5625.Air Pollution (1)

8/6/2019 5625.Air Pollution (1)

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Air Pollution

8/6/2019 5625.Air Pollution (1)


AtmosphereTroposphere - 0-11 Km

70% mass of atmosphereAir is uniform and homogeneous due to constant circulation of airmasses in this regionTurbulent layerTemp. falls with increasing altitudeTropopause – The boundary where change in temperature occurs iscalled tropopause

Stratosphere - 11- 50 KmQIESCENT LAYER-Inactive and QuietTemperature increases with increase in altitudeOzone in this layer absorbs ultraviolet radiation and raises temperatureIt acts as a protective shield for life from injurious effects of ultraviolet rays

Mesosphere - 50- 85 KmTemperature falls with increasing alti tude

Thermosphere - 85- 500 KmTemperature rises with increase in altitudeGases (oxygen and nitric oxide ) split into atoms and undergoionization

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Air Pollution and BiosphereAtmospheric pollutants are mainly present in thetroposphere and lower stratosphere0-100 m – Highly polluted. Pollutants are partly absorbed bevegetation, water surface and buildings100-2000m – Lesser pollutants. Turbulent air currents,drizzle, rain and fog divert and dilute the concentration of pollutants

2000-10000m–

This layer extends to the top of thestratosphere. Water vapor and clouds dissolve somepollutants and bring them back to the earth as rain

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Air Pollution and BiosphereIn the Stratosphere, because of slow mixing in thestratosphere , the residence time of molecule in this region islongIf pollutant can reach or are injected into the stratosphere,they pose long term global hazardsPollutants from volcanic eruptions, nuclear explosions andphotochemical reactions stay in the stratosphere for a longtimeLarge quantity of particulate from smoke from fossil fuelsincreases atmospheric turbidity and reduces visibility

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Air pollution Air pollution is defined as the addition of undesirable material intothe atmosphere either due to natural phenomena or due to humanactivity on the earth which adversely affects quality of the air and hence affects the life on the earth

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Sources of Air Pollutiona) Natural Sources

Volcanic eruption emitting poisonous gases like CO, H2S,SO2

Forest firesVegetation decayPollen grains of flowers

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Volcanic eruptionemitting poisonousgases like CO, H2S,SO2

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Forest fires

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Anthropogenic or man made sources

Burning of fossil fuelse.g. Coal, petroleumPoisonous gases – CO, CO 2, SO2 , oxides of nitrogen

Oxides of sulphur and nitrogen are highly soluble in waterForm sulphuric acid and nitric acid (acid rain)Responsible for destruction of ecosystem

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Vehicular discharges75% of air pollution in urban areais caused by automobile emissionsPollution from exhaust gasesTetraethyl lead in gasoline as anti

knocking agentCO (77%), oxides of nitrogen(8.4%), hydrocarbons (14 %)andleaded gas along with particulate

of lead is emitted due toincomplete combustion of hydrocarbons

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Population explosionEmission of greenhouse gases and globalwarmingRise in sea levelDestruction and loss of forest cover andwildlifeRapid IndustrializationChemical industry, paper and pulp mills,petroleum refineries etc

Pollutant- CO, CO 2, NO, NO 2 , SO2 , H2S

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Agricultural activities

Insecticides & pesticides used in agriculture pollute air throughair currentAir -hazardous both to human and animalsModern warfareNuclear weapons, Nuclear reactors, nuclear explosionEmit radioactive radiations causing extensive air pollution

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Types of Air Pollutants

Primary air pollutants - Materials that whenreleased pose health risks in their unmodified formsor those emitted directly from identifiable sources.

Secondary air pollutants-Primary

pollutants interact with one another, sunlight, ornatural gases to produce new, harmful compounds

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8/6/2019 5625.Air Pollution (1)


Primary Air PollutantsFive major materials released directly into the atmosphere inunmodified forms.

Oxides of CarbonSulfur dioxideNitrogen oxidesHydrocarbonsParticulate matter

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Oxides of Carbon

CARBON MONOXIDE (CO)

Description: Colorless, odorless gas that is poisonous to air-breathing animals;

(2 C + O 2 2 CO)forms during the incomplete combustion of carbon-containing fuels e.g. from forests, volcanoesAnaerobic decomposition of organic matter and Oxidation of methane in swamps and humid tropics

Major human sources: Cigarette smoking (p. 409), incomplete

burning of fossil fuels. About 80% (95% in cities)comes from motor vehicle exhaust.

