HANDBOOK OF ENVIRONMENTAL ENGINEERING VOLUME 1
Air Pollution
Control
Engineering
Air Pollution
Control
Engineering
Edited by
Lawrence K. Wang, PhD, PE, DEE
Norman C. Pereira, PhD
Yung-Tse Hung, PhD, PE, DEE
Edited by
Lawrence K. Wang, PhD, PE, DEE
Norman C. Pereira, PhD
Yung-Tse Hung, PhD, PE, DEE
Air Pollution Control Engineering

Air Pollution
Control Engineering
Edited by
Lawrence K. Wang, PhD, PE, DEE
Zorex Corporation, Newtonville, NY
Lenox Institute of Water Technology, Lenox, MA
Norman C. Pereira, PhD
Monsanto Company (Retired), St. Louis, MO
Yung-Tse Hung, PhD, PE, DEE
Department of Civil and Environmental Engineering
Cleveland State University, Cleveland, OH
Consulting Editor
Kathleen Hung Li,
MS

VOLUME 1
HANDBOOK OF ENVIRONMENTAL ENGINEERING
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Air pollution control engineering / edited by Lawrence K. Wang, Norman C. Pereira, Yung-Tse Hung;
consulting editor, Kathleen Hung Li.

p. cm.—(Handbook of environmental engineering ; v. 1)
Includes bibliographical references and index.
ISBN 1-58829-161-8 (alk. paper)
1. Air–pollution. 2. Air quality management. I. Wang, Lawrence K. II. Pereira, Norman C. III. Hung,
Yung-Tse. IV. Series: Handbook of environmental engineering (2004) ; v. 1.
TD170 .H37 2004 vol. 1
[TD883]
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[628.5] 2003023596
Preface
v
The past 30 years have seen the emergence of a growing desire worldwide to
take positive actions to restore and protect the environment from the degrad-
ing effects of all forms of pollution: air, noise, solid waste, and water. Because
pollution is a direct or indirect consequence of waste, the seemingly idealistic
goal for “zero discharge” can be construed as an unrealistic demand for zero
waste. However, as long as waste exists, we can only attempt to abate the sub-
sequent pollution by converting it to a less noxious form. Three major ques-
tions usually arise when a particular type of pollution has been identified:
(1) How serious is the pollution? (2) Is the technology to abate it available? and
(3) Do the costs of abatement justify the degree of abatement achieved? The
principal intention of the Handbook of Environmental Engineering series is to help
readers formulate answers to the last two questions.
The traditional approach of applying tried-and-true solutions to specific pol-
lution problems has been a major contributing factor to the success of environ-
mental engineering, and has accounted in large measure for the establishment of
a “methodology of pollution control.” However, realization of the ever-increas-
ing complexity and interrelated nature of current environmental problems ren-
ders it imperative that intelligent planning of pollution abatement systems be
undertaken. Prerequisite to such planning is an understanding of the perfor-

mance, potential, and limitations of the various methods of pollution abatement
available for environmental engineering. In this series of handbooks, we will
review at a tutorial level a broad spectrum of engineering systems (processes,
operations, and methods) currently being utilized, or of potential utility, for pol-
lution abatement. We believe that the unified interdisciplinary approach in these
handbooks is a logical step in the evolution of environmental engineering.
The treatment of the various engineering systems presented in Air Pollution
Control Engineering will show how an engineering formulation of the subject
flows naturally from the fundamental principles and theory of chemistry, phys-
ics, and mathematics. This emphasis on fundamental science recognizes that
engineering practice has in recent years become more firmly based on scien-
tific principles rather than its earlier dependency on empirical accumulation of
facts. It is not intended, though, to neglect empiricism when such data lead
quickly to the most economic design; certain engineering systems are not
readily amenable to fundamental scientific analysis, and in these instances we
have resorted to less science in favor of more art and empiricism.
Because an environmental engineer must understand science within the con-
text of application, we first present the development of the scientific basis of a
particular subject, followed by exposition of the pertinent design concepts and
operations, and detailed explanations of their applications to environmental
quality control or improvement. Throughout the series, methods of practical
design calculation are illustrated by numerical examples. These examples clearly
demonstrate how organized, analytical reasoning leads to the most direct and
clear solutions. Wherever possible, pertinent cost data have been provided.
Our treatment of pollution-abatement engineering is offered in the belief that
the trained engineer should more firmly understand fundamental principles, be
more aware of the similarities and/or differences among many of the engineering
systems, and exhibit greater flexibility and originality in the definition and innova-
tive solution of environmental pollution problems. In short, the environmental
engineers should by conviction and practice be more readily adaptable to change

