PLUME DISPERSION IN ALBERTA ydlbcria ENVIRONMENT Digitized by the Internet Archive in 2015 https://archive.org/details/plumedispersioniOOangl CANABIAJ^A JAN 2 2 1993 PLUME DISPERSION IN ALBERTA by R. P. Angle and S. K. Sakiyama* Standards and Approvals Division Alberta Environment December 1991 * Current affiliation: Air Resources Branch, British Columbia Ministry of Environment, Lands and Parks 777 Broughton Street, Victoria, B.C. V8V 1X5 This report may be cited as: Angle R.P. and S.K. Sakiyama. 1991. Plume dispersion in Alberta. Standards and Approvals Division, Alberta Environment, Edmonton, Alberta. 428 pp. PREFACE This compendium is the outcome of two separate, but related activities in which the authors have been engaged for more than a decade. Reviews of world literature and local studies of diffusion were undertaken prior to issuing Alberta Environment's first modelling guideline in 1978 and releasing a new draft for public comment in 1989. Over the years, the authors often taught short courses on dispersion meteorology and modelling, mainly for professionals in other scientific and technical specializations. In this volume we have combined our educational notes about the fundamentals of our science with the results of ongoing review of the scientific literature. The purpose of this document is to summarize current information about plume dispersion in the province of Alberta, within the context of general scientific understanding of the lower atmosphere. Each topic is introduced with an explanation of concepts and a definition of technical terms. The review encompasses virtually all published Alberta work up to the end of 1988; some more recent work was added during the final editing. Alberta references are always cited directiy in the text; world literature references are cited in parenthesis following a statement of generally accepted scientific understanding. Emphasis is given to topics of local relevance. Meteorology is the science dealing with the phenomena of the atmosphere. This includes not only the physics, but the history, chemistry, geology and biology of the atmosphere and many of the direct effects of the atmosphere upon the earth's surface, the oceans and life in general. The study of atmospheric processes governing the behavior and fate of airborne chemicals constitutes a specialization called air quality meteorology. The atmosphere may be viewed in different ways: as a medium for various physical processes, as a carrier for chemical, geological or biological substances, or as a setting in which a n umber of geophysical, chemical and biological processes take place. This review is concerned primarily with the continuous emission of chemicals from exhaust stacks (or chimneys as they are sometimes called). When the material leaving a stack is visible it assumes a distinctive featherlike form called a p lume. By extension the word plume is also used to describe invisible emissions since measurements can still indicate the presence of the structure. The report does not deal with accidental releases of toxic substances, urban air quality, dense gases, fog interactions, acid rain or the greenhouse effect. Its focus is on the ground-level concentrations that result from plumes in the atmosphere. Diffusion is defined as the exchange of air parcels and their conservative properties (such as heat, moisture, momentum) between neighboring regions of the atmosphere. The rate of transfer or mixing is several orders of magnitude greater than that due to molecular agitation. To be rigorous about the terminology one should probably refer to turbulent diffusion or eddy diffusion as distinct from molecular diffusion. The above definition places no restriction on the scale of the fluid motions involved in the exchange. Therefore, it c an include the process commonly called transport, which is defined as the movement of identifiable air parcels form one place to another in an organized manner that can be treated by the equations of motion. However, when the term transport is used in this manner, the term diffusion is usually restricted to those jqjparently random motions of a scale too small to be treated by the equations. The dictionary defines dispersion as the act or process of breaking up and going in different directions, spreading or distributing irregularly, scattering in different directions. Thus dispersion is a term even broader than diffusion and includes all processes that affect the fate of an airborne chemical, such as chemical transformation, rainout and surface removal. The primary elements of air quality meteorology are three: (1) wind; (2) temperature stratification; and (3) turbulence. These are introduced in the first chapter; descriptions of measurement methods and data display techniques may be found in the jqjpendices. The three elements are integrated in the discussion of the boundary layer, and the rise of a plume into the atmosphere. This leads directly to atmospheric diffusion over gende terrain and a brief description of the removal processes. Finally, the complex subject of flow and diffusion over rugged terrain is surveyed. Each chapter has a separate reference