eem 402 summer 2014 lect 2 measure of air pollutants[edited]

7/21/2019 EEM 402 Summer 2014 Lect 2 Measure of Air Pollutants[Edited]

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Measurement of Air Pollutants

and Particulate Matter

Dr. Shahid Amjad

Institute of Business Management(IoBM)


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Air Quality There are big industrial estates, and small cottage industries

that generate hazardous and toxic chemicals.

The fertilizer plants, textile industry, glass industry, steelplants etc.

They contribute SO2NO2, smoke, volatile organiccompounds, chlorine gas, ammonia, CO, CO2, phenol, cyanideand particulate matter, into the atmosphere.

The human health is affected by different-sized airborneparticulate matter.

Larger particles PM10are trapped in the nose and throat,whereas smaller particles (PM2.5) penetrate the lungs and are

associated with a range of respiratory symptoms.


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Problems:

Degradation of ambient air quality. Air pollution is hazardous to health of all living

beings.

Adds Emission to green house gases. Meteorological aspects of Air pollution


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The Pressure Gradient Force and Other Effects on Wind

Within the atmosphere, there are several forces thatimpact the speed and direction of winds. The most

important though is the Earths gravitational force. Asgravity compresses the Earths atmosphere, it creates airpressure- the driving force of wind. Without gravity, therewould be no atmosphere or air pressure and thus, no wind.

The force actually responsible for causing the movement of

air though is the pressure gradient force. Differences in airpressure and the pressure gradient force are caused by theunequal heating of the Earths surface when incoming solarradiation concentrates at the equator. Because of theenergy surplus at low latitudes for example, the air there iswarmer than that at the poles.

Warm air is less dense and has a lower barometric pressurethan the cold air at high latitudes. These differences inbarometric pressure are what create the pressure gradientforce and wind as air constantly moves between areas ofhigh and low pressure.


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Meteorological Aspects Of Air Pollution

Air pollutants, after emission from the source, get

transported and diluted in the atmosphere beforethese undergo various physical and photochemicaltransformations.

This natural process of dispersion prevents thebuilding up of pollutant concentrations near thesources of emissions to dangerous levels.

Dispersion is, to a very large extent, controlled bythe prevailing meteorological conditions of theatmosphere in the area.

The main controlling meteorological parametersare the degree of stability of the atmosphere andits turbulence.


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Temperature Lapse Rate and Stability. When a packet of air moves upwards in the atmosphere, it

experiences less pressure and hence it expands and cools

down (expansion is done at the cost of internal energy ofthe air molecules and hence it cools down) and thesurrounding air gains heat and becomes a little warmer.

On the other hand, when the packet moves down, morepressure will compress the air in the packet and its

temperature will increase, consequently the surroundingair will be a little cooler.

The rate of change in the air temperature with altitude iscalled lapse rate.

This rate of change in the air temperature with altitude or

the lapse rate is also known as Ambient Lapse Rate,(ALR),Prevailing Lapse Rate (PLR) and as Environmental LapseRate.(ELR).


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The Environmental Lapse Rate (ELR) differs

from place to place, time to time even at the

same place and depends on the wind speed,geographical factors and sunlight.

Experimentally, this can be measured by

sending a balloon equipped with athermometer and a barometer measuring

temperature and pressure at different

altitudes.


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Adiabatic Lapse Rate.

When a packet of air moves upwards in the

atmosphere, it experiences less pressure andhence, expands and cools down, and thesurrounding air gains heat and becomes a littlewarmer.

Now, if we assume that as the packet moves,there is no heat transferred across its boundary,the process is adiabatic. that is, no heat istransferred to or gained from the surroundings.

Under this condition, the lapse rate is calledAdiabatic Lapse Rate.


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Ideally a parcel of air cools at about 1C/100m

or 9.8k/km. The word lapse implies a

negative rate of change or decrease.

The 1C/100m always holds, regardless of

what the actual temperature at variouselevations might be.


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The ease with which pollutants can dispersevertically into the atmosphere is largely

determined by the rate of change in the airtemperature with altitude (Lapse rate).

For some temperature profiles, the air is stable,i.e., air remains stagnant at a given elevation and

thus discourages dispersion and dilution of thepollutant.

For some temperature profiles, the air is unstableand under such conditions there is rapid verticalmixing which encourages pollutant dispersal andincreases air quality.


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A super adiabatic lapse rate occurs when the

atmospheric temperature drops more than

1C per100m.

A sub adiabatic lapse rate occurs when the

drop is less than 1C per 100m. A special caseof sub adiabatic lapse rate is inversion, a

condition where warmer air is above colder

air.


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Inversions Generally, the higher we go, the cooler we feel, but some times a

dense cold stratum of air at ground level is found which is covered bylighter warmer air at higher level. This phenomena is known asInversion.

During inversion, vertical air movement is stopped and air pollutantswill concentrate in the denser air at ground level. As a result, duringtemperature inversion, the atmosphere is stable and very little mixingtakes place. Under such conditions, the pollutants in the air do not

disperse. Inversion occurs frequently in the autumn and winter months, theaccumulation of smoke and other contaminants further increasepollution by blocking the sun's rays from warming the cooler groundand the adjacent air.