and progress.
Coverage of the unusually broad field of environmental engineering has
demanded an expertise that could only be provided through multiple
authorships. Each author (or group of authors) was permitted to employ,
within reasonable limits, the customary personal style in organizing and pre-
senting a particular subject area, and, consequently, it has been difficult to
treat all subject material in a homogeneous manner. Moreover, owing to limi-
tations of space, some of the authors’ favored topics could not be treated in
great detail, and many less important topics had to be merely mentioned or
commented on briefly. All of the authors have provided an excellent list of
references at the end of each chapter for the benefit of the interested reader.
Because each of the chapters is meant to be self-contained, some mild repeti-
tion among the various texts is unavoidable. In each case, all errors of omis-
sion or repetition are the responsibility of the editors and not the individual
authors. With the current trend toward metrication, the question of using a
consistent system of units has been a problem. Wherever possible the authors
have used the British system (fps) along with the metric equivalent (mks, cgs,
or SIU) or vice versa. The authors sincerely hope that this doubled system of
unit notation will prove helpful rather than disruptive to the readers.
The goals of the Handbook of Environmental Engineering series are (1) to cover
the entire range of environmental fields, including air and noise pollution con-
trol, solid waste processing and resource recovery, biological treatment pro-
cesses, water resources, natural control processes, radioactive waste disposal,
thermal pollution control, and physicochemical treatment processes; and (2) to
employ a multithematic approach to environmental pollution control since air,
water, land, and energy are all interrelated. No consideration is given to pollu-
tion by type of industry or to the abatement of specific pollutants. Rather, the
organization of the series is based on the three basic forms in which pollutants
and waste are manifested: gas, solid, and liquid. In addition, noise pollution
control is included in one of the handbooks in the series.

This volume of Air Pollution Control Engineering, a companion to the volume,
Advanced Air and Noise Pollution Control, has been designed to serve as a basic
air pollution control design textbook as well as a comprehensive reference
book. We hope and expect it will prove of equally high value to advanced
undergraduate or graduate students, to designers of air pollution abatement
systems, and to scientists and researchers. The editors welcome comments from
readers in the field. It is our hope that this book will not only provide informa-
vi Preface
tion on the air pollution abatement technologies, but will also serve as a basis
for advanced study or specialized investigation of the theory and practice of
the unit operations and unit processes covered.
The editors are pleased to acknowledge the encouragement and support
received from their colleagues and the publisher during the conceptual stages
of this endeavor. We wish to thank the contributing authors for their time and
effort, and for having patiently borne our reviews and numerous queries and
comments. We are very grateful to our respective families for their patience
and understanding during some rather trying times.
The editors are especially indebted to Dr. Howard E. Hesketh at Southern
Illinois University, Carbondale, Illinois, and Ms. Kathleen Hung Li at NEC
Business Network Solutions, Irving, Texas, for their services as Consulting
Editors of the first and second editions, respectively.
Lawrence K. Wang
Norman C. Pereira
Yung-Tse Hung
Preface vii

ix
Contents
Preface v
Contributors xi

1 Air Quality and Pollution Control
Lawrence K. Wang, Jerry R. Taricska, Yung-Tse Hung,
and Kathleen Hung Li 1
1. Introduction 1
2. Characteristics of Air Pollutants 3
3. Standards 6
3.1. Ambient Air Quality Standards 6
3.2. Emission Standards 8
4. Sources 10
5. Effects 10
6. Measurements 13
6.1. Ambient Sampling 14
6.2. Source Sampling 17
6.3. Sample Locations 18
6.4. Gas Flow Rates 19
6.5. Relative Humidity 22
6.6. Sample Train 24
6.7. Determination of Size Distribution 27
7. Gas Stream Calculations 28
7.1. General 28
7.2. Emission Stream Flow Rate and Temperature Calculations 29
7.3. Moisture Content, Dew Point Content,
and Sulfur Trioxide Calculations 30
7.4. Particulate Matter Loading 32
7.5. Heat Content Calculations 33
7.6. Dilution Air Calculations 33
8. Gas Stream Conditioning 35
8.1. General 35
8.2. Mechanical Collectors 35
8.3. Gas Coolers 36

8.4. Gas Preheaters 36
9. Air Quality Management 37
9.1. Recent Focus 37
9.2. Ozone 38
9.3. Air Toxics 42
9.4. Greenhouse Gases Reduction and Industrial Ecology Approach 43
9.5. Environmental Laws 45
10. Control 50
11. Conclusions 52
12. Examples 52
12.1.Example 1 52
12.2.Example 2 53
Nomenclature 53
References 55
2 Fabric Filtration
Lawrence K. Wang, Clint Williford, and Wei-Yin Chen 59
1. Introduction 59
2. Principle and Theory 60
3. Application 64
3.1. General 64
3.2. Gas Cleaning 64
3.3. Efficiency 66
4. Engineering Design 68
4.1. Pretreatment of an Emission Stream 68
4.2. Air-to-Cloth Ratio 68
4.3. Fabric Cleaning Design 71
4.4. Baghouse Configuration 73
4.5. Construction Materials 73
4.6. Design Range of Effectiveness 74
5. Operation 74

