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J13AIP-E1

The University of Nottingham

DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL ENGINEERING

A LEVEL 3 MODULE, SPRING SEMESTER 2012-2013

AIR POLLUTION 1

Time allowed TWO Hours

Candidates may complete the front cover of their answer book and sign their desk card butmust NOT write anything else until the start of the examination period is announced

Answer THREE questions

Only silent, self contained calculators with a Single-Line Display or Dual-Line Display arepermitted in this examination.

Dictionaries are not allowed with one exception. Those whose first language is not Englishmay use a standard translation dictionary to translate between that language and English

provided that neither language is the subject of this examination. Subject specific translationdictionaries are not permitted.

No electronic devices capable of storing and retrieving text, including electronic dictionaries,may be used.

DO NOT turn examination paper over until instructed to do so

ADDITIONAL MATERIAL: Aide MemoireThermodynamic Properties of Fluids & Other Data (in S.I. Units)

INFORMATION FOR INVIGILATORS:

Question papers should be collected in at the end of the exam do not allow candidates totake copies from the exam room.

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1. Answer ALL parts of this question.

A landfill site is proposed for the disposal of domestic municipal waste in aformer quarry. The quarry site is located 1.5 km upwind of the village ofLambley on the outskirts of the city of Nottingham. The village and former

quarry are located on a rural river flood plain.

During the early years of operation it is expected that the landfill will emit118 mgs-1 of hydrogen sulfide gas that has an odour threshold of 0.76 gm-3.The landfill gases produced will initially be collected and then vented toatmosphere by a stack. From meteorological records it is expected that the windvelocities at the stack height will range from 4 to 12 ms-1.

(a) Determine the minimum stack height that should be designed to ensurethat the ground level hydrogen sulfide concentrations are no more than0.1 times the odour threshold at the near boundary of the village on a

class B stability day. To be conservative, the stack should be designedassuming that there is no plume rise. [8]

(b) If additional housing is built on the perimeter of the village nearest to thelandfill site, determine whether any of the residents may experienceodour concentrations that are higher concentrations than thoseexperienced by the current residents under the worst climatic conditions? [2]

(c) During the later year of its operation the landfill may be licensed toreceive additional construction and demolition (C&D) waste containinggypsum products that will increase the potential production of hydrogen

sulphide.

Outline five types of methods that may be employed to mitigate thehydrogen sulphide emissions to atmosphere. Provide a brief description ofthe operation and effectiveness of each of the technologies. [15]

2. Answer ALL parts of this question.

The emissions from a rural boiler furnace are released into an isothermal

atmosphere through a stack which has an effective height of 100 m. The boilerreleases NOx emissions at a rate of 1.0 gs-1. The wind is recorded to be blowingat a rate of 4.6 ms-1 at a height of 10 m.

(a) Calculate the maximum downwind ground level concentration of the NOxgases and the distance at which the maximum concentration occurs. [13]

(b) If under the operation of the near surface same atmospheric stabilityconditions a temperature inversion forms at a height of 200 m aboveground level, determine the concentration of the NOx gases at groundlevel at a distance of 10 km downwind of the stack. [12]

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3. Answer ALL parts of this question.

The depletion of the ozone layer contained within the stratosphere has been thesource of major scientific concern over the past twenty-five years. However, thelevel of ozone creation has more than doubled in the troposphere over the last

100 years.

(a) Outline two examples of the sources and the secondary atmosphericchemical reactions that are responsible for the rise of ozone levels in thetroposphere. [6;6]

(b) Detail three source chemicals and secondary atmospheric chemicalreactions they undergo, which are suggested to be predominatelyresponsible for the depletion of the stratospheric ozone layer. [3;3;3]

(c) Discuss briefly the deleterious effects that ozone depletion in the

stratosphere may cause, and describe the international treaty andtimetables that have been implemented to tackle this major globalenvironmental challenge. [4]

4. Answer ALL parts of this question.

(a) By the application of Newton's Second Law of Motion, derive an equationthat represents the forces acting on a particulate suspended in air. Give aphysical interpretation of each of the individual forces acting on the

particle. Write down the dimensions and SI units for each of the terms inexpression. [5]

(b) Write down an expression for Stokes' Law that relates the drag forcesacting on the motion of the particle (due to the viscosity of the air) and itssettling velocity. Outline as part of your answer the range of assumptionsthat must hold for this law to govern the motion of the suspendedparticle. [5]

(c) By combining the expressions developed in (b) and (c) above derive anexpression that represents the settling velocity of the particle. [3]

(d) Course mineral particles with a mean diameter of 0.05 mm and massdensity of 1,960 kgm-3 are emitted from a tall stack of a process plant.The wind is measured to be blowing at stack height at a velocity of 8 kmper hour. The distance from the centreline of the stack to the plantsproperty line is 18 stack heights. By computing the two major velocitycomponents of a typical particle along the centreline of the plume,comment on the likelihood that most of the mineral particles will fallwithin the boundary of the plant. State any assumptions you make as partof your answer. (The density and viscosity of the ambient air may beassumed to be 1.2 kgm-3 and 1.85 X10-5 kgm-1s-1, respectively). [12]

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Module: Air Pollution J13AIP-E1

Aide Memoire

1. Gaussian Plume Dispersion Equation

}2

z)(Hexp

2

z)(H{exp

2

yexp

u2

QH)z;y,C(x,

2z

2e

2z

2e

2y

2

zy

(1)

where

C is the air pollutant concentration [kgm-3]

