Differential Optical Absorption Spectroscopy: Principles and Applications (Physics of Earth and Space Environments)

Contents......Page 8
1 Introduction......Page 17
2 Atmospheric Chemistry......Page 21
2.1 Atmospheric Structure and Composition......Page 23
2.1.1 Trace Species in the Atmosphere......Page 25
2.1.2 Quantification of Gas Abundances......Page 26
2.2 Direct Emission of Trace Gases to the Atmosphere......Page 30
2.2.1 Nitrogen Species......Page 32
2.2.2 Sulphur Species......Page 34
2.2.3 Carbon-Containing Species......Page 35
2.3 Ozone in the Troposphere......Page 37
2.3.1 Mechanism of Tropospheric Ozone Formation......Page 39
2.3.2 Ozone Formation in Urban Centres and Downwind......Page 41
2.4 Radical Processes in the Atmosphere......Page 43
2.4.1 Sources of Hydrogen Radicals (OH and HO[sub(2)])......Page 45
2.4.3 Chemistry of Hydrogen Radicals (OH and HO[sub(2)])......Page 48
2.5 Oxides of Nitrogen in the Atmosphere......Page 54
2.5.1 Classical Chemistry of Oxides of Nitrogen in the Atmosphere......Page 55
2.5.2 Tropospheric Chemistry of Nitrate Radicals, NO[sub(3)]......Page 57
2.5.3 Nitrous Acid, HONO in the Atmosphere......Page 61
2.6 Tropospheric Chemistry of VOCs......Page 63
2.7.1 Sulphur Dioxide – SO[sub(2)]......Page 66
2.7.2 Reduced Sulphur Species: DMS, COS, CS[sub(2)], H[sub(2)]S......Page 68
2.7.3 Influence of Sulphur Species on the Climate, the CLAW Hypothesis......Page 70
2.8.1 Tropospheric Sources of Inorganic Halogen Species......Page 71
2.8.2 Tropospheric Cycles of Inorganic Halogen Species......Page 74
2.8.3 Potential Impact of Inorganic Halogen Species on Tropospheric Chemistry......Page 78
2.9 Oxidation Capacity of the Atmosphere......Page 79
2.10.1 Stratospheric Ozone Formation: The Chapman Cycle......Page 81
2.10.2 Stratospheric Ozone Chemistry: Extension of the Chapman Cycle......Page 83
2.10.3 Stratospheric Ozone Hole......Page 88
2.10.4 Recovery of Stratospheric Ozone......Page 91
3.1 Electromagnetic Radiation and Matter......Page 92
3.2 Energy Levels and Transitions in Atoms......Page 93
3.3 Energy Levels and Transitions in Molecules......Page 94
3.3.1 Rotational Energy Levels and Transitions......Page 95
3.3.3 Electronic Energy Levels......Page 96
3.4 Population of States......Page 97
3.5 Molecular Spectra......Page 98
3.6 Broadening Mechanisms and Line Width of Absorption Lines......Page 99
3.6.2 Pressure Broadening (Collisional Broadening)......Page 100
3.6.3 Doppler Broadening......Page 101
3.6.4 Realistic Broadening in the UV- and Visible Spectral Ranges......Page 102
3.7.1 The Fluorescence Techniques......Page 103
3.7.2 Absorption Spectroscopy......Page 104
4.1 Basic Quantities Related to Radiation Transport......Page 106
4.2.1 Absorption Processes......Page 107
4.2.2 Rayleigh Scattering......Page 108
4.2.3 Raman Scattering......Page 109
4.2.4 Polarisation Properties of Vibrational Raman Scattered Light and Line Filling in......Page 113
4.2.5 Scattering and Absorption of Radiation by Particles (Mie Scattering)......Page 114
4.3 The Radiation Transport Equation......Page 117
4.3.2 Scattering of Radiation......Page 118
4.3.3 Thermal Emission......Page 119
4.4.1 Wide Beams in the Atmosphere, the Two-Stream Model......Page 120
4.4.2 Narrow Beams in the Atmosphere......Page 122