5.1. General Considerations 74
5.2. Collection Efficiency 74
5.3. System Pressure Drop 75
5.4. Power Requirements 75
5.5. Filter Bag Replacement 76
6. Management 76
6.1. Evaluation of Permit Application 76
6.2. Economics 77
6.3. New Technology Awareness 79
7. Design Examples and Questions 80
Nomenclature 92
References 93
Appendix 1: HAP Emission Stream Data Form 95
Appendix 2: Metric Conversions 95
3 Cyclones
José Renato Coury, Reinaldo Pisani Jr., and Yung-Tse Hung 97
1. Introduction 97
2. Cyclones for Industrial Applications 98
2.1. General Description 98
2.2. Correlations for Cyclone Efficiency 101
2.3. Correlations for Cyclone Pressure Drop 105
2.4. Other Relations of Interest 106
2.5. Application Examples 107
3. Costs of Cyclone and Auxiliary Equipment 118
3.1. Cyclone Purchase Cost 118
3.2. Fan Purchase Cost 119
x Contents
3.3. Ductwork Purchase Cost 120
3.4. Stack Purchase Cost 120
3.5. Damper Purchase Cost 121

3.6. Calculation of Present and Future Costs 121
3.7. Cost Estimation Examples 122
4. Cyclones for Airborne Particulate Sampling 125
4.1. Particulate Matter in the Atmosphere 125
4.2. General Correlation for Four Commercial Cyclones 127
4.3. A Semiempirical Approach 128
4.4. The “Cyclone Family” Approach 135
4.5. PM
2.5
Samplers 136
4.6. Examples 140
Nomenclature 147
References 150
4 Electrostatic Precipitation
Chung-Shin J. Yuan and Thomas T. Shen 153
1. Introduction 153
2. Principles of Operation 154
2.1. Corona Discharge 157
2.2. Electrical Field Characteristics 158
2.3. Particle Charging 162
2.4. Particle Collection 165
3. Design Methodology and Considerations 171
3.1. Precipitator Size 173
3.2. Particulate Resistivity 176
3.3. Internal Configuration 179
3.4. Electrode Systems 181
3.5. Power Requirements 181
3.6. Gas Flow Systems 184
3.7. Precipitator Housing 184
3.8. Flue Gas Conditioning 185

3.9. Removal of Collected Particles 185
3.10.Instrumentation 187
4. Applications 187
4.1. Electric Power Industry 187
4.2. Pulp and Paper Industry 188
4.3. Metallurgical Industry 188
4.4. Cement Industry 188
4.5. Chemical Industry 188
4.6. Municipal Solid-Waste Incinerators 189
4.7. Petroleum Industry 189
4.8. Others 189
5. Problems and Corrections 189
5.1. Fundamental Problems 189
5.2. Mechanical Problems 192
5.3. Operational Problems 192
5.4. Chemical Problems 192
6. Expected Future Developments 193
Contents xi
Nomenclature 193
References 195
5 Wet and Dry Scrubbing
Lawrence K. Wang, Jerry R. Taricska, Yung-Tse Hung,
James E. Eldridge, and Kathleen Hung Li 197
1. Introduction 197
1.1. General Process Descriptions 197
1.2. Wet Scrubbing or Wet Absorption 198
1.3. Dry Scrubbing or Dry Absorption 199
2. Wet Scrubbers 199
2.1. Wet Absorbents or Solvents 199
2.2. Wet Scrubbing Systems 200

2.3. Wet Scrubber Applications 203
2.4. Packed Tower (Wet Scrubber) Design 204
2.5. Venturi Wet Scrubber Design 215
3. Dry Scrubbers 222
3.1. Dry Absorbents 222
3.2. Dry Scrubbing Systems 222
3.3. Dry Scrubbing Applications 225
3.4. Dry Scrubber Design 226
4. Practical Examples 227
Nomenclature 296
References 298
Appendix: Listing of Compounds Currently Considered Hazardous 302
6 Condensation
Lawrence K. Wang, Clint Williford, and Wei-Yin Chen 307
1. Introduction 307
1.1. Process Description 307
1.2. Types of Condensing Systems 308
1.3. Range of Effectiveness 309
2. Pretreatment, Posttreatment, and Engineering Considerations 309
2.1. Pretreatment of Emission Stream 309
2.2. Prevention of VOC Emission from Condensers 311
2.3. Proper Maintenance 311
2.4. Condenser System Design Variables 311
3. Engineering Design 311
3.1. General Design Information 311
3.2. Estimating Condensation Temperature 312
3.3. Condenser Heat Load 313
3.4. Condenser Size 314
3.5. Coolant Selection and Coolant Flow Rate 315
3.6. Refrigeration Capacity 316