Health effects:Reacts with hemoglobin in red blood cells and reduces the ability of blood to bring oxygen to body cells

and tissues. This impairs perception and thinking; slows reflexes; causes headaches, drowsiness, dizziness,and nausea;can trigger heart attacks and angina;damages the development of fetuses and young childrenaggravates chronic bronchitis, emphysema, and anemiaAt high levels it causes collapse, coma, irreversible brain cell damage, and death

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Oxides of Carbon – Carbon dioxide (CO 2 )

Produced by burning of organic material (coal, gas, wood,trash, etc.)Used by plants for photosynthesisNo direct effect on health but above 10%, causes globalwarming, acid rain and Greenhouse effect.

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Nitrogen OxidesNITROGEN DIOXIDE (NO 2)

Description: Reddish-brown irritating gas that gives photochemical smog its brownish color; in theatmosphere can be converted to nitric acid (HNO3), a major component of acid deposition.

Major human sources: Fossil fuel burning in motor vehicles (49%) and power and industrial plants (49%).

Health effects: Lung irritation and damage; aggravates asthma and chronic bronchitis; increasessusceptibility to respiratory infections such as the flu and common colds (especially in young childrenand older adults).

Environmental effects: Reduces visibility; acid deposition of HNO3 can damage trees, soils, and aquatic lifein lakes.

Property damage: HNO3 can corrode metals and eat away stone on buildings, statues, and monuments;NO2 can damage fabrics.

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HydrocarbonsDescription: organic compounds with hydrogen, carbon. Contribute to smog. Emitted from eucalyptus,

cottonweed, oak, spruce trees as isoprene.

Major human sources: From incomplete burning or evaporated from fuel supplies in automobiles.Production of coke and smoldering of refuse piles near coal mines

Health effects:

High concentrations (500-1000 ppm) are carcinogenic, hence harmful for the lungs

Inhalation of benzene and toluene causes irritation of mucous membrane

Inhalation of hydrocarbon vapor increase secretion of mucous thus blocking the respiratory tract which

puts pressure of the trachea and bursting of alveoli membrane might occurCombine with nitrogen oxides ad produce photochemical smog that causes eye, nose and throatirritation

Environmental effects: Yellowing of leaves in plants that are exposed to high levels of hydrocarbon

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Sulfur DioxideSULFUR DIOXIDE (SO 2)

Description: Colorless, irritating; forms mostly from the combustion of sulfur containing fossil fuels such ascoal and oil (S + O2 SO2); in the atmosphere

can be converted to sulfuric acid (H2SO4), a major component of acid deposition.

Major human sources: Coal burning in power plants (88%) and industrial processes (10%).

Health effects: Breathing problems for healthy people; restriction of airways in people with asthma; chronicexposure can cause a permanent condition similar to bronchitis. According to the WHO, at least 625million people are exposed to unsafe levels of sulfur dioxide from fossil fuel burning.

Environmental effects: Reduces visibility; acid deposition of H2SO4 can damage trees, soils, and aquatic life inlakes.

Property damage: SO2 and H2SO4 can corrode metals and eat away stone on buildings, statues, andmonuments; SO2 can damage paint, paper, and leather.

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Particular Matter

Organic Particular Matter – Naturalparticulate matter present in aerosol e.g.particulates originating from volcanoes,

dust storms, forest, grassland fires &living vegetation.Inorganic particulate matter – Metaloxides formed during burning of fossilfuels, industrial processes, vehicularexhaust & acid rain.

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SUSPENDED PARTICULATE MATTER (SPM)PM10 - Suspended particulate matter of less than 10 micron size is called Respirable Suspended Particulate

Matter (RSPM).PM2.5 - Suspended particulate matter of less than 2.5 micron size

Description: Variety of particles and droplets (aerosols) small and light enough to remain suspended inatmosphere for short periods (large particles) to long periods

(small particles; Figure 20-6, p. 441); cause smoke, dust, and haze.