4.6 The Effect of Atmospheric Turbulence......Page 123
4.7 Practical Considerations About Radiation in the Atmosphere......Page 125
5 Measurement Techniques for Atmospheric Trace Gas Concentrations and Other Parameters......Page 128
5.2 The Role of Measurements in Atmospheric Chemistry......Page 129
5.2.2 Regional and Episodic Studies......Page 130
5.3 Requirements for Measurement Techniques......Page 131
5.4 Grouping Measurement Techniques in Categories......Page 132
5.5 Experimental Evidence for the Presence of Radicals in the Atmosphere......Page 134
5.6.1 Microwave Spectroscopy......Page 139
5.6.2 IR Spectroscopy......Page 140
5.6.3 UV/Visible Absorption Spectroscopy......Page 141
5.7.1 Tuneable Diode Laser Spectroscopy (TDLS)......Page 142
5.7.3 Light Detection And Ranging (LIDAR)......Page 143
5.7.5 White Light LIDAR......Page 145
5.7.6 Laser-Induced Fluorescence (LIF)......Page 146
5.7.8 Mask Correlation Spectroscopy (COSPEC)......Page 147
5.7.9 Differential Optical Absorption Spectroscopy (DOAS)......Page 148
6.1 The History of Absorption Spectroscopy......Page 150
6.2 Classical Absorption Spectroscopy......Page 152
6.3 The DOAS Principle......Page 153
6.4.1 Active DOAS......Page 156
6.4.2 Passive DOAS......Page 159
6.5 Trace Gases Measured by DOAS......Page 161
6.6 Precision and Accuracy of DOAS......Page 167
6.7.1 Fundamentals of the DOAS Approach......Page 170
6.7.2 Application of the DOAS Approach in Practical Situations......Page 173
7.1 Design Considerations of DOAS Instruments......Page 190
7.2 Key Components of DOAS Systems......Page 192
7.3.1 Characteristics of Artificial Light Sources......Page 193
7.3.2 Natural Light Sources......Page 205
7.3.3 Calibration Light Sources......Page 207
7.4.1 Some Principles of Optics......Page 209
7.4.2 Mirrors......Page 213
7.4.4 Lenses......Page 217
7.4.5 Apertures, Entendue, Lagrange Invariant......Page 219
7.4.6 Diffraction at Apertures......Page 220
7.4.7 Quartz-fibres, Mode Mixers, and Cross-section Shaping......Page 221
7.4.8 Filters......Page 223
7.4.9 Retro-reflectors......Page 224
7.5 Spectrometers/Interferometers for DOAS Systems......Page 227
7.5.1 Diffraction Gratings......Page 228
7.5.2 Spectrometers......Page 230
7.5.4 Characteristics of Spectrometers......Page 234
7.6.1 Geometrical Focal Plane Sampling Requirements......Page 238
7.6.2 Optomechanical Scanning Devices and Photomultiplier Tube......Page 243
7.6.3 Solid-state Array Detectors and Characteristics......Page 245
7.6.5 CCD Array Detectors......Page 251
7.6.6 CMOS Detectors......Page 255
7.7 Telescope Designs......Page 256
7.8 Optical Multi-pass Systems......Page 257
7.8.1 White Multi-reflection Cells......Page 258
7.8.2 Herriott Multi-reflection Cells......Page 260
7.8.3 Passive Resonators (CEAS, CRDS)......Page 261
7.9.1 \'Classic\' Active Long-path System......Page 262
7.9.2 High-resolution DOAS Spectrometers......Page 263
7.9.3 Recent Designs of Active Long-path DOAS System......Page 265
7.9.4 DOAS Systems with Optical Multi-pass Systems......Page 267
7.10.2 Zenith Scattered Light DOAS......Page 268
7.10.3 Off-axis, MAX-DOAS Instruments......Page 270
7.10.4 Imaging DOAS (I-DOAS) Instruments......Page 272
7.10.5 Aircraft-based Experiments......Page 274
7.10.7 Satellite Instruments......Page 275