3.7. Recovered Product 316
4. Management 316
4.1. Permit Review and Application 316
4.2. Capital and Annual Costs of Condensers 316
xii Contents
5. Environmental Applications 320
6. Design Examples 321
Nomenclature 326
References 327
Appendix: Average Specific Heats of Vapors 328
7 Flare Process
Lawrence K. Wang, Clint Williford, and Wei-Yin Chen 329
1. Introduction 329
2. Pretreatment and Engineering Considerations 331
2.1. Supplementary Fuel Requirements 331
2.2. Flare Gas Flow Rate and Heat Content 331
2.3. Flare Gas Exit Velocity and Destruction Efficiency 333
2.4. Steam Requirements 334
3. Engineering Design 334
3.1. Design of the Flame Angle 334
3.2. Design of Flare Height 334
3.3. Power Requirements of a Fan 334
4. Management 335
4.1. Data Required for Permit Application 335
4.2. Evaluation of Permit Application 335
4.3. Cost Estimation 336
5. Design Examples 340
Nomenclature 343
References 344
8 Thermal Oxidation

Lawrence K. Wang, Wei Lin, and Yung-Tse Hung 347
1. Introduction 347
1.1. Process Description 347
1.2. Range of Effectiveness 349
1.3. Applicability to Remediation Technologies 349
2. Pretreatment and Engineering Considerations 351
2.1. Air Dilution 351
2.2. Design Variables 352
3. Supplementary Fuel Requirements 355
4. Engineering Design and Operation 356
4.1. Flue Gas Flow Rate 356
4.2. Combustion Chamber Volume 356
4.3. System Pressure Drop 356
5. Management 357
5.1. Evaluation of Permit Application 357
5.2. Operations and Manpower Requirements 358
5.3. Decision for Rebuilding, Purchasing New or Used Incinerators 360
5.4. Environmental Liabilities 360
6. Design Examples 360
Nomenclature 365
References 366
Contents xiii
9 Catalytic Oxidation
Lawrence K. Wang, Wei Lin, and Yung-Tse Hung 369
1. Introduction 369
1.1. Process Description 369
1.2. Range of Effectiveness 372
1.3. Applicability to Remediation Technologies 375
2. Pretreatment and Engineering Considerations 375
2.1. Air Dilution Requirements 375

2.2. Design Variables 376
3. Supplementary Fuel Requirements 379
4. Engineering Design and Operation 382
4.1. Flue Gas Flow Rates 382
4.2. Catalyst Bed Requirement 382
4.3. System Pressure Drop 383
5. Management 384
5.1. Evaluation of Permit Application 384
5.2. Operation and Manpower Requirements 384
5.3. Decision for Rebuilding, Purchasing New or Used Incinerators 385
5.4. Environmental Liabilities abd Risk-Based Corrective Action 385
6. Design Examples 386
Nomenclature 392
References 393
10 Gas-Phase Activated Carbon Adsorption
Lawrence K. Wang, Jerry R. Taricska, Yung-Tse Hung,
and Kathleen Hung Li 395
1. Introduction and Definitions 395
1.1. Adsorption 395
1.2. Adsorbents 396
1.3. Carbon Adsorption and Desorption 396
2. Adsorption Theory 397
3. Carbon Adsorption Pretreament 399
3.1. Cooling 399
3.2. Dehumidification 400
3.3. High VOC Reduction 400
4. Design and Operation 400
4.1. Design Data Gathering 400
4.2. Type of Carbon Adsorption Systems 402
4.3. Design of Fixed Regenerative Bed Carbon Adsorption Systems 402

4.4. Design of Canister Carbon Adsorption Systems 405
4.5. Calculation of Pressure Drops 406
4.6. Summary of Application 406
4.7. Regeneration and Air Pollution Control
of Carbon Adsorption System 409
4.8. Granular Activated Carbon Versus Activated Carbon Fiber 410
4.9. Carbon Suppliers, Equipment Suppliers, and Service Providers 411
5. Design Examples 411
Nomenclature 418
References 419
xiv Contents
11 Gas-Phase Biofiltration
Gregory T. Kleinheinz and Phillip C. Wright 421
1. Introduction 421
2. Types of Biological Air Treatment System 422
2.1. General Descriptions 422
2.2. Novel or Emerging Designs 424
3. Operational Considerations 426
3.1. General Operational Considerations 426
3.2. Biofilter Media 428
3.3. Microbiological Considerations 430
3.4. Chemical Considerations 431
3.5. Comparison to Competing Technologies 433
4. Design Considerations/Parameters 433
4.1. Predesign 433
4.2. Packing 435
5. Case Studies 435
5.1. High-Concentration 2-Propanol and Acetone 435
5.2. General Odor Control at a Municipal
Wastewater-Treatment Facility 436