Fog is commonly associated with inversion because the temperature

of the air at ground level falls below the dew point of water vapour inthe air.

Narrow valleys are favourable to inversion since horizontal airmovement is restricted. At the time of inversion visibility is greatlyreduced.


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Atmospheric Stability

Atmospheric stability is important because it determines the abilityof pollutants to disperse vertically into the atmosphere and itsability to dilute pollution. Difference between the Environment

Lapse Rate (ELR) and Adiabatic Lapse Rate (ALR) determines thestability of the atmosphere.

There are three different scenarios of atmospheric stability:

1. When ELR> ALR, then the atmosphere is unstable. i.e., when theinternal temperature of the air packet is higher than thesurroundings, its density is lower and it keeps going up. This

condition is helpful in the dissipation of pollutions into the upperatmosphere and hence, eliminates air pollution problems.

2. When ELR


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Stack and Plume

The dispersion of emitted gases from the sourceof their production is known as plume and thesource is known as stack.

The diffusion or dispersion of pollutants into theatmosphere is governed by the EnvironmentalLapse Rate (ELR) as well as Adiabatic Lapse rate(ALR),i.e., atmospheric temperature profile oratmospheric stability.

On the basis of ELR and ALR the nature of plumecan be of different types.


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Static Stability of the Atmospherecontrols the local air quality

Actual lapse rate < the dry adiabatic lapse rate stable. Actual lapse rate = the dry adiabatic lapse rate neutral.

Actual lapse rate > the dry adiabatic lapse rate unstable.

In the following charts, the red dashed lines represent the dry adiabatic lapse rate and solid black lines represent theactual lapse rates of the air

You only need to compare the slope of the lines to determine the stability.


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You can tell the air stability by watching the motion of the chimney

smoke


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Looping plume is of wavy nature and occurs in super adiabaticenvironment (ELR>ALR),which produces highly unstable atmosphere

because of rapid mixing. As a result of this, high concentrations of

pollutants may occur near the ground. To disperse these pollutants, it

is advisable to design high stack where atmosphere is generally super

adiabatic.


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Under sub-adiabatic conditions (ELR


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Fanning plume is encountered under strong atmospheric inversions

and in the presence of very light winds. Vertical mixing does not take

place because of very stable lapse rate. Horizontal mixing takes

place. The pollutants travel almost parallel to the ground.


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Fumigation is a type of plume in which the pollutants reach the groundlevel after a short distance. This occurs when the lapse rate changes from

unstable to stable at the stack height or above. Stable condition prevents

vertical mixing above the stack height. Fumigating plume, is therefore not

a good condition for dispersion of pollutants. Fumigation is favored by

clean skies and light winds.


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Lofting is a type of plume behaviour reverse of fumigation. It occurs when thelapse rate changes from stable to unstable at or below the stack height. The

dispersion of pollutants therefore becomes rapid and pollutants cannot come to

the ground. Such kind of a plume is ideal for dispersion of air pollutants and

protection of living beings to a great extent.


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Trapping occurs when the plume emission is caught between two

inversion layers. Diffusion of emission is restricted to only the

unstable layer. This plume is not ideal for dispersion of pollutants as

it cannot go above a certain height.


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Neutral plume occurs in neutral atmospheric conditions (ELR=ALR).

Such type of plume rises vertically in an upward direction. The upward

lifting of the plume will continue till it reaches a height where density

and temperature of surrounding air are equal it.


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Plume rise depends on momentum and

buoyancy. Buoyancy factor is due to thetemperature difference of the stack gases and

surrounding air and the momentum due to

the molecular weight of the exhaust gases

against air.


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.


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Ans, We Know that


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Exercise

A coal power plant has a physical stack height

(chimney) height of 500 m, with an inside

diameter of 10 m. The stack gas velocity is 20

m.sec-1 . The stack gas temperature is 200oC

(473 K) and the ambient air temperature is10oC (283 K). The atmospheric pressure is 1

bar; average wind speed is 5m. sec-1 .

Calculate the effective stack height. Ans = 1150.74 m


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There are six pollutants which have the main

contribution in creating air pollution. They are

primary pollutants like carbon monoxide (CO),

sulphur dioxide (SO2),

nitrogen dioxide (NO2),

lead (Pb), and

particulate matters (PM),

with secondary pollutants like ground level

ozone (O3).


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Major Air Pollutant Sources


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Sulphur dioxide (SO2)

It is a colourless, poisonous gas, highly soluble in water.It has a pungent and suffocating odour.

Sources: Burning of fossil fuels

Thermal power plants

Fertilizer plants

Textile industry Steel plants

Sulphuric acid plants

Petroleum industry

Oil refining Smelting of sulphid ores


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On an average, about 25 million tons of sulphur dioxide is emittedinto the atmosphere annually.

The main source of sulphur is fossil fuels like coal, that has themaximum content of sulphur, about 1 to 6 percent. When fossil

fuels are burnt, the main gas released into the atmosphere is SO2along with trace amount of sulfite (SO3) and sulfate(SO2) also canreact with OH' radical (obtained from photo dissociation of H2Omolecules), followed by series of reactions.