7.11 Light Utilisation in a Long-path Spectrometer......Page 281
7.12 Software Controlling DOAS Instruments......Page 284
7.13 Optimising DOAS Instruments......Page 286
7.13.1 Optimum Light Path Length in Active DOAS Systems......Page 287
7.13.3 Optimum Measurement Time......Page 289
7.14.1 Active DOAS Systems – Standard Approach......Page 292
7.14.2 Active DOAS Systems – MCST......Page 294
7.14.4 Off-axis Scattered Sunlight DOAS Systems......Page 295
7.15 Mechanical Actuators......Page 297
7.15.1 Stepper Motors......Page 298
7.15.2 Other Actuators......Page 299
7.16 Information Needed for Later Analysis......Page 300
8 Evaluation of DOAS Spectra, Sensitivity, and Detection Limits......Page 301
8.1 Linear Fitting Methods......Page 302
8.1.1 Unweighted Linear Least Squares Fit......Page 303
8.2.1 Gradient Method......Page 304
8.2.3 Levenberg–Marquardt Method......Page 305
8.3 DOAS Analysis Procedure......Page 307
8.3.1 The Linear Model......Page 308
8.3.2 High- and Low-pass Filtering......Page 309
8.3.3 Wavelength Alignment......Page 312
8.3.4 Realisation......Page 313
8.3.5 Error Analysis......Page 316
8.4 Determination of Reference Spectra......Page 331
8.4.1 Theoretical Basis of Reference Spectra Simulation: Convolution......Page 332
8.4.2 Practical Implementation of Reference Spectra Simulation......Page 334
8.4.3 Optimum Resolution of Literature Reference Spectra......Page 335
8.5 Detection Limits......Page 337
8.6 Residual Spectra......Page 338
8.7 Systematic Errors in the Analysis......Page 339
8.7.2 Spectrometer Stray Light and Offsets......Page 340
9 Scattered-light DOAS Measurements......Page 343
9.1 Air Mass Factors (AMF)......Page 346
9.1.1 Direct Light AMF......Page 347
9.1.2 Scattered Zenith Light AMF......Page 349
9.1.3 Scattered Off-axis and Multi-axis AMF......Page 353
9.1.4 AMFs for Airborne and Satellite Measurements......Page 356
9.1.5 Correction of Fraunhofer Structures Based on AMFs......Page 357
9.1.6 The Influence of Rotational Raman scattering, the \'Ring Effect\'......Page 359
9.2 AMF Calculations......Page 361
9.2.1 Single-scattering RT Models......Page 362
9.2.2 Multiple-scattering RT Models......Page 364
9.2.3 Applications and Limitations of the \'Traditional\' DOAS Method for Scattered Light Applications......Page 365
9.3.1 ZSL-DOAS Measurements......Page 368
9.3.2 Off-axis-DOAS Measurements......Page 371
9.3.3 MAX-DOAS Measurements......Page 372
9.3.4 Accuracy of MAX-DOAS AMF Calculations......Page 380
9.3.5 The Box-AMF Concept......Page 383
9.4 Aircraft Observed Scattered Light (AMAX-DOAS)......Page 385
9.5 Satellite Observed Scattered Light......Page 386
9.5.1 Radiative Transfer in Nadir Geometry – the Role of Clouds......Page 387
9.5.2 The Analysis of Satellite-limb Scattered Light Observations......Page 391
10 Sample Application of \'Active\' DOAS with Artificial Light Sources......Page 392
10.1.1 Measurement of Urban Pollutants......Page 393
10.1.2 Vertical Profiles of Air Pollution by Multiple DOAS Light Beams......Page 411
10.2 Investigation of Free Radical Processes in the Atmosphere......Page 414
10.2.1 Measurement of OH Radicals by DOAS......Page 416
10.2.2 Measurement of NO[sub(3)] Radicals......Page 417
10.2.3 Measurement of Halogen Oxides......Page 425
10.3 Investigation in Photoreactors (Smog Chambers) by DOAS......Page 430