Major human sources: Burning coal in power and industrial plants (40%), burning diesel and other fuels in

vehicles (17%), agriculture (plowing, burning off fields), unpaved roads, construction.

Health effects: RSPM causes nose and throat irritation, lung damage, and bronchitis; aggravates bronchitis andasthma; shortens life; toxic particulates (such as lead, cadmium, PCBs, and dioxins) can cause mutations,reproductive problems, cancer.

PM2.5 penetrate deep into lungs and damage lung tissues. Can cause Black lung disease, silicosis.

Environmental effects:

Reduces visibility by scattering solar radiation;Acts as condensation nuclei for formation of clouds, rain, and snow.acid deposition of H 2SO4 droplets can damage trees by blocking stomata and hindering respiration, soils, andaquatic life in lakes.Toxic substances get deposited on soil and render it unproductive

Property damage: Corrodes metal; soils and discolors buildings, clothes, fabrics, and paints.

RSPM levels in India are found to exceed the National Ambient Air Quality Standards (NAAQS) in many states.

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Secondary PollutantsOzonePAN (peroxy acetyl nitrate)Photochemical smog

Aerosols and mists (H2SO4)

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Ozone

Ozone (O3) is a highly reactive gas composed of three oxygen atoms.It is both a natural and a man-made product thatoccurs in the stratosphere and the troposphere.Tropospheric ozone – what we breathe -- isformed primarily from photochemical reactions

between two major classes of air pollutants,volatile organic compounds (VOC) andnitrogen oxides (NOX).Ozone in the lower atmosphere is an airpollutant with harmful effects on therespiratory systems of animals and will burnsensitive plantsozone layer in the upper atmosphere is beneficial, preventing potentiallydamaging electromagnetic radiation fromreaching the Earth's surface.

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PAN (Peroxy Acetyl nitrate)Smog is caused by the interaction of some hydrocarbons and oxidants underthe influence of sunlight giving rise to dangerous PAN.

Powerful respiratory and eye irritants present in photochemical smog.Irritate nose, throat and cause respiratory distress

Particulates deposit on plant leaves and block their stomata which inhibitsphotosynthesis and respiration. This results in reduced crop yield andretarded growth

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Photochemical smogPhotochemical smog is a mixture of pollutants which includes particulates,nitrogen oxides, ozone, aldehydes, peroxyethanoyl nitrate (PAN), unreactedhydrocarbons, etc. The smog often has a brown haze due to the presence of nitrogen dioxide. It causes painful eyes.

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Aerosols and mists (H2SO4)Aerosols and mists are very fine liquid droplets that cannot be effectivelyremoved using traditional packed scrubbers. These droplets can be formedfrom gas phase hydrolysis of halogenated acids (HCl, HF, HBr), metal halides,organohalides, sulfur trioxide (SO3), and phosphorous pentoxide (P2O5).

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Meteorology & Air PollutionMeteorology is the science of weather or study of the atmosphere.Meteorological parameters can directly or indirectly affect air pollution:

Primary meteorological parameters – WindSecondary meteorological parameters – Solar radiation, precipitation, humidity

1. Geographyi. Equator is warmer than the poles, hence the winds blow fro equator towards the poles taking with it

the pollutants in the air.

ii. Lands heats up faster than water in the daytime. Air becomes light and rises and the cool air from sea blows inland. However, at night land and air above it cools faster than the sea and hence the air blowstowards the sea carrying the pollutants with it.

2. ClimatePattern of weather variation over a span of timei. Depends on evaporation of water mass

ii. Reflection of solar radiationiii. Heat storing capacityiv. Topography of the areav. Densely populated urban areas trap more pollutants than rural areas,

which form a micro-climatic region. This is due to excessive heat release,automobile exhaust, industry emissions and concrete jungles.

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8/6/2019 5625.Air Pollution (1)


Meteorology & Air Pollution3. Weather - The state of the atmosphere at a given time and place, with respect to

variables such as temperature, moisture, wind velocity, and barometric pressurei. During the day air on the surface of the earth is heated by the sun. The hot air carrying

the pollutants rises up and the cool air settles down resulting in vertical mixing.ii. Inversion - A temperature inversion is a thin layer of the atmosphere where the

decrease in temperature with height is much less than normal (or in extreme cases, thetemperature increases with height).

iii. The usual way an inversion forms is by cooling of the surface air overnight during thewinter season, when nights are long and solar heat is lessened by the angle of the sun's

rays through the atmosphere.iv. An inversion, also called a "stable" air layer, acts l ike a lid, keeping normal convective

overturning of the atmosphere from penetrating through the inversion. This can causeseveral weather-related effects. One is the trapping of pollutants below the inversion,allowing them to build up forming smog.