SO2+ OH' -> HOSO2

HOSO2+ O2-> SO3+HO2

Thus, the SO3formed reacts very fast with H2O to form sulphuricacid, the principle cause of acid rain.

SO3+ H2O -> H2SO4

The acid molecules then either deposit on particulates existing inthe air, or merge with water vapours to form droplets. Thus, in theatmosphere we may obtain significant amount of sulphur (SO4)aerosols.


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Effects of SO2on Human Health

High solubility in water allows it to get absorbed in the moistpassages of upper respiratory tract, causing increased breathingrate and feeling of air starvation.

Suffocation. Respiratory irritation.

Asthma and chronic bronchitis.

Irritation of throat and eyes.

SO2affects plants severely. SO2gas enters plants through the

stomata and gets oxidized to SO3there. This SO3reacts with H2Oand forms H2SO4. The acid interferes in metabolic process andproductivity falls.

SO2causes yellowing of paper and reduces its mechanical strength,affecting the storage of books. It discolours paint, causes organicfiber to weaken. Even metals get corroded easily by SO

2.

Prolonged exposure to sulphate causes damage to buildings andmarble monuments, as the carbonates like lime stone and CaCO3react with H2SO4to produce gypsum (CaSO4), which is washed awayleaving behind the eroded surface. It is now believed that there is asevere acid rain threat on the Taj Mahal.

C b id


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Carbon monoxide

It is a colourless, odourless, tasteless, poisonous gas. Itcombines with Haemoglobin, the oxygen carrier of theblood in the body, to form carboxy haemoglobin, a stable

compound. The oxygen transportation is thus, disturbed and in

extreme cases it can be fatal. However, it is a blessing thatsoil fungi and higher plants absorb it and destroy it byconverting it to CO2

Sources

Incomplete combustion of coal, wood, fossil fuel in steelplants, automobiles, thermal power plants, jet engines.

Mid ocean surface water. Oxidation of CH4formed through anaerobic decomposition

of organic matter.

Tobacco smoking.


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Oxides of Nitrogen

There are six oxides of nitrogen, viz., nitric

oxide (NO), nitrogen dioxide (NO2), nitrousoxide (N2O), dinitrogen trioxide (N2O3),

dinitrogen tetroxide (N2O4) and nitrogen

pentoxide (N2O5), which are known to occur.However, two oxides of nitrogen, which are

important air pollutants are (NO) and (NO2).

It is a reddish brown gas and exists at roomtemperature.


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Sources:

Burning of fossil fuels

Nitrogen based fertilizer plants

Explosive industry

Coal fired and gas fired furnaces

Textile industry

Manufacture of HNO3

Decomposition of organic waste

Thunder showers

Automobile exhaust

Effects:

Respiratory irritation

Impairment of lung defense

Headache Bronchitis

Loss of appetite

Corrosion of teeth

Leaf damage to sensitive plants


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Atmospheric Pollution

Exercises and Case Study


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d


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Procedure1. you have the data from a 24-hour run of a Mini Volume

SPM sampler. The data include:

Weight of the filter before sampling Weight of the filter after sampling

Total time the sampler was running

Average flow rate of the sampler

2. Using the data provided, perform the step-by-stepcalculation of ambient particulate concentration.

3. Compare and explain variation in the results of particulate

matter during summer and winter to the NationalEnvironmental Air Quality Standard (NEQs)/Air QualityIndex (AQI)

C S d


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Case Study A survey was undertaken to monitor the levels of atmosphere Suspended

Particulate Matter (SPM) in the industrial area of Korangi using a high

volume sampler. The SPMmonitoring was done in December andsubsequently as a follow up, the process of particulates monitoring wasalso repeated in month of July.

During the December observations, the fiber glass filter paper used had aninitial weight of 7.02345 gms. After 24 hrs of sampling using a high Volumeair sampler, the filter paper weighed 8.56432 gms. The volume of air flow(measured using a rotameter) at the start and at the end of theexperiment was recorded to be 1.2 m3/min and 0.8 m3/min. respectively.

Similarly, in monsoonal month of July. The initial and final weight of thefiberglass filter paper was 8.00234 and 8.16012 gms. The air flow at thestart and at the end of the experiment was recorded to be 2.2 m3/min and1.8 m3/min. The sampling time was 24 hrs. respectively.

Calculate the concentration of suspended matter in the atmosphere inug/m3at the Korangi location in December and July accordingly. Explainvariation in SPM during July and December months. Does the air qualitymeet the NEQs Standards of 500 g/m3


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Solution

Calculate the weight of particulate matter Final

and Initial weight of the Filter paper in g(multiply weight in gm by 1000000.)

Calculate the average air flow (from the

rotameter data) (Start +End data/2) air Volumesampled

Calculate the sampling duration in 24 hrs (i.e total

air flow duration of sampling. (Av flow x 60 x 24). Total Suspended Matter Weight of Particulate

matter/Volume Air flow sampled).


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eem 402 summer 2014 lect 2 measure of air pollutants[edited]

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