6. Process Control and Monitoring 440
7. Limitations of the Technology 440
8. Conclusions 441
Nomenclature 443
References 444
12 Emerging Air Pollution Control Technologies
Lawrence K. Wang, Jerry R. Taricska, Yung-Tse Hung,
and Kathleen Hung Li 445
1. Introduction 445
2. Process Modification 446
3. Vehicle Air Pollution and Its Control 446
3.1. Background 446
3.2. Standards 447
3.3. Sources of Loss 447
3.4. Control Technologies and Alternate Power Plants 448
4. Mechanical Particulate Collectors 453
4.1. General 453
4.2. Gravitational Collectors 454
4.3. Other Methods 455
4.4. Use of Chemicals 465
4.5. Simultaneous Particle–Gas Removal Interactions 465
5. Entrainment Separation 466
6. Internal Combustion Engines 467
6.1. Process Description 467
6.2. Applications to Air Emission Control 469
7. Membrane Process 471
7.1. Process Description 471
7.2. Application to Air Emission Control 474
Contents xv
8. Ultraviolet Photolysis 475

8.1. Process Description 475
8.2. Application to Air Emission Control 476
9. High-Efficiency Particulate Air Filters 477
9.1. Process Description 477
9.2. Application to Air Emission Control 479
10. Technical and Economical Feasibility of Selected Emerging
Technologies for Air Pollution Control 480
10.1.General Discussion 480
10.2.Evaluation of ICEs, Membrane Process, UV Process,
and High-Efficiency Particulate Air Filters 480
10.3.Evaluation of Fuel-Cell-Powered Vehicles
for Air Emission Reduction 481
Nomenclature 489
References 491
Index 495
xvi Contents
Contributors
WEI-YIN CHEN, PhD • Department of Chemical Engineering, University of Mississippi,
University, MS
J
OSÉ RENATO COURY, PhD, MENG • Department of Chemical Engineering, Universidade
Federal de Sao Carlos, Sao Carlos, Brazil
J
AMES E. ELDRIDGE, MA, MS, MENG • Lantec Product, Agoura Hills, CA
Y
UNG-TSE HUNG, PhD, PE, DEE • Department of Civil and Environmental Engineering,
Cleveland State University, Cleveland, OH
G
REGORY T. KLEINHEINZ, PhD • Department of Biology and Microbiology, University
of Wisconsin-Oshkosh, Oshkosh, WI

K
ATHLEEN HUNG LI, MS • Senior Technical Writer, NEC Business Network Solutions,
Inc., Irving, TX
N
ORMAN C. PEREIRA, PhD (RETIRED) • Monsanto Company, St. Louis, MO
R
EINALDO PISANI JR., DEng, MEng • Centro de Ciencias Exatas, Universidade de Ribeirao
Preto, Ribeirao Preto, Brazil
T
HOMAS T. SHEN, PhD • Independent Environmental Advisor, Delmar, NY
J
ERRY R. TARICSKA, PhD, PE • Environmental Engineering Department, Hole Montes,
Inc., Naples, FL
L
AWRENCE K. WANG, PhD, PE, DEE • Zorex Corporation, Newtonville, NY and Lenox
Institute of Water Technology, Lenox, MA
C
LINT WILLIFORD, PhD • Department of Chemical Engineering, University of Missis-
sippi, University, MS
P
HILLIP C. WRIGHT, PhD • Department of Chemical and Process Engineering, Univer-
sity of Sheffield, Sheffield, UK
C
HUNG-SHIN J. YUAN, PhD • Institute of Environmental Engineering, National Sun
Yat-Sen University, Kaohsiung, Taiwan
xvii

1
1
Air Quality and Pollution Control

Lawrence K. Wang, Jerry R. Taricska,
Yung-Tse Hung, and Kathleen Hung Li
CONTENTS
INTRODUCTION
CHARACTERISTICS OF AIR POLLUTANTS
STANDARDS
SOURCES
EFFECTS
MEASUREMENT
GAS STREAM CALCULATIONS
GAS STREAM CONDITIONING
AIR QUALITY MANAGEMENT
CONTROL
CONCLUSIONS
EXAMPLES
NOMENCLATURE
REFERENCES
1. INTRODUCTION
The Engineer’s Joint Council on Air Pollution and Its Control defines air pollution as
“the presence in the outdoor atmosphere of one or more contaminants, such as dust,
fumes, gas, mist, odor, smoke or vapor in quantities, of characteristics, and of duration,
such as to be injurious to human, plant, or property, or which unreasonably interferes
with the comfortable enjoyment of life and property.”
Air pollution, as defined above, is not a recent phenomenon. Natural events always
have been the direct cause of enormous amounts of air pollution. Volcanoes, for
instance, spew lava onto land and emit particulates and poisonous gases containing ash,
hydrogen sulfide (H
2
S), and sulfur dioxide (SO
2

