United States
Environmental Protection
Office of      Environmental Sciences Research
Research and    Laboratory
Development    Research Triangle Park, North Carolina 27711
EPA-l>00, 7-77-020
March 1977
             IN  COMPLEX TERRAIN: An
             Appraisal of Current
             Research and Development
             Program Report

                       RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S.
Environmental Protection Agency, have been grouped into seven series.
These seven broad categories were established to facilitate further
development and application of environmental technology.  Elimination
of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields.  The seven series

     1.  Environmental Health Effects Research
     2,  Environmental Protection Technology
     3.  Ecological Research
     4.  Environmental Monitoring
     5.  Socioeconomic Environmental Studies
     6.  Scientific and Technical Assessment Reports (STAR)
     7.  Interagency Energy-Environment Research and Development

This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series.  Reports in this series result from
the effort funded under the 17-agency Federal Energy/Environment
Research and Development Program.  These studies relate to EPA's
mission to protect the public health and welfare from adverse effects
of pollutants associated with energy systems.  The goal of the Program
is to assure the rapid development of domestic energy supplies in an
environmentallycompatible manner by providing the necessary
environmental data and control technology.  Investigations include
analyses of the transport of energy-related pollutants and their health
and ecological effects; assessments of, and development of, control
technologies for energy systems; and integrated assessments of a wide
range of energy-related environmental issues.
This document is available to the public through the National Technical
Information Service, Springfield, Virginia  22161.

                                          March 1977

       An Appraisal  of Current Research
Robert C. Koch, W.  Gale Biggs, Paul  H.  Hwang,
    Irving Leichter, Kenneth E.  Pickering,
      Eric R.  Sawdey, and John L.  Swift

             GEOMET, Incorporated
              15 Firstfield Road
        Gaithersburg, Maryland  20760
     Phase I - Contract Number 68-02-2260
               Project Officer

             George C. Holzworth
     Meteorology and Assessment Division
  Environmental Sciences Research Laboratory
Research Triangle Park, North Carolina  27711


          This report has been reviewed by the Environmental Sciences
Research Laboratory, U.S. Environmental Protection Agency, and approved for
publication.   Mention of trade names or commercial products does not con-
stitute endorsement or recommendation for use.


          This report reviews the literature of scientific studies of the behavior
of stack plumes from fossil-fueled electric power plants in complex (hilly or
mountainous) terrain.  Non-conservative chemical  transformation and depletion,
and conservative transport and diffusion of pollutants, are considered.   Studies
of S02 oxidation rates in power plant plumes are described and the primary
mechanisms for conversion to sulfate are detailed.  Homogeneous gas phase
reaction of S02 with OH is of importance, with conversion rates reported from
1 to 13 percent per hour.  Aqueous phase SC>2 oxidation has higher conversion
rates, in presence of NH3 and with iron, lead or manganese as catalysts, but
is less well-studied.  Early depletion of background ozone by stack plumes is
documented; evidence indicates that ozone above background levels reappears in
plumes at great distances from the stack.  Little information on field studies
of plume chemistry of NOX, CO, or hydrocarbons was found.  Scavenging of S02
from plumes by precipitation is shown to increase with distance from the source
and has been modeled.  Surface contact may be an  important plume depletion pro-
cess but quantitative models have not been validated.
          Current theories of airflow, turbulence and diffusion phenomena in
complex terratn are described, and are exemplified through the review of sixteen
field observation programs of the physical behavior of plumes from continuous
elevated sources in complex terrain.  The review discusses program objectives,
data, sampling methodologies, model-to-measurement comparisons associated with
the field programs and program conclusions.  The types of models available to
simulate plume behavior numerically are discussed in the contexts of these
programs.   In addition, results are reported of an Independent GEOMET analysis
A view of the plume from the Four Corners Power Plant in New Mexico, crowing ihe Hogback and going through two
                   Ice-wave oscillations.  The plant U situated to the east (right) of this photograph.

Abstract                                                           11i
Photograph of the Four Corners Power Plant Plume 	   v
Figures	ix
Tables	,	xiii

Part 1.  Scope of Effort and Results	    1

Section I.    Introduction  ....  	    1
                  Background 	    1
                  Objectives 	    3
                  Approach  .	    4
Section II.   Summary and Conclusions	    6
                  Plume Chemistry	    7
                  Plume Depletion	    9
                  Plume Transport and Diffusion	10
Part 2.  Nonconservative Aspects of Plume Behavior
Section  III.  Principles and Laboratory Research  	   13
                  Direct Photo-Oxidation  	   T
                  Indirect Photo-Oxidation	";'3
                  Air Oxidation  in Liquid Droplets  	   2Z
                  Metallic-Catalyzed Oxidation  in Liquid  Droplets    f 6
                  Other Aqueous  S02 Oxidation Mechanisms  	   ol
                  Heterogeneous  Studies	32
                  Related Chemical Processes  	   36
                  Precipitation  Scavenging  	   39
Section  IV.   Models of Plume  Chemistry and Depletion-Deposition
              Processes	   42
Section  V.    Field Studies of Plumes	55
                  Colbert Power  Plant	  ,	55
                  Crystal River  Power  Plant.	']'.
                  Morgantown Power Plant	.\?
                  Keystone ana Nort.-port  Plant	      ,  .   .5:
                  Four Corners Plant	5~
                  MISTT Program	66
                  S02 Deposition Studies  	   FJ
                  Precipitation  Scavenging  Studies  	   75


Section VI
                         CONTENTS   (Concluded)
Evaluation	  7b
Part 3.   Transport and Diffusion of Plumes Under Influence
         of Complex Terrain.	84

Section  VII.   Principles and Observations 	  85
                  Airflow in  Complex Terrain	 .  85
                  Turbulence  and Diffusion Enhancement ......  91
Section  VIII.  Modeling of Terrain Influence on Plume Behavior . . 101
                  "NOAA" Gaussian Model	106
                  U.S. EPA Single Source (CRSTER) and "VALLEY"
                  Models .... 	 ...... 109
                  ERT PSDM Model	 110
                  Aerovironment Statistical  Turbulence Model ... Ill
                  INTERA Model	114
                  TVA Model	116
Section IX.    Field Studies	117
                  Dugway, Utah	117
                  Vandenberg  Air Force Base	119
                  Dickerson Power Plant.	 121
                  Naughton Plant	122
                  Four Corners Plant ...... 	 125
                  Navajo Plant	129
                  Huntington  Canyon	137
                  Garfield Smelter 	 146
                  Kaiparowits	152
                  LAPPES Program ........ 	 155
                  Kingston Power Plant 	 167
                  Summary of  Field Studies 	 173
Section X.     Recapitulation and Commentary .  	 181
                  Enhanced Turbulence	"81
                  Terrain Imp-; Demerit	"82
                  Plume Dimensions	133
                  Plume Center-line Concentrations	184
                  State-of-tne-Art for Modeling Transport and
                  Diffusion of Continuous Elevated Plumes in
                  Complex Terrain. .	187

     A.   Bibliography on Nonconservative Plume Behavior	188
     B.   Bibliography on Transport and Diffusion of Plumes
         under the Influence  of Complex Terrain    .        ... 206


Number                                                             Page

   1       Possible atmospheric paths for S02 upon emission
            from a power plant stack	15

   2      Effect of hydrocarbon structure on nitrogen dioxide
            formation rate	38

   3      A falling raindrop and the associated transport and
            washout mechanisms acting upon it in the atmosphere.  .  41

   4      Schematic of physical interactions modeled by SMICK.  .  .  48

   5a     Profiles of crossplume ozone concentration at various
            elevations downwind of the Morgantown Power Plant.  .  .  61

   5b     Profiles of sulfur dioxide and ozone crossplume con-
            centrations at 600 m altitude at various downwind
            distances from the Morgantown Power Plant	62

   6a     Conceptual illustration of the variation of both
            homogeneous and heterogeneous S02 conversion
            mechanisms as a function of time of year for a
            specific stack location. .... 	  8C

   6b     Conceptual illustration of the variation of both
            homogeneous and heterogeneous S02 conversion
            mechanisms as a function of time of day for a
            specific stack location	80

   6c     Conceptual illustration of the variation of both
            homogeneous and heterogeneous S02 conversion
            mechanisms as a function of distance from the stack.  .  3".

   7a     A schematic cross section of the lower turbulence
            zone (LTZ) based on six case studies, showing the
            potential temperature field	89

   7b     Strong vertical shears and large lor.c'ltudinal speed
            changes, especially in the vicinity or the uodrafts
            and the rotor are associated with the wind speed
            maximum in the stable layer at the top of tne i_TZ  .  .  b^


                         FIGURES  (Continued)

Number                                                             Page

   7c     Distribution of moderate or greater intensities
            of turbulence found within the LTZ in the wave
            cases 	  ............ 	   89

   7d     The larger dimensions of the LTZ and the greater
            extent of the area of severe turbulence distinguish
            the streamline and turbulence distribution of
            hydraulic jump types from wave types	   89

   8      Schematic illustration of mountain top influences upon
            the gradient level flow component and the downward
            transporting of gradient flow momentum	  .   95

   9      Schematic illustration of circulations triggered by
            slope density flows and air drainage from a side
            feeder canyon .	   95

  lOa     Schematic view of the type of terrain capable of  <
            affecting the wake turbulence 	 .....   96

  lOb     Schematic illustration of turbulent wake effects
            caused by obstacles protruding into the primary
            flow pattern.	   97

  11      Coordinate system showing Gaussian distributions in
            the horizontal and vertical	102

  12      Configuration of elevated line source releases with
            respect to wind direction and orientation of mountain
            system near Dugway, Utah	118

  13      Vertical plume dimensions (az) inferred from cross
            width (a ) and surface center!ine concentration
            assuming^SO percer.t deposition at -;he surface  ...     ;2G

  14a     Helicopter and grour.c samples for D stability ...    .  "i39

  14b     Helicopter samples only for D stability elevated
            release tests	',39

                         FIGURES  (Concluded)
Number                                                             Page

  15a     Helicopter and ground samples for F stability
            release at ground-level  conditions of down-
            canyon flow	    140

  15b     Helicopter samples only for F stability release
            at ground-level in conditions of down-canyon flow .  .    140

  16      Terrain cross-sections at three sites of varying
            degrees of roughness  	    143

  17a     Results of Garfield aerial sampling test with
            stability class "B" conditions	    148

  17b     Results of Garfield aerial sampling test with
            stability class "C" conditions	    148

  18      Profiles of elevation toward 14 directions from
            Keystone Power Plant	    162

  19      Elevation profile from Kingston plant to each
            receptor	    171


Number                                                             Page

   1       Mechanisms that convert sulfur dioxide to sulfates. .  .    16

   2       Studies of the photo-oxidation of sulfur dioxide in
            sunlight	    18

   3       Nine initiating reactions for homogeneous gas phase
            oxidation of sulfur dioxide and their lifetimes for
            conversion to H2S04 in the troposphere	    19

   4       Summary of teflon bag experimental  conditions for
            S02/NO/N02/l-Butene system	    23

   5       Nomenclature and values used for plume S02 oxidation
            calculations	    28

   6       Summary of eight experiments involving S02 reactions
            in the presence of various particulates 	    34

   7       Summary of typical  secondary atmospheric sulfate types.    35

   8      Key reactions proposed for the $62 conversion to
            sulfate via OH radicals .	    44

   9      S02 oxidation studies - Colbert Steam Plant Plume ...    56

  10      Normalized and averaged data from 11  plume sampling
          runs made at the Keystone Power Plant	    64

  11       Meteorological stability categories 	 ...   103

  12       Model and measurement comparisons for peak hourly
            average S02 concentrations (ppm) observed at
            elevated terrain  features  near Navajo Generating
            Station	134

  13       Average ratio and range of calculated to observed
            relative concentration values x'  cal/x' obs for
            three different terrain configurations	144

                                 -XI 1-

                          TABLES  (Concluded)
Number                                                             Page

  14      Garfield data model-to-measurement comparisons of
            ground-level concentrations 	    150

  15      Comparative model results of the ratios of the mean
            calculated to mean observed values of each of four
            tracer tests near Kaiparowits 	    154

  16      Dispersion parameters a  and a  derived from plume
            cross-section measurements in the LAPPES program. .  .    158

  17      Summary of observed and standard a value, observed
            minus standard, and equivalent Pasquill stability
            class for combined Keystone and Conemaugh data. ...    161

  18      a  values as obtained by Nilsson (1975) as well as
           ^correlation coefficients and slopes of the regression
            curves	    169

  19      Comparison of computed and observed mean ground-level
            S02 concentrations	    172

  20      Summary of field studies of transport and diffusion
            in complex terrain from elevated sources	    174

                                 PART 1
                      SCOPE OF EFFORT AND RESULTS
                               Section I

          At the end of October, 1975, the Meteorology and Assessment
Division of the U.S. Environmental  Protection Agency,  at Research  Triangle
Park, North Carolina, awarded GEOMET, Incorporated a contract to  under-
take a study - including literature research, field observations,  and
analytic modeling - into the behavior of  stack plumes  from large  fossil -
fueled power plants in complex terrain.   The first product of that study,
an appraisal of the extent, utility and limitations of existing knowledge
in this field, is the subject of this report.
          This report is the culmination  of Phase  I of GEOMET's work
under EPA Contract Number 68-02-2260.  A  Phase II  report, describing
results of a long-term program for field  monitoring of sulfur oxides
and other plume components begun by GEOMET in the  vicinity of the  700  MW
coal-fired Clinch River Power Plant at Carbo, Virginia in April,  1976,
will be issued in late 1977.
          Fossil-fueled electric power plants are  major sources of air
pollution.  Particulate matter, sulfur dioxide, nitrogen oxides,  and
trace metals are - in the absence of effective control equipment -
dispersed into the air from power plant stacks.  All can be hazardous
to health and welfare in the plant environs.  Chemical reactions of
pollutants in power plant plumes may result in formation of sulfates,
nitrates, and photochemical oxidants which are advected over great dis-
tances, resulting in health hazards in areas remote from the power plant
source of the pollution.  Permissible maximum ambient concentrations of
sulfur dioxide (S02), nitrogen oxides (NOX), total suspended particu-
late (TSP), and oxidants (Ox) have been established in law and are
enforced under State Air Quality Control  Implementation Plans.  National

standards for ambient sulfate and nitrate concentrations do not yet
exist, but may be expected in the future.
          Particulate matter emissions can be effectively controlled
at large power plants through electrostatic precipitation.   Sulfur
dioxide emission control procedures are technically feasible but are
expensive; they have not been widely adopted.  The electric power industry
has typically relied upon the dispersive power of the atmosphere to reduce
ambient ground level S02 concentrations, through discharge of emissions
from tall stacks.  Effective means for the control of NOX emissions are
still in development, not yet applicable to large-scale commercial pro-
duction of electricity.
          Growing reliance upon coal as a fuel for power generation -
switching from imported oil and scarce gas - has increased the national
concern about the SOg and sulfate air pollution problem.  Much of the
coal available in the United States has a relatively high sulfur content
(more than one percent), but this fuel is our most sure source of future
energy for many years to come.
          Coal and oil-fired power plants were originally built near
load centers, typically in or near urban areas.  With the development
of improved high voltage, long distance power transmission systems it
has become economical to build very large (1000 MW and more) coal-fired
power plants in coal mining areas, transmitting power hundreds of miles
to load centers.  Power plants in such remote areas are often located
in complex mountainous terrain, in whicri ground elevations at  ..-,  o.^
higher than the top of plant stacks occur,within the area traversed cy
the pollutant plumes from the plant.  This condition may also occur -In
hilly, settled country, particularly where smaller or older power plants
have stacks less than about 150 m in height.
          For the design and siting of new power plants, and for the
control of pollutants from existing ones, it is necessary to have reliable
techniques for calculating the ambient air quality impact of stack

emissions from large power plants - particularly for S02, NOX and their
transformation products.  The problem has been studied in depth for many
years.  A body of modeling technology exists, suitable for calculating the
physical behavior of a stack plume based upon input knowledge of pollutant
emissions, stack configuration, and meteorology - but the models perform
well only under limited conditions of terrain uniformity; and they do
not perform well for non-conservative, reactive pollutants.
          Existing models generally assume a uniform terrain roughness.
Some models take differential terrain elevations into account, with broad
simplifications and limited success.  Models available to planners are
typically weak (or totally lacking) in ability to handle plume depletion
due to chemical transformation and non-conservative behavior.
          A need exists to develop improved techniques for calculating
the behavior of pollutants in the plumes of large power plants in com-
plex terrain.  Realistic goals for new studies can only be established
through an examination of the extent, capability, and limitations of
the existing body of knowledge.  That examination is the subject of
this report.
          The study which produced this report had the following

              Provision of an up-to-date description of existing
               knowledge of (1) concentrations of S02 and sulfate
               (and pollutants interacting with these), resulting
               from the operations of large fossil-fueled power
               plants in complex terrain, (2) relationships between
               meteorological data, terrain characteristics, and
               plume behavior, and (3) the pollutant transfor-
               mation and depletion.
              Appraisal of the adequacy of typical meteorology,
               air quality and emissions data - of kinds routinely
               available to power plant plume analysts in non-research

               situations  - for use in calculating  ground  level
               concentrations  of S02 and sulfates,  due  to  power
               plant emissions, in areas of complex terrain.

          Implicit in these objectives are the  concepts of identifying
deficiencies in current knowledge and recommending  new  research  which
could improve our ability  to calculate the air  pollution impact  of power
plant plumes in complex terrain.
          Precise definitions  of "large power plant" or of "complex
terrain" are difficult to  outline.   In general, a large power plant may
be thought of as one in which  more than 700 MW  of capacity are installed
at one location.  For plume study purposes, the complexity of terrain is
a function of its influence upon plume behavior.   As a  working definition,
complex terrain is terrain in  which stack pollutants appear at ground
surfaces in concentrations significantly different  from those which would
be expected to occur if the terrain were essentially level.
          The study was essentially performed in  a  six-month  period,
from November, 1975 through April, 1976.  The method was primarily
that of a literature search, supplemented by discussions with researchers
active in related areas.  Research literature was sought out, reviewed,
summarized, and appraised  in the two major categories of (1)  chemical
transformations in power plant plumes and (2) the concentrations of
pollutants in plumes moving under meteorological  influences over complex
terrain.  In these categories  information was sought on field observa-
tions of relevant data and also upon analytic efforts to develop, improve,
and validate models for calculating pollutant behavior.  GEOMET  made
some independent modeling  analyses of S02 and meteorological  data taken
by others in previous field studies.  In these  modeling analyses GEGMET
sought preliminary insights into relationships  between  terrain complexity
and variations in the horizontal  and vertical standard  deviations (ay ar.d

az) of pollutant distribution models conventionally used to describe the
dispersion of a plume.  The results have been used to suggest further
directions for study.

                                Section II
                         SUMMARY AND CONCLUSIONS

          Over 200  studies,  directly or indirectly  relating to the subject
of plume behavior from  elevated point sources  in  complex terrain, were
reviewed for the preparation of this report.   The titles and authors of
these studies are listed in  an appended Bibliography.   Aspects of plume
behavior have been  broadly categorized into two areas  of information,
namely, (1) non-conservative aspects relating  to  chemical  transformation
and depletion processes and  (2) transport and  diffusion aspects.*
          Information presented regarding plume chemistry includes a
discussion of the principles and results of investigative laboratory
work for each of four classes of sulfate formation  processes, a review
of the approaches which have been used in plume chemistry modeling, and
descriptions of major field  observation programs.   Other information pre-
sented regarding plume  depletion processes includes a  discussion of the
principles of precipitation  scavenging and chemical processes other than
sulfate formation,  modeling  approaches for treating wet and dry deposition,
and a description of major field observation programs  involving precipi-
tation scavenging measurements.  An evaluation of the  current state-of-
the-art knowledge of the non-conservative aspects of plume behavior
follows the discussions of principles, modeling,  and field programs.
          With regard to transport and diffusion  aspects of plume
behavior, the principles and observations of airflow and turbulence
and diffusion enhancement in complex terrain are  reviewed, followed by
a discussion of the modeling of terrain influence on plume behavior and
by detailed descriptions of 16 major field studies.  An evaluation is
made of the current state-of-the-art knowledge of the  transport and
diffusion of plumes under the influence of complex  terrain.
* In this review we have used transport, diffusion and dispersion with the following meanings: Transport -
  Movement of plume components by winds, at scales large enough to be treated by the equation of motion-
  Diffusion Exchange of plume components and other atmospheric elements between regions in space, in
  apparently random motions, at a scale too small to be treated by the equations of motion; Dispersion - The
  combined result of the transport and diffusion processes.

          Based on the review of previous studies of plume behavior and
on a new analysis of the behavior of plumes from three power plants
located in the Appalachian mountain regions of Pennsylvania and in
Tennessee, we have drawn conclusions regarding the present state-of-the-
art and needs for further research to treat plume behavior from a coal-
fired power plant in complex terrain.  Conclusions reached regarding the
current state-of-the-art of non-conservative plume processes are presented
first.  The findings concern available measurements, modeling,  sulfate
conversion mechanisms, and plume depletion-deposition processes.  The
conclusions reached with regard to plume transport and diffusion then
          A wide range of S02 oxidation rates (varying from zero to over
50 percent per hour) have been deduced from field study measurements.
The rates reflect variations in meteorology (especially relative humidity),
time of year, location, source emissions, and background atmospheric con-
taminants; most of these variables cannot be controlled in field experi-
ments.  A field program design that can serve as a guide in planning future
studies is needed.  Normally plume measurements show a depletion of ozone
below the normal background concentration.  However, levels greater than
background have been evident in several studies of plant plumes at distances
in excess of 50 km from the plume source.  Current and future field pro-
grams are being designed to determine if ozone is formed in plumes under
certain conditions.  Very limited field observations have been made of chem-
ical processes (other than the S02 to sulfate conversion) which involve ozone,
NO, N02, CO, hydrocarbons, water, and radical chemistry.
          Although several plume chemistry models have been developed,
there is a definite lack of data to  test these models.  Additional research
is needed in the areas of plume physics, plume photochemistry,  and plume
measurement methodology.  Improved information on the dominant  S02 con-
version mechanisms and their reaction rates are  required for realistic
depiction of plume chemical processes.

