Aerosol Technology

William C. Hinds, ScD, was Emeritus Professor in the Department of Environmental Health Sciences at the UCLA Fielding School of Public Health. His research studied aerosols and industrial control of airborne contaminants. Yifang Zhu, PhD, is Professor in the Department of Environmental Health Sciences at the UCLA Fielding School of Public Health. Her research focus is on air pollution, environmental exposure assessment, and aerosol science and technology.

Preface to the First Edition xi

Preface to the Second Edition xiii

Preface to the Third Edition xv

List of Principal Symbols xvii

1 Introduction 1

1.1 Definitions 2

1.2 Particle Size, Shape, and Density 5

1.3 Aerosol Concentration 8

Problems 11

References 12

2 Properties of Gases 15

2.1 Kinetic Theory of Gases 15

2.2 Molecular Velocity 18

2.3 Mean Free Path 20

2.4 Other Properties 21

2.5 Reynolds Number 24

2.6 Measurement of Velocity, Flow Rate, and Pressure 27

Problems 35

References 36

3 Uniform Particle Motion 37

3.1 Newton’s Resistance Law 37

3.2 Stokes’s Law 39

3.3 Settling Velocity and Mechanical Mobility 40

3.4 Slip Correction Factor 42

3.5 Nonspherical Particles 44

3.6 Aerodynamic Diameter 46

3.7 Settling at High Reynolds Numbers 47

3.8 Stirred Settling 54

3.9 Instruments that Rely on Settling Velocity 56

3.10 Appendix: Derivation of Stokes’s Law 58

Problems 60

References 63

4 Particle Size Statistics 65

4.1 Properties of Size Distributions 65

4.2 Moment Averages 71

4.3 Moment Distributions 72

4.4 The Lognormal Distribution 77

4.5 Log-Probability Graphs 80

4.6 The Hatch-Choate Conversion Equations 84

4.7 Statistical Accuracy 88

4.8 Appendix 1: Distributions Applied to Particle Size 89

4.9 Appendix 2: Theoretical Basis for Aerosol Particle Size Distributions 90

4.10 Appendix 3: Derivation of the Hatch-Choate Equations 90

Problems 92

References 94

5 Straight-Line Acceleration and Curvilinear Particle Motion 97

5.1 Relaxation Time 97

5.2 Straight-Line Particle Acceleration 98

5.3 Stopping Distance 101

5.4 Curvilinear Motion and Stokes Number 104

5.5 Inertial Impaction 105

5.6 Cascade Impactors 110

5.7 Virtual Impactors 115

5.8 Time-of-Flight Instruments 117

Problems 119

References 120

6 Adhesion of Particles 121

6.1 Adhesive Forces 121

6.2 Detachment of Particles 123

6.3 Resuspension 124

6.4 Particle Bounce 126

Problems 127

References 127

7 Brownian Motion and Diffusion 129

7.1 Diffusion Coefficient 129

7.2 Particle Mean Free Path 132

7.3 Brownian Displacement 134

7.4 Deposition by Diffusion 137

7.5 Diffusion Batteries 141

Problems 144

References 145

8 Thermal and Radiometric Forces 147

8.1 Thermophoresis 147

8.2 Thermal Precipitators 151

8.3 Radiometric and Concentration Gradient Forces 153

Problems 155

References 155

9 Filtration 157

9.1 Macroscopic Properties of Filters 157

9.2 Single-Fiber Efficiency 163

9.3 Deposition Mechanisms 165

9.4 Filter Efficiency 169

9.5 Pressure Drop 174

9.6 Membrane Filters 174

Problems 176

References 176

10 Sampling and Measurement of Concentration 179

10.1 Isokinetic Sampling 179

10.2 Sampling from Still Air 185

10.3 Transport Losses 188

10.4 Measurement of Mass Concentration 189

10.5 Direct-Reading Instruments 192

10.6 Measurement of Number Concentration 195

10.7 Sampling Pumps 197

Problems 199

References 200

11 Respiratory Deposition 203

11.1 The Respiratory System 203

11.2 Deposition 206

11.3 Deposition Models 210