) into the atmosphere. It has been esti-
mated that all air pollution resulting from human activity does not equal the quantities
released during three volcanic eruptions: Krakatoa in Indonesia in 1883, Katmai in
Alaska in 1912, and Hekla in Iceland in 1947.
From: Handbook of Environmental Engineering, Volume 1: Air Pollution Control Engineering
Edited by: L. K. Wang, N. C. Pereira, and Y T. Hung © Humana Press Inc., Totowa, NJ
01_chap_wang.qxd 05/05/2004 11:45 am Page 1
Lightning, another large contributor to atmospheric pollution, activates atmospheric
oxygen (O
2
) to produce ozone (O
3
), a poisonous gas [ozone in the upper atmosphere,
however, acts as a shield against excessive amounts of ultraviolet (UV) radiation, which
can cause human skin cancer]. In addition to the production of ozone, lightning is the
indirect cause of large amounts of combustion-related air pollution as a result of forest
fires. The Forest Service of the United States Department of Agriculture reported that
lightning causes more than half of the over 10,000 forest fires that occur each year.
For centuries, human beings have been exposed to an atmosphere permeated by other
natural pollutants such as dust, methane from decomposing matter in bogs and swamps,
and various noxious compounds emitted by forests. Some scientists claim that such nat-
ural processes release twice the amount of sulfur-containing compounds and 10 times
the quantity of carbon monoxide (CO) compared to all human activity.
Why, then, is society so perturbed by air pollution? The concern stems from a combi-
nation of several factors:
1. Urbanization and industrialization have brought together large numbers of people in
small areas.
2. The pollution generated by people is most often released at locations close to where they
live and work, which results in their continuous exposure to relatively high levels of the
pollutants.

3. The human population is still increasing at an exponential rate.
Thus, with rapidly expanding industry, ever more urbanized lifestyles, and an increas-
ing population, concern over the control of man-made air pollutants is now clearly a
necessity. Effective ways must be found both to reduce pollution and to cope with existing
levels of pollution.
As noted earlier, natural air pollution predates us all. With the advent of Homo sapiens,
the first human-generated air pollution must have been smoke from wood burning, followed
later by coal.
From the beginning of the 14th century, air pollution from coal smoke and gases
had been noted and was of great concern in England, Germany, and elsewhere. By
the beginning of the 19th century, the smoke nuisance in English cities prompted the
appointment of a Select Committee of the British Parliament in 1819 to study and report
on smoke abatement.
Many cities in the United States, including Chicago, St. Louis, and Pittsburgh, have
been plagued with smoke pollution. The period from 1880 to 1930 has often been called
the “Smoke Abatement Era.” During this time, much of the basic atmospheric cleanup
work started. The Smoke Prevention Association was formed in the United States near
the turn of the 20th century, and by 1906, it was holding annual conventions to discuss the
smoke pollution problem and possible solutions. The name of the association was later
changed to the Air Pollution Control Association (APCA).
The period from 1930 to the present has been dubbed the “Disaster Era” or “Air
Pollution Control Era.” In the most infamous pollution “disaster” in the United States, 20
were killed and several hundred made ill in the industrial town of Donora, Pennsylvania
in 1948. Comparable events occurred in the Meuse Valley, Belgium in 1930 and in
London in 1952. In the 1960s, smog became a serious problem in California, especially
in Los Angeles. During a 14-day period from November 27 to December 10, 1962, air
2 Lawrence K. Wang et al.
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pollution concentrations were extremely high worldwide, resulting in “episodes” of
high respiratory incidents in London, Rotterdam, Hamburg, Osaka, and New York. During