          Different S02 oxidation mechanisms may be important in power
plant plumes under different environmental  conditions.   The significance
of different conditions can only be hypothesized at this time.   The four
major processes of sulfate formation that have been identified  from
theoretical considerations to be potentially active in  plant plumes
include homogeneous indirect photo-oxidation, homogeneous air oxidation
in liquid droplets, quasi-homogeneous catalyzed oxidation in liquid drop-
lets and heteorogeneous catalyzed oxidation on dry surfaces.
          The gas phase reaction of S02 with OH is the  most notable
homogeneous sulfate formation process.  An S02 sulfate  conversion rate
of 2 percent hr"1 is a representative average rate for  this reaction.
Further quantification of the importance of the homogeneous OH-S02
mechanism compared to heterogeneous processes can be determined with
more complete information on OH atmospheric profiles.   S02 conversion
rates for homogeneous gas phase reactions vary from 1  to 13 percent hr~'.
          Sulfate conversion rates of 0.1 to 2.0 percent per minute have
been reported in studies of aqueous phase S02 oxidation.  The process
rate is highly variable due to its sensitivity to several parameters
including temperature, relative humidity, and pH.  The  important role of
NH3 in promoting this conversion by maintaining a high  pH has been docu-
mented.  Available information for measuring NH3 in the short time frames
and low concentrations typical of airborne plume measurements is not
adequate for field studies; similar problems exist with regard  to field
monitoring of the roles of trace metal catalysts.
          Various transition metal ions (e.g., MnT+, Cu^, Fe++, and
Co++) have a catalytic effect on the conversion of S02  to sulfate Dy a
wide variety of heterogeneous reactions in solution conditions.  Studies
point to S02 conversion rates from 0 to 6 percent hr"1, with the most
efficient catalysts being leac and iron.  Research has  shown ory ^art<-
culate vanadium to be relatively inactive as an effective catalyst -.n
the heterogeneous oxidation of S02-

          The few field studies of precipitation scavenging of reactive
pollutants from power plant plumes have measured the washout process by
examining ground rainwater samples.  The most comprehensive and recent
study at the Centralia power plant in Washington showed that scavenging
rates of S02 increase with distance from the plant, and that sulfate
concentrations in rainwater due to the plume presence are not significant
less than 10 km from the stack.  The Scavenging Model Incorporating Chemical
Kinetics (SMICK) has been developed and has the capability to predict preci-
pitation scavenging of reactive pollutants from power plant plumes.
          The complexities involved in measuring the numerous parameters
necessary to represent the rainout mechanism as it applies to power plant
plume depletion have resulted in a large information gap.  To realistically
model the rainout mechanism requires data on specific cloud parameters
such as depth, temperature and water distributions, electrical activity,
as well as information about the sulfate aerosol, such as size distribu-
tion, concentration, wettability and activity as a nucleus.
          While surface contact is probably an important plume depletion
process for S02, methods of estimating this effect are not sufficiently
well developed to make accurate quantitative estimates of a depletion
rate.  The rate of pollutant removal by vegetation and soil has been
shown in laboratory studies to be affected by wind velocity, canopy
height, light intensity, soil pH, and moisture content.  Based on the
laboratory findings, as much as 49 percent of the S02 emitted from a
large coal-fired plant would be depleted under some conditions within
32 km due to the average uptake rate of a 40 cm alfalfa canopy
during daylight.
          Numerical models of the dry deposition process, still rather
primitive, have relied mainly on wind tunnel data to predict deposition
velocities.  They require atmospheric data for validation purposes.  The
source depletion approach, in which source strength is reduced as a

function of downwind distance has been commonly used in Gaussian plume
equations to represent the plume depletion processes.   A steady-state one
dimensional mass transfer model  is also available.
          Sixteen field observation programs directly  related to the
diffusion of a plume from a continuous elevated point  in complex terrain
were reviewed.  Most of the field programs have been very limited in
scope, either in terms of the intensity of observations or the duration
of observations; typically a program consists of one week of plume mea-
surements.  The majority of the field programs have focused on observing
the worst case situations which have usually been judged to be associated
with very stable conditions.
          The principal characteristics of flow over complex terrain
which create enhanced turbulence are (1) thermally driven drainage and
up-slope flows and (2) waves in the lee of a ridge.  Channeling and
physical diversion of flow may also increase the turbulence.
          The most abundant data available to confirm  turbulence enhance-
ment due to complex terrain are from bivanes and tetroons.  Measurements
of plume contaminants confirm the relevance of these measurements to p'iurne
behavior.  Wind fluctuation data are especially important for estimating
plume dispersion rates in rough terrain.
          There is some evidence that horizontal  spreading (i.e., ay),
is amplified to a greater extent than vertical  spreading in complex
terrain, particularly under stable conditions.   The resultant increase
of ay has been attributed primarily to plume separation processes ana
plume meandering which occur when the higher terrain elevations are con-
fronted by the plume.  Overall,  the observed plume dimensions ir. complex
terrain (compared to flat terrain for similar stability conditions) nave
a larger cross-section and the plume is generally more dilute in the
core by a factor of two or more.
          Although several  models are available for estimating ground-
level  concentrations  from an elevated point-source in  complex terrain,

validation analyses suggest that each is subject to systematic errors which
may occur because the effects of terrain are not adequately represented.   In
general, the models are capable of estimating ground concentrations, measured
at distances greater than 10 km from the source, within a factor of two.
Larger errors occur for distances closer to the-source.
          Practical methods of characterizing the effects of terrain on the
path and the diffusion of an elevated plume need to be developed.  There  are
many difficulties in providing a working model of mountain wind fields in com-
plex terrain even though adequate theories for local wind in simple ridge and
valley situations have been developed.  The topography amplifies all the  prob-
lems typically associated with initializing and grid meshing in mesoscale
dynamics modeling.  Analytic methods for generating and quantifying terrain
characteristics with sufficient reality and economy for modeling are needed.
          Results from one series of tracer studies suggest that the turbulent
downward transport of the plume during transitional fumigation periods between
stable morning and neutral/unstable afternoon conditions, may cause higher
ground-level concentrations than the passing of the plume close to or impinging
on elevated features under stable conditions.  More information  (for example,
extensive temperature profile data atop ridges near point sources when potential
fumigation conditions exist) must be available from field measurement programs
to define the behavior mechanisms associated with the highest ground concentra-
tions in complex terrain situations.
          Meteorological data used in previous studies, obtained from local
radiosondes, pilot balloons, constant-volume balloon flights, aircraft, and
surface networks, may not have been an adequate representation of the variation
of meteorological conditions throughout the areas of complex terrain which
affected behavior of the plumes under study.  Readings obtained do not appear
to have fully reflected orographically induced eddies, directional wind shear,
and thermal convection processes which are vital to the plume transport pro-
cess.  Even with batteries of specially placed sensors, mobile ground vans,
and helicopter observations (such as have characterized most of-the  16 f-':.d
studies of plume advection and dispersion in complex terrain examined in
this report) it has not so far been possible to assemble and process field

data in ways which define the circumstances  under which plume impingement
(or near impingement) occurs in complex terrain.   If this has been the
case for data gathered in specially-equipped research programs,  an inescap-
able conclusion is that the kinds of meteorological, air quality,  and pol-
lution emissions data now routinely available to  air quality analysts for
power plant plume studies are inadequate -  in the present state-of-the-art
plume modeling - for the acceptably accurate calculation of ground-level
concentrations due to a power plant plume in complex terrain.
          There is a need for the development of  improved modeling tech-
niques which will  permit the calculation of  validatable plume concentration
estimates (and plume impingements if these occur)  in complex terrain.   These
modeling techniques should be based upon data which  are routinely  measured
and are routinely available, at an economically affordable cost, for the
vicinities of power plant sites.

                                 PART 2

          The dispersion and the fate of effluents from power plant
stacks are a function of conservative and non-conservative aspects  of
plume behavior.  If the effluent plume were to consist entirely of
non-reactive gases it would be transported by wind and diluted by tur-
bulence, but the total mass of the original gas would remain unchanged
in the dispersion process.  The plume behavior would be conservative.
The ideal gas described by conventional Gdussian plume dispersion models
has a conservative behavior.  In reality such behavior can be approxi-
mated for short periods of time by plumes of fine particulates and  of
relatively non-reactive stack effluents such as sulfur dioxide, but the
approximation is inadequate for periods of more than a few hours (or
less for more reactive effluents) because of chemical and physical
transformations which may change both the composition and the total
mass of material remaining in the plume.  These chemical and physical
transformations are the non-conservative aspects of plume behavior.
          Considerations of non-conservative plume behavior must neces-
sarily modify all efforts to provide a realistic, quantitative description
of the overall behavior and the ambient air pollution impact of stack
plumes from large fossil-fueled power plants - whether in complex or in
simple terrain.
          A discussion of existing research into non-conservative plume
behavior is presented in the next four sections (III, IV, V, and VI) of
this report.  Conservative plume behavior is discussed subsequently in
Part 3.

                              Section III

          The combustion of fossil fuels, whether coal, petroleum
products or natural gas, is an oxidation process in which carbon and

hydrocarbons plus air are converted  principally to carbon dioxide and
water vapor which are exhausted from the stack as  effluents.   A residue
of solid ash may be removed in the power plant (through the use of
precipitators and similar cleaning devices)  or the ash may be largely
discharged from the stack as particulate matter.   Most fossil fuels con-
tain some sulfur, which is largely oxidized  to sulfur dioxide and leaves
the plant in the stack plume unless  in-plant sulfur removal processes
are used.  Trace metals in the fuels appear  in the stack effluents.  A
by-product of high-temperature fuel  combustion is  the oxidation of some
of the molecular nitrogen in the combustion  air to nitric oxide and
nitrogen dioxide; these gases also appear in the stack effluent.
          Sulfur dioxide is the stack effluent of  major interest,
because of its known adverse effects upon human health and vegetation,
and because of its propensity to oxidize to  sulfates which may cause
greater damage.  All identified pollutants in stack gases are, however,
of interest for plume behavior studies.
          The main combustion processes  of fossil  fuels in power plants
are accompanied by numerous intermediate side reactions, resulting from
the variety of trace chemical constituents,  temperatures, and oxygen
concentrations encountered within the combustion system.  Upon emission,
the S02 component of the plume is not in chemical  equilibrium with its
rapidly changing surroundings and enters into further reactions in the
plume.  Knowledge of the chemistry of sulfur oxides in the atmosphere
is still incomplete but, strong evidence indicates that the ultimate
fate of sulfur oxides in the atmosphere  is oxidation to some form of
sulfate, whether by a homogeneous path with  reactants in the same phase
(the gas phase, liquid phase, or solid phase), or a multi-phased heter-
ogeneous path.  The plume-atmosphere interactions  which are known to
exert an influence on ultimate S02 fate  are depicted in Figure 1 from
Hales et al. (1971a).
          It is the intent of this Section III to provide a review of
the mechanisms that convert sulfur dioxide to sulfates, the detailed
chemistry and dynamic processes associated with these changes, and the

Figure 1.  Possible Atmospheric Paths for SO2 Upon Emission From a
           Power Plant Stack (after Hales et al.  1971).

principles  of the active  scavenging  and deposition processes  which may
ultimately  deplete the  gaseous and aerosol products from the  atmosphere.
           Five important  sulfate formation mechanisms have  been identified
(see Table  1), most of  which involve reactive  agents such as  photochemical
smog, ammonia, catalytic  metals and  fine particulates.  Relative humidity,
temperature and the concentrations of the reactants control  the oxidation
rates associated with these mechanisms.
       Overall Reaction
                                Factors on Which Sulfate
                               Formation Primarily Depends
 1.  Direct Photo-oxidation

 2.  Indirect Photo-oxidation
 3.  Air Oxidation in Liquid

 4.  Catalyzed oxidation in
    liquid droplets
 5.  Catalyzed oxidation on
    dry surfaces
                              Light, Oxygen.
        ;, Water, NO.
     Organic oxidants, OH
                                                 2  4
     Liquid water
      a -
NH4 + H SO,
  o   2  3
                      + SOT
     Oxygen,  liquid water^
     T  '       ,      *
     Heavy metal ions
      Carbon, water
                        2  4
Sulfur dioxide concentration,
sunlight intensity
Sulfur dioxide concentration,
organic oxidant concentration,
Ammonia concentration
Concentration of heavy metal
(Fe, Mn) ions
Carbon particle concentration
(Surface area)
           Exposure  of pure sulfur  dioxide and  sulfur dioxide-oxygen
mixtures  to certain ultraviolet radiation wavelength regions can result
in slow oxidation and the formation of sulfur  trioxide.   If water  is
present in the environment, the $03 is rapidly hydrated,  condensation
of the  resulting H2S04  acid takes  place and  subsequent acid reactions
with  particulate matter are common.  Laboratory chamber  investigations
of the  reaction kinetics of homogeneous photo-oxidation  are subject  to
uncontrolled variables  and unknown experimental parameters, such as
intensity and spectral  distribution of radiation, humidity, temperature,

gaseous impurities, aerosol impurities, and reactive container surfaces.
For example, Cox and Penkett (1970) found the conversion rate for the
decay of gaseous SC>2 in natural sunlight was as high as 100 percent per
hour and attributed the results to possible wall effects.  The interaction
of S02 with trace impurities in the air was suspected to be the cause of
increased condensation nuclei in the dark when S02 was activated in the
same experiment.
        .Examination of the absorption spectrum for S02 shows two bands
above 2900  A  (the second significantly stronger than the first) involved
in the transition of S02 to an excited state.  Early studies sought to
examine the quantum yields  (<|>) for the photo-oxidation of S02 in the first
allowed region  and the outcomes of these efforts resulted in a variety of
values for  a variety of experimental conditions and reactant concentrations.
The results with the S02 pressures used were generally extrapolated to ppm
concentrations  usually found in the atmosphere.  Of the experiments designed
to investigate  the photo-oxidation of S02 at low concentrations in the air
using natural sunlight (see Table 2), conversion rates indicated by the
first order rate constants obtained are seen to vary from the low values
of 0.05% hr'1 - 0.65% hr'1  (Hall 1953; Gerhard and Johnstone 1955; Urone
et al. 1968; and Cox and Penkett 1970) to that of 24% hr'1 (Renzetti and
Doyle 1960).  The low values are believed the more realistic for low con-
centrations of  S02> since most of these workers used very pure gases,
resulting in minimal interference from trace impurities.  Sethi et al.
(1969), Cadle and Allen (1970) and McQuigg and Allen (1970) have presented
results which tend to eliminate homogeneous direct photo-oxidation as an
important mechanism for oxidation of S02 in the troposphere.  Their low
quantum yield results of ~ 5 x 10-3 and the more recent lower value of
1  x 10~9 reported by Friend et al. (1973) indicate that the mechanism
is too slow to account for transformations observed in periods of a few
hours.  Direct photo-oxidation is possibly important only for extremely
long-range transport of low levels of pollution such as on a global scale.

            Laboratory Technique Utilized
Rate Indicated (for Sunlight)
By First Order Rate Constant
                  Hall (1953)
Measured the photo-oxidation rate to SO3 (56-230 nm)
with O2 (50-200 nm) in sunlight.
                  Gerhard and
Measured the amount of sulfuric acid aerosol found in
the photolysis of SO^ at low concentrations in moist
air using both a mercury sunlamp (295-305 nm) and
natural sunlight.
                 Renzetti and
                   Doyle (1960)
Measurements of the decrease in the gas phase SO2 con-
centration after SO2 air mixtures had been exposed to a
mercury u. v.  lamp for a known time.
3 x 10
                 Urone et al.
Used technique similar to Renzetti and Doyle (1960);
compared their 310-420 nm u. v.  source with natural
sunlight and suggest that lower estimates of photo -
oxidation rates in sunlight are more realistic.
                                                                                                                    0.05% hr
      0. 1 to 0. Z% hr
      24% hr
                      0. 1% hr'1
                 Cox and Penkett
Low concentrations of gaseous SO2 and a sulfur-containing
aerosol were monitored both in the dark and sunlight using
radioactive    SO2 and the rate of the photochemical
reaction determined from SO2 decay and aerosol yield.
                 Friend et aL
A system was designed for the purpose of studying
aerosol formation when trace gases in air are
irradiated with ultraviolet light.
                                                                                                 1.0 x 10
                      0. 65% hr
                    <0.01% hr

          Chemical  reactions  involving S02 in mixtures of air containing
oxides of nitrogen  only,  or with oxides of nitrogen and hydrocarbons have
a wide range of  potential  reaction paths.   Researchers are seeking to
define these paths  and  the S02 oxidation kinetics associated with each of
these reaction systems.
          Davis  (1975b)  identified nine possible initiating reactions
(see Table 3) of homogeneous  gas-phase oxidation processes which might be
involved in the  conversion of S02 to H2S04 aerosol in the troposhere.  The
lifetimes for conversion  range from 10   days down to 3 days for the dif-
ferent reactant  species.
                                (after Davis 1975b)
SO2 + hl>(2400-3400A) ->SO|
SO2 + O( P) + M->SOs+M
SO2 +O3--SO2 +O2
SO2 + NOs -* 803 + NO2
SO2 +N2O5 --SO3 + N24
SO2 + HO2 ->SOs + OH
S02 + OH + M -V HSOs + M
SO2 + CH3O2 -vSOs + CHsO
Estimated Concentration of
2nd Species (Molec/cm^)
~ 1 x 104
~ 106
1 x 1012
~ 1 x 107
., 6 x 106
~ 5 x 108
.. 5 x 106
.. 108
Lifetime (Days)
4x 107
~ 6 x 104

In the absence of high organic radical concentrations and catalytic
surface sites the prime conversion mechanisms in the atmosphere, as
reported by Davis (1975b) and other researchers (Friend et al.  1973,
Crutzen 1974), appear to be the S02 reaction with either OH or H02
(Reactions 7 and 8 in Table 3).  Free radicals are the neutral  fragments
of molecules.  In unpolluted tropospheric air, the most important radicals
appear to be OH and H02 because they are essentially inert toward the main
atmospheric constituents (N2, 02, Ar, C02, and H20), but react readily
with many trace gases.  In particular, the reaction of OH with N02 has
been suggested as a significant source of atmospheric nitric acid and
the reaction of OH with methane has been suggested as a significant
(although disputed) source of atmospheric carbon monoxide.  The source
of the OH radical is the reaction of water vapor with metastable oxygen
(0('D)), a species produced by photolysis of ozone.  For this reason,
the presence of ozone may be indicative of the coexistence of the OH
radical (Davis 1976, personal communication).  Rate constants must be
determined for numerous reactions involving the OH radical to determine
the importance of these reactions as efficient conversion mechanisms in
the atmosphere.  The concentrations of S02 and other transient chemical
species must be jointly measured to effectively study reactions; a laser-
induced fluorescence system has been developed (Lubkin 1975) so that
hydroxyl radical  concentrations can be analyzed in a more quantitative
manner than other currently available techniques permit.  Despite the
low rates of Reaction 2 at atmospheric concentration levels, this reaction.
is apparently the most important S02 oxidation mechanism in experimental
tests of irradiated S02-NOx-air systems.  N02 added to an S02-Air
mixture will  undergo photolysis and liberate oxygen molecules which
encourage Reaction 2.  In a study of the N020s-S02-03 reaction system,
Daubendiek and Calvert (1975) suggest the homogeneous gas-phase reaction
systems N03 + S02 - N02 + $03 and N205 + S02 -> ^04 + SOs (Reactions 5
and 6)  are not important removal  paths based on their recent
of the rate constants of these reactions.

          The addition of hydrocarbons to a system of S02 and NOX and
subsequent  irradiation results in observed S02 oxidation rates that are
much greater than in the S02~NOX system.  The direct reaction of SC^
and hydrocarbons has been the subject of study for the past quarter of a
century and unfortunately only a few of these studies are available which
report a base of experimental data spanning a wide range of initial reac-
tant concentrations to deduce the chemical kinetics of a particular photo-
chemical system.  The smog-chamber work of Wilson and Levy (1970 and 1972)
and Smith and Urone (1974) are two of the very few studies available which
report at least partial concentration-time data.
          Smith and Urone (1974) conducted a laboratory experiment utilizing
pyrex flasks in which they irradiated 2 ppm [S02] and 0, 0.85, 1.7, 3.4,
5.1, and 10.2 ppm [N02] respectively in the presence of H20.  The S02
oxidation rate reached a maximum of 3.3 ppm min-1 for an initial N02 con-
centration  of 0.85 ppm.  An  initial N02 concentration of 10.2 ppm and
similar experiment conditions resulted in an observed S02 oxidation rate
of 1.8 ppm  nrin~l.  The initial photochemical rate was 1.7 x 10~4 ppm/min
in air with no N02 present.  The rate was found to increase when the
S02/N02 ratio was 1 or 2, but a decrease was evident when the ratio was
0.6 or less.  In experimental conditions duplicating those just described,
propane was added to the system in initial concentrations ranging from 3
to 12 ppm.  Both sets of data exhibited an inhibition in the S02 oxidation
rate with increasing N02-  Hydroperoxyl radicals in the N0x-Hydrocarbon-
S02 system  may have been responsible for the inhibition effect on the S02
          Wilson and Levy (1970 and 1972) studied the smog-chamber irra-
diation of  a number of S02-N0x-Hydrocarbon mixtures for hydrocarbon
species such as 1-butene, 1-heptene, 2,2,4-trimethylpentane, and toluene.
Quantitative values did not  come out of these studies because of the high
degree of scatter in the experimental data.  The rate of S02 disappearance
was found to correlate with  hydrocarbon activity.  Relative humidity was
found to have a dramatic effect on the overall reaction rate in certain
high humidity runs.

          Groblicki and Nebel (1971), Cox and Penkett (1972), and McNeils
(1974) have investigated the oxidation of S02 to H2S04 aerosol  when S02
was added to olefin-03 systems.   A (biradical) short-lived intermediate
product of the ozone olefin reaction was postulated to react with the S02.
The consequence of this reaction in plume chemistry can only be speculated
upon at this time.
          Roberts and Friedlander (1976) irradiated a 96m3 teflon bag in
natural sunlight to study unfiltered ambient air containing added amounts
of S02, 1-heptene and NOX.   Other hydrocarbons such as cyclohexene, 2-methyl
2-butene, 2,3-dimethyl-2-butene, and 1,7-octadiene were also studied in
less detail.  The experiments were designed to study the formation of
sulfur containing aerosols  under photochemical smog environment conditions.
A sulfur balance was carried out on the system by simultaneous  measurements
of the conversion of S02 and the formation of particulate sulfur.  The
results for all of the experiments were qualitatively similar:   S02 decay
was found to be slight until the 03 concentration became larger than 5 pphm,
at which point there was a  sharp downward trend in the S02 concentration.
Two major behavior regimes  were  observed in these experiments:
          1.  As NO is converted to N02, the concentrations of  S02, 03,
              1-heptene and bscat (decrease in visibility) are  constant
          2.  Aerosol formation  results from the 03 induced decay of
              both S02 and  1-heptene.
          Depending on the  initial S02 level (and even with surprisingly
low relative humidities), the reaction rates varied from 0 to 99 percent
per hour,  based on psuedo first  order depletion of S02-   Table  4 summarizes
the teflon bag experimental  conditions.

                      FOR S02/NO/N02/1-BUTENE SYSTEM
                       (fiom Roberts and Friedlander 1976)

[NO]0 (ppm)
Abscat (10" m~ )
k (% hr-1)
03] max (pphm)
T ( C)
Run Number
          In the  Roberts  and  Friedlander study a kinetic scheme was pro-
posed for aerosol  formation  based on a mechanism similar to that of Cox
and Penkett  (1972).   In the  gas  phase:
          03 + Olefin -- reactive intermediate
          reactive intermediate  -> condensable organic compounds
          reactive intermediate  + S02 - SOa + condensable organic compounds
          $03 + H20 > H2S04  + sulfates
          What has been determined from all, the studies of S02 oxidation
rates in NOx-hydrocarbon-S02  systems is that known reactions (involving
S02 for which rate constants  have been determined) are in themselves insuf-
ficient to account for the oxidation rates in these chemical systems.
          Important oxidation reactions in the aqueous phase are at least
quasi-homogeneous  by  nature,  since all of the participating reactants are
in solution.  Aerosol particles, which constitute the nucleation sites for

droplet formation, are considered as participants in these reactions
because molecules of S02 and other gases quickly diffuse into the interior
of a water droplet where they may directly encounter the nucleating particle
and allow the oxidation process to proceed throughout the droplet.  This
process consists of the hydration and subsequent dissociation of the dis-
solved gases and oxidation of sulfite or bisulfite ions.
          Van den Heuvel and Mason  (1963), Scott and Hobbs (1967), McKay
(1971), and Miller and DePena  (1972) investigated the aqueous phase mech-
anism of S02 oxidation catalyzed by NH3.  Van den Heuvel and Mason (1963)
examined the following reaction paths:

                            2S02 +  02 -* 2S03
                            S03 + H20 * H2S04 ->2H+ + S04=
                            NH3 + H20 -> NH40H  NH4+ + OH"

          The rate of formation of (NH4)2S04  was measured by  supporting
approximately 100 drops of H20 on a  quartz fiber grid in a 5  liter glass
flask exposed to air containing gaseous S02 and NH3.   An oxidation con-
version rate of 2.5% min'1  was obtained by extrapolation of data to con-
ditions in an industrial  atmosphere  containing 100 ygm~3 S02  and 10 pgrrf3
NH3.  The amount of fonmed sulfate when the sulfur dioxide alone was  in
air was at least two orders of magnitude smaller than when the sulfur
dioxide was mixed with ammonia.
          Scott and Hobbs (1967) considered a set of nine chemical equi-
librium equations for the S02-NH3-liquid H20  system,  including caroon
dioxide equilibria.   The  rate  of production of S04~ was assumed to be
limited by the oxidation  of the sulfite ion described by the  first, order
rate equation


Analysis of  the data of Van den Heuvel and Mason (1963) resulted in a
choice of  K  = 0.1 min"^ as the rate constant.  A plot of the theoretical
results obtained from the calculations made with the above assumptions
did not result in a limiting value for sulfate formation or a direct
proportionality between sulfate and the initial S02 partial pressure.
The theoretical curves indicated that for the concentration of sulfate
in waterdrops as a function of time, the presence of ammonia will increase
the amount of sulfate produced by the reaction after it has run for some
time.  An  adequate explanation of the S02-NH3-liquid HoO system can
be based on  the theory of this research.  The rate of sulfur dioxide
oxidation  derived in this study was about 2.5 percent hr-1.
           McKay (1971) examined the kinetics of sulfate oxidation by
taking the rate law of Fuller and Crist (1941) and substituting ionization
constants  from the Scott and Hobbs (1967) study, suggesting that the
reaction is  roughly on an order of magnitude faster than Scott and Hobbs
had assumed.  Evident from the research was the enhancement of the reaction
rates with a lowering of the temperatures; the increased solubility of
ammonia and  sulfur dioxide at lower temperatures are cited as the cause by
the authors.  At the time of the McKay (1971) research, the large negative
temperature  correlation in his work had not been noted by other workers in
the field, although this feature has now been noted by various other investi-
gators.  An  oxidation rate of approximately 13% hr~l is suggested from this
           Miller and De Pena (1972) measured the rate of sulfate ion for-
mation in distilled water drops (raindrop size) for a range of SC>2 partial
pressures, following the experimental methodology of Van den Heuvel and
Mason (1963), and utilizing the basic model of Scott and Hobbs (1972).
The region of experimental values for the first order reaction (d[S04=]/dt =
K [S03=] showed K =3 x 10"3 sec'1, in good agreement with the operative
value in the study of Scott and Hobbs.  Oxidation rates of only 0.1% hr'1
were calculated from the Miller and De Pena data.