10.4 Validation of Active DOAS......Page 431
11 Sample Application of \'Passive\' DOAS......Page 441
11.1 Atmospheric Measurements by Direct Light Spectroscopy......Page 442
11.1.1 Ground-based Measurement of Atmospheric Species......Page 443
11.1.2 Balloon- and Aircraft-borne Measurement of Stratospheric Species......Page 444
11.2 Stratospheric Measurements by Ground-based Scattered Light DOAS......Page 448
11.2.1 Determination of Stratospheric NO[sub(2)] and O[sub(3)] from the Ground......Page 449
11.2.2 Observation of Halogen Radicals in the Polar Stratosphere......Page 453
11.2.3 Halogen Radical Observation in the Mid-latitude Stratosphere......Page 454
11.2.4 Observation of Stratospheric Trace Gas Profiles......Page 456
11.3 Measurement of Tropospheric Species by Ground-based DOAS......Page 460
11.3.1 MAX-DOAS Observations in Polluted Regions......Page 461
11.3.2 MAX-DOAS Observations of Halogen Oxides at Mid-latitudes......Page 462
11.3.4 Halogen Oxide Radicals in the Free Troposphere......Page 465
11.3.5 Trace Gases in the Marine Environment......Page 467
11.3.6 Determination of Aerosol Properties from MAX-DOAS Observations......Page 468
11.3.8 Emission from Point Sources......Page 471
11.3.9 Imaging Trace Gas Distributions (I-DOAS)......Page 476
11.4 Scattered Light Aircraft Measurements of Stratospheric Species......Page 478
11.5 Scattered Light Aircraft Measurements of Tropospheric Species......Page 480
11.6 Satellite Observations Using DOAS Techniques......Page 481
11.7.2 Stratospheric NO[sub(2)]......Page 485
11.7.3 Stratospheric OClO......Page 487
11.8 Satellite Observations of Tropospheric Species......Page 489
11.8.1 Tropospheric O[sub(3)]......Page 490
11.8.2 Tropospheric NO[sub(2)]......Page 491
11.8.3 Tropospheric Formaldehyde......Page 493
11.8.4 Tropospheric SO[sub(2)]......Page 495
11.8.5 Tropospheric BrO......Page 497
11.8.6 Tropospheric Carbon Monoxide......Page 499
11.8.7 Tropospheric Methane......Page 500
11.8.8 Tropospheric Water Vapour......Page 501
11.9.2 Path Length Distributions from High Resolution Measurement of Strong Absorbers......Page 503
11.9.3 Measurement of Trace Gases Inside Clouds......Page 506
12.1 Passive DOAS Applications......Page 507
12.1.1 MAX-DOAS......Page 509
12.1.5 Satellite Instruments......Page 510
12.2.1 New Trace Gases......Page 511
12.2.5 BTX Monitoring......Page 512
12.2.8 Range Resolved Technology/Broadband LIDAR......Page 513
12.3.2 New Detectors......Page 514
12.3.4 Improved System Design......Page 515
Literature......Page 517
A.1 Cadmium Lines......Page 581
A.3 Hydrogen Lines......Page 582
A.4 Neon I Lines......Page 583
A.5 Zinc Lines......Page 584
B.2 Nitrogen Dioxide, NO[sub(2)]......Page 585
B.4 Formaldehyde, HCHO......Page 587
B.6 Sulphur Dioxide, SO[sub(2)]......Page 588
B.8 Ozone, O[sub(3)]......Page 589
B.9 Monocyclic Aromatic Hydrocarbons......Page 590
B.11 Nitrous Acid, HONO......Page 593
B.12 Halogen Monoxides......Page 594
B.12.2 Bromine Monoxide, BrO......Page 595
B.13.2 Bromine Dioxide, OBrO......Page 596
B.15 Water Vapour, H[sub(2)]O......Page 597
B.17 OH Radicals......Page 598
B.18 Oxygen, O[sub(2)]......Page 600
B.19 Oxygen Dimer, O[sub(4)] or (O[sub(2)])[sub(2)]......Page 601
C......Page 604
H......Page 605
N......Page 606
S......Page 607
Z......Page 608