this period, people in many other cities in the United States experienced serious pollution-
related illnesses, and as a result, efforts to clean up the air were started in the cities of
Chicago, New York, Washington, DC, and Pittsburgh. The substitution of less smoky
fuels, such as natural gas and oil, for coal, for power production and for space heating
accounted for much of the subsequent improvement in air quality.
Air quality in the United States depends on the nature and amount of pollutants
emitted as well as the prevalent meteorological conditions. Air pollution problems in
the highly populated, industrialized cities of the eastern United States result mainly
from the release of sulfur oxides and particulates. In the western United States, air
pollution is related more to photochemical pollution (smog). The latter form of pol-
lution is an end product of the reaction of nitrogen oxides and hydrocarbons from
automobiles and other combustion sources with oxygen and each other, in the pres-
ence of sunlight, to form secondary pollutants such as ozone and PAN (peroxy acetyl
or acyl nitrates).
Temperature inversions effectively “put a lid over” the atmosphere so that emissions
are trapped in relatively small volumes and in correspondingly high concentrations. Los
Angeles, for example, often suffers a very stable temperature inversion and strong solar
input, both ideal conditions for the formation of highly localized smog. Rain and snow
wash out the air and deposit the pollutants on the soil and in water. “Acid rain” is the
result of gaseous sulfur oxides combining with rain water to form dilute sulfuric acid
and it occurs in many cities of eastern United States.
2. CHARACTERISTICS OF AIR POLLUTANTS
Air pollutants are divided into two main groups: particulates and gases. Because
particulates consist of solids and/or liquid material, air pollutants therefore encompass
all three basic forms of matter. Gaseous pollutants include gaseous forms of sulfur
and nitrogen. Gaseous SO
2
is colorless, yet one can point to the bluish smoke leaving
combustion operation stacks as SO
2

or, more correctly, SO
3
or sulfuric acid mist. Nitric
oxide (NO) is another colorless gas generated in combustion processes; the brown color
observed a few miles downwind is nitrogen dioxide (NO
2
), the product of photochem-
ical oxidation of NO. Although the properties of gases are adequately covered in basic
chemistry, physics, and thermodynamics courses, the physical behavior of particulates
is less likely to be understood. The remainder of this section is thus devoted to the
physical properties of particulate matter, not gaseous pollutants.
Particulates may be subdivided into several groups. Atmospheric particulates consist
of solid or liquid material with diameters smaller than about 50 µm (10
−6
m). Fine par-
ticulates are those with diameters smaller than 3 µm. The term “aerosol” is defined
specifically as particulates with diameters smaller than about 30–50 µm (this does not
refer to the large particulates from aerosol spray cans). Particulates with diameters
larger than 50 µm settle relatively quickly and do not remain in the ambient air.
The movement of small particles in gases can be accounted for by expressions
derived for specific size groups: (1) The smallest group is the molecular kinetic group
and includes particles with diameters much less than the mean free path of the gas
Air Quality and Pollution Control 3
01_chap_wang.qxd 05/05/2004 11:45 am Page 3
molecules (l); (2) next is the Cunningham group, which consists of particles with diam-
eters about equal to l; (3) the largest is the Stokes group, which consists of particles with
diameters much larger than l. The reported values of l are quite varied, however, for air
at standard conditions (SC) of 1 atm and 20ºC and range from 0.653 × 10
−5
to 0.942 ×

10
−5
cm. One can also estimate l for air at a constant pressure of 1000 mbar using
(1)
where l is the mean free path of air (cm) and T is the absolute temperature (K).
One also can estimate the terminal settling velocity of the various size spherical par-
ticles in still air. The Stokes equation applies for that group and gives accuracy to 1%
when the particles have diameters from 16 to 30 µm and 10% accuracy for 30–70 µm:
(2)
where v
s
is the terminal settling velocity (cm/s), d is the diameter of the particle (cm),
g is the gravitational acceleration constant (980 cm/s
2
), ρ
p
is the density of the particle
(g/cm
3
), and µ
g
is the viscosity of the gas (g/cm s, where µ
g
for air is 1.83 × 10
−4
).
Particles in the Cunningham group are smaller and tend to “slip” through the gas
molecules so that a correction factor is required. This is called the Cunningham correction
factor (C), which is dimensionless and can be found for air at standard conditions (SC):
(3)

where T is the absolute temperature (K) and d
1
is the particle diameter (µm). When Eq.
(2) is multiplied by this factor, accuracy is within 1% for particles for 0.36–0.80 µm and
10% for 1.0–1.6 µm. Particles of the molecular kinetic size are not amenable to settling
because of their high Brownian motion.
Liquid particulate and solids formed by condensation are usually spherical in shape
and can be described by Eqs. (1)–(3). Many other particulates are irregularly shaped, so
corrections must be used for these. One procedure is to multiply the given equations by
a dimensionless shape factor (
K):
(4)
where K′ is the sphericity factor and
K = 1 for spheres
K = 0.906 for octahedrons
K = 0.846 for rod-type cylinders
K = 0.806 for cubes and rectangles
K = 0.670 for flat splinters
Concentrations of air pollutants are usually stated as mass per unit volume of gas (e.g.,
µg/m
3
, or micrograms of pollutant per total volume of gases) for particulates and as a vol-
ume ratio for gases (e.g., ppm, or volume of pollutant gas per million volumes of total
gases). Note that at low concentrations and temperatures (room conditions) frequently
present in air pollution situations, the gaseous pollutants (and air) may be considered as
ideal gases. This means that the volume fraction equals the mole fraction equals the
pressure fraction. This relationship is frequently useful and should be remembered.
Special methods must be used to evaluate the movement of particulates under conditions
in which larger or smaller particles are present, of nonsteady state, of nonrectangular
KK=