          Sulfur dioxide may be oxidized to H2S04 in aqueous solution accord-
ing to the following process:

                   2S02 + 2H20 + 02 catalySt->2H2S04

which requires water, dissolved oxygen and the presence of a catalyst.
Ammonia has already been previously mentioned as one such catalyst; metal
ions such as Fe3+, Mn2+, and Cu2+ constitute the other major grouping of
catalyst-oxidation candidates in the atmosphere (Johnstone and Coughanowr
1958).  These metal ions are contained in iron and manganese salts normally
found as suspended particulate matter in the ambient air from burned coal
fly ash.  The particulates behave as sites of nucleation which at higher
humidities may either dissolve in the droplets or remain as solid con-
densation nuclei centers.   The role of iron as an efficient catalyst
in the oxidation of S02 in the atmosphere has been studied by Junge and
Ryan (1958), Johnstone and Coughanowr (1958), Foster (1969), Brimblecombe
and Spedding (1974) and Freiberg (1974 and 1975).
          Junge and Ryan (1958) examined the iron-catalyzed reaction of S02
oxidation in acid solutions, without investigation of the kinetics.  Air
containing S02 was bubbled through dilute catalyst solutions and a linear
relationship was found between the final extent of $04" formation and the
S02 partial pressure of the reaction.  The pH of the catalyst solutions
was cited as the governing factor of the S02 oxidation process; S02 solu-
bility decreases as acidity is increased due to sulfate formation, anc
eventually a situation is  attained where sulfate formation ceases oecause
of liquid phase S02 depletion.   This bubbling technique has been criticized
by Cheng et al.  (1971) as  an unrealistic representation of an aerosol gas
system due to the influences of mixing effects and mass transfer mechanisms
on the kinetics of the reaction.
          Johnstone and Coughanowr (1958) approached the absorption and
reaction aspects of their  catalytic oxidation studies by mathematically

considering the reaction system as one of gas diffusion into a liquid drop
with a concurrent zero order reaction in the liquid phase.  The value of
the zero order rate constant was acquired from 'previous experiments invol-
ving homogeneous S02 liquid phase oxidation.  In an experiment which
exposed a single drop of manganese sulfate solution to an environment
consisting of air and trace amounts of S02, it was estimated that mangan-
ese sulfate crystals of 1 micron at 1 ppm S02 yielded a rate of oxidation
in fog droplets on the order of 1 percent min"1.  Cheng et al . (1971) had
doubts about the validity of the assumption that the reaction rate was
controlled by liquid phase gas diffusion.
          Foster (1969) derived theoretical growth rates of H2S04 droplets
to test the effectiveness of MnS04 crystallites as a catalyst for S02 oxi-
dation in humid, polluted surroundings.  Review and comparison with pre-
vious theoretical works on the subjects of manganese and iron solution
catalytic oxidation of S02 led to the following rate expressions, the
symbols of which are explained in Table 5, along with the values (when
provided) utilized for the calculations:

        Rate  of  S02  oxidation = 22.4  KiCiV   loor  -  -1
          by  Mn+2  catalyst             GD   x IUU/0 min
              * on    -j 4--           DWKu (1  - fo)    K.n-f.
        Rate of SO-2 oxidation _ o? /,     H _ '_    i  i  i     inno/ min
          by Fe+2 catalyst    ' 22'4  -    -     M1     x 100/0 min
When these values are substituted into the equations, S02 plume oxidation
rates of 0.09% min~^ for Mn and rates of 0.15 - 1.5% min~l for Fe are the
results.  This work  implies that the major catalytic role for aqueous phase
S02 oxidation in plumes is played by oxides of iron.

                        CALCULATIONS (from Foster 1969)






Effluent dust burden, g/ liter
Effluent SO2 content, ppm
Effluent dilution factor
Fraction of total sulfur oxidized

Droplet sulfate concentrations, mo I/ liter
Oxide molecular weight, g/mol
Number of catalytic ions per molecule
Fraction by weight of dust soluble
Rate constant
Catalytic concentration within the droplets
Oxide molecular weight, g/mol
Number of catalytic ions per molecule
Fraction by weight of dust soluble
Solubility constant
2x 10
2-5 x 103

2- 29 x 10
2 x 10-4
l-60x 102
 * Values not provided.

           Matteson  et al.  (1969) studied the mechanism  of S02 oxidation
catalyzed  by manganese sulfate aerosol.  The kinetic  theory proposed for
the oxidation  process was  based on a four-step chemical  reaction involving
the formation  of  intermediate complexes.
Mn2+ + S02 t Mn-S022+
2Mn-S022+ + Oj
H2Q 2 Mn2+
2 H2S04.
                                          02] + 2Mn-S03
The rate expression  which  was determined was
where the experimental  rate  constant = 2.4 x 105 mole-"!  s'1

Negligible S04~ concentrations were formed for relative humidities below
95 percent in the experiments apparently as a result of inadequate hydration
of the metal salt.  Rates on the order of 0.5% day"^ '-were recorded.  The
experimental data obtained were basically incorrect (Cheng et al. 1971)
due to errors in the recorded reaction times.
          Selected metal salts which had been reported to act as aerosol
catalysts (MnSCty, MnCl2 and CuSCty) were tested for their effectiveness in
promoting atmospheric oxidation of S02 to H2S04 in laboratory work by
Cheng et al. (1971).  The experiment was carried out using an aerosol
stabilizing technique, whereby teflon beads with deposited aerosol particles
were packed into a flow reactor, and exposed to influent S02 concentrations
ranging from 3 to 18 ppm in humid air.  Higher S02 oxidation rates were
found to be positively correlated with higher relative humidities; in
addition, the chemical reaction in the liquid phase in conjunction with
absorption of S02 by aqueous catalyst drops controlled the overall rate
of reaction.  Using NaCl as a base for comparison, aerosols of MnS04,
MnCl2> and CuS04 were found to be 12.3, 3.5, and 2.4 times more effective
than NaCl in assisting the oxidation of S02 on a milligram-to-milligram
basis.  To approximate the rate of absorption and oxidation of S02 by fog
droplets in a natural fog, laboratory results were extrapolated to condi-
tions typical of an urban industrial atmospheric environment.  The following
assumptions were made for this estimation:

          1.  15 ym was the average diameter of fog droplets
          2.  S02 concentration in the atmosphere was  0.1  ppm.
          3.  Fog droplet concentration of catalyst is equivalent
              to 500 ppm MnS04; one-half of the fog droplets con-
              tain the catalyst capable of oxidizing S02 to H2S04
          4.  0.2 g of water per cubic meter of air defined the
              fog concentrations.

The atmospheric oxidation rate under these conditions was found to be
2 percent hr"1.

          Brimblecombe and Spedding (1974) noted that many of the experi-
mental data used in the interpretation of the oxidation of S02 within the
atmosphere in previous studies were characterized by concentrations several
orders of magnitude higher than those expected in the aqueous aerosol, and
were therefore unrealistic.   These researchers attempted to establish the
rate of oxidation of low concentrations of S02 (about 10~5 molar) in aqueous
solutions containing traces  of Fe3+ (about 10-6 molar)  as these concentra-
tions approach those which might be likely in the atmospheric aerosol.  A
radiochemical method utilizing 35$02 monitored the oxidation process in
the experimental procedure over a range of added Fe3+ catalyst concentrations
up to 1.6 x 10~8 molar.  A radical mechanism was favored due to the high
reaction rates noted in dilute solution; hydroxylated Fe3+ was postulated
as the initiator in the production of $03" radicals:

          SOg" + FeOOH + 3H+ + Fe2+ + 2H20 + SOs"

          To explain the termination of the radical  chain, Brimblecombe
and Spedding (1974) state that the Fe2+ is oxidized back to the +3 oxidation
state by reacting as follows:

          SOg + Fe2+ -* SO2.-  + Fe3+

Small amounts of Fe3+ in the atmosphere would be capable of oxidizing a
large quantity of sulfur dioxide by such a step which would allow regen-
eration of Fe3+: 2Fe3+ + H20 + H2S03 -* SO^" + 4H+ + 2Fe2+.  Assuming an
S0 concentration of 28 yg/m3 and a Fe3+ concentration of lO'6 molar,
Brimblecombe and Spedding arrive at a S02 conversion rate in fog of ~ 3.2
          Freiberg (1974, 1975) examined the mechanism of iron-catalyzed
oxidation of S02 in oxygenated acid solutions by beginning with the rate

                    d[S04=]    KCK/ [H2S03]2 [Fe3+]


          Kc = rate constant
          k^ = first dissociation constant of sulfurous acid

Since the pH increases as relative humidity rises, the reaction rates were
found to be especially dependent on high relative humidity; an increase
from 80 percent to 90 percent  RH resulted in an eightfold increase of i>on-
catalyzed oxidation of S02 whereas a relative humidity increase from
80 percent to 95  percent resulted in a  sixty-four-fold increase in the oxi-
dation reaction rate.  Freiberg also examined the dependence of the oxidation
rate of S02 on temperature.  The relationship involves numerous physical-
chemical processes which influence the  reaction in a way different from the
expected reaction rate increase with temperature alone; the end result is
a significant decrease in the  yield of  the reaction as the temperature
increases.  An increment of 5C results in a net decrease in reaction rate
of iron catalyzed oxidation of S02 by about an order of magnitude.
          When water droplets  are present in a mixture of S02, 03 and air,
both S02 and 03 are observed to vanish  swiftly, indicating that the reaction
S02 + 03 -* $03 +  02 proceeds more efficiently in the liquid phase than it
does in the gas phase.
          The mechanism of aqueous phase S02 oxidation by ozone has been
investigated by Espenson and Taube (1965), Penkett (1972), and Penkett and
Garland (1974).   In the study  by Espenson and Taube (1965), two elements
of this mechanism were examined; namely the acid solution reaction of S02 +
03 + H20 -* H2S04 + H+ + 02 and the basic solution reaction of SOs" + 03 ->
S04= + 02.  Unfortunately, quantitative information did not result from the
          Penkett (1972) investigated the reaction path of HS03~ + 03 ->
HS04~ + 02 (S02 in the form of bisulfite ions) with the rate of oxidation
provided by d[0s]/dt = K[0s] [HSOs'J.   In the kinetic work, the rate

constant K = 3.32 +_0.13 x TO5 NHs-1, and a 0.05 ppm ozone concentration
resulted in an extrapolated S02 oxidation rate of - 0.21% min"1 at 9.6C;
this compares to the slower rate of 2.5% hr-1 predicted by Scott and Hobbs
(1967) for S02 oxidation catalyzed by NHs.
          Penkett and Garland (1974) studied the same reaction path as
Penkett (1972) and, for a pH range from 4 to 7 at 10C with 0.1 ppm 862
and 0.05 ppm 63 in fog water, determined the reaction rate coefficient of
the expression -d[S03=]/dt = K[S03=] to be K = 4.18 x 10~4 + 1.77 [H+]1/2 sec'1.
          Corn and Cheng (1972)  examined the heterogeneous catalysis of sul-
fur dioxide in the laboratory with respect to interactions with insoluble
particulate matter.   Micron and  submicron particles of CaC03,  \/205,  Fe-Oo
and flyash from a coal-burning power plant were utilized along with  suspended
particulate matter from an urban environment, Mn02 and activated carbon.
Through the use of an aerosol stabilizing technique, the aerosol  particles
were deposited on teflon beads which were packed into a flow reactor in order
to obtain kinetic data.   Mn02, Fe203 and the suspended particulate matter
from Pittsburgh air were found to sorb S02, with physical adsorption as the
primary process.  Steady-state rates of conversion of 0.013 and 0.021 yg of
S02 min~l mg~^ at S02 concentrations of 8.0 and 14.4 ppm, respectively, were
found for the activated charcoal.  Under the conditions of the tests, CaC03,
V20s and flyash were discovered to be essentially inert to S02 at room temper-
ature.  Twenty mg of \/205 at 95 percent relative humidity removed only ',.2 per-
cent of the total S02 after 50 minutes of exposure, which is surprising,
considering that at a high temperature of 500C or beyond, vanadium pentox'.ae
is known to participate in the oxidation of S02 to 503 according to the

                        V25 + S02 * V24 + S03

          Low et al. (1971) studied the gas-solid reaction of S02 with CaO
by means of infrared spectroscopic techniques as a segment of research designed
to investigate the removal of S02 from power-plant stack gases by way of

catalytic oxidation of powdered limestone introduced into the stack stream.
A similar study was conducted by Goodsel et al (1972) for sorption of S02
on MgO in research to find the removal rates of S02 from plant stack gases
by catalytic oxidation with introduced dolomite.  Both studies showed the
formation of a surface sulfite as the main irreversible interaction product
when the CaO and MgO were degassed.  Sulfates were formed when the surface
sulfite was exposed to heat in an oxygen environment.
          A combination of colorimetric and radio-tracer techniques were
employed by Urone et al. (1968) in studies of reactions of parts per
million concentrations of sulfur dioxide, with laboratory environments con-
taining hydrocarbons, nitrogen dioxide, moisture, particulates and ultra-
violet radiation.  Powdered oxides of aluminum, calcium, chromium, iron,
lead and vanadium were found to react with S02 within minutes without the
presence of sunlight or ultraviolet radiation, whereas gaseous mixtures
of S02 and clean air kept in the dark for days did not react.  A reaction
rate on the order of 0.1 percent hr~^ was found for the photochemical
reaction of sulfur dioxide in clean air with ultraviolet radiation equiv-
alent to noonday sunlight.  Inert solids such as NaCl and calcium carbonate
resulted in negligible heterogeneous reaction rates with $02; however the
reaction was significant for heterogeneous reactions involving other
particulate matter such as iron and lead in some instances, as shown in
Table 6.

                            (from Urone et aL, 1968)
SO2 Concentration
14 (ppm)
(CaO + Ag203)
2nd Reactant
30.3 (mg)
(16.6, 19.8)
0 (min)
(0, 0)
Total Time
in F lask
1100 (min)
SO2 Reaction
0.2% hr"1
0.5% hr"1
0. 7% hr" 1
1.7% min"1
6.0% min"1
3.0% min"1
.04% min-1
17% of SO2 reacted
          Smith et al.  (1969) developed a method  for  studying  adsorption
 at  solid-gas  interfaces  in aerocolloidal systems  by generating submicron
 sized aerosols  (0.01  to  0.1 ym) using an exploding-wire  technique and
 radio-labeled-gases to achieve adequate sensitivity in sorption measure-
 ments.  Preliminary measurements of  35S-labeled S02 with Fes04, Al20a,
 and platinum  aerosols at ambient conditions,  showed that low S02 concen-
 trations resulted in  preferential chemisorption followed by multilayered
 physical adsorption at higher concentrations.  Although  significant  adsorp-
 tion was evident on the Fe304, Al20s and platinum surfaces, the oxiGotion
 rates were not presented in the Smith et al.  (1969) research.   Overall,  it
 is seen that dry heterogeneously catalyzed S02 oxidation systems are rela-
 tively ineffective when compared to aqueous phase oxidation systems.
          The sulfate forms that result as products of S02 oxidation in  the
 atmosphere are tabulated in Table 7 along with brief  descriptions of their
 chemical nature (Wilson et al. 1976).  The sulfate types are secondary  in
 nature;  primary surface types (e.g., those emitted directly by industrial
or by natural  sources) are not listed.  The probable  size class by mass
particle diameter for each of these sulfate forms is  between 0.1  and 1.0 ym.
Whitby and Liv (1974) examined the size distribution  of  the general  atmosphere

aerosol,  and  found  the  number concentration to be dominated by particles  in
the  0.002 to  0.02 ym range and the major part of the aerosol  surface area in
the  0.05  to 0.5  ym  size range; a bimodal  distribution characterized particle
volume  and mass.  The "accumulation mode,"  defined as the size range between
0.1  and 1.0 ym,  is  estimated  to  be the  size fit for 80 percent of  atmospheric
sulfate.   Secondary accumulation-mode aerosol  can have a  very long life time
in the  atmosphere,  traveling  great distances,  and having  the  opportunity  to
participate in other chemical  processes before removal  by fallout  or rainout.
                              (from Wilson et al. 1976)
Sulfuric acid (oil of vitriol)
Acid ammonium sulfate
Triammonium acid disul-
fate (Letovicite)
Ammonium sulfate (Mascag-
Atmospheric oxidation of
SO2; direct from manufac-
Oxidation of SO2 with NH3
Oxidation of SO2 plus NHj.
Oxidation of SO2 plus NHj.
Notable Chemical
Strong acid, very hygro-
scopic (drying agent at
low RH).
Strong acid, hygroscopic.
Acidic, deliquescent at
~ 65 percent RH.
Weak acid, water soluble
deliquescent at 80 percent
          Charlson  et  al.  (1974)  investigated  the  hygroscopic  properties
of the sulfate  aerosol  in  the  St.  Louis  region and found  that  the
can absorb water  and increase  in  size  at all humidities,  as  can
while (Nh^^SO* can do  so  at relative  humidities above  about 65  percent.
SuTfuric acid is  known  to  give rise  to heteromolecular  nucleation  of  drop-
lets in the presence of water  vapor, and will  condense  on preexisting
nuclei (Stauffer  et al. 1973 and  Cox 1973).  Unfortunately,  detailed  esti-
ma-tes of. growth parameters  for aqueous solution droplets  of  sulfuric  acid
are not available at this  time.   Research on the growth of solution drop-
lets of sulfuric  acid  as well  as  other important solutes  as  a  function  of

relative humidity will  be useful in the analysis of aerosol growth curves
to identify the chemical  composition and understanding of the solute-
solvent interaction in the process of growth of solution droplets.  Nair
and Vohra (1975) indicate that the relative increases in size and mass
depend on the quantity of solute per particle.  They show that sulfuric
acid nuclei in the Aitken size range (< 0.1 urn) can grow to cloud nuclei
as the relative humidity increases.  Nuclei can grow continuously at rela-
tive humidities below 100 percent due to the instability produced by the
chain process of sequential condensation of water and solute molecules onto
the nuclei.  Katz and Mirabel (1974) examined how certain kinds of suspended
liquid aerosols can be generated in the atmosphere by the binary homogeneous
nucleation of water vapor and a polluting reactant such as sulfuric or nitric
acid; humidities as low as 10 percent in the presence of ^$04 were found to
result in large nucleation rates.
          Field programs  designed to investigate the plume chemistry of
processes other than sulfate formation are rare in the literature.  An
excellent example of one such study is the Davis et al.  (1974) investigation
of nitrogen oxides and S02 chemistry in the Morgantown power plant plume, in
which the power plant plume was postulated to have had a significant effect
in producing increased ambient 03 concentrations far downwind of the plant.
The Morgantown power plant plume investigation is described in Section V.
          Whereas sulfur  dioxide plume chemistry primarily involves the
transformation of S02 to  sulfate (S04=), nitrogen oxide chemistry involves
the transformation of NO  to N02, with the subsequent formation of ozone,
other oxidants, and nitrates.  The literature is filled with photochemical
reactions involving 03,  NO, N02, hydrocarbons and free radicals.  These
data have been a product  of laboratory work concerned with the polluted
urban environment, or more recently have been data gathered in studies of
rural  ozone and in attempts to determine the downflux of stratospheric ozone.

           The  photolysis of  nitrogen dioxide is the only reaction known to
 generate  important  numbers of oxygen atoms necessary for the production of

                             N02 +  hv +  NO + 0                   (1)

 Once the  oxygen atoms  are present,  they react with oxygen molecules, involv-
 ing a nitrogen molecule or another  oxygen molecule as the third body to form
 ozone according to:

                          02 + 0 +  M ->  03 + M                   (2)

 Reaction  (1),  the photolysis of N02, is a very rapid reaction,  but simul-
 taneously, the reaction of ozone with NO is a rapid 03 removal mechanism:

                           NO + 03  *> N02 + 02                   (3)

 and additionally, ozone is also removed by a relatively slow reaction with

                          N02 + 03  * NOs + 02                   (4)
Chemical reactions  involving 'organic molecules or radicals which drive
or maintain the concentration ratio of N02 to NO at high levels are
responsible for high steady-state  (i.e., 03 production rate = 03 destruc
tion rate) levels of ozone.  In a  polluted urban environment, depending
on the nature of the hydrocarbons  present (i.e., paraffin, olefin or
aromatic), a branching reaction sequence occurs which allows photolysis
of N02 to create additional N02 at the expense of NO.  Figure 2 from
Hanst and Bufalini  (1971) illustrates how various hydrocarbons will oxi-
dize NO at different rates in smog-chamber experiments.  It has been
theorized that for  power plant plumes, a mechanism not affiliated with
hydrocarbons could  oxidize NO + N02 to elevate the [N02l/[NO] value,

 thus  increasing  ozone concentrations.   Two  such mechanisms have  been
 suggested; the  first, a  sulfur mechanism and  the second, a chlorine
 mechanism (Tesche et al.  1976); however recent studies  of plumes in areas
 with  low background hydrocarbon concentrations have detected no  net ozone
          Internal Olefins
1, 3 Butadiene
                                           Terminal Olefins
             P araf ins
  Figure 2. Effect of Hydrocarbon Structure on Nitrogen Dioxide Formation Rate (From Hanst and Bulfalini 1971).

          Two  basic processes act to scavenge an aerosol from the atmosphere.
The first process  is the result of the aerosol serving as a cloud nucleus or
undergoing capture by cloud water or ice particles, and is termed "rainout."
The removal of the subcloud aerosol by raindrops as they fall is the second
process, "washout."
          Fundamentals of the influence of rain on the precipitation scaven-
ging of gases  have been reviewed by Postma (1970) and Hales (1972).  The
possibility that a gas plume could become redistributed in the atmosphere
due to the action of "reversible" washout has been discussed by Hales.  The
gas concentration  in each raindrop, as it traverses a plume, approaches a
concentration  saturated with respect to the concentration of the plume (Slinn
1974).  The drop can emerge from beneath the plume with a concentration super-
saturated with respect to ambient conditions, if no irreversible chemical con-
version of the gas occurs within the drop, and desorption of the gas is
possible.  An  increased dosage to low-level receptors is the effective result
of this lowering of the plume center!ine elevation.  A complete mathematical
description of the rate at which this sorption-desorption phenomenon might
lower a gas plume  is a formidable undertaking unless a number of assumptions
are imposed.  Slinn (1974) assumed it was reasonable to use a convective
diffusion equation (assuming the stack exit is high enough and the atmosphere
stable enough), ignoring longitudinal diffusion compared with transport,
neglecting wind shear, and treating the diffusion coefficients as constants
in his attempt to predict this rate of plume redistribution.  The "washdown"
speed of the plume is a function of the rainfall rate and Henry's law con-
stant (dimensionless).  An example cited shows that an S02 plume exposed
to a rainfall rate of 10~4 cm s"1, with a Henry's law constant of 3.3 x 103,
results in a velocity of 3.33 x 10~  cm s~ .   Another example demonstrated
that a plume would have fallen 30 m after a time of 10  s^	
          Bolin et al. (1974) described the efficiency of the rainout
mechanism as dependent on (a) the efficiency of the microphysical processes
in the clouds and  (b) the frequency of precipitation.  The consumption of

aerosol particles by the cloud drop varies greatly with particle radius; and
the absorption of gases to cloud elements depends on the chemical  composition
of the cloud drops.  More work is required to understand these processes
quantitatively but it is interesting to note that there is evidence of a
rather rapid transformation of sulfur dioxide into sulfuric acid in clouds
as long as the pH of the cloud drop water is significantly higher than 4
(Brosset 1973).  It is clear, however, that the most important factor in
determining the efficiency of the rainout mechanism for removal of pollutants
from the atmosphere is the frequency of rains (Rodhe and Grande!1  1973).  If
rainout were the only sink mechanism, the average residence time for a pollu-
tant in the atmosphere estimated in the Rodhe and Grande!! Swedish study
would be about 40 hours in the winter and 90 hours in the summer based on
seasonal precipitation data collected during a one-year period.  Low intensity
precipitation periods were appreciably longer in winter than in summer.   Rodhe
and Grande!! also derived the distribution function for the probability of
rainout of a pollutant released at an arbitrary instant.
          Hales et a!.  (1971) describe the complex processes of liquid
mixing in a falling drop and their relation to mass-transfer, obscured
further by film effects at the interface and by the possibility of
chemical reaction within the liquid (see Figure 3).  Hales (1972)  explains
that in order for pollutant gas molecules to be captured, they must first
migrate from the atmosphere to the surface of the liquid.  They then may
pass through the liquid-vapor interface and, finally, migrate into the
liquid interior where they may react chemically or exist simply as unreacted
dissolved gas molecules.  The existence of dissolved gas molecules results
in a concentration of gas in the liquid which, owing to the finite solubil-
ity of the gas, will be characterized by a vapor pressure.  Thus,  there wi'i".
be a tendency for gas molecules to desorb from the liquid and, retracing the
mechanisms by which they were captured, return to the atmosphere.   The gen-
eral problem of modeling microphysical systems in the atmosphere is discusses
in Section IV as it relates to the pertinent microphysical phenomena of drop-
gas interactions.

