generally occurs in the atmosphere. NO2 is relatively insoluble and upon inhalation causes damage to the lung tissues. It form HNO2 & HNO3 which are highly irritating & cause damage to the lungs

tissue Long-term exposure even with 1ppm may lead to health problem like biochemicalchange in blood

Hydro carbons and Photochemical Oxidants

At the concentrations usually found in the urban air, causes no adverse effects onhuman health. The oxidant produced in photochemical smog causes irritation tothe nose, throat and causes chest constriction.

Aromatics causes irritation on mucous membrane PAN & PBN causes irritation on eye, nose, throat & 5 min exposure

with 0.005ppm PBN may lead death


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Effects on VegetationLeaf structure damage is visible incase of vegetation.

The pollutants try to enter through stomata and diffuse to

the surface of the cells within the leaf causing damage topalisade and spongy mesophyll.

The damages are necrosis (dead areas), chlorosis (loss orreduction chlorophyll), epinasty (downward curvature of

the leaf).

Chemicals such as arsenic and fluorides when deposited onthe leaves can poison animals.



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Effect on materials

Particulates such as dust and fumes can damage the

exposed surfaces because of their abrasive nature

The most notorious pollutant responsible for metallic

corrosion is SO2.

Ozone is also very reactive substance and causes thecracking of synthetic rubbers at the levels of 0.01 to 0.02

ppm.



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Green house effect: Global warming

Out of total light energy 20% is absorbed by gases inatmosphere, 50% is absorbed by earth surface, 30% is reflected

back into the space by clouds, ice, snow, sand etc.

The warm earth emits radiation absorbed by it as infrared (heat) radiation

Gases like CO2, in the atmosphere absorbs this heat radiation

The gas molecule then re - emit the absorbed radiation in all directions

A part of this radiation is re diverted to the earth's surface. These processeskeep the earths surface and its atmosphere warm and is called Greenhouse effect.



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Major Air Pollution Disasters


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j

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Ozone HoleOzone layer or natural sunscreen is located in stratosphere

It filters ultraviolet rays of the sunlight, which is harmful tohumans and other forms of life.

Certain gases like Freons or chlorofluoro compounds(CFCs)used as fluids in refrigerators and also as propellants in spraycans of deodorants, perfumes etc is the main cause for theatmospheric ozone depletion.

Cl2CF

2+ h Cl. + ClCF2.

Cl. + 03 ClO + 0

2


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Properties of air pollutants


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p p

Carbon monoxides

Constitutes the single largest pollutant in the urbanatmosphere

Has a B.Pt of -192 0C

Affinities towards hemoglobin in blood stream & isdangerous asphyxiant Main sources of CO in urban air are smoke, exhaust fumes,

from devices burning coal, gas or oil

Hydrocarbons

Gaseous & volatile liquid hydrocarbons are particular airpollutants

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Air Pollution Laws


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To control, to reduce & to monitor

Oldest anti-pollution law Smoke nuisanceAct1920 for Bombay city

Central Air Act,1981 and empowered centralBoard formed for Prevention & Control of WaterPollution,1974

The State PCB are also authorized to close,prohibit/regulate any industry/operation forimproper implementation of acts

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Function of Central PCB


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Advise GOI about prevention, control & abatement ofair pollution acts

Coordination with state PCBs

Plan, arrange & execute training programs on Air PollutionPrevention & Control (APPC)

Sponsor research to mass media on APPC

Publish technical data, measuring devices, manuals, codes]and lay down standards

Recognize a laboratory for air quality analysis

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Air Pollution Standards


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In most country the Govt. set Legal Standards

Standards depends on: population density, meteorological& geographical features

In India, PCB classify state-land into 3 category: Industrial areas Residential & rural areas Sensitive areas (hill station, tourist resort, parks)

Indian Ambient Air Quality Standards (IAAQS) setspermissible limit of air pollutants

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Air Quality Standards


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In USA, the standards are set by United State Environment

Protection Agency

2 types of air quality standard US: Primary & Secondary

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Chapter-2 (Problems)


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Problem-1

Carbon monoxide (CO) is present in standardatmospheric air at a concentration of 50 ppm.Compute volume concentration, mass-volumeconcentration and mass concentration values forthe CO concentration in the atmosphere.

Given: air density at standard condition is 1.185kg/m3 and the molecular weight (MP) is 28.

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Solution


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Given data:Concentration of CO = 50 ppm

Volume concentration,yp =yppm x 10-6 = 50 x 10-6 = 5 x 10-5

Mass volume concentration, p

Mass concentration wp, can be calculated as follows:Divide mass concentration to volume concentration equation

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Solution


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But the term (ma+mp/va+vp) can be written as

Taking the density of air, a, as equal to ma/va, and densityof pollutant, p = (mP/vP)yp; we get

pa

pa

p

p

p

p

mm

vv

v

m

y

w

p

p

p

a

a

a

pa

pa)1( y

v

my

v

m

vv

mm

000048.01026.57)00005.01(185.1

1026.57

)1( 6

6

ppa

p

p

yw

57


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Chapter-2 (Problems)


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BITS Pilani, K K Birla Goa Campus11th Jan.2014 (CourseCode:etzc362)

Problem 3

The behavior of particulate pollution in the atmosphere is

influenced by their relative sizes. Explain how the size of

particulates makes a difference.

Particles larger than 10 m have high settling rates & has

short residence time in atm

Terminal`s velocity is related to particle`s density

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