4. Wind – Temperature gradient between equator and the poles results in winds.Winds disperse and dilute gases and particulate matter mainly from point sourceslike chimneys.

i. Wind is the natural horizontal motion of the atmosphere. It occurs when warm air rises,and cool air comes in to take its place. Differences in pressure cause air to move fromhigh pressure areas to low pressure areas, resulting in wind.

ii. Wind is caused by differences in pressure in the atmosphere. The pressure is the weightof the atmosphere at a given point. The height and temperature of a column of airdetermines the atmospheric weight.

iii. Wind speed can greatly affect the pollutant concentration in a local area. The higher thewind speed, the lower the pollutant concentration.

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8/6/2019 5625.Air Pollution (1)


Air QualityMethods for measuring ambient air quality

Stock emissions – When samples of air are measured on thespotAmbient air quality – Depends on climatic conditions likevelocity and wind direction. A large volume of sample isrequired.

The Central Pollution Control Board has fixed the standard forambient air quality in India under the Act of 1981 which has been revised in 1994.This specifies the maximum amount of a particular pollutantpermitted in the air around us.

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Air Quality

Pollutant Time Weightedaverage

Concentration in ambient air

IndustrialArea

Residential,Rural & otherArea

Sensitiveareas

Dioxide (SO 2 ) Annual Average* 80 60 15

24 hours** 120 80 30Oxides of Nitrogen as NO 2 Annual Average* 80 60 15

24 hours** 120 80 30Suspended Particulate Matter(SPM)

Annual Average* 360 140 70

24 hours** 500 200 100

Respirable Particulate matter(size less than 10 um)(RPM)

Annual Average* 120 60 50

24 hours** 150 100 75Lead (Pb) Annual Average* 1.0 0.75 0.50

24 hours** 1.5 1.00 0.75Carbon Monoxide (CO) 8 hours** 5.0 2.0 1.0

1 hour 10.0 4.0 2.0

Ambient Air quality standards in India, 1994 (concentration is µg/m3 )

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Air Quality Control TechniqueFor suspended particulate matter1. Settling chambers - Devices for collecting dust particles

bigger than 100 mm2. Cyclones/Multiclones – Uses the principle of dust

separation by centrifugal force. Particles up to 10 micronsare thrown at the periphery and clean air escapes from thecenter

3. Electrostatic precipitators –

Uses the principle of charging dust by high voltage current to separate them out.ESP is simple, cost effective and is widely used in thermalpower plants and industries

4. Filters – The dust laden air is passes through filter bags. Itneeds periodic cleaning

5. Scrubbers – Use a liquid stream to remove solid particlesfrom gaseous pollutants and particulate matter. Appropriateliquid brings pollutants from gaseous phase to liquid orsolid phase. The liquid has to be treated before disposal.Scrubbing requires large quantities of water and power.Scrubbers are of different kinds like; venturi, spray andimpingement.

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8/6/2019 5625.Air Pollution (1)


Air Quality Control Technique6. Absorption - This involves the use of liquids (commonly water with additives) to scrub

contaminants from waste gas streams— In general, absorbers can achieve removal efficiencies grater than 95 %. One potential problem withabsorption is the generation of waste-water, which converts an air pollution problem to a waterpollution problem

7. Adsorption - Solid collecting media with large surface-to-volume ratios, such as activated charcoal,are used to remove contaminants from waste gas streams

— The most common industrial adsorbents are activated carbon, silica gel, and alumina, because theyhave enormous surface areas per unit weight.

8. Combustion - Incineration or combustion, is most used to control the emissions of organiccompounds from process industries.This control technique refers to the rapid oxidation of a substance through the combination of oxygenwith a combustible material at high temperature or a catalyst like Cu, Ni, V, Zn compounds at lower

temperature in the presence of heat. Catalytic converters installed in vehicles use this principle toconvert nitrogen oxides into N2 before emission.When combustion is complete, the gaseous stream is converted to carbon dioxide (CO2) and watervapor (H2O)Equipment used to control waste gases by combustion can be divided in three categories:- Direct combustion or flaring; Thermal incineration and Catalytic incineration.