 Figure 3. A Falling Raindrop and the Associated Transport and Washout Mechanisms Acting Upon it
                                  in the Atmosphere.

                              Section  IV

          The ideal chemistry model must be able to identify the principal
chemical reactions that occur in a plume and to explain the rates of change
of concentrations of the various components.  Such a model generally com-
prises a set of differential equations, each of which expresses the conser-
vation of mass of a species.  In an atmosphere containing numerous chemical
species, simulation of the chemical reactions involved could^be extremely
difficult due to uncertainty of what reactions take place, doubt about rate
constants, and nonlinearities in reaction rates.  Add this to the mathema-
tical complexities of the nonlinear transport equations defining physical
behavior of plumes under the influence of complex terrain and one can
see why no one all-inclusive chemical  reaction-depletion atmospheric
dispersion model is an operational reality at this time.  The SO^-sulfate
mechanism, the rates of S02 transformation, the extent of reaction and
the final state are not well known at  this time for operational  modeling
of the S02 chemical reactions of a given power plant plume, although
the basic chemical kinetic features of a reactive plume from a large
point source are now receiving attention.   The research trend up until
now has been to focus on individual conversion mechanisms for S02 to
          Takahashi et al.  (1975) proposed a purely theoretical  kinetic
model of sulfuric acid aerosol formation from the photo-oxidation of
sulfur dioxide vapor based on thermodynamic principles.   The three stage
mechanism consisted of 1) the photo-oxidation of sulfur dioxide to
sulfur trioxide, and through the combination with water molecules, the
formation of sulfuric acid vapor; 2) the combination of several  numbers of
water molecules and sulfuric acid resulting in the nucleation of sulfuric
acid vapor to a critical sized cluster or embryo; and 3) the condensation
of sulfuric acid and water molecules,  as well as through the coagulation
with other particles to allow growth of the nucleated embryo to a larger

aerosol particle.  The riucleation rate for a system of water and sulfuric
acid vapor was calculated at various relative humidities according to the

                           I = C exp (-AG/RT)

          C   is a factor containing the probability of capture of
                a molecule of vapor by a critical embryo
          AG  is the free energy to form an embryo
          R   is the gas constant
          T   is the absolute temperature

The nucleation rate was found to increase rapidly with an increase of
sulfuric acid vapor pressure, and was relative humidity dependent.
Equations were formulated for the number concentration of sulfuric
acid vapor and particles, the time change of the number of sulfuric acid
molecules in a particle, the deposition rate of sulfuric acid vapor to
already formed aerosol particles, and the equilibrium particle radius.
Generally the sulfuric acid vapor molecule concentration was found to
increase rapidly at the initiation of irradiation and then slowly decrease
after reaching a maximum value, determined by the photo-oxidation rate.
Indications were that nucleation was predominant in the early stage of
the process, with vapor condensation becoming significant in the later
stage.  In the early stages when nucleation was predominant, the vapor
concentration was not always high enough for effective condensation to
occur, leading to growth in particle size.  However, in some cases of
low relative humidity, the nucleation rate was very small so that most of
the sulfuric acid vapor condensed to make the particles grow larger.
Thus, the relative humidity and the acid vapor oxidation rate characterized
the rate of growth of particles.  Although its time change is very slow,
the sulfuric acid concentration in particles increased, as the condensation

of vapor became  effective.  Unpublished experimental  data by Cox (1973)
and Takahashi  et al.  (1975) indicated that particle  number concentration
at a relative  humidity as low as  10 percent or less  was  much higher than
that predicted by this kinetic model; differences were partially attributed
to uncertainity  in the calculated values of the nucleation rate.  At  such
a low relative humidity, natural  ionizing radiation  may  play a significant
role in nucleation of sulfuric acid embryos (Vohra et al. 1972).  Problems
mentioned  by Takahashi et al. (1975)  concerning aerosol  modeling include
the proper assumption for the particle size distribution change with  time,
and the effect of wall deposition and air flow pattern in future model
applications to  chamber studies.
           Davis  (1976) proposes  the possible key reactions of the S02 con-
version to sulfate via OH radicals (see Table 8) to  explain the ozone bulge
noted in the study of the Morgantown Power Plant  (see Section V).

(a) S02 +
(b) HS03
(c) HS03
(d) HSO5
(e) HSO5
(f) HS04
(g) HS04

(h) HSO4
(i) HS06
(j) HS06

OH + M
+ O2 + M
+ HO2
+ NO
+ H02
+ H02
+ HS04

+ 02 + M
+ NO
+ SO

-* HS03 +
+ HSOS +
* H2S03 -
-> HS04 +
* H2S05** + 02
-+ H2S04 -
-> H2S208

- HSOg +
-> HS05 +
- HSOr +

  * It should be noted that the detailed kinetics of only reaction (a.) have been well-studied in the
    laboratory.  Chamber studies, however, indicate that some combination of processes (b)-(j) are
    quite fast compared to (a).
 ** Both H2SO$ and H2S2Og are known to hydrolyze in the presence of water to form H2SO4.

The HSOg, proposed to be produced when 02 is added to HS04, oxidizes two
NO molecules to reform HS04 which then repeats the process.  This NO oxida-
tion is postulated to explain the ozone bulge (Davis et al. 1974), but has
been disputed in the literature.
          Systems Applications, Inc.  (Liu 1975) has developed a chemical
kinetic model to study the basic features of a reactive plume from a large
point source.  The Reactive Plume Model (RPM) handles the  transport and
diffusion processes in a simple fashion, while the chemical kinetics are
given more detailed attention.  The considerations which were taken into
account to arrive at such a model format included the exceedingly complex
photochemistry prevalent in plumes where NOX/HC ratios are high and the
difficulty of solving nonlinear transport equations as compared to the
ordinary controlling differential equations which describe the chemical
kinetics.  The following is the derived modeling equation  for a plume
along a wind trajectory:
where the rate of production of species i through chemical reactions is
represented by the first term oh the right-hand side, and the rate of
dilution of pollutant species i within the plume along the trajectory
path (x) due to horizontal spreading (w) and the variation in mixing
depth (h), respectively are represented by the second and third terms
on the right-hand side.  A simple mass balance for the pollutant species
characterizes the model equation.

          A modified version of the Hecht-Seinfeld-Dodge kinetic reaction
mechanism (1974) for photochemical smog formation, employing five reaction
steps involving S02, describes the rate of change of species i due to
chemical reactions.  These S02 reactions include:

          H02 + S02 > OH- + S03               where k = 1.3 ppm'1 min'1
          S02 + N03 + NOo + SO,               where k = 10.0 ppm'1 min'1
          RO^ + S02 # RO- + S03               where k = 1.5 ppm'1 min'1
          RCO^ + S02 + (02) -> R0 + S03 + C02 where k = 1.5 ppm"1 min'1
          OH- + S02 & [HS03J 52 H02 + S03     where k = 900 ppm'1 min'1
Uncertainties about atmospheric S02 chemistry dictate that these
reaction steps remain provisional  until  the appropriateness of the
S02 mechanism is better asserted by results of planned field studies.
          The reactive plume model  is found to be especially sensitive
to variations in four of the input variables, specifically 1) plume
geometry as a function of downwind distance; 2) pollutant emission
rates; 3) ultraviolet radiation flux and; 4) the initial concentrations
of NO, N02, S02, 03, and hydrocarbons.
          Huang et al. (1974) followed the methodology of Hazbun et al.
(1971) in the Tennessee Valley Authority's derivation of a kinetic model
designed to provide a detailed account of the rates of change in concen-
trations of the various components resulting from their chemical inter*
actions and the effect of meteorological conditions upon these reactions.
The Hazbun approach was to construct profiles by measuring the concentra-
tions of the various species under differing meteorological conditions at
a number of downwind distances.  On the basis of then available literature,
a kinetic model was devised for probable chemical reactions and various

rate constants determined from experimental data were selected to formu-
late a set of rate equations.  The set of rate equations was integrated
to give the theoretical profiles of the various components.   The chemical
reactions possible (from a literature search at that time) were upwards
of 60; however, only 29 reactions were considered important from con-
siderations of the magnitudes of the rate constants and reactant concen-
trations.  Unfortunately, exclusion of the OH + S02 reaction and numerous
updated values of the rate constants have basically antiquated this model.
          Model validation studies have not as yet been conducted in the
atmosphere since data in sufficient detail to validate model predictions
in plumes are simply nonexistent.
          A numerical model has been developed for predicting precipita-
tion scavenging of reactive pollutants from power plant plumes (Dana et
al. 1976).  The Scavenging Model Incorporating Chemical Kinetics (SMICK)
can calculate collection, liquid-phase chemical reaction, and (possible)
desorption of multiple plume-bound pollutants as they interact with fall-
ing raindrops to be ultimately deposited on the ground.  A schematic of
these physical interactions is shown in Figure 4.  SMICK also possesses
the capability to perform calculations for any specific aqueous-phase
kinetics mechanism expressed in a proper subroutine form.  Initial  appli-
cations of the Scott and Hobbs (1967) aqueous-phase oxidation mechanism
for SOo (which depends strongly on the presence of dissolved ammonia)
showed that in comparisons of these predicted results with field measure-
ments, taken at the Centralia power plant  (see Section V), the mechanism
is not adequate to account for the sulfate formation rates observed.  To
calculate washout concentrations, the following equation is utilized:

                                                          in Raindrop
                                                          Material  in
                               Figure 4.  Schematic of Physical Interactions Modeled by SMICK (from Dana et al. 1976).

          c   = the liquid phase concentration  (moles/cm^)
          z   = distance above ground at stack  base (cm)
          Ky  = overall mass-transfer coefficient  (mole/cm^-s)
          Vz  = the terminal fall velocity of a raindrop of
                radius a (cm/s)
          a   = radius of a raindrop  (cm)
          Y   = mole fraction of pollutant a in local gas phase
          H1  = solubility parameter  (cm3/mole).

Provided values of Ky, Vz, Y, and H1, the above equation is numerically
solved for a number of selected drop  sizes; the results are then distri-
buted according to the raindrop spectrum to obtain average concentrations.
In addition to performing this function, the computer code allows for a
number of sophistications including nonlinear solubility behavior, lofting
plumes and nonvertical rainfall.
          A steady-state, one-dimensional mass  transfer model describing
the  dry deposition process has been developed by Sehmel et al.  (1973) and
has  been employed by Sehmel and Hodgson (1974)  to  predict particle deposi-
tion velocities to simple surfaces.   The minimum experimental data required
to successfully employ the model are  friction velocity, roughness height,
particle size distributions, and atmospheric stability.  Conceptually,
the  model is a three-box simulation of particle transport utilizing the
continuity equation.  The three elements consist of:

          Box 1 - The atmospheric turbulent layer  in which the
                  transfer processes  are best described by micro-
                  meteorological eddy diffusivity.

          Box 2 -  A layer  just above  the  vegetative canopy  or
                  surface  elements  in which  the  transfer  processes
                  are modified by the presence or structure of  the
                  canopy or  surface.

          Box 3 -  A layer  (occupied by the canopy or surface elements)
                  in which the final  transfer process is  best  expressed
                  by surface mass transfer coefficients,  where  the
                  interaction between the surface material  and  the
                  pollutant  is important.

The basic model assumptions, as stated by Sehmel  and Hodgson (1974) are:

          1.   Particles diffuse at  a  constant flux from a uniform
              concentration  of particles.
          2.   A relationship for particle eddy diffusivity  can  be
          3.   The  effect of  gravity can be described by the terminal
              settling velocity.
          4.   Particle agglomeration  does not occur.
          5.   The  particles  are completely retained by the  surface.

With the basic model assumptions, the deposition flux to  a  surface  is
described by

                          N  = -U+D)    - VtC

          N = deposition flux to environmental surface (particles cnr2s-"l)
          e = particle eddy diffusivity (cm^s"')
          D = Brownian diffusivity (cm^s-l)
          C = particle concentration (particles cm~3)
          z = height (cm)
         Vt = absolute value of terminal settling velocity (cm s~l)

          This equation is then integrated to provide integral diffusional
resistances, which may be related to deposition velocity.  Predicted depo-
sition velocities were graphically presented for a 1  meter reference
concentration height, for stable and unstable atmospheres, with the
parameters for each figure being either friction velocity (range of 10
to 200 cm s'1) or roughness height (10~3 to 10 cm).  In general, depo-
sition velocities increase with an increase in either friction velocity or
roughness height parameters.  For all combinations of these two parameters
the minimum deposition velocities were found to occur in the particle
diameter range of 0.04 to 0.4um.  Deposition velocities were determined
to be nearly independent of particle diameter only in the 0.1 to I.Oym
size range (note; this is the'accumulation mode" where 80 percent of
atmospheric sulfate is found (E.P.A. 1974)).
          Horst (1974)  developed a surface depletion  model  which improves  on
the usual  Gaussian  plume model  "source  depletion"  representation of loss of
airborne contaminant due to deposition.  The Gaussian source depletion
approach appropriately reduces the source strength as a function of down-
wind distance.   In  the Horst approach,  the air concentration at any location

can be calculated  as  the  sum  of the  nondepositing  diffusion  from a
primary source at  coordinates (0,0,h)  plus  the  diffusion  from all of
the upwind surface sources  which account  for deposition.   The derived
equation for the source depletion model considering the crosswind-
integrated air concentration  is:

             7 (x,z)  = IT (x,z,h) (QQ - JQ  Vd x U, zd) d e)


          x (x,z)  is  the crosswind integrated air  concentration
          Q0  is the  undepleted source strength at x =  o
          Vd  is the  deposition velocity  (constant of proportionality)
           {   represents deposition  coordinates at downwind  point  (x,y,z)
          Zd  is the  reference height

          D"   is a diffusion function.

          The Horst model and its predecessor were compared  for a  variety of
conditions to judge the efficiency of the source depletion model with respect
to the surface depletion model.  Calculations were made for  a variety of source
heights  (2 m, 10 m, and 100 m) and for three Pasquill stability categories,
(A, D, and F).  It was determined that the differences  between the two models
increase with increasing stability.   The  source depletion model was charac-
terized  by an overprediction of total deposition and a  consequent under-
prediction of the remaining airborne material.  In one  case of moderately
strong deposition and stable conditions,  the source depletion model for
parameters at a downwind distance of 10 km was found to be  in error by
factors of 3 and 4.  At greater downwind  distances and  in cases of stronger
deposition, these factors can increase substantially.  The  source depletion

model was found to be entirely sufficient for low deposition conditions
but to increase in error for high deposition case.  For example, for
Vd/u~ = 10~3 the source depletion model is in error by 10 to 20 percent
for three release heights and three stabilities; for V^/u" = 10~2 and
unstable thermal stability the greatest error is approximately 35 per-
          Droppo (1974) described the types of input necessary for
developmental modeling of dry deposition processes on high and low
vegetation canopies.  Four regimes characterize the model  of overall
deposition over a canopy, these include  1) air layer above the canopy;
2) air-vegetation layer within the canopy; 3) the surface layers over
the individual plant elements and 4) inside the plant elements where
internal processes limit the rate of assimilation of certain materials
into the plant.  With the assumption that atmospheric and canopy
characteristics can be expressed as height and time functions, the
functional relationship for a given site is:

                r(z,t) = r^z.t) + r2(z,t) + r3(z,t)

          r   is the total resistance (to flow of material)
          r-|  is the resistance in the first regime
          TI  is the resistance in the second regime
          r3  is the resistance in the third regime

There is no defined r^ since these processes will directly affect the
third regime.
          The model input variables consist of a series of plant character-
istics and processes (functions of height and time).  These are:  Physical
Characteristics, such as canopy height, density of foliage, canopy
roughness and leaf area index; Physiological Characteristics, such as

stomata openings and surface characteristics and finally Concurrent
Fluxes such as momentum,  latent heat,  and sensible heat.   No quantitative
data were provided in the Droppo (1974)  paper,  but a series of qualitative
results were given.   The  deposition  process  is  expected to differ
depending on physical characteristics  of the canopy; greater amounts  of
deposition will  occur in  the lower regions of the  low canopies than
in higher less dense canopies.   The  upper portions of higher vegetation
canopies are the locations for  significant deposition of material.  Results
of diffusion, wind profiles, energy  budget and  physiological  research
relating to vegetation canopies will be  incorporated into this model
as it is developed.

                               Section V
                        FIELD STUDIES OF PLUMES

          Data have been gathered on plume transformation chemistry,  and
theories have been developed and tested, in field studies of specific plumes.
The methods and results of a number of these studies are discussed below.
          In pioneering work of the use of the helicopter as a plume  track-
ing tool, a limited field study program was undertaken at the TVA's coal
burning Colbert Power Plant to measure the rate of atmospheric oxidation of
S02 during different weather conditions (Gartrell et al. 1963).   At that
time the plant, located approximately 20 km southwest of Wilson  Dam,  Alabama,
had four 200 mw units, each with a 97 m (300 feet) stack.  About 70 percent
of the flyash was removed by mechanical flyash collectors.  The  reported
results of earlier laboratory studies were utilized in the planning of this
project to provide the investigators with a basis of comparison  and indica-
tions of what to expect from the field study.
          Sampling from a helicopter was designed to directly determine
S02 and 803 components, utilizing a filter paper separation technique.
(The instrumentation at that stage of the technology was not adequate for
making S03 or H2SO, measurements; unfortunately reliable measurements of
ambient HUSO^ levels are still not a reality even today.)  Auxiliary  in-
strumentation included the altimeter, a spring-wound clock, and  in later
tests, wet and dry temperature probes.  A voice recorder was utilized to
store data from these instruments for subsequent analysis.  Measurements
were made during early morning inversion conditions for easy plume detec-
tion and presence of maximum S02 plume concentrations.  Close to the  plant
(1 to 2 miles), longitudinal flights were made along the center!ine of the
relatively narrow plume to shorten the total sampling time necessary  for
each sample.  Further away from the plant, where the plume was wider, the

helicopter conducted replicate flights across the center!ine  of  the  plume
in progressive sections.  A data summary of the flights  (Table 9), taken
from the Gartrell et al. (1963) study, depicts the  range of S02  oxidation
rates encountered for a variety of different time,  distance,  and relative
humidity conditions.  The oxidation rates are seen  to  range from 0 to
3.7 percent for measurements characterized by low humidity, to rates of
21 and 32 percent for humidities close to 75 percent.  An S02 oxida-
tion rate of 55.5 percent for a time of 108 minutes was  observed in  one
sample run.  A common starting time for calculating oxidation rates  was
not a condition of the sampling methodology.

Dace Sample
1960 No.

8/2 1
9/2 1
10/14 1
10/26 1
10/2S 1

5/3 I
8/19 1
10/11 1
Travel from Point of Emission
in Plume
"Low Rates"


L_ 70
"Hi?h Rates"


SO 2



          Gartrell et al.  (1963) state that the limited data obtained in
their study do not provide a basis for accurate estimates of the post-
emission absolute rate of S02 oxidation.   The investigators postulate
that the dominating factor controlling the oxidation rates was moisture
within the plume or ambient strata; especially at relative humidity
values greater than 70 percent.  Newman et al.  (1975) contend that upon
closer inspection of the Gartrell et al.  (1963) data, a dependence on
humidity is not that clear, and attribute the observed high S02 oxidation
rates to very high particulate loading in the plume.
          The TVA's Colbert plant was selected once again for the collection
of data on the characteristics of a coal-fired power plant plume, including
the chemical constituents and their concentrations with respect to downwind
distance (Huang et al. 1974).  A kinetic model  of plume chemical interac-
tions was developed from data gathered, and has been described in Section IV.
At the time of the field program late in 1972, the plant was characterized
by a 980 mw capacity, with three stacks, two at 93 m (300 feet) and one at
152 m (500 feet).
          A Sikorsky model S-58 helicopter was equipped with instruments
designed to measure sulfur dioxide, total sulfur, nitrogen dioxide, nitric
oxide, ozone, nitrous acid, toluene, particles, humidity and temperature
for the project duration.   During the program,  the helicopter would leave
the TVA airport in Muscle Shoals, Alabama, at sunrise and fly to the
vicinity of the Colbert plant.  During the flight to the steam plant the
background (ambient) concentrations of the pollutants were measured.  Upon
arrival  at the plant a vertical temperature profile was made to -an altitude
of 1200 m (4000 feet).  Once the temperature profile was completed, plume
measurements were initiated across the plume centerline at predetermined
distances downwind.  Samples were taken and continuous gas analysis was
started when the helicopter entered the plume.   A minimum of 60 seconds
in the plume was allowed for plume sampling; circling within the plume
was required for samples in the narrow portions of the plume.  To allow

the sampling probes to function properly, an airspeed of near 35 knots
was maintained during a sampling run.  The sulfur analyzer was continuously
operated and utilized as an indication of plume boundary location.  Temp-
erature and dew point were measured simultaneously with the pollutants, and
before entering the plume.  The plume traverses were continued until the
morning inversion was completely broken and the plume was too dispersed to
measure.  A second vertical temperature profile was made at the end of the
sampling periods.  The traverses of the plume by the helicopter were made
at downwind distances of 0.8, 1.6, 3.2, 6.4, and 9.5 kilometers.  The plume
was traversed at distances greater than 16.1 km (10 miles) when the atmosphere
was extremely stable.  Measurements of ground level meteorological para-
meters, specifically dry and wet-bulb temperatures, solar radiation, and wind
speed and direction were made concurrent with the airborne studies.  Winds
aloft were determined by releasing and tracking pibals.
          The gathered experimental data were utilized to construct concen-
tration profiles.  Theoretical concentration profiles were constructed by
the integration of 35 rate equations for the kinetic model chemical reac-
tions assumed to be the most likely to occur.  These theoretical profiles
were altered by varying the rate constants until the resulting profiles
agree as closely as desired with the observed profiles, and these were
taken to be a likely description of the plume chemistry.  However, it appears
that the 35 reactions used by Huang et al. form a weak representation of
reality.  The reactions of radical chemistry were poorly represented; rate
constants could be estimated with an accuracy of no more than an order of
          Due to the suspected inaccuracy of the'experimental results, the
overall  rate of oxidation of S02 could not be determined from either (1) the
change in concentration of SC>2 by separating the effects of dispersion and
oxidation or (2) a comparison of concentrations of S02 and sulfates.  S02
oxidation rates  appeared to be slow in any event.   The authors expressed
the desire  that  the results in their report should not be accepted as quanti-
tative due  to the limitations involved.