11.4 Inhalability of Particles 213

11.5 Respirable and Other Size-Selective Sampling 215

Problems 223

References 224

12 Coagulation 227

12.1 Simple Monodisperse Coagulation 227

12.2 Polydisperse Coagulation 233

12.3 Kinematic Coagulation 238

Problems 240

References 241

13 Condensation and Evaporation 243

13.1 Definitions 243

13.2 Kelvin Effect 246

13.3 Homogeneous Nucleation 247

13.4 Growth by Condensation 248

13.5 Nucleated Condensation 251

13.6 Condensation Particle Counters 255

13.7 Evaporation 257

Problems 261

References 263

14 Atmospheric Aerosols 265

14.1 Natural Background Aerosol 265

14.2 Urban Aerosol 269

14.3 Global Effects 274

Problems 275

References 275

15 Electrical Properties 277

15.1 Units 277

15.2 Electric Fields 278

15.3 Electrical Mobility 280

15.4 Charging Mechanisms 283

15.5 Corona Discharge 289

15.6 Charge Limits 291

15.7 Equilibrium Charge Distribution 292

15.8 Electrostatic Precipitators 294

15.9 Electrical Measurement of Aerosols 297

Problems 301

References 302

16 Optical Properties 305

16.1 Definitions 306

16.2 Extinction 307

16.3 Scattering 313

16.4 Visibility 317

16.5 Optical Measurement of Aerosols 322

Problems 329

References 330

17 Bulk Motion of Aerosols 333

Problems 338

References 338

18 Dust Explosions 339

Problems 344

References 344

19 Bioaerosols 345

19.1 Characteristics 345

19.2 Sampling 347

Problems 350

References 351

20 Microscopic Measurement of Particle Size 353

20.1 Equivalent Sizes of Irregular Particles 353

20.2 Fractal Dimension of Particles 358

20.3 Optical Microscopy 362

20.4 Electron Microscopy 365

20.5 Asbestos Counting 369

20.6 Automatic Sizing Methods 371

Problems 371

References 372

21 Production of Test Aerosols 375

21.1 Atomization of Liquids 375

21.2 Atomization of Monodisperse Particles in Liquid Suspensions 380

21.3 Dispersion of Powders 382

21.4 Condensation Methods 387

Problems 388

References 389

Appendices 391

Appendix A1. Useful Constants and Conversion Factors 391

Appendix A2. Some Basic Physical Laws 393

Appendix A3. Relative Density of Common Aerosol Materials (Multiply Values by 1000 for Density in kg/m 3 and by 1.0 for Density in g/cm 3) 394

Appendix A4. Standard Sieve Sizes 394

Appendix A5. Properties of Gases and Vapors at 293 K [20 ∘ C] and 101 kPa [1 atm] 395

Appendix A6. Viscosity and Density of Air versus Temperature 395

Appendix A7. Pressure (a), Temperature (b), Density (c), and Mean Free Path (d) of air versus altitude 396

Appendix A8. Properties of Water Vapor 397

Appendix A9. Properties of Water 398

Appendix A10. Particle Size Range of Aerosol Properties and Measurement Instruments: (a) Application Range for Aerosol Size Measuring Instruments and (b) Size Range of Aerosol Properties (See Also Fig. 1.6) 398

Appendix A11. (a) Properties of Airborne Particles at Standard Conditions (SI Units) 400

Appendix A12. Slip Correction Factor for Standard and Nonstandard Conditions: (a) Slip Correction Factor Minus One versus Particle Diameter and Standard Conditions; (b) Slip Correction Factor versus Particle Diameter Times Pressure (per atm) for Temperatures from 233 to 893K [–40 to 600 ∘ C] 402

Appendix A13. Properties of Selected Low-Vapor-Pressure Liquids 403

Appendix A14. Reference Values for Atmospheric Properties at Sea Level and 293.15

Ki20 ∘ C] 404

Appendix A15. Greek Symbols Used in This Book 405

Appendix A16. SI Prefixes 405

References 405

Index 407