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Ambient Air Monitoring

1. High Volume sampler – Used for the monitoring of PM10 and PM2.5— Particulate samplers used for collection of particulate matter of 10μ m or smaller in

size.— Most widely used sampler is High Volume PM10 sampler (HVPM10)— Standard high volume total suspended particulate sampler with modified size specific

inlet— Flow controller to trap particles smaller than 10 on a quartz microfiber filter

2. Virtual impactor sampler/Dichotomous PM10— Device for dividing aerosol particle population into two size fractions

(PM10 and PM2.5) during sampling— Facilitate chemical analysis of the collected sample on inert teflon filters

3. PM10 Automatic Seven Day Sampler (PASS)— Used for long sampling periods.— Two kinds of PASS:

I. High volume samplers associated with a cyclone sampler at the inletII. Impacter separation based sampler

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Ambient Air Monitoring I. High volume samplers associated cyclone

separators— Air enters the inlet and passes through the cyclone.— Coarse non-respirable dust is separated by

centrifugal force and collected in bottles fitted at the bottom

— Fine dust (RSPM) passes through cyclone with airstream to a filter paper between top cover and filteradaptor assembly.

— Clean air exits through the blower and RSPM isretained by the filter

II. Impactor separation-based sampler— Air is inserted into the sampler from the bottom andpassed through the impactor— Impactor traps the particulates larger than specified

size (PM10 and PM2.5) as the filter paper pores aremade smaller than the diameter of the particulatematter

— The air that comes out is articulate free and isevacuated through an exhaust pipe using a motor

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National Ambient Air Quality Monitoring (NAAQM)

In 1999, the NAAQM program was renamed Nation Air MonitoringProgram (NAMP)The objectives of the N.A.M.P. are:

to determine the status and trends of ambient air qualityto ascertain whether the prescribed ambient air quality standards areviolatedto Identify Non-attainment Citiesto obtain the knowledge and understanding necessary for developingpreventive and corrective measures and to understand the natural cleansingprocess undergoing in the environment through pollution dilution,dispersion, wind based movement, dry deposition, precipitation andchemical transformation of pollutants generated.

The network consists of three hundred and forty two (342) operatingstations covering one hundred and twenty seven (127) cities/towns intwenty six (26) states and four (4) Union Territories of the country

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Nation Air Monitoring Program (NAMP)

Under N.A.M.P., four air pollutants have been identified for regular monitoring at all the locationsSulphur Dioxide (SO2)Oxides of Nitrogen as NO2Suspended Particulate Matter (SPM)Respirable Suspended Particulate Matter (RSPM / PM10)

The monitoring of meteorological parameters such as wind speed and wind direction, relativehumidity (RH) and temperature were also integrated with the monitoring of air quality.The monitoring of pollutants is carried out for 24 hours (4-hourly sampling for gaseous pollutantsand 8-hourly sampling for particulate matter) with a frequency of twice a week, to have one hundredand four (104) observations in a year.The monitoring is being carried out with the help of

Central Pollution Control Board;

State Pollution Control Boards;Pollution Control Committees;National Environmental Engineering Research Institute (NEERI), Nagpur

CPCB co-ordinates with these agencies to ensure the uniformity, consistency of air quality data andprovides technical and financial support to them for operating the monitoring stations. N.A.M.P. is being operated through various monitoring agencies.

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Air Pollution Control Measures

Fossil fuel use should be replaced by use of renewable sources like wind, solar,tidal and biogasEnforcement of land-use zoning regulations (closure and relocation of industryfrom non-conforming areas, development of green belts/areas).Introduction and enforcement of new and more stringent emission norms for

new and in-use vehicles. NAMP should be practiced by the state and centralpollution control boardTreating flue gases through dry and wet scrubbers & discharging treated gasusing high stacksRaw materials which cause less pollution should be usedCatalytic converters should be used in automobilesTightened and better enforced emissions norms which follow NAAQS leadingto installation of pollution control devices

5625.Air Pollution (1)

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