list and a separate summary section so that it can be read somewhat independently. The division of labor between authors gave principal authorship of chapters 1, 2 and 4 to R.P. Angle and of chapters 3 and 5 to S.K. Sakiyama. ii CONTENTS Page PREFACE i TABLES V HGURES viii ACKNOWLEDGEMENTS xiii L ELEMENTS OF DIFFUSION METEOROLOGY l-I 1.1 Wind 1-1 1.2 Temperature Stratification 1-22 1.3 Turbulence 1-39 1.4 Weather Systems 1-78 1.5 Summary 1-99 1.6 References 1-101 2. THE ATMOSPHERIC BOUNDARY LAYER 2-1 2.1 The Neutral Boundary Layer 2-1 2.2 The Unstable Boundary Layer 2-6 2.3 The Stable Boundary Layer 2-13 2.4 The Thickness of the Planetary Boundary Layer 2-19 2.5 Power Law Forms of the Wind Profile 2-26 2.6 Boundary Layer Evolution 2-28 2.7 Plume Behavior 2-40 2.8 Summary 2-54 2.9 References 2-55 3. PLUME RISE 3-1 3.1 General Considerations 3-1 3.2 Plume Rise in Neutral and Unstable Conditions 3-4 3.3 Plume Rise in Stable Conditions 3-8 3.4 Final Rise in Neutral and Unstable Conditions 3-11 3.5 Final Rise in Stable Conditions 3-15 3.6 Plume Penetration of Elevated Inversions . 3-15 3.7 Stack Aerodynamic Downwash 3-18 3.8 Behavior of Moist Plumes 3-21 3.9 Plume Rise from Gas Turbines and Reciprocating Engines . . . 3-22 3.10 Summary 3-23 3.11 References 3-24 iii CONTENTS Page 4. ATMOSPHERIC DISPERSION OVER GENTLE TERRAIN 4-1 4.1 The Gaussian Plume Model 4-2 4.2 Empirical Systems for Plume Spreads 4-9 4.3 Plume Spreads from Taylor's Theory 4-24 4.4 Plume Spreads from Interrelated Theories 4-29 4.5 Averaging Time 4-34 4.6 Buoyancy 4-43 4.7 Plume Height 4-45 4.8 Longer Travel Time 4-48 4.9 Wind Shear 4-50 4.10 Surface Roughness 4-51 4.11 Along-wind Spread 4-52 4.12 Nonstationarity and Calms 4-53 4.13 Concentration Fluctuations 4-55 4.14 Chemical Transformations 4-59 4.15 Removal 4-61 4.16 Summary 4-64 4.17 References 4-66 5. FLOW AND DIFFUSION OVER RUGGED TERRAIN 5-1 5.1 Wind and Turbulence Effects 5-1 5.2 Mathematical Modelling of Flow over Ridges and Hills .... 5-21 5.3 Mathematical Diffusion Modelling Over Rugged Terrain .... 5-24 5.4 The Effect of Buildings on Plume Dispersion 5-42 5.5 Physical Modelling of Transport and Diffusion Over Complex Terrain 5-55 5.6 Summary 5-61 5.7 References 5-63 APPENDIX A. MEASUREMENT TECHNIQUES A.1 Wind A-1 A.2 Temperature Stratification A-10 A.2 Turbulence A- 12 A.4 Boundary Layer Height A-20 A.5 Dilution A-22 A. 6 References A-24 APPENDIX B . DATA PRESENTATION TECHNIQUES B. l Wind Direction B-1 B.2 Wind Speed B-5 B.3 Wind Vector (Speed and Direction) B-5 B.4 References B-1 8 iv TABLES Page 1.1 Averages of inversion types for Edmonton '. . 1-38 1 .2 Joint frequency distribution of temperatme gradient with wind direction for Edmonton CBC Tower 1-42 1 .3 Joint frequency distribution of temperattire gradient with wind direction for Calgary Bonny brook Tower 1-43 1.4 The 18-m to 8-m temperature gradient at Ellerslie 1-44 1 .5 Summary of inversion characteristics measured by minisonde near Edmonton 1977 - 1982 1-45 1.6 Key to stability categories 1-66 1.7 Frequency of occurrence of Pasquill stability classes 1-67 1.8 Stability classification using net radiation 1-71 1.9 Turbulence classification based on wind fluctuations 1-72 1.10 Bulk Richardson numbers measured on 91-m towers in Calgary and Edmonton 1 - 74 1.11 Relation among turbulence typing methods 1 - 76 1.12 Relation between Pasquill class, Monin-Obukhov length and roughness . 1-75 1.13 Values of Kazanski-Monin parameter corresponding to Pasquill classes . 1-77 1.14 Airmasses and fronts in the conventional Canadian classification . . . . 1-80 2.1 Summary of experimentally determined roughness lengths 2-4 2.2 Summary of equations describing the neutral atmospheric boundary ... 2-7 2.3 Summary of equations describing the unstable atmospheric boundary . . 2-9 2.4 Summary of equations describing the stable atmospheric boundary ... 2-16 2.5 Mean maximum (aftemoon) mixing heights at Edmonton 2-21 V TABLES Page 2.6 Median values of kink mixing height at EUerslie 2-24 2.7 Alternative definitions of the thickness of the atmospheric boundary layer 2-27 2.8 Summary of power law exponents observed in Alberta 2-29 2.9 Seasonal hourly values of mixing height at Fort McMurray 2-36 2.10 Types of plume behavior and associated meteorology 2-44 2. 1 1 Monthly distribution of stability at Calgary 2-53 3 . 1 Observational studies in Alberta of buoyant plume rise in neutral Ainstable conditions 3-6 3.2 Observational studies in Alberta of buoyant plimie rise in stable conditions. 3-10 3.3 Final rise formulations 3-13 3.4 Observations in Alberta of final rise in neutraVunstable conditions 3-16 4.1 Current working theories of diffusion 4-3 4.2 Summary of basis and scope of original Pasquill-Gifford curves .... 4-14 4.3 Single power law j^proximations to the Pasquill-Gifford curves .... 4-15 4.4 BNL plimie standard deviations 4-19 4.5 TVA diffusion coefficients . 4-19 4.6 Briggs plume spread formulas for elevated small releases 4-22 4.7 Summary of Draxler's equations 4-27 4.8 Other universal functions 4-28 4.9 Power law approximations of vertical spread 4-30 4.10 Sigma values from neutral to unstable using convective scaling .... 4-33 vi