          A series of investigations at the Florida Power Corporation's
coal burning Crystal River Power Plant, utilizing aircraft, had a goal
of testing a method for evaluating S02 decay rates in the plume
(Stephens and McCaldin 1971).  The 375 MW capacity plant has a single
152 m (500 ft.) discharge stack and is situated on the flat Gulf Coast
plain 129 km (80 miles) north of Tampa, Florida.
          To differentiate between a decrease in S02 concentration due to
atmospheric dispersion processes and a decrease in concentration due to
oxidation or any other chemical or physical decay factors, a technique
believed by Stephens and McCaldin (1971) to be "conservative" in nature
was utilized.  The technique consisted of a comparative ratio of sulfur
dioxide concentration to a conservative tracer concentration (consisting
of submicron-sized particulate matter emitted from the stack); supposedly
the ratio of particulates to S02 would approximate a constant as the plume
aged and diffused, if the SOp were conservative.  The ratio would increase
as the plume ages if the S02 demonstrates a measurable decay rate.  Such
a procedure has been challenged by Friend et al.  (1972), who explained that
particulates cannot be used as a conservative tracer since the sulfate
particles formed as a result of the oxidation of sulfur dioxide can sig-
nificantly contribute to the total mass.
          It was determined that the time required for the decay of one-
half of the sulfur dioxide indicated a first order rate equation for the
reaction.  The range of SO- loss rates were described to vary from a
negligible value at low relative humidity  (30-40 percent), to a half-life
of approximately 140 minutes at medium relative humidity  (40-50 percent),
and 70 minutes at high relative humidity (78-80 percent).
          Field studies at the Morgantown Power Plant of the Potomac
Electric Power Company were conducted by Davis et al. (1974) to determine

the extent to which NOY and S02 chemistry occurs as a function of distance
from the emission source.  The plant, which burned an oil-coal fuel mix-
ture (75 percent residual #6 oil  and 25 percent coal) is located 64 km
(40 miles) south of Washington, D.C., and has a 1250 MW capacity.  The
collection of field data, which took place from October 1973 to August
1974, was accomplished through use of a single engine Cessna 205 airplane
early in the program and a Cessna 172 later in the program.  Extensive
field data were collected from instrumentation aboard the Cessna 205
aircraft which included a Monitor Labs 8410 chemiluminescence ozone
analyzer, a Monitor Labs 8440 chemiluminescence NO-NO--NO  analyzer and
a Meloy SA-160R flame photometric SOp analyzer.  Instruments designed to
monitor CO and hydrocarbons were also employed.  Horizontal cross-
sectional traverses were made of the plume at altitudes ranging from 213
to 914 meters at various downwind distances up to 56 km.  A major obser-
vation in the field program was the depletion of ambient ozone within the
plume near the stack at distances of 5 to 8 km, and an increase in ozone
at 50 km downwind with a decrease in plume S02.  The plume depletion
features close to the plant are illustrated in Figures 5a and 5b from the
Davis et al. (1974) report.  An increase of roughly 30 percent over ambient
ozone levels was noted at 56 km, but the profiles at this downwind distance
were not available.  The details of the atmospheric chemistry theory pro-
posed by Davis et al. (1974) to explain the net generation of ozone in
plumes have been described earlier in Section IV and will not be repeated
          The extent of oxidation of sulfur dioxide to sulfate was examined
in a study of the Pennsylvania Electric Company's Keystone coal-fired power
plant by Newman et al.  (1975a), and the Long Island Lighting Company's
Northport, New York oil-fired power plant by Newman et al. (1975b).  The
Keystone Plant generates a total  of 1800 MW using two boilers-whose units
are equipped  with electrostatic precipitators rated at 99.5 percent efficiency,

                                  1300  EST 23 NOV., 1975
                                                1.6 KM OUT
                                              1900 FT ALT
 4.8  KM OUT
1900  FT ALT
                                               11.2 KM  OUT
                                               1700 FT  ALT
                                                 16 KM OUT
                                               1700 FT ALT
                     Kilometers  (Approximate)
Figure 5a. Profiles of Crossplume Ozone Concentration at Various Elevations Downwind
            of the Morgantown Power Plant (from Davis et al. 1974a).

        2  ppm
        so2    o3
        1  ppm   50ppb-|
                              22 JLINR,  1974
                              14SO-1500  EST
                                                      1.6  KM



                                   24 KM
  2  ,_-''


      32  KM

                                      -1 KM-
Figure 5b.  Profiles of Sulfur Dioxide and Ozone Crossplume Concentrations at 600 m Altitude
      at Various Downwind Distances from the Morgantown Power Plant (from Davis et al. 1974).

each unit served by a 244 m stack.  At Northport, the 760 mw plant
operates with two boilers, each with a 183 m stack.  Mechanical  cyclone
type precipitators on these units have a rated efficiency of 85 percent.
          In both plant studies, a single-engine Cessna 182 was utilized
to obtain plume samples for isotopic ratio and concentration measurements
of the 32S:34S naturally occurring in the fuel sulfur.  The aircraft was
instrumented with a hi-vol for sampling of sulfate (on fiberglass filters)
and S02 (on alkaline impregnated filters), an electroconductivity S02
analyzer for locating the plume, and auxiliary equipment for measuring
temperature, relative humidity, altitude, airspeed and aircraft location.
Background measurements of S02 and sulfates were obtained upwind of the
plume at plume altitude and repeated crosswind traverses at a minimum of
five distances (when feasible) were made in the plume during data gathering,
Sulfate sampling under the plume was conducted at two distances downwind.
          Concentrations of the conservative tracer SFs, compared to S02
as a function of distance, were used to assess the S02 losses by oxidation
and deposition.  Hi-vol samplings of sulfate particulates were so small
that a reliable analysis could not be conducted to fit the data obtained
to the oxidation process postulated for both coal and oil-fired plumes;
measurements of S02 converted to sulfate were therefore based upon the
assumption that reductions of S02 concentrations greater than those found
for SFs should be attributed to conversion to 504.
          The fraction of S02 converted at measurement points in the plume
downwind from the stack was also calculated from the expression:
                    (1 - f) =  6S2  (fue1) ~ 6S2
                                     1000 a

          f = the fraction of S02 converted
       6S02 = the "del value" which is a measure of deviations
              of the ratio 32$/34s at the point of measurement
              from a standard isotopic sulfur ratio for
              32$/34s of 22.210

          a = k-1,  where k is the equilibrium constant  between
              S02 and S03 for the reaction
                34so2 + 32so3 5 32so2 + 34so3.
          Eleven standard plume  sampling  runs  were made at the Keystone
power plant.  The S02 concentrations were measured in the flue gas at
the stack and at six downwind distances.  The  data obtained on these runs
were combined, normalized and averaged with  the  results summarized in
Table 10.
                 KEYSTONE POWER PLANT (from Newman et al. 1975a)
Downwind Distance from Plant (km)
6 * (del value)
Percent SO conversion to SO based on
6 calculations
Percent SO- conversion to SO based on
' 4
measured concentrations
  * The del values are normalized to the average flue gas value of 2.8.

          The percents of S02 conversion shown in  this  table refer to con-
version in the atmosphere after leaving the stack,  and  to a common base of
0.0 percent at the stack.  Reductions in conversion with  increasing distance
were attributed to removal of 864 from the atmosphere after its  formation.
          The following observations were obtained  from these data:
          1.  The indicated decrease with  distance in percent
              SO;? converted based  on concentration supports
              evidence for the apparent  dropping out of sulfate
              from the plume.
          2.  The percent 862 conversion to  sulfate based on isotopic
              ratio measurement tends  to attain  a steady value of 3
              to 4 percent, which  is independent of time or distance;
              however, the authors point out that super-imposed on

              these percentages, which are depicted as a function of
              distance, are wind velocities that ranged over a factor
              of four.  Part of the variability may be associated with
              a large range in the isotopic ratio of the sulfur in the
              coal at the plant.

          The low S02 conversion rates of less than 5 percent are attri-
buted to a rate limiting process.  This is supported by the low particulate
content of the Keystone plant plume, on the order of 105 yg/m3.
          A calculated S02 plume oxidation half-life of 10 hours was
derived from a humidity-independent second order kinetic expression,
and from a resulting rate constant of 1 pprrT1 hr"1.  The oil-fired plume
had no reported particulate loadings.  Vanadium particulates, originating
from fuel oil were postulated (by Newman et al. 1975b) to be the catalyst
in a mechanism whereby the S02 is in equilibrium with water on these par-
ticulates and catalytic oxidation subsequently occurs.  Newman et al.
(1975a) did not postulate a similar mechanism involving Fe2C>3 in the
coal-fired particulate matter.  The noted highly variable S02 conversion
in both oil- and coal-fired plumes and the lack of a definite correlation
of the percent S02 conversion with relative humidity are major research
outcomes of these studies.
          Further evidence for low S02 oxidation rates in coal-fired
power plant plumes was provided by the University of Utah Research
Institute (1974) in a study carried out at the Four Corners power plant
in New Mexico.  The program objectives were to measure the degree of
S02 conversion and to evaluate its impact on concentrations of atmospheric
sulfate and visibility.  Parameters measured to determine the conversions
of S02 to particulate sulfate included particulate ammonium sulfate;
upwind and downwind difference in concentrations compared to ambient
S02, and the speed of wind.  One test resulted in a 0.37 percent hr-1
conversion of $62 to particulate sulfate at about 21 km downwind, and
relative humidities of 30-51 percent.  Another test resulted in a 0.76 per-
cent hr~l conversion 21 km downwind with relative humidities of 26-40 per-
cent.   Conversions of 0.45 percent hr~^ at about 60 km downwind were noted


in this same test.  Both tests were characterized by S02 concentrations
ranging from 0.01-0.06 ppm.  This study possibly provides a more realistic
measure of plume S02 oxidation rates due to the fact that the S02 rates
of oxidation provided are the result of direct, positive sulfate analysis
and not deduced from the comparison of S02 loss with plume tracer mater-
          Extensive studies involving three-dimensional mapping of  large
plumes from multiple urban sources were accomplished in the St. Louis area
as part of the Regional Air Pollution Study (RAPS) and the Midwest  Inter-
state  Sulfur Transport and Transformation Study (MISTT) during the  summers
of 1973-1975 and  during February of 1975 (Wilson et al. 1976).  These
studies challenged the adequacy of the usual technique of calculating the
fractional conversion of S02 to sulfate from S02 concentration and  sulfate
data obtained by  aircraft flying through the plume on a variety of  flight
paths.  Based on  observational data 'of typic'al cross-plume profiles of
Aitken nuclei concentration, light scattering aerosol, S02 and ozone, it
is believed that  the S02 conversion rate ifc different in various parts of
the plume, the higher rates favoring the plume edges rather than center,
although this difference is not evident in all cases.  The conclusion
reached by Wilson et al. (1976) is that measurements of S02 and sulfate mass
flow rates in the plume are the best indicators of conversion rate.
          Aircraft mapping of the plumes of the 2400 MW Labadie plant,
emanating from three stacks 213.5 m (700 ft) tall  located west-southwest
of St.  Louis was conducted out to plume distances approaching 100 km.  The
basic concept was the measurement of the gaseous and particulate sulfur
flow rates at increasing distances from the source to derive pollutant
budgets and ultimately to allow estimates of the rate at which trans-
formations and removal  processes act on the individual pollutants.  The
coordinated efforts of two instrumented aircraft, an instrumented van
and three mobile pilot balloon units were utilized in the plume mapping
          Plume  aerosol  volume flows were calculated from aircraft  size
distribution  measurements with an electrical aerosol analyzer and an

optical particle counter made during  horizontal  passes  and from upwind
spirals through the plume.  The results  of  plume aerosol  flow rates and
calculated sulfur conversion obtained  for one  test  day  showed little
sulfate formation in the first 30  km,  and a conversion  of some 2% hr
in the region 30-50 km from the source.  An important observation of the
MISTT studies is low SOT formation  until NO is converted  to NO,, and then
subsequent higher S07 formation:   this stresses  the necessity of long
distance measurements from the stack  source, since  at closer distances
(i.e., 16-32 km) only the stack sulfate, derived from $03 from in the com-
bustion process, may be present.
          Pacific Northwest Laboratories (Nickola and Clark 1974) designed
a technique for field measurements  of  deposition of a particulate plume by
tracking with an inert gas plume.   The inert gas, Krypton-85, was simulta-
neously released with fluorescent  zinc sulfide particulate tracer from a
single site 26 m in elevation; the  air concentrations of  both plumes were
examined downwind of the release point.  The mass median  diameter of the
zinc sulfide was 5 ym; removal processes such  as impaction and gravitational
settling became important if the particle diameter  was  greater than this
value  (Dabberdt and Smith 1975).   The  deposition process  can be credited
with the expected deficit of mass  in  the particulate plume as both chem-
ically stable plumes travel downwind;  an estimation of  the amount of
zinc sulfide deposited was conducted  by  a graphical study of the differ-
ences between the two vertical profiles  of  concentration  near the ground.
The field sampling grid was comprised  of more  than  600  filters at 1.5 m
height placed about the tracer release tower in  a concentric fashion, on
sectors of six arcs at distances of approximately 0.2,  0.4, 0.8, 1.2, and
3.2 km* from the point of release.  The  results  showed  that under moderately
 * Arcs at 0.8, 1.6 and 3.2 km were actually concentric about a point 100 m due south of the release
   point.  Thus, the distance from release point to arc varies with azimuth.

stable conditions about 7 percent of the particulate plume was deposited
during passage to a distance of 842 m.   Zero to 1  percent of the particu-
late tracer was deposited within 812 m from the release point under more
stable atmospheric conditions.   Approximately 1 percent of the zinc sulfide
tracer is estimated to have touched down within 200 m of the source during
a case characterized as flat with sagebrush and steppe grasses dominating
the region.                        _  ____  __                       ______
          Garland~~(T974)~has measured the rate of S0? dry deposition both
in  the field and in the laboratory using   S02, a radioactive tracer as
one technique and the concentration gradient method as the other.  Several
of  the field efforts, utilizing the radioactive tracer method to measure
the deposition velocity to grass, consisted of releasing a small amount
of  S02 containing 50 millicuries 35S over a 30-minute_period at a
height of  1 m, 50 m upwind of an arranged sampling area near the center
of  a  large field.    S0? concentrations were determined by air bubbler
samplers mounted above marked plots.  Exposure samples of the grass were
removed  from several of these plots and the uptake of   S was resolved by
transferring the total extracted sulfate to a liquid scintillation counter.
The results were interpreted as a deposition velocity defined by:

          y  _ radioactive particle counts in grass per unit ground area
           y            concentration in air X time of exposure

          The gradient method,  when used to determine the flux of S02,
assumes  that momentum, heat, and S02 fluxes are constant with height over
the range of measurement.  An area of uniform surface extending for at
least 100 times the measurement height upwind is required.  The diffus-
ivity of momentum or the diffusivity of heat are used as approximations
of the flux of S02; the diffusivity for momentum was used in the Garland
(1974) study.   These diffusivities are defined as:
                      Km =      l   or Ku =
                             4>          H

          Km = diffusivity of momentum (m^ s~l)
          KH = diffusivity of heat (cal  m'1  s-1)
           k = von Karman's constant, an empirical constant of value 0.4
          u* = friction velocity defined in terms of shear stress
               on the surface due to the wind (nrl)
           z = height above surface (m)
           d = reflects the effect of tall crops in elevating the height
               of the momentum sink above the surface (m)
               the dimension! ess shear of momentum
               the dimensionless shear of heat.
          The results of three sets of field measurements of the dry
deposition of S02 over grass vary depending on the time of year and
characteristics of the canopy.  For short grass in March and June, the
mean Vg was 0.55 cm s"U medium grass (radioactive method) in June-November
gave a mean Vg of 1.19 cm s~^ ; using the gradient method from November -
January over medium grass gave a mean Vg of 0.77 cm s~T.  Over long grass,
using the radioactive method, a mean result of 0.85 cm s~1 was found; this
compares to a Vg of 0.61 cm s~^ for 14 measurements reported by Shepherd
(1974), and to the deposition velocity of 0.4 cm s   over a wheat field
found by Fowler and Unsworth (1974).
          Most of the research concerned with the absorption of atmo-
spheric water soluble gases by vegetetion has been conducted using
environmental chambers constructed to simulate different field environ-
ment conditions.  In the research of Hill and Chamberlain (1974), two
environmental chambers were designed that accomplished this simulation
by controlling wind velocity, ($2 concentration, temperature, relative
humidity, light intensity, and pollutant concentration.  The standard
alfalfa canopies used in the chamber were found to result in S02 and N02
concentration profiles that indicated that these substances were

efficiently removed from the atmosphere by the surface and subsurface
vegetation of the upper portion of the plant canopy.   The rate of
pollutant removal by vegetation was shown to be affected by wind velocity,
canopy height, and light intensity, with the removal  rate of pollutant
found to increase linearly with the increase of pollutant concentration
until those pollutant levels when serious physiological  affects take over
the plant.  Due to the lack of actual  field data, the authors describe a
hypothetical situation in which they attempt to evaluate the role of vege-
tation as a sink for air pollutants in any specific area.  A large coal-
fired power plant was assumed to produce average ambient S02 concentrations
of about 6 ppb within 32 km of it.  Vegetation cover in this area, with
an average S02 uptake rate equivalent to that of a 40 cm alfalfa canopy
(17 yl min"1 nr2 pphnr1) during daylight hours, would give an uptake rate
of 1.24 x 105 kg/day in the 32.5 x 108 m2 within 32 km of the plant.  This
would be 49 percent of the S02 emitted from the plant; the percentage removed
would be greater if the area were a forest, or less if the vegetation were
scarce.  The authors bring up an important point, relating the conversion of
S02 to 864 in the atmosphere to vegetation pollutant sinks.  The low conver-
sion rate of 862 to S0| particles, in rural areas where photochemical smog
reactions are less important, will result in high percentages of S02 removed
by vegetation before it is oxidized to sulfate, if vegetation acts as an
S02 sink.
          To assess the extent of depletion from a diffusing plume, an
experimental investigation was conducted at the Keystone Power Plant
(located in a polluted area) as part of the LAPPES program to measure the
sulfur dioxide washout by natural  precipitation (Hales et al. 1971).
Precipitation samplers were strategically placed on a surface sampling
line which extended across the overhead plume.   The compound of primary
interest was S02, although sulfate, nitrite, and nitrate levels were also
determined from selected  samples.   Samples were delivered to a mobile

laboratory for analysis as quickly as possible upon their collection.
The mass of water-soluble particulate recovered from each precipitation
collector indicated the degree of pollutant deposition from the plume through
precipitation scavenging and dry deposition.  The sulfate and nitrate results
exhibited a large amount of scatter which according to the authors was suspected
to have arisen due to artifacts within the samples.  The sulfur dioxide distri-
butions observed in the experiments were not sufficiently well-defined for the
calculation of washout coefficients.  Observed values of S02 washout flux were
stated to be less than theoretical estimates by factors of 50 to 100.  Notable
was the absence of a positive correlation of washout sulfur dioxide concentration
with the location of the Keystone plume, attributed to the plume shallowness
at short distances from the source which permits the least time for sulfur
dioxide sorption and the greatest time for its desorption.  In several cases,
a negative correlation of washout beneath the plume was discovered.  The
results indicated that the S02 scavenging process was more complicated than
the investigators had suspected.  The conclusions reached, based on the data
obtained, were as follows:

          1.  The actual  removal rate of S02 from the plume by the washout
mechanism from the stack source at 244 m (800 ft) above ground level  was
up to two orders of magnitude less than predicted by preexisting theory.
Washout fluxes in rainfall and snowfall were clustered about a value of
10 ymoles (m2 hr)~l for precipitation rate normalized to 1 mm hr-1.
          2.  A factor of two difference was noted from the relationship
between the observed washout and precipitation rate and the relationship
derived from preexisting theory.  More efficient washout by large drops
than is predicted by preexisting theory is attributed to the larger
exponent of precipitation rate in the observed relationship.
          3.  Increases in washout concentrations of SOo were apparent
with distance from the stack.  Lateral diffusion of the plume, according
to preexisting theory, is responsible for decreases with distance of con-
centrations proportional  to the vertically integrated mass of sulfur

          4.   Washout of background sulfur dioxide concentrations
appeared to interfere strongly with plume-washout observations.   Remote
sources about 20 km to the southeast of the Keystone plant contributed
heavily to the S02 washout observed.
          5.   There were indications that sulfur dioxide washout was
inhibited in  some way by the Keystone plant or that the S02 was  converted
to sulfate.  A depression of S02 concentration observed in precipitation
collected beneath the plume under certain circumstances when the washout
of background sulfur dioxide was relatively high supported this.

          Three experimental studies of the washout of power plant
effluents were conducted at the State of Washington's Centralia  coal-
fired plant (Dana et al. 1975, 1976).  The Centralia stacks have a
height of  143 m above the ground.  Heavily forested hills, rising to
within 50 km of the stack tops comprise the rugged terrain within a few
kilometers in the normal downwind direction, however no problems were
encountered in site selections for precipitation sampling.  In contrast
to the washout studies performed near the heavily polluted Keystone plant,
the effects of the Centralia effluent plume were isolated by rain con-
centration measurements.  The effect of the plant on local levels of S02
SO^, and H  was determined from laboratory analysis of the precipitation
samples.  The rain sampling positions were concentrated in accordance
with the predominant wind direction during rainfall  at Centralia.  Ninety
fixed collection sites were arranged to reflect the prevalent  area under
the plume at  distances from 0.4 to 11 km downwind in the latest  experi-
ment study.  A scavenging "plume" of SOp on the ground sampling  array
was clearly indicated.  The measured scavenging rates for SCL  as a
function of downwind distance show rates of 3.0 and 27.0 (gram-moles/cm
       9                                                          Q
s) x 10  at 0.4-0.5 km downwind, 100 and 42 (gram/mo!es/cm-s)  x  10
at 4.5 km, 54 (gram-moles/cm-s) x 10  at 7.0 km and 115 ar.d 129   (gram-
moles/cm-s) x 10  at 10-11.5 km downwind.  Sulfate molar concentrations
were, in general,  not large compared with those of S02, so a deposition
plume for sulfate  was difficult to define, except for some discernible
plume-related sulfate deposition at downwind distances greater than about

7 km.  No correlations were found between locations of the power plant
plume and the measured concentrations in rainwater of ammonium, nitrite,
nitrate, or phosphate ions.
          Along with the involved field experiments at the Centralia
plant was a research program directed at the development of a numerical
model for predicting precipitation scavenging of reactive pollutants
from power-plant plumes.  The model is described in Section IV.  Compari-
sons of the calculated results were conducted using the model with experi-
mental data employing the liquid phase ammonia (Scott and Hobbs 1967)
mechanism.  Indications were that the mechanism is insufficient to explain
observed sulfate formation rates in the tested plume and raindrop situations.
          The primary conclusions drawn from the Centralia field program
were:   (1) At downwind distances less than about 10 km, sulfate concen-
trations in rainwater due to the presence of the plume do not appear
significant.  (2) Ammonium, nitrate, and soluble (ortho) phosphate ion
concentrations in the samples obtained were close to normal background
levels.  (3) SCL and hydrogen ion were the only measured species which
showed plume related deposition patterns at all distances from 0.4 to 11 km
where samples were collected.
          In a different investigation seasonally averaged sulfate concentration
in rainwater samples collected near the TVA Colbert plant were analyzed by con-
verting the data to isopleths of sulfate washout at 17 sampling sites located
in an area 1.6 to 25.7 km  (1-16 miles) from the plant  (Hutcheson and Hall 1974).
The washout process was defined as the mass of sulfate per unit area per inch
of rain.  The washout pattern was found to be skewed in the general direction
of maximum precipitation rates.  Unlike the Keystone power plant, the Colbert
plant is situated in an area of low background atmospheric sulfur concentration
and has stacks only 91.5 m (300 ft) high.  Little S02 washout compared to the
sulfate aerosol washout was observed at Keystone; at Colbert, the major features
of the washout pattern derived from the data cannot be accounted for by sulfate
aerosol scavenging but can be accounted for if most of the washout is attributed
to S02 scavenging.  Kale's (1971) theoretical argument is supported by this

study, which indicates  that the  background  acidity  of rain  (with  large
raindrops being less acid  than small  drops  and  therefore  absorbing  greater
quantities of SCL),  the height of  the pollutant source and  the  rainfall
rate (high precipitation rates are associated with  larger mean  raindrop
size) all strongly influence the relative importance  of sulfate aerosol
and S$  scavenging in the  very complex sulfur washout process.