′
(
)
0 843 0 065. log .
CT d d T=×
(
)
(
)
{}
+−×
(
)
[]
{}
−−
12790894 2 47 10
11
3
+210 exp
4
.
vdg
sp
=
2
g
ρµ
18
lT=×

−
223 10
8
.
4 Lawrence K. Wang et al.
01_chap_wang.qxd 05/05/2004 11:45 am Page 4
Air Quality and Pollution Control 5
Fig. 1. Log probability distribution of a blanket dryer exhaust.
coordinates, and in the presence of other forces. Detailed procedures for handling these
and other situations can be found in the volume by Fuchs (1) and other references.
The size distribution of particulate air pollutants is usually a geometric, or log-
normal, distribution, which means that a normal or bell-shaped curve would be
obtained if size frequency were plotted against the log of the particle size. Also, if
the log of the particle size were plotted versus a cumulative percentage value, such
as mass, area, or number, straight lines would be obtained on a log probability graph,
as shown in Fig. 1. The values by mass in Fig. 1 were the original samples, and the
surface area and number curves can be estimated mathematically, as was done to
obtain the other lines shown. Of course, these data could be measured directly (e.g.,
by optical techniques).
The mean diameter of such a sample is obtained by noting the 50% value and must
be reported as a mean (
d
50
) by either mass, area, or number. In Fig. 1, the mass mean is
3.0 µm. The standard deviation can be obtained from the ratio of diameter for 84.13%
01_chap_wang.qxd 05/05/2004 11:45 am Page 5
(d
84.13
) and 50%, or the ratios for 50% and 15.87% (d
15.87

). This geometric standard
deviation (σ
g
) becomes:
(5)
In Fig. 1, σ
g
is 3.76. Note that the slopes of the curves (σ
g
) should be similar for all
three methods of expressing the same material.
If the particulate matter is composed of more than one material or if it is a single
substance in different physical structures, it will most likely be bimodal in size distri-
bution. This can be true for material in the stack effluent and mixtures in the free
(ambient) atmosphere. For example, combustion-flue gases contain particulates com-
posed of a large fraction mainly entrained as partially unburned fuel, plus a smaller
fraction consisting of ash. Particulates sampled from a stoker-fired, chain grate boiler
(2) are shown in Fig. 2. Note how this material must be plotted as two intercepting
lines on log probability coordinates.
As shown in Fig. 2, atmospheric particulates are also bimodal in size distribution
(3). These data are plotted as
∆mass/∆log diameter versus the log of diameter to
amplify the bimodal distribution character. In general, atmospheric particulates con-
sist of a submicron group (<1 µm) and a larger group. Although the data shown in Fig.
3 are typical for the United States, similar results are obtained throughout the world,
as reported, for example, in Japan (4) and Australia (5). These authors note that atmo-
spheric sulfates and nitrates dominate the smaller group, which by mass accounts for
40% and include particles with diameters from 0.5 to 1.5 µm, which account for
another 40%.
3. STANDARDS

3.1. Ambient Air Quality Standards
Ambient air is defined as the outside air of a community, in contrast to air confined
to a room or working area. As such, many people are exposed to the local ambient air
24 h a day, 7 d a week. It is on this basis that ambient air quality standards are formu-
lated. The current standards were developed relatively quickly after the numerous
episodes of the 1960s. The feeling of many people were summed up by President
Johnson’s statement in 1967: “If we don’t clean up this mess, we’ll all have to start
wearing gas masks,” and “This country is so rich that we can achieve anything if we
make up our mind what we want to do.” There are those who believe that some require-
ments in the standards disregard costs of control compared with costs of benefits, but
all benefits and costs cannot be accurately assessed. Even so, we would be reluctant to
put dollar values on our own health and life.
The Clean Air Act Amendments of 1970 (Public Law 91-601, signed December 31,
1970) include ambient air standards that consist of two parts: primary standards, which
are intended for general health protection, and the more restrictive secondary standards,
which are for protection against specific adverse effects on health and welfare. “Welfare”
here includes plants, other animals, and materials. The primary standards are effective as
of 1975, and the secondary standards are effective as of June 1, 1977. An abbreviated list
of these 1997 standards for particulate matter and categories of gaseous pollutants is
σ
g
dddd==
84.13
50
50
15 87.
6 Lawrence K. Wang et al.
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