Q is the pollutant emission rate [kgs-1]u is the wind speed at the point of release [ms-1]

y is the standard deviation of the crosswind concentration

distribution at a distance x downstream [m]z is the standard deviation of the vertical concentration distribution

at a distance x downstream [m]

He is the effective height of the centre line of the plume [m]

2. Gaussian Plume Dispersion Equation Line Sources

C is the air pollutant concentration [kgm-3]

q is the pollutant emission rate [kgm-1s-1]

u is the wind speed at the point of release [ms-1]y is the standard deviation of the crosswind concentration

distribution at a distance x downstream [m]z is the standard deviation of the vertical concentration distribution

at a distance x downstream [m]H is the height of the centre line of the plume [m]

Is the angle at which the wind intercepts the line source

2z

2

z 2

Hexp

u2sin

2qH)C(x,0;

21

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3. Briggs Formulation for Plume Rise:The buoyancy flux parameter:

sass T/TTVgF

[m4s-3] (2)

sas

2

s

T/TTrgvF [m4s-3] (3)

aapaTcgQF [m

4s-3] (4)

For dry ambient air at 20 C (293 K) equation (4) provides the following equation for F in terms of

the stack sensible heat emission Q:

F = 8.80x Q, [m4s-3] (5)

where Q is given in MW, mega watts, 106

watts

The stability parameter:

dz

dT

T

g

dz

d

T

gs

aa

[s-2]

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3. Temperature Inversions

If inversion conditions exist above the effective stack height, the Gaussian equation must be

modified to account for the limiting effect this has

L is the elevation of the bottom of the inversion layer

XLis the downwind distance at which the plume first encounters the inversion layer

Turner suggested that XL occurs at the point where,

(12)

The above equation is used to calculate the vertical dispersion coefficient and then the dispersion

parameter graph displayed on Section 5 can be used to find XL(or x as it is on the graph)

For x < XLuse the standard Gaussian equation

For x > 2XLuse equation below

For XL < x < 2XLinterpolate between the two

Under inversion conditions, at x > 2XL, the modified equation is used,

(13)

2XL

XL

L

H

z

Inversion

x

2y

2

y 2

yexp

Lu)(2

Qy)C(x,

21

H)0.47(Lz

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4. Dispersion Parameters:The Rural Dispersion Coefficients, yand z(after D Bruce Turner, Workbook of Atmospheric

Dispersion Estimates: An Introduction to Dispersion Modeling, CRC Press, 1994)

Figure:The Rural horizontal, crosswind (transverse) dispersion coefficients, y

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Figure:The Rural vertical, transverse dispersion coefficient, z

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Figure:Turners Graph for determining peak downwind concentration and the

position at which it occurs (after D Bruce Turner, Workbook of Atmospheric

Dispersion Estimates: An Introduction to Dispersion Modeling, CRC Press, 1994)Rural Dispersion Coefficients

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For rural terrains the following equation is employed to determine the vertical and

crosswind dispersion coefficients for a downwind distance x in km:

(14)

Where

Pasquill

Stability

Class

z y

I J K I J K

A 6.035 2.1097 0.2770 5.357 0.8828 -0.0076

B 4.694 1.0629 0.0136 5.058 0.9024 -0.0096

C 4.110 0.9201 -0.0020 4.651 0.9181 -0.0076

D 3.414 0.7371 -0.0316 4.230 0.9222 -0.0087

E 3.057 0.6794 -0.0450 3.922 0.9222 -0.0064F 2.621 0.6564 -0.0540 3.533 0.9191 -0.0070

Urban Dispersion Coefficients:

For urban terrains the following equation is employed to determine the vertical and

crosswind dispersion coefficients for a downwind distance x in km:

(15)

Where

Pasquill

Stability

Class

z y

L M N L M N

A-B 240 1.00 0.50 320 0.40 -0.50

C 200 0.00 0.00 220 0.40 -0.50

D 140 0.30 -0.50 160 0.40 -0.50

E-F 80 1.50 -0.50 110 0.40 -0.50

NMx)(1(Lx)

2y,z )x(lnK)x(lnJIexp

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5. Stability Classifications:Pasquill Stability Class Ambient Temperature Gradient

(C/100 m)A Very unstable < -1.9

B- Unstable -1.9 to -1.7

CSlightly unstable -1.7 to -1.5D Neutral -1.5 to -0.5

E Slightly stable -0.5 to 1.5

F Stable > 1.5

Table 1:Classification of Pasquill Stability Classes by ambient temperature gradient

Surfacewindspeed[ms-1]

Day-time insolation Night-time cloud cover

Strong Moderate Weak >4/8th

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6. Wind speed profile exponents

[ms-1](16)

Table 3: Power Law exponents for different stability classes

Stability Class Description Exponent, p

Rural Urban

A Very unstable 0.09 0.15

B Moderately unstable 0.09 0.15

C Slightly unstable 0.12 0.20

D Neutral 0.15 0.25

E Slightly stable 0.24 0.40F Stable 0.36 0.60

7. Terminal settling velocity

(17)

where tv is the settling velocity, p is the particle density [kgm-3], pd is the

diameter of the particle [m], gis the acceleration due to gravity [kgm-1

s

-2

], fand f are the density [kgm

-3] and viscosity [kgm-1s-1]of air respectively andCis

the Cunningham correction factor which is given by,

pd

52.21C

(18)

with being the mean free path of an air molecule and has a value of 0.08microns [m] and that the particle daimeter dpis expressed in microns [m].

p

hzh

zuu

g18

d)(Cv

f

2pfp

t