                               Section VI

          Studies of S02 oxidation rates in power plant plumes show a
diversity of results, with reported values ranging from under 1 percent
per hour to as much as 30 percent per hour.  The Gartrell et al.  (1963)
study of the coal-fired Colbert power plant plume in Alabama presented
S02 oxidation rates of about 1-3 percent per hour for low humidity cases,
while higher rates on the order of 30 percent per hour were found for
higher relative humidities, with one case yielding an S02 oxidation rate
of 55 percent during a period of 108 minutes.  The Stephens and McCaldin
(1971) field study of the coal-fired Crystal River power plant plume in
Florida resulted in data which showed the S02 half-life to be 144 minutes
at relative humidities ranging from 40-55 percent, and 70 minutes for rela-
tive humidities of 78-80 percent.  Although there is controversy concern-
ing the assumption made by Stephens and McCaldin that particulate matter
in the submicron range can be used as a conservative tracer, their results
bring out the concept of the importance of relative humidity in the plume
and ambient air as a major factor in the atmospheric oxidation of S02.
Studies of the coal-fired Keystone plant in Pennsylvania (Newman et al.
1975a) and the oil-fired Northport plant in New York (Newman et al. 1975b)
yielded S02 oxidation rates in the coal-fired plumes that were surprisingly
lower than those of the oil-fired plant.  The oxidation rates ranged from
0 to 5 percent in the Keystone plumes and from 0 to 26 percent in the
Northport plumes; the low particulate content of the coal-fired plume is
believed to be responsible for the correspondingly low S02 oxidation rates.
Definite correlations of oxidation with relative humidities were not
evident for the experimental humidity range of 40-95 percent.  At the Four
Corners power plant in New Mexico (University of Utah Research Institute
1974) a recent trend of observing lower S02 oxidation rates in studies of

coal-fired plant plumes  was  evident.   Reported  values  for conversions of
S02 to particulate sulfate ranged  from 0.37 percent per hour at a dis-
tance of 21 km downwind  (at relative  humidities of 36-51 percent in one
test), to 0.76 percent per hour at 21  km downwind, and 0.45 percent per
hour at 60 km downwind,  with relative humidities of 26-40 percent in
another test.  The dryness of the  region is believed to be responsible
for the low conversion rates.  In  the MISTT program, mapping of the Labadie
plant plume near St.  Louis resulted in pollutant budgets inferred from
estimates of rates of transformation  and removal in the plume which showed
almost no sulfate formation within the first 30 km of the plant, and a
conversion of some 2% hr"  at downwind distances of 30-50 km.
          A study of the Morgantown plant plume in Maryland by Davis et
al. (1974) is controversial  because of the evidence of an "ozone bulge" in
the plume profile data 50 km downwind of the plant.  A series of reaction
steps was postulated to  help interpret the bulge and there is the possi-
bility that under certain conditions,  the initiating S0? + OH mechanism
in this reaction sequence may be the  dominant S02 conversion mechanism to
ultimately result in ^$04 and other  aerosol  products  under certain con-
ditions.  This conveniently leads  into an evaluation of what the literature
has shown to be the relevant S02 conversion mechanism in power plant plumes.
          Five primary mechanisms  for SOp oxidation in the atmosphere have
been postulated.  These  include the homogeneous processes of direct photo-
oxidation, indirect photo-oxidation,  aqueous phase oxidation, the hetero-
geneous process involving catalyzed oxidation in liquids and dry hetero-
geneous reaction.  Homogeneous photo-oxidation  of S02 has generally been
agreed to be an insignificant cause of sulfate  formation in plumes, with
the slowest rates of S02 conversion typically occurring in pure air and
sunshine.   The reported  rates range from about  0.1 percent per hour in
laboratory work (Gerhard and Johnstone 1958, Urone et al. 1968, Cox and
Penkett 1970) to actual  atmospheric observations such as a 2 percent per
hour value described by  Katz (1950) and one value of 12 percent per minute
found by Shirai et al.  (1962).

          Indirect homogeneous photo-oxidation of S02 may be a significant
reaction sequence in plume chemistry.  The dominant gas phase removal  mech-
anism for SCL may be the oxidation of S02 by OH and H02 as shown by Davis
et al. (1974), Castleman et al.  (1974), and Calvert and McQuigg (1975).
A better understanding of the impact of this mechanism on S02 plume con-
version rates will be forthcoming as more reliable measurements of OH
concentrations in plumes are available.  One current estimate of 2 percent
per hour for S02 conversion through OH and H20 oxidation has been put
forth by Castleman et al. (1975).  It is difficult to calculate the homo-
geneous rate of oxidation of S02 in photochemical smog systems due to  the
diversity of test results and complexities introduced by the use of dif-
ferent S02-NOx-hydrocarbon and $02-03-0!efin mixtures and conditions in
varying experimental laboratory procedures.
          Studies of homogeneous aqueous phase reactions yield S02
conversion rates ranging from the order of 0.1 percent hr~l (Miller and
dePena 1972), through 2.5 percent hr'1 (Scott and Hobbs 1967), to 13 per-
cent hr~l (McKay 1971) for the ammonia-S02-water system.  Dana et al.
(1976), in their field work regarding precipitation scavenging of reactive
fossil-fuel plumes, place strong emphasis on the need for experimental
measurements of ammonia solubility in water at low concentrations prior
to any further speculation regarding the role of ammonia in S02 oxidation
          The effect of metal catalysts in the aqueous phase oxidation of
S02 has been shown to result in a range of from 0.1 to 2.0 percent per
minute, with possible higher rates.  Foster (1969) estimated the rate of
oxidation by a Mn catalyst to be 0.09 percent min"1 and 0.15-1.5 percent
min~^ for the rate of oxidation for Fe, showing the importance of iron as
a catalyst.  Cheng et al. (1971) extrapolated their laboratory results to
the atmosphere and arrived at an S02 oxidation rate of about 2 percent
hr-1 for a MnS04 catalyst concentration believed to be typical in a power
plant plume.   The oxidation of S02 for the Cheng et al. study is seen

to be four times  larger than  Foster's  level.   The high  variability in
oxidation rates  is attributed to the  sensitivity of this  mechanism to
parameters such  as pH,  relative humidity,  temperature and catalyst con-
centration.   The  most effective catalysis  occurs in solution under pre-
cipitation conditions;  Dana et al.  (1976)  have pointed  to faster S02
chemical conversion rates  in  plumes,  with  a chemistry believed to be more
complex than for  fair weather.  The mechanisms that could be active under
precipitating conditions include (1)  an  accelerated gas-phase reaction
process, (2) a liquid phase reaction  process  in precipitation, (3) a liquid
phase process in  cloud droplets and subsequent efficient  scavenging of cloud
drops by precipitation, or (4) combinations of the above.
          Heterogeneous solid-gas phase  oxidation studies in the laboratory
may not extrapolate quantitatively to the  atmosphere.  In power plant plumes,
it is the small  particles, less than  1  ym  in  diameter,  that are potential
catalysts for chemical  reactions because of their large specific surface
area and probably high trace  metal  content.  A realistic  estimation of the
surface area available for catalytic  aqueous  phase oxidation or catalytic
oxidation on dry surfaces  requires data  on particle surface composition,
particle surface structure, and particle concentration  in the plume; such
data has not been gathered in past studies.  Of interest  is the role of
dry particulate  vanadium in the heterogeneous oxidation of S02; but the
role of vanadium as an effective catalyst  is  disputable as Corn and Cheng
(1972) and Urone  et al. (1968) have shown  it  to be relatively inactive.
          Researchers have presented  theories which favor either homo-
geneous or heterogeneous mechanisms as  being  dominant in  S02 oxidation in
plumes, but a review of all studies suggests  that each  mechanism probably
is of major importance but under quite  different conditions.  For example,
the homogeneous  gas phase  process involving OH radicals most definitely
has a strong positive temperature dependence  due to the requirement of
high H20, high 03, and high UV flux for  the generation  of maximum OH con-
centrations  (the  very small negative  temperature dependence of the OH + S02

reaction would be insignificant compared with the strong positive tem-
perature dependence for OH production).  In the case of heterogeneous
processes, things are much more complex; here both positive and negative
temperature dependence terms are likely to be involved.  Other significant
negative effects result from absorption and adsorption of gaseous species
(e.g., 03 or $02) on or into a liquid or solid surface.  In general, it
appears that in the more complex heterogeneous systems, counterbalancing
temperature terms render these processes rather insensitive to temperature
or that this reaction mode has a net negative temperature dependence
(McKay 1971).  If so, this could mean that under cool weather or winter-
time conditions (also possibly summertime night conditions) heterogeneous
reactions are the major S02 conversion mode (Davis, personal communication,
          One line of thought may be that at a given power plant location,
there may be no one predominant SO- conversion mechanism (homogeneous or
heterogeneous) acting on an annual basis, as each mechanism can operate
efficiently only when a specific (and as yet undefined) set of environ-
mental parameters are present.  For example, in the summer months with
characteristically higher temperatures and relative humidities prevalent,
the production of OH free radicals may be accelerated, thus favoring enhan-
ced homogeneous processes of S02 plume oxidation in the plume.  On the
other hand, it may be that heterogeneous processes are less effective at
higher temperatures.  The entire situation may be reversed in the winter
months; the entire concept is qualitatively illustrated in Figure 6a as a
cyclic phenomenon with annual periodicity.  On a diurnal basis, the high
UV flux during daylight favors the homogeneous mechanisms, while hetero-
geneous reactions dominate the nighttime hours (see Figure 6b).  At a
given time, examination of plume S02 conversion mechanisms as a function
of distance may show heterogeneous processes dominating close to the stack
but dropping off with downwind distance.  The ready availability of metal
catalysts from the plume allows the heterogeneous mechanisms to operate
almost immediately, whereas the homogeneous processes  (specifically the

            Figure 6a.  Conceptual Illustration of the Variation of Both Homogeneous and Heterogeneous
                     SO2 Conversion Mechanisms as a Function of Time of Year for  a Specific
                                                Stack Location.
                                                Homogeneous Mechanisms
           Early Morning
Early Evening
                                                                               Late Night
                                       Diurnal Cycle
            Figure 6b.  Conceptual Illustration of the Variation of Both Homogeneous and Heterogeneous
                      SO  Conversion Mechanisms as a Function of Time of Day for a Specific
                                                Stack Location.

S02 + OH  reaction) take some distance downwind  (10's  of kilometers) to
become important,  possibly closely correlated with  the  rate of ozone pro-
duction,  and  reaching a maximum  at some point where formation is limited
by dilution of S02 (see Figure 6c).
                                                       Homogeneous Mechanisms
          Chemical  kinetic models to study the basic features of a reactive
plume from a large  point source are currently not available, but certainly
will be forthcoming as quantitative information becomes available on the
subjects of plume SCL-sulfate conversion mechanisms, rates of S02 trans-
formation and the extent and final  state of reaction.   Systems Applications,
Inc. (Liu 1975) has developed one such model  which employs a provisional
set of SOp reaction steps until field studies can validate the appropriate-
ness of the SO- mechanism.  The recent recognition of the importance of
S02 conversion to ^04 and other sulfates via OH radicals by Davis (1976)
and others is a key accomplishment in the state-of-the-art.
          Dry deposition in the atmosphere is a function of the type of
pollutant material, the deposition  substrate character, and the meteoro-
logical conditions, such as wind speed and direction,  surface roughness
length, friction velocity and atmospheric stability.  Recent investigations
(Owers and Powell 1974, Shepherd 1974, Garland et al.  1974) establish the
                                                       2     1
velocity of deposition of SC^ to be in the order of 10   m s  .  Submicron
atmospheric sulfate particles may have deposition velocities about an order
of magnitude smaller than the corresponding values established for S02
(Chamberlain 1966).
          Numerical modeling of the dry deposition process is still in the
early stages, and field measurements, rather than laboratory-simulated con-
ditions, are needed for validation  purposes.   Sehmel and Hodgson (1974)
developed a steady-state, one-dimensional mass transfer model and with wind
tunnel  data, determined that for their conditions of experimentation depo-
sition velocities were nearly independent of particle diameter only in the
0.1 to 1.0 ym size  range.  This corresponds to the "accumulation mode"
where 80 percent of atmospheric sulfate is found.  The minimum deposition
velocities were found to occur in the particle diameter range of 0.04 to
0.4 ym.
          Laboratory studies of the absorption of atmospheric water-soluble
gases by vegetation show the rate of pollutant removal to be affected by

wind velocity, canopy height, and light intensity, with the removal rate
linearly increasing with increase of pollutant concentration to a limit.
          The effects of the washout mechanism on power plant plume deple-
tion are documented mostly through the research of the Battelle group in
northwest Washington.  The washout process depends greatly on rain charac-
teristics such as the raindrop size distribution and the aerosol  collection
efficiency of the raindrops.  The S02 rainfall deposition pattern in the
region of the Centralia coal-fired plant based on rain collector  samplers
located on the ground along the cross-plume line clearly indicated a
scavenged "plume" of S02 on the sampling array (Dana et al.  1976).  The
field experiments concluded that sulfate concentrations in rainwater due
to the plume's presence do not appear to be significant at downwind dis-
tances less than 10  km; ammonium nitrate and soluble (ortho) phosphate ion
concentrations were  at or near normal background levels; and, the only
species measured which showed plume-related deposition patterns at all
distances where samples were collected (0.4-11 km) were S02 and hydrogen
          The Battelle group has also developed one of the few numerical
models for predicting precipitation scavenging of reactive pollutants from
power plant plumes (Dana et al. 1975, 1976).  The model can predict ground
level washout fluxes and average concentrations from precipitation as a
function of location beneath a plume.  Initial applications and comparisons
of the model predictions to field data indicated that the Scott and Hobbs
(1967) aqueous-phase dissolved ammonia oxidation mechanism for S02 is not
adequate to account for observed rates of sulfate formation.
          The rainout process is known to be a function of the nature of
the aerosol, its size distribution, concentration, wettability, activity
as a nuclei; cloud parameters such as the nature of the cloud itself, its
depth, temperature and water distributions, electrical activity and other
parameters.  Research into this mechanism, as it applies to power plant
plumes has been virtually non-existent due to the complexities involved
with data gathering.

                                  PART 3
                             COMPLEX TERRAIN

          In contrast to the previous section, which discussed various
aspects of atmospheric plume chemical transformations,  this section  deals
with the physical and conservative behavior of plume components,  i.e.,  with
conditions in which chemical transformations do not occur  (or are  ignored)
and in which the total mass of pollutant in the plume is treated as  remain-
ing unchanged over time.  Neither of these situations is truly representa-
tive of the behavior of actual S02 and NOX plumes from  power  plants,  although
both are often assumed to be sufficiently true to provide  acceptable  results
in short-term modeling calculations of pollutant concentrations from  power
plant stacks.
          Our ability to address directly questions of  pollutant disper-
sion* in complex terrain is a function of our understanding of the major
physical laws that govern airflow, turbulence and diffusion mechanisms
under differing meteorological and topographical conditions.  It  is,
therefore, appropriate to begin this evaluation of  the  state-of-the-art
of plume transport and diffusion in complicated terrain with  a review of
the current theories and observations based upon research  concerning  air-
flow, turbulence and diffusion phenomena in such topographical surround-
ings.  These subjects are discussed in Section VII, "Principles and
Observations."  Section VIII will describe the types of models available
to numerically simulate these phenomena.  The next  section (Section  IX)
will be a review of field work with regard to complex terrain situations;
studies concerned with the transport and diffusion  aspects of actual  stack
plumes or tracer material will be discussed in detail,  with emphasis  on the
program objectives, the methodologies of data sampling  utilized, model-to-
measurement comparisons associated with these field studies,  and  project  results
and conclusions.  Included within the field studies is  our own analysis of  c
* Dispersion in this review is defined as the combined result of transport and diffusion processes.

and az relationships in the Gaussian plume model over complex terrain as
derived from LAPPES and TVA power plant plume concentration data.  An over-
all matrix summary of these field studies concludes Section IX.  Finally,
Section X is an appraisal of current capabilities for calculating airflow
and diffusion based upon analysis of the field studies and modeling com-

                              Section VII

          For the purposes of this document, consideration of airflow in
complex terrain will include only studies of phenomena related to orographic
features, e.g., problems of up-slope and down-slope flow.  Other flows of
a  local nature which are not immediately relatable to differences in terrain
elevation (e.g., lake and sea breezes) will not be discussed in this report.
With  the exceptions of mountain  lee waves - only briefly touched upon in this
document - and flow channeling described subsequently in discussions of
field  studies, the conditions described are totally influenced by diurnal
effects.  Daytime solar heating  and nighttime radiational cooling generate
the driving  force for the mountain and valley flows.  Whether or not these
flows  establish themselves is largely dependent upon the gradient conditions
existing in  the synoptic flows.  Gradient conditions can either assist or
inhibit the  development of these local flows.
          Several investigators  have determined that a gradient wind speed
of approximately 6 m sec"  is necessary for the breakup of the nocturnal
drainage flow.  Kangos et al. (1969) have summarized much of the research
that  has been undertaken concerning the extent of mountain and valley winds.
Maximum velocities have been found at altitudes from 1/4 to 1/2 the ridge
height for upslope and downslope winds.  Smith  (1965) found that the depth
of the drainage flow for a ridge at Twentynine Palms, California, was at
least  80 m.  In the same study a dome of cold air was found to develop in
the valley to the west of the ridge as a result of drainage.

          Egami et al. (1974) conducted a study of plume dispersion near
the Mohave Generating Plant which is located in a river valley with ridges
extending to 1000-1300 meters above the valley floor.  Pibal measurements
of wind speed and direction were taken and the summary of results concen-
trated heavily on the mountain and valley wind patterns.  The up-valley
winds were of greater depth (4000 m) than the down-valley flow (500-1000 m).
The greater extent of the up-valley flow was attributed to daytime trans-
port of momentum from higher levels due to unstable conditions.
          Two wind systems have been noted by Tyson and Preston-Whyte (1972)
in Natal:  (1) mountain and valley winds occurring in the deep valleys and
(2) mountain-plain and plain-mountain winds occurring above ridge level and
above the influence of surface topography.  At the time of maximum solar
radiation the entire up-valley flow was as much as 1000-1250 m deep, with
the maximum wind speed of about 10 m sec~l at the 250-300 m level.  The
mountain-plain drainage wind was most fully developed at 2 hours before sun-
rise and became as deep as 1000 m.
          The thermal circulations in a small canyon located in the Wasatch
Range of northern Utah were studied by Thompson (1967).  The major events
of a typical night of radiational cooling were as follows:  (1) formation
of a thin film of cold air on the floor of the canyon and a short distance
up the canyon slopes; (2) rapid wind shift from up-canyon to down-canyon
wind; (3) rapidly increasing wind speed accompanying the continued cooling
followed by steady wind the remainder of the night; (4) cold core persisted
in the canyon as morning heating progressed and (5) rapid wind shift fror
down-canyon to up-canyon in the morning.  The major difference be^een rr,-,i
and conditions in other larger canyons is that the inversion and nocturnal
flow regime probably begin earlier and develop more rapidly in this .artic-
ular small  canyon.
          Kangos et al.  (1969) summarized work relating to air flows over
mountain peaks and ridges and the resulting production of lee waves.  The
following summarization  will  confine itself only to those cases where the
wind blows  perpendicular to a ridge.   In an attempt to classify motions

over a ridge, wave characteristics such as length and amplitude were found
to be important and on the basis of these, three categories were defined,
namely, laminar flow, small-wave flow, and large-wave flow.
          Small-wave flow is characterized by a wavelength less than or
equal to the width of the ridge and by moderate winds which increase with
height through a considerable depth.  Stabilities are not as great as for
large waves, where the wavelength exceeds the ridge width.  When stream-
lines become packed as air passes over the ridge, large waves are produced.
Rotor flow or hydraulic jump flow is usually present with large waves.
Jump flow is characterized by a marked temperature inversion at some level
above ridge height.  The waves form a single prominent peak in the vicinity
of the ridge.  Large wind speeds result in the subsequent trough, and then
the flow "jumps" to a higher level downstream with no further wave activity.
Such a situation is depicted in Figure 7d (Lester and Fingerhut 1974).
From energy conservation considerations the turbulence in this region must
therefore be great.
          In addition to wind speed, an important consideration in defining
air flow over ridges would be the stability of the atmosphere.  Those
slopes facing the sun would undergo heating and hence generate upflow winds.
Those slopes on the backside or receiving no sunshine could have forces act-
ing to generate down-slope flows.  The forcing equations for these up- or
down-slope conditions would then need to be superimposed upon the general
airflow (or synoptic flow) existing at the time.
          Thus a leeward-facing slope that was receiving direct sunshine
could tend to promote and enforce the rotary flow that might be generated
in the lee of a mountain.  Conversely, during the nighttime, or with a
shaded flow the forces generating a rotary circulation would tend to be
inhibited.  Studies at NCAR have shown that the extremely damaging winds
that occur in the Boulder area are a combination of down-slope and synoptic
flows reinforcing each other.

          In test releases of fluorescent particles (FP) upwind of a 300 m
                                               _1                  _]
ridge by Smith (1965),  airflows of 5 to 7 m sec   and 1  to 5 m sec   pro-
duced waves.  According to theory, wind speeds this light should be charac-
terized by flow that is displaced upward by the ridge and then returns to
its previous height behind the ridge without the oscillatory pattern of
well-developed lee waves.   Highest concentrations  of a plume should occur
well above the lee slope.   In the case of this particular ridge at Twenty-
nine Palms, California, the lee slope was still quite gentle and only
slight downward motions were required to bring the FP plume to the surface.
The change from drainage flow to wave flow occurred abruptly as stability
increased during the evening.
          Lester and Fingerhut (1974) investigated the lower turbulent
zone (LTZ), a highly turbulent region of near-neutral stability located
immediately to the lee of a range of mountains, between the ground and
the stable  layer in which wave motion occurs.  Aircraft flights measured
potential temperature,  horizontal velocity, and longitudinal gust velocity.
Cross-sections of wind speed and direction and potential temperature were
analyzed for a case of large amplitude lee waves and strong turbulence
over the plains just east of the Colorado Rockies.  The effect of the
passage of a weak cold front was noted.  The lee wavelength increased from
20 to 32 km, amplitude increased from 0.5 to 0.75  km, and there was an
increase in overall turbulence intensity.  It was  not possible to isolate
spatial changes in LTZ structure resulting from differences in upstream
terrain since synoptic changes masked these effects.  The LTZ extended
40 km downstream of the first lee wave trough.  Maximum turbulence was
associated with the updraft area just upstream of  the rotor (see Figures 7a
through 7c) and minimum turbulence was found in and near the troughs.  How-
ever, in another case a stronger and more rapidly  moving cold front had
the opposite effect (i.e., wavelength, amplitude,  depth of LTZ, and turbu-
lent levels were all  decreased).  In the hydraulic jump cases (see Figure 7d),

                                     0       1O      20      30      40      50     60       7O      80
                                          Isentropes     	^  Streamlines
                            Figure 7a.  A Schematic Cross Section of the Lower Turbulence Zone^LTZ) Based
                             On Six Case Studies, Showing  the Potential Temperature Field.  Evident Are
                               The Typically Weak Potential Temperature Gradient, and the Relatively
                               Strong Stability at the Top; The Low  Level Potential Temperature Minima
                              Are Interpreted as Evidence of Air Moving Upward From  the Surface Layers
                                                     In the Rotor Circulation,
 Figure 7c.  Distribution of Moderate or Greater Intensities of Turbulence Found
1                     Within the LTZ In the Wave Cases.
                                                             HI    Wind Speed Minimum
                                                                   Max. Wind Speed Gradients
                              Figure 7b.  Strong Vertical Shears and Large Longitudinal Speed Changes,
                              Especially In  the Vicinity of the Updrafts and the Rotor are Associated with
                                 The Wind Speed Maximum In the Stable Layer at the Top of the LTZ.
                10     20      30       40
                    Distance (km) from Ridge
                                                                                                               Figure 7d.  The Larger Dimensions of the LTZ and the Greater Extent of the Area
                                                                                                                      Of Severe Turbulence Distinguish the Streamline and Turbulence
                                                                                                                           Distribution of Hydraulic Jump Types from Wave Types.

severe turbulence was found over larger dimensions of the LTZ.  In this
study, the rotor circulations were deduced from examination of the streamline
patterns implied by aircraft Doppler wind measurements and cross-sectional
potential temperature distributions.
          Channeling of airflow by mountain and valley systems was studied
by Nappo (1975) as a portion of ETTEX (Eastern Tennessee Trajectory Experi-
ment).  Wind soundings were made simultaneously at five stations over a
mesoscale network to determine the topographic effects on airflow caused
by the Great Smoky Mountains, Cumberland Plateau, and the Tennessee Valley.
It was anticipated that channeling by the Tennessee Valley would be most
evident with stable night conditions.  However, pronounced up-valley turn-
ing of the wind in the lowest 700 m was noted for an unstable case, and
the channeling effect increased with lower altitudes.  In a stable case
slight up-valley channeling was noted even at approximately 1200 m above
the valley floor; between 600 and 700 m a sharp change in wind direction
was observed.  This was the transition from the free atmosphere to the
surface layer which was being influenced by the strong terrain effects.
The vertical wind profiles, highly localized, showed a linear shear layer
near the ground and smooth profile above, characteristic of stable con-
ditions.  Cross-valley and down-valley drainage winds were found in this
lower layer.  From limited analyses of the data, it was concluded that
during stable conditions, large scale topographic features always affect
the mesoscale flow, with the effects extending to elevations greater than
2000 m above the ground and to distances beyond 50 km.
          Potential flow theory, involving use of either the stream func-
tion or velocity potential, has been extremely useful in assessing theoret-
ical pollutant transport over mountainous terrain.  The major limitations
to this approach are the neglect of viscous effects and the inability to
include stratification effects.  Results of this type of modeling have
shown that for two-dimensional flow and in the absence of diffusive mixing,
ground-level concentrations resulting from an elevated point source are

the same over vertically differentiated terrain as over flat terrain.  The
plume is closer to the surface near the top of ridges but there is also
a decrease in the plume's vertical dimension (packing of streamlines) and
an increase in velocity over the ridge.  Streamline deformation is smaller
for flow over a "hemispherical hill" than over a ridge aligned normal to
the flow.  Thus, there is potentially greater impact of elevated plumes
on the two-dimensional hill.
          For stratified flow most theoretical work has centered on solu-
tions of the "mountain wave" equation in two dimensions.  For neutral
stability or for a narrow ridge, streamlines are symmetrical about the
crest and the perturbations decrease with height,  Egan (1975) has esti-
mated that the effect on the ground-level concentrations at the upwind side
of a ridge under such conditions would be similar to those produced  by
potential flow over a ridge.  Streamline crests tilt upwind for stably
stratified flow or for flow over broad ridges.  The closest approach of
a plume and the greatest velocity occur on the leeward slope.  A major
conclusion reached from this type of theoretical study is that streamlines
approach the surface more closely under stable conditions than under neu-
tral conditions.

          Since turbulence is partly caused by the roughness of the sur-
face over which air flows and since turbulence is the principal mechanism
which results in the dispersion of the pollutants from a power plant stack,
the dimensions of the plume, e.g., a  and cz, are frequently used to charac-
terize the effect of terrain on the plume.  Measurements of the degree of
turbulence have normally been taken by means of wind observations, using
bivanes to obtain both horizontal and vertical wind components or by use
of tetroons to follow a particular parcel of air.
          Kao et al.  (1974) utilized a network of 15 continuous wind record-
ing stations in the Salt Lake Valley to investigate typical wind patterns
and the topographical  effect on diffusion in valleys.  The general flow

patterns exhibited the expected diurnal  variation with drainage winds pre-
vailing in the early morning and evening and up-valley winds prevailing
in the afternoon.   Analysis of the data  found that the distributions of
the mean and turbulent motions in the valley were generally non-homogeneous
and non-stationary.   Maxima of both the  mean and turbulent kinetic energy
occurred in the late morning and again in the early to mid-afternoon.
Alternately, trajectories of marked air parcels released successively at
10 minute intervals were computed also by Kao et al.  (1974).  Air trajec-
tories of the center of mass of all marked particles  released in a 3-hour
period and the ensemble averages of the mean squares  of the north-south
and east-west components of the distance between particle trajectories for
every 3-hour time period were computed for analysis of mean transport and
turbulent diffusion, respectively.  The mean spread of the parcels was
generally greater in the afternoon than in the morning, and the east-west
component of the spread (along the narrow dimension of the valley) was
greater than for the north-south component.   Spread was greater during the
transitional evening hours than during early morning  stable conditions.
          Since cooling and the subsequent development of temperature inver-
sions in valleys causes drainage of air down the slopes, inversions can be
said to enhance turbulence in this situation.  Leahey and Halitsky (1973)
investigated turbulence at very low wind speeds at the Consolidated Edison
Nuclear Plant at Indian Point, New York, located in the Hudson Valley.
Wind fluctuation data were obtained from a bivane, and a turbulence clima-
tology for winds <_ 2 m s~* was derived.   The bivane observations were
taken on a 30.5 m tower which was approximately 500 m from the river.  The
Hudson valley at this location is about 5 km wide and mountains from 150
to 350 m high enclose the valley.  Diffusion was related to the turbulent wind
fluctuations by the method of Hay and Pasquill (1959).  Estimates were made
for a distance of 1100 m from a ground-level source for all wind directions
and thermal stratifications.  Investigation of the data showed no occurrence
of diffusion rates lower than those associated with the neutral (D) sta-
bility category.*  Turbulence levels in the down-valley and down-slope
* For definition, see Table 11.

flow increased as the intensity of the inversion increased, probably due
to the role of inversions in producing katabatic winds.
          Leahey and Rowe (1974) completed a bivane study of airflow over
a river bank near a coal-fired generating station in Alberta.  Vertical
distance from valley floor to rim was 52 m and the valley width was 1.5 km.
The bivane was on a 30 m tower located on the valley rim.  Data including
four tetroon trials, each with four tetroon flights, were collected in
situations ranging from very stable to near neutral.  Dispersion coeffi-
cients were calculated using the mean tetroon trajectory for each trial
and computing the root-mean-square of the lateral and vertical distances
between individual trajectories at several downwind positions.  The median
values of the horizontal diffusion coefficient were twice as large as the
expected flat terrain coefficient (Turner 1969) out to 3 km downwind, and
about equal beyond this distance.  The median values of the vertical dif-
fusion coefficient were about twice those of Turner; the increased vertical
diffusion was attributed to terrain influences.
           In another study in Alberta, over Copithorn Ridge, S02 measure-
ments were taken by helicopter by Leahey  (1974).  Copithorn Ridge is 99 m
high and is located 1.2 km downwind of a stack which had an emission
height of  69 m.  A comparison of a  and a  during neutral conditions with
the expected dimensions using a D category* indicated that the experimental
results were respectively 1.7 and 1.2 times  larger  than would  be anticipated
over flat  terrain, i.e., greater diffusion than  expected took  place.
           In the study of diffusion in a deep, steep-walled canyon  in Utah
(Start et al. 1973), three physical mechanisms were postulated to enhance
mechanical turbulence.  The first effect is the  downward transfer of momen-
tum into the canyons from the considerable turbulence generated around
rough mountain tops.  This effect is illustrated in Figure 8 where  the
downward transport of momentum is related to the cross-canyon  component
* For definition, see Table 11.

flow.  During conditions of strong temperature inversions, and with down-
ward momentum transport from the mountain tops minimal, downslope density
flows from side or feeder canyons may drain out into the main canyon and
may have enough momentum to reach the opposite main canyon slope.  They
may then rise in a form of overshoot.  Helical-like circulations may result
when these feeder canyon air drainage flows act in conjunction with down-
slope density flows along the main canyon wall (Figure 9).  The third tur-
bulence-enhancing mechanism is wake turbulence.  It is brought about
by flow over and around protruding cliffs, and across small, steep-
walled draws and indentations (see Figures Ida and lOb).   The wake
region downwind of these topographical features is characterized by a
region, called a cavity, of reduced wind speed and enhanced turbulence.
Wake turbulence is the smallest in scale of the three turbulence mech-

                                    GRADIENT  FLOW
Figure 8.  Schematic Illustration of Mountain Top Influences Upon the Gradient Level Flow Component and the
                           Downward Transporting of Gradient Flow Momentum.
                                        (from Start et al. 1973)
            Figure 9. Schematic Illustration of Circulations Triggered by Slope Density Flows and
                                Air Drainage from a Side Feeder Canyon.
                                          (from Start et al. 1973)


Figure lOa.  Schematic View of the Type of Terrain Capable of Affecting the Wake Turbulence.
This same terrain is depicted in Figure lOb with arrows added to show the type of secondary air
               flow caused by such protrusions into the primary flow of the canyon.
                                  (from Start et  al. 1973)

Figure lOb.  Schematic Illustration of Turbulent Wake Effects Caused by Obstacles Protruding Into
                           the Primary Flow Pattern.

          A portion of the ETTEX project (Eastern Tennessee Trajectory
Experiment) involved a study of the relative diffusion of tetroon pairs
during convective conditions (Hanna 1975).   Radar was used to track
tetroons within the afternoon mixing layer  between 500 and 1500 m above
the surface.   Instantaneous readings of tetroon range, elevation angle,
and azimuth angle were taken by the radar every two minutes.  Thirteen
relative dispersion experiments were conducted near mid-day for cases of
sunny or partly cloudy skies and light wind conditions.  Two tetroons
were released in each run; az values based  on the tetroon positions ranged
from 60 to 430 m at distances varying between 4 and 26 km downwind.  Con-
vective eddies caused considerable vertical motion from near the surface
to 2000 m.  The turbulence of the wind speed (aw) did not correlate with
the wind speed, which is typical of turbulence production due to convec-
tion.  Wind directions generally had a SW or NE component, which are
directions corresponding to the alignment of the ridges and valleys of
eastern Tennessee.
          Based on similarity theory, the predicted separation was three
times greater than the observed.  Part of this discrepancy may have been
caus.ed by the inability of tetroons to respond W rapid fluctuations of
air motion.  Statistical turbulence theory  is valid if both tetroons
remain within the same atmospheric layer; however, the large vertical
separations detected between individual balloons may render statistical
theory void for this application.  Other'types of experiments such as
the use of smoke puffs might give better results.  No discussion of the
specific effects of topography on the results of the tetroon runs was
contained in  the report, since the findings did not indicate an increase
in turbulence over the predicted values for flat terrain.
          Analysis by MacCready et al. (1974) of turbulence characteristics
of LO-LOCAT data (from the Lo-Low Altitude  Clear Air Turbulence Project)
which was conducted over a variety of terrain in the southwest U.S.
including high and low mountains showed that the turbulence spectra
obtained from the study fit the von Karman  spectrum formula rather well,

especially the -5/3 law at the small end of the spectrum.  For very stable
cases in complex terrain the minimum lateral turbulence observed was inde-
pendent of wind speed up to about 5 m sec   and then increased with wind
speed.  Values of the standard deviation of vertical wind speed (a ) were
generally 60-70 percent of the standard deviation of crosswind speed (a )
under stable and very stable conditions.  Standard deviations of horizontal
wind direction (aQ) were greater than "standard" a. values for the stability
                 D                                t)
classes as presented in AEC Safety Guide 23, at low wind speeds for all
stability classes.  The values for stable and very stable cases were always
much greater than would have been inferred by the standard method of relat-
ing turbulence to temperature stability classifications* which is applicable
for essentially flat terrain.
          MacCready et al. (1974) also devised a method for relating a
roughness terrain factor  (atr) obtained from U.S. Geological Survey
topographic maps, to estimates of horizontal turbulence  (a ).  A regres-
sion analysis was employed to determine a best fit curve relating turbu-
lence intensity to wind speed, height above the ground, and a. .  Results
showed that turbulence values were influenced strongly by a.  and only
very weakly by the former two variables.  However, there was  no effort
made to stratify the data according to location in complex terrain (i.e.,
in the lee of a mountain, valley, ridge top, etc.) or by the  type of
meteorological conditions.  It is also questionable whether the particular
terrain-turbulence relation derived in MacCready's study is applicable in
other areas of the U.S. in addition to the southwest.
          Most studies have indicated that complex terrain contributes to
alterations in air flow and to increased amounts of turbulent diffusion
compared to those for flat terrain.  Airborne concentration measurements
appear to be the best way to observe these effects; tetroon studies have
limitations in their usefulness in determining the degree of  turbulence.
Drainage flow and lee waves seem to be the flow characteristics most
responsible for increased turbulent effects.
 *  See Table 11 for category definition.

          Another method of air flow investigation has been laboratory
simulation, but this has proved difficult for estimating dispersion and
especially over irregular terrain.   This has been mainly due to the lack
of an ability to achieve similarity of Reynolds Number, Richardson
Number, Rayleigh Number, and other  nondimensional parameters (Snyder 1972).
Perhaps the largest difficulty to overcome in achieving similarity in these
numbers relates to the dual  nature  of turbulence.  For those classes of
studies for which mechanical turbulence is the dominant influence, labora-
tory simulation has proven to be extremely beneficial  and can be scaled
appropriately for similarity between the simulation and the real world.
For those classes of problems in which thermally induced turbulence is an
important factor (which includes almost all  classes of atmospheric disper-
sions) there does not appear to be  a satisfactory means of scaling the
problem for laboratory simulation.   Until  a  relationship can be obtained
for scaling thermally induced turbulence,  the use of laboratory simulation
for dispersion studies will  be a limited application.

                              Section VIII

          A large number of mathematical models, most but not all being
adaptations of a Gaussian distribution concept of plume dispersion com-
bined with a plume rise formula, have been used in concert with terrain
data to calculate plume dispersion under influences of elevated and com-
plex terrain.  We begin this section with a brief description of classical
Gaussian atmospheric dispersion estimates over flat terrain, and we then
discuss models which have been developed to date for calculating plume
dispersion from elevated point sources in complex terrain, with emphasis
on their assumptions and modifications to the standard Gaussian equations.
          Gaussian empirical formulas are derived from data obtained over
flat terrain, utilizing the various atmospheric stability categories.*
Turner's (1969) workbook adequately delineates the classical use of the
empirical formulas for flat terrain situations, as recommended by
Pasquill (1961) and advanced by Gifford (1961).  The typical Gaussian
coordinate system, containing both horizontal and vertical planes is shown
in Figure 11.  Equation 1 describes the concentration of gas or aerosols
at x, y, z from a continuous source with an effective emission height.
The basic assumption includes a Gaussian distribution in both horizontal
and vertical planes of plume spread with oy and az respectively representing
horizontal and vertical standard deviations of plume concentration
         **Note:  exp  - a/b = e ~a'  where  e  is  the  base  of  natural
                  logarithms and is approximately equal  to 2.7183.
 *  See Table 11 for class definitions.


    (0,  0, 0)
                                                                                        (*, -y,
                                                                                        (*, -y,  0)
Figure 11.  Coordinate System Showing Gaussian Distributions in the Horizontal and Vertical.

          x = concentration of effluent  (g m   )
          Q = emission rate of effluent  (g s~^)
          u~ = mean wind speed affecting  the plume  (m  s~^)
         a  = standard deviation of plume concentration  in  the
              horizontal  (m)
         az = standard deviation of plume concentration  in  the
              vertical (m)
          H = h  + Ah = effective plume  height (m)
         hs = physical stack height  (m)
         Ah = plume rise  (m)

          Several popular, similar, diffusion  categorization  schemes
have evolved, stating relationships between the  standard deviation  of
pollutant concentration as a function  of distance  and measured meteorological
parameters.  One of the first diffusion  categorization schemes, utilized
insolation, time of day,  wind speed and  cloud  cover to define stability
(see Table 11).                                '

Nighttime Conditions
speed Daytime insolation or >4/8 <3/8
(m s~l) Strong Moderate Slight cloudiness cloudiness
<2 A A-B
2-3 A-B B
3-5 B B-C
5-6 C C-D
>6 C D
A. Extremely unstable conditions.
B. Moderately unstable conditions.
C. Slightly unstable conditions.
D. Neutral conditions.*
E. Slightly stable conditions.
F. Moderately stable conditions.

* The neutral condition D, should
be assumed for overcast condi -
tions during day or night.

          The stability classification scheme as modified by Turner (1970)
and defined in Table 11 has been computerized and is readily available for
use on surface data.  This program is available through the NOAA National
Climatic Center in Asheville and is entitled STAR.   The STAR program uses
as input data the hourly or three-hourly data as collected at National
Weather Service or FAA observing stations and the longitude and latitude of
the observing station.
          Another stability categorization scheme developed by TVA (1970)
uses dispersion parameters for six stability classes each  representing one
of the following average potential temperature changes with height:

                Neutral                     0.00C/100m
                Slightly Stable             0.27C/100m
                Stable                      0.64C/100m
                Isothermal                  1.00C/100m
                Moderate Inversion          1.36C/100m
                Strong Inversion            1.73C/100m

This categorization only considers the stable cases  and is not intended for
use during unstable conditions.
          The NRC (formerly the AEC)  uses a stability classification based
upon both a temperature difference as exists close  to the  surface  and  a
wind direction standard deviation (oe) value as follows:

          Stability Class        AT (C/100m)         oe_
                 A                      <-1.9         25
                 B               -1.9 to -1.7         20
                 C               -1.7 to -1.5         15'
                 D               -1.5 to -0.5         10C
                 E               -0.5 to +1.5          5
                 F               +1.5 to +4.0          2.5
                 G                      >+4.0          1.7

          The present standard for estimating pollutant dispersion in the
atmosphere is the Gaussian plume equation.  The use of this equation implies
that the dimensions of the plume can be reasonably well defined as func-
tions of travel distance, and in terms of a a  and a  as defined in
Turner's Workbook (1970) or other curves, e.g., the TVA curves (TVA 1970),
obtained in previous studies.  We describe subsequently, in Section IX,
GEOMET's efforts to obtain a preliminary insight into the impacts of ter-
rain in degrading the performance of the conventional Gaussian plume dis-
persion model.  Since ground-level concentrations are often incorrectly
estimated by the model, it is of interest to know how much the use of
measured estimates of a  and a  improve the model agreement with measured
concentrations.  If significant improvement occurs, it is of interest, as
a second step, to investigate the extent to which variations of measured
o  and a  can be correlated with terrain features.  For this analysis we
needed airborne monitoring data describing plume concentrations from large
power plants in complex terrain.  We selected LAPPES and Kingston Plant
data because previous analyses had not addressed this data from the view-
point taken here, which is to examine whether terrain influenced dispersion
within the plume.  A description of our analyses, addressed toward this
end, is in Section IX.  Before presenting the GEOMET analysis we present
a review of model modifications by other investigators and review the
results by others of applying these models to available field data.
           The results of several concentration measurement programs per-
formed in complex terrain areas of both Eastern and Western United States,
have led to the development of modifications to the flat-terrain diffusion
model to account for the effects of terrain.  Several modifications, each
with differing assumptions of terrain modified wind flow and enhanced
diffusion are delineated in what follows.


          Diffusion calculations were made in the Southwest Energy Study

(Van der Hoven et al. 1972)  for five planned or existing power plants

located in areas of generally complex terrain (Mohave, Navajo, Four

Corners, San Juan, and Huntington Canyon)  with a Gaussian plume model

having the following terrain-related assumptions:

              For neutral  and unstable conditions, the plume center-
               line elevation above surrounding terrain was always
               equal to the  initial effective plume height.  Thus, the
               following standard Gaussian equation for ground-level
               concentrations beneath the  plume centerline was used:
                                      exp-J-%-^                      (2)

                    x = short-term concentration, (applicable for
                        periods of 10 minutes to about one hour)

               For stability classes* E and F, the plume was assumed to
               remain at a constant elevation above mean sea level and
               to impact upon surrounding terrain of equal or greater
               elevations.  In this case, the above equation is modified
               so that the numerator of the term in brackets is H-hj,
               where hy = terrain height above stack base (m).
               When the terrain height exceeds H, then H-hy is
               set to zero.

               For fumigation conditions, centerline concentrations
               were estimated by
                           Zf   /2TZT (CT  +2J)  zf                      0)


                   zf  =  H  -  hT.
 * See Table 11 for class definitions.


          Maximum concentrations resulting from vertical  fumigation
          through a layer from the  terrain to  the plume  center were
          assumed to apply as follows:  a critical distance, x, at
          which maximum  concentrations caused  by_fumigation should
          be  considered,  was determined by X.T  = u t  4 where

                           fpp 9Z \,      vMh-h-i
                              r     \l AU U_M      I  i  I.  1                Ml1

                ^- =  change of  potential temperature with
                az    height (C m-1)
                Cp =  specific heat of air  at constant  pressure
                      (ergs g-1  C-1)
                tm =  time required for the inversion to rise from
                      the top of the stack  to the plume center (s)
                 p =  ambient air density (g nf )
                 R =  net rate of sensible  heating of an air column
                      by solar radiation  (ergs s-' cm-2)
           and the rest of the  symbols are as defined  for Equation (1)

           The following equation was applied for limited mixing
           conditions  when the  pollutant is uniformly  mixed in  the
           vertical and the receptor is below the plume centerline:
                    is the mixing depth of constant height  above the
                    terrain  in meters.
* The form of equations 3 and 4 differs somewhat from the equations presented in D. B. Turner's Workbook
  for Atmospheric Dispersion Estimates for fumigation conditions. Equations 3 and 4 assumed fumigation
  conditions between ground and plume centerline, while the Workbook assumes the mixing layer to be
  between the ground and the plume top (where the top is defined as 2<7Z above plume centerline). As a
  result,  centerline concentrations under fumigation conditions as estimated in the Southwest Energy Study
  are greater, by a. factor of 1 + 2
               Long-term concentrations  (monthly,  seasonal  or  annual
               time  periods)  are  represented  by  two  equations:
                              u  0xa
                                           (hs +  Ah-hj)
                   f  =  relative  frequency with which winds  blow in
                        a  given wind  sector
                   e'=  angular width of sector (radians),

               for limited mixing conditions.

          Equations (5)  and (6)  were used (Martin and Tikvart 1968)  with
average mixing heights,  frequency distributions  of wind speed and direction
by stability class (generated by the "STAR"  program), average terrain
height profiles in each  of eight sectors  from  the plants and assumed
average plant loads of about 80  to 85 percent  to calculate annual concen-
trations at various locations near each  of the five plants.
          Output of this model for short-term  concentration calculations
under stable conditions, with the associated terrain impaction assumption,
has been compared with observed  concentrations (both tracers and $02)
more often, and for more different elevated sources in complex terrain (at
least five), than has been the case with any other model.  However,  the
comparisons in all cases have been limited to  results for only a few days
(< 10) at each site; further, little or no validation of the fumigation
or limited mixing models has been attempted.

           The consensus  is that the NOAA model  representation is  an over-
 simplification of the complicated wind  field-terrain  interaction,  and  of the
 important terrain parameters such as the slope  of the terrain and the
 width  of raised terrain  barriers in the plume path.
           The Office of  Air Quality Planning and Standards (OAQPS) of  the
 U.S.  Environmental  Protection Agency has used two variations of the
 conventional  Gaussian model for the evaluation  of air quality in  complex
 terrain  (Mears 1975). The CRSTER model uses equations very similar to
 those  presented above for the standard  and limited mixing conditions in
 the NOAA model.  The terrain adjustment procedure is  the same except that
 it is  applied for all stability conditions.*  The stability class, wind
 speed  and direction, and mixing depth can be determined through subprograms
 from standard U.S.  Weather Service surface and  upper air (radiosonde)  data;
 these  processed data can then be input  to the model  with effective plume
 height data to obtain hourly concentration values for selected receptor
 points which  are then arithmetically averaged to obtain average values
 which  correspond to the  time scales of  the various air quality standards
 (i.e., 3-hour, 24-hour,  annual average).  Although this model has been
 extensively used to evaluate the air quality impact of a number of power
 plants in complex terrain, only limited comparisons  with measured concen-
 trations have been published.
           The second of  OAQPS's complex terrain models is called  "VALLEY"
 and is used for a worst case 24-hour average prediction of plume  impact
 for cases where the plume centerline is below the elevation of receptors
 located on nearby terrain.  It also utilizes a Gaussian formula very
 similar to that of the NOAA model for stable conditions (i.e., with the
 same basic terrain adjustment formula)  with the following differences:

           t    The height of the plume  centerline above the ground  is
                decreased by the elevation of the ground above the base
                of the stack.
* See Table 11 for stability definitions.


               The effluent is uniformly distributed in the
                horizontal over a 22.5 sector for estimates of
                crosswind dispersion.

               The plume center!ine is never less than 10 meters
                from the ground.

               The wind direction is  within a given 22.5 sector
                for 6 hours out of 24.

              Constant 2.5 m/s winds  and E stability class are
               assumed throughout the  24-hour period.


           Environmental  Research and  Technology,  Inc.  (Egan 1975)  has

developed a modified Gaussian model  for application to  point sources in

complex terrain, for neutral, unstable and stable  conditions with assump-

tions as follows:

           9    For receptors located  on terrain above  the
                effective plume height, the model  assumes  the
                plume to remain at a distance generally taken
                to be one-half of the  effective plume height
                over flat terrain away from the surface, for
                neutral and unstable conditions.

               For stable conditions  the plume is assumed to
                pass around the side of a hill  rather than
                over it.

There is no evidence of validation of  this model  in the literature.

          Egan (1975) has made further modifications to the Gaussian model

based on results of laboratory analyses of flow oast a  cylinder and sphere

for neutral conditions.  The modified  ground-level centerline plume equation,

including reflection at the surface, is
x = 	*i	exp

      D  , DZ = Coefficients used to modify the ay and az values due
       ^       to the effects of complex terrain,  (i.e., Dy and Dz would
               equal one for flat terrain)
           C = (3^/9H)/(9i}i/3z), the ratio of the vertical gradient of the
               stream function at the effective stack height to the
               gradient at the plume centerline over the surface (dimen-
               sionless).  The ratio reduces to one for flat terrain.
           n = (z - z )/H, where z  (m) is the local height of the plume,
               z  (m) is the local height of the terrain, and H(m)
               is the effective height of the stack.  This ratio reduces
               to one for flat terrain.
           This model constitutes a departure from the conventional
Gaussian formula  in  that  it  (1) accounts for the alteration of flow
fields by complex terrain  (through introduction of the parameter "c"),
and  (2) allows a  conceptual  separation of the effects of complex terrain
on the flow field and turbulent diffusivities.  Unfortunately, these
changes require estimates  (either from a flow-model or from measurement
studies) of the relative  height above the surface of the plume centerline
(a function of terrain),  and the streamline spacing in the vicinity of
the  plume in order to be  applied effectively.  This requires a more extensive
meteorological data  base  (at least with respect to spatial resolution) than
is normally available for  estimating diffusion in complex terrain with the
standard Gaussian models.
          MacCready et al. (1974)  have developed an interesting model
in which they have used classical  turbulence-diffusion theory together
with turbulence spectra determined from the Air Force - Boeing LO-LOCAT
program conducted in areas of mountainous terrain of the southwest to
develop a modified Gaussian model  for use in complex terrain.

          The relationship between turbulence  and diffusion is developed
starting with Pasquill's (1974) theoretical  equation describing  expanding
crosswind dispersion of a puff in an  isotropic homogeneous environment, given by
y2 = v'2t2/ F
                                       sin Trnt/3
                             0        S-

                                                     dn                      (9)
      a   is the  crosswind dispersion coefficient (m)
       V is the  turbulent velocity in the direction crosswind to  the
             mean wind  direction with the averaging referring to an
             infinite ensemble average (m s~l)
        t is the  time of travel (s)
        3 is the  Lagrangian* correlation coefficient (dimensionless),  and
 Fe(n) dn is the  Eulerian** power spectral density in the frequency  width dn.

The  averaging  refers to an  infinite ensemble average, and material is
released  at time t = 0.  MacCready et al.  (1974) states  that Taylor's
hypothesis  which converts temporal to spatial frequency, together with
empirical  estimates of  e and  the  von  Karman turbulence spectra  (which
the  LO-LOCAT data were  shown  to represent well) were then used  to arrive
at the  formulas

                               ay2  = 0.44 avU                             (10)

                               az2  = 0.44 awLt                             (11)

           L is the Eulerian longitudinal  length scale  (m)
  a   and a  are  Eulerian  lateral  and  vertical components of turbulence,
                 respectively  (m s"').
 *  The concentration statistics are described in terms of the statistical properties
   of the displacements of groups of particles released in a. fluid.

 ** Statistics are formulated in terms of the statistical properties of the velocities measured
   at fixed points in the fluid.

Substitution of (10) .and (11) into the basic Gaussian formula gives

                         X/Q =

for centerline concentrations, for stack height = 0 and continuous emissions,
          The above equation was deemed to be applicable for one hour
concentration averages, and does not take into account ground reflection
or vertical shear.  Regarding the latter, the authors suggest use of a
a     rather than a  given by
                         a      =0.07  u + 1.2a
       a    is  the  measured  lateral  turbulence  (m s~  ).

           The validity  of  this  assumption has not been tested; the authors
 suggest  confirmation  from  additional  turbulence data when they become
 available.  The principal  drawbacks of  this approach are:

                Turbulence statistics ay and  aw and the  length
                scale L must  either be  measured at  the site for
                which concentration estimates are desired (at
                a point of sufficient height  to be  at least
                midway  between  the ground and effective  stack
                height) or estimated  from other data.
                It has  not been successfully  validated.

           The authors have suggested  a  method whereby av can be  estimated
 from a terrain roughness factor O^R, which is found by spectrum  analysis
 of terrain height values in the vicinity of the source in question.  Once

 otR  is  known,  the  relationship between av and otR derived from LO-LOCAT
 data can  be  used to derive av.  The following objective method is sug-
 gested  for determining atR:

           (1)   On  a 1:250,000 USGS map plot four symmetrical  lines  of
                45  nautical mile length in a tic-tac-toe pattern  around
                the site  of interest, with the middle of each  line coming
                to  10 miles from the center point,
           (2)   Take height readings at 0.5 mile intervals for each  line,
           (3)   For each  7.5 mile segment on a line calculate  the root-
                mean-square about the mean height (call it 07.5). and
           (4)   Find the  average of all the a7 5 for all segments on all
                lines, and multiply by 2.3 to give atR.

 This method  was derived  by taking root-mean-square values for segments of
 various lengths for the  legs of various LO-LOCAT flights over rough
 terrain,  and seeing what segment length appeared to work best and what
 multiplication factor gave the best fit.
          Supporting the validity of this objective method is the fact
 that the  data  on which it is based (LO-LOCAT) are extensive,  consisting
 of 8,800  turbulent spectra determined for complex terrain of  varying
 degrees (i.e.,  high mountains, low mountains) and in different geographic
 areas (California, Colorado, New York).  The spectra were also determined
 for  all seasons  and times of day.  The chief drawbacks are that  (1) the
 spectra are  representative of only two altitudes, 76 m and 229 m above
 ground;  (2)  the relationship between ay and atR show a large  degree of
 scatter,  and (3) aw must be inferred from av based on the correlation
 between the  two.
          INTERA Environmental  Consultants  (Hoffnagle et  al.  1975)  have
recently developed  a combined  potential flow-turbulent  diffusion  model
for use over  complex terrain.   The model  consists of  the  modified Navier-Stokes

equations with some basic assumptions.   These assumptions are that pressure
changes do not affect density; density  changes have a negligible  effect  on
viscous terms of the equations; turbulent effects  are expressed  in terms  of
eddy viscosity (vy); and density can be presented  as a function  of position.
Turbulence is expressed in terms of the pressure equation as:
                 V2p =

%   dt
8  /  dw\
az fpdt}
                          ^T v^vu  + ^7 v^vv +  37 VMVW
where the first bracketed term represents the inertial  sources  and  the  second
bracketed term represents the viscous sources (a complex tensor function  of
the flow field).
          As far as the boundary conditions are concerned,  the'  z direction
is bounded by the ground surface with variable elevation, and by the top
of the turbulent boundary layer.  It is assumed that
                  u = f (y,z) (known)
                      v = w = 0
                 at x = 0
 The y  boundaries  and  the  top  of the turbulent boundary layer are assumed
 to be  frictionless, and u  = v = w = o at the ground.  A vertical pressure
 gradient is  specified at  the  outflow face.  Viscosity is calculated from
 the measurement of shear  stress at the top of the turbulent boundary layer.
 For the  detailed  equations, the reader is referred to "Evaluation of Selected
 Air Pollution  Dispersion  Models Applicable to Complex Terrain"  (INTERA
           The  INTERA  model computes a terrain induced wind field which is
 then used in the  diffusion equation solution, thus avoiding the parallel
 or horizontal  flow assumptions made in the NOAA and EPA Gaussian models.
 This model has  been rather extensively compared with observed concentrations

of either S02 or tracer resulting from elevated point source releases at
several  different sites in complex terrain,  where power plants or smelters
currently exist (i.e.,  Navajo Generating Station, Garfield Smelter), or have
been proposed (Kaiparowits Power Plant).  The results of these comparisons
are described in Section IX, for the respective study sites.  The limitations
in the use of the INTERA model  are that the  model, as it currently exists,
prevents the formation  of recirculating flow in the lee of an obstacle (i.e.,
flows as depicted in Figure 7d) and that the elimination of consideration of
the energy balance equation prevents calculation of natural convective flows
such as mountain/valley flows and lake and sea breezes.
          The TVA model (Montgomery et al. 1973) is actually a set of
Gaussian calculational  techniques very similar to the NOAA model, with
each technique being appropriate to a different meteorological condition.
It is not specifically  designed for application in complex terrain situ-
ations.  The model differs from the other standard Gaussian models (EPA
"VALLEY," NOAA) in that the diffusion coefficients used (a  and o ) are
not the same as the standard coefficients (Turner 1969), and were
essentially derived from observations of power plant plumes.
          The diffusion coefficients obtained were primarily derived for
the stable atmospheric  conditions of limited mixing and inversion breakup.
It is interesting to note that one recent study (Dames and Moore 1976)
compared the NOAA and TVA coefficients using Denver, Colorado data.  The
NOAA model identified inversion breakup as a potential problem in meeting
Colorado standards and  showed limited mixing as being no problem.  Using
the TVA approach, just  the opposite was found, i.e., limited mixing was
the problem and inversion breakup was not.

                               Section IX
                             FIELD STUDIES

          Field studies concerned with the physical behavior (i.e., transport
and/or diffusion) of actual stack plumes or tracer material in complex ter-
rain will be discussed in this section.  Many of the 12 study locations dis-
cussed deal with tracer releases and not with actual effluents.   The text
will first describe some of the early fluorescent particle (FP)  diffusion
trials in complex terrain (McMullen and Perkins 1963, Hinds 1970), and
discuss the turbulence measurements near the Dickerson Power Plant in
Maryland (Weil 1974).  Programs at the Naughton Plant (Spangler et al.
1973), the Four Corners Plant (Niemann 1973, Smith and Anderson  1974),
the Navajo Plant (Hovind et al. 1973b, NAWC 1974, Rockwell, MRI  and SAI
1975), the Huntington Canyon (Hovind et al. 1973a, c, 1974, Start et al.
1973, 1975), the Garfield Smelter (Start et al. 1974) and Kaiparowits
(NAWC 1974) are presented next, followed by descriptions and GEOMET
analyses of LAPPES program data (Schiermeier 1970, 1972) and data from
the TVA Kingston Plant.
          Some of the earliest FP diffusion trials conducted in  complex
terrain involved four instantaneous elevated line source releases over
mountainous terrain near Dugway, Utah (McMullen and Perkins 1963).  The
site chosen for the trials provided successively, in a west to east
direction, a large flat area at an elevation of approximately 1300 m MSL,
a ridge rising to 2000 m MSL, followed by a broad valley.  Elevated line
source releases were carried out from 305 to 670 m. above the terrain.
The objective of the trials was to determine the degree to which an FP

 tracer cloud disseminated above a  ground  inversion enters into the drain-
 age wind system characteristic of  nighttime  flow in a canyon-like complex
 terrain environment.  The orientations  of all  of the elevated cross-wind
 line releases were approximately perpendicular to the main north-south
 ridge of the mountain system (see  Figure  12).   Three of the four trials
 were characterized by moderate to  strong  low level  inversions, while high
 winds prevented well-established drainage conditions during the other trial
 The wind direction was predominantly  south-southeast during each of the
 trials, and thus lent similarity to the roughness fetches in each case.
                                          Line Source Plume
              Figure 12,  Configuration of Elevated Line Source Releases with
                 Respect to Wind Direction and Orientation of Mountain
                           System Near Dugway, Utah.
          Larger  amounts  of tracer particles were recovered  by  Rotorod
samplers at ground  level  over  the  rough terrain than over the flat  terrain,
thereby indicating  enhanced rates  of mixing in the irregular terrain.  This
was further substantiated by observing that over rough terrain  FP was  recov-
ered much closer  to the source.  McMullen and Perkins suggest that  two sep-
arate diffusion regimes contributed to the total tracer recoveries:   direct
diffusion from the  main cloud  as  it passed overhead, and diffusion  within
the drainage flow.  The drainage  transport would lag in time the detection

of the initial pjume.  A sampler would first detect the passage of the main
plume as it went overhead; then, at some later time, the flows that were coming
out of the canyons which had accumulated some FP material  would start to
show up on the sampler as their drainage flows would pass  over the sampler.
The percentage of FP material recovery was determined by first knowing
the mean efficiency of the Rotorod samplers for the FP material used;
then calculating the effective flow rate and dividing this flow rate into
the reported recovery, thus giving the corresponding dosage.  Direct dif-
fusion was estimated to account for 85 percent of the recovery for non-
canyon samples, however, drainage transport was estimated to account for
as much as 50 percent of the recovery at samples within the canyon.  The
plume was definitely ill-defined, as there was no systematic variation in
the total recovery with sampler location in the canyon.
          McMullen and Perkins found that terrain-induced mechanical
turbulence was sufficient to give significant FP recoveries at the surface
in all trials both in the lateral canyons and over the open sampling area,
despite low-level stability.  They also found that vertical mixing is
much more rapid over complex terrain than for an equal distance of travel
over flat terrain.  The authors suggest that the second conclusion would
probably not be true for FP particles released with the flow perpendicular
to the ridges instead of parallel to them.
          Hinds (1970) reported on a series of 113 diffusion tests over
the mountainous terrain in the southern portion of Vandenberg Air Force
Base in Southern California.  The releases were from ground-level point
sources and consisted of 15-30 minute releases of zinc sulfide.  Elevations
in the area varied from 30-500 m AMSL.  A comparison of diffusion over
mountainous terrain and flat terrain in the same maritime climate showed
that daytime unstable conditions minimized the importance of terrain,
whereas nighttime stable conditions especially in winter led to apparently
significant interactions between terrain-induced drainage flow and
synoptic-scale onshore gradient flow in the complex terrain.   Figure 13,

from the Hinds  study,  shows this comparison.  The  solid line represents
moderately unstable  conditions (Stability B)  as  suggested by Pasquill  (1962)
                             Night tests
                             Doy tests
                                    * * I 
                                Distance, m
              Figure 13,  Vertical Plume Dimensions (oz) Inferred from Cross
                Width (
The variables chosen were travel time, standard deviation of wind direction
(a0), temperature lapse rate, and wind speed.  Downwind travel time was
found to be a relatively good predictor, but ae was the poorest indicator
of dispersion.  The lack of dependence on OQ was attributed to the non-
homogeneity of the flow field in complex terrain.  Impingement of the
plume was probably great on the ridges, as the canyon exposures were
typically only half the concentrations found on the ridge tops.
          Increased turbulence due to rough terrain was clearly demon-
strated at the Dickerson Power Plant along the Potomac River in Maryland.
The study for the Maryland Power Plant Siting Program (Weil 1974) involved
comparison of stability classes from Dulles Airport, which is located on
flat terrain, and from the Dickerson site in moderately rough terrain,
30 km distant.  The terrain in the vicinity of the Dickerson plant is
characterized by generally rolling terrain but with mountains located
8 km west of the plant (Catoctin Mountains) with elevations above the
plant stack top and which could equal or exceed the effective plume
height on occasion.  The stack base is situated approximately 90 m above
MSL.  The topography rises to approximately 65 m above the stack top at
10-15 km to the east of the plant.  One hundred twenty-eight crosswind
traverses were made with a mobile van during which the S02 plume from the
Dickerson Plant was encountered.  Sampling from the van was supplemented
by pibal releases during the sampling period, by temperature and wind
profiles measured two or three times a day with radiosondes and instru-
mented aircraft, and by wind and lateral turbulence measurements at two
levels (10 and 100 meters) on an instrumented tower near the plant.
          Stability classes based on Dulles data were computed every
3 hours for June 1973, and for each such stability class the standard
deviation of the fluctuation of horizontal wind direction (ae) was com-
puted from lower and upper (10 m and 100 m) tower winds at Dickerson for
three 10-minute periods centered around the Dulles reading.  Wind direction
observations were taken every 10 seconds at the Dickerson tower.  A

classification system was developed (Slade 1960) with a ae value of 25
assumed to be equivalent to the A stability class and with oe values
ranging down to 2.5 for F stability.   This system was then applied to
both the 10 m and 100 m levels.  For the 10 m level the median stability
class using Dickerson data for each 30-minute period were tabulated against
the stability class using Dulles data.   Low-level turbulence was greater at
Dickerson than at Dulles, as the medians for Dickerson were more often
less stable than the respective stability classes for Dulles.  However,
the Dickerson 100 m level tended to be  more stable than Dulles.  This was
to be expected since Dulles represents  low-level turbulence over flat
land.  The Dickerson topography caused  extra low-level turbulence, but
this mechanical turbulence was dissipated by the time it reached 100 m.
          Using the standard Gaussian formula without terrain adjustment
(i.e., assuming the plume remains at a  height equal to the Initial effective
stack height over complex terrain), and with the assumption that stability
classes determined from weather observations at nearby Dulles Airport are
applicable in the area of the plant, calculated concentrations stated by
the authors to under-estimate 128 measured five minute ground level S02
center!ine concentrations by as much as two orders of magnitude.  The
model was then rerun using the assumptions that (1)  the plume remained at
a constant height above MSL regardless  of location (this was applied for
all stability classes, as for the EPA single-source CRSTER model), and
(2)  the presence of rougher terrain effectively shifted  the stability class
by one class toward more unstable conditions.  The modification resulted
in an improved relationship between calculated and measured values, the
former being within a factor of two of  the latter most of the time.
          North American Weather Consultants (Spangler et al. 1973) con-
ducted a six-day plume tracking experiment in the vicinity of the Naughton
Plant (owned by Utah Power and Light)  near Kemmerer, Wyoming, under "a
variety" of meteorological conditions.   Their initial draft summary report
pertained mainly to results obtained during one day (March 25, 1973), on
which an extremely stable air mass dominated the area, and the wind was

blowing towards the three surface S02 monitors.  The study had three
objectives:  (1) to measure the initial plume dilution during the momentum-
dominated phase of plume rise, (2) to measure the magnitude of the plume
centerline concentration downwind, and (3) to relate plume measurements
to ground concentration measurements from three existing monitoring
stations.  Along with S02 measurements, aerial temperature profiles were
taken; one just upwind of the Naughton Plant and the other 4,8 km down-
wind.  Surface wind observations were made at the three SC^ monitoring sites,
and two pibals were launched at mid-morning on March 25,  The temperature
profiles showed the very strong inversion in the lowest 470 m, and the winds
at the plume level were 4,8 m/s and 4,6 m/s from the west for the two
pibals launched.  This led the researchers to classify the morning as a
class F stability case.
          In trying to discover the amount of initial plume dilution after
the momentum-dominated phase of plume rise, a helicopter penetration into
the plume, in an upwind direction (toward the stacks) done at various
angles and altitudes, was used.  The results indicate that the calculated
concentration directly above the stack centerline was higher than the
measured values.  Out of 8 dilution factors calculated from measurements
on various days, 5 were in the 45-50 range, with the full range being
23-60.  No pattern of dilution factor versus stability condition was
immediately obvious.  On the morning of March 25 (the extremely stable case),
the initial stack concentration was calculated to be 211 ppm S02-  Initial
dilution after the momentum-dominated phase of plume rise was measured at
4.90 ppm at the plume centerline.  In this case, the reduction factor was 43.
          The second objective of the study was to determine the plume
centerline concentration downwind.  The centerline of the plume was
located and measured with the helicopter by flying -downwind and "wagging"
(side to side)  and "porpoising" (up and down) to stay on the centerline
of the plume.   The centerline S02 concentration results obtained during
the March 25 case are presented below.   At 4.8 km and 24.1 km downwind of
the plant, cross-wind traverses were flown at incremental altitudes.  At
4.8 km the range of the maximum concentration at the different levels

ranged from 0.08 ppm at 2300 m MSL to  1.06  ppm  at  2450  m MSL  to 0.07 ppm
at 2600 m MSL.  At 24.1 km the range was from 0.11  ppm  at 2350  m MSL to
0.59 ppm at 2450 m MSL to 0.07 ppm at  2500  m MSL.*  No  traverses were made
below 2350 m MSL or above 2500 m MSL 24.1 km downwind of the  plant.   A
"porpoising" maneuver between 2400 m MSL and 2550 m MSL 14.5  km downwind
from the plant gave a range of S02 concentrations of 0.05 ppm at 2400 m MSL
to 0.78 ppm at 2450 m MSL to 0.06 ppm  at 2550 m MSL.  These measured
results were compared with the SOp concentrations predicted by  the
Gaussian distributions used in the NOAA model (Turner 1969).
          The comparisons were for one day  during which the area was under
the influence of a high pressure system, with accompanying very stable
lapse rate conditions.  Further, the comparison was made only for measured
values obtained in the plume at distances out to about  20 km  east of the
plant, where terrain features are much less rugged  than the mountainous
areas to the west of the plant.  The results of the comparison  were  simi-
lar to those obtained under similar stability conditions at the Four
Corners and Navajo Plants, specifically, greater model  overestimation of
concentrations occurred at distances close  to the plant than  at greater
distances.  The NOAA model S0 centerline concentrations were greater
than 7 times those observed at distances within 2  km of the Naughton plant,
but were within a factor of 2 at distances  beyond  7 km.  As for the  compari-
sons made at the Four Corners and Navajo plants, the failure  of the  model
to adequately take into account the initial dilution (a factor  probably not
related to surrounding terrain) was also the cause  of the model-to-measure-
ment discrepancies close to the plant.                                    _
          The third objective of the study  was  to relate plume  measure-
ments to ground concentration measurements  from three existing  air quality
monitoring stations located at about 2100 m MSL.   Data  from the ground con-
centration measurements at the three existing air quality monitoring stations
were only reported for the very stable case on  March 25, 1973.   The  plume
was observed to clear all terrain by a minimum  of 120 m.   No  significant
  The plant elevation, not given in the report, is about 2100 m MSL.

concentrations were recorded in the morning, but after destabilization of
the lower atmosphere up to the height of the plume at 1045 MST (marked by a
sudden decrease in elevated centerline concentrations), concentrations
slightly above the background concentrations were recorded.   The maximum
concentrations before 1045 MST were 0.015 ppm at 0900 and 1000 MST.   The
maximum afterwards was 0.046 ppm at 1800 MST.  While the S02 concentrations
measured after 1045 MST were higher than the background levels, they were
still considered to be low.
          All three surface SOo monitors were east or northeast of the
plant; no surface samplers were located in the more mountainous terrain
to the west of the plant where plume impingement on elevated terrain might
be more likely to occur.  It is not known whether any airborne sampling
was conducted in the latter area; if it was, results were not discussed
in the initial summary report.  Owing to the limited nature of the surface
sampling network, as well as the short time period characterizing the
study as a whole, any conclusions which could be made from the data would
be of limited significance with regard to the effect of complex terrain
on the behavior of the Naughton plume.
          Plume tracking studies covering somewhat similar time periods
(less than one week) were conducted 1n the vicinity of the New Mexico Four
Corners Power Plant by North American Weather Consultants (Niemann 1973)
and Meteorology Research, Inc. (Smith and Anderson 1974).  Both of the
studies Involved airborne sampling of pollutants (S02 1n the first case
and both S02 and NOX in the latter case).
          The objective of the MRI study was to test certain factors in
the NOAA Model.  These factors were:  (1) The possible effects of buoyancy
and exit velocity on the initial plume dilution, and (2) The subsequent
rate of plume growth downwind.  The objectives of the NAWC study were to
measure:  (1) the initial dilution factor in the initial momentum-dominated
phase, (2) the plume centerline concentration, (3) plume geometry, (4) the
crosswind concentration distribution downwind, and (5) the dissipation due
to turbulence over flat and complex terrain.

          Three days were selected as test cases by MRI:  February  17,  18,
and 19, 1974.*  Terrain downwind of the Four Corners Plant for  the  Febru-
ary 19 case was not exceedingly rough, but the important features included
a drop of 122 m in terrain within the first 1.6 km of the plant site, with
several subsequent rises at various buttes within 16.1  km.  Turbulence
dissipation measurements were taken for each case by a  "Universal Indicated
Turbulence System" aboard the aircraft.  Greater dilution rates were observed
for February 17 and 18 than for February 19.
          Considerable variation existed from one day to the next,  depend-
ing on the particular roughness fetch, without any change in stability
category as given by the temperature lapse rate.  On February 17, concen-
trations remained lower than predicted throughout the entire observed
plume travel (29 km), indicating enhanced dilution.  Smith and  Anderson
considered turbulence measurements necessary in accurately estimating
plume diffusion, particularly when the layer containing the plume is not
connected to the surface layers by turbulent mechanisms (i.e.,  the  plume
was above the low-level drainage flow).  They concluded that significant
differences in plume dimension and dilution could occur without any major
change in the stability category as a result of turbulence variations at
the plume level.
"    Comparisons of normalized plume center!ine concentrations of S02
(i.e., Xu/Q values) obtained aloft from airborne plume  tracking observations
under stable (E and F) conditions were made to those calculated using the
NOAA model.  For E stability, the model calculated values were  greater than
the observed values at a distance of 1 km downwind by a factor  of about 5
on February 17, 1974, and by a factor of 15 on February 15, 1974 and
February 19, 1974.  For the F category, model calculated values for 1 km
downwind were greater than observed by a factor of about 7 on February 17,
1974, and a factor of about 30 on February 15, 1974 and February 19, 1974.
At distances approaching 12 km downwind the measured values approached the
model  predictions to a very close degree; within a factor of 2  for  the
E category and within a factor of 3 for the F category  in all cases.
* Data were collected on a total of five days - February 15, 17, 18, 19, and 20, 1974.

          Niemann (1973) has compared instantaneous S02 plume center!ine
concentrations observed aloft for the Four Corners Plant under neutral  and
stable conditions to corresponding values calculated from the conventional
Gaussian formula for flat terrain and from the stable version of the NOAA
model, respectively.  He found that both models overestimated the measured
concentrations close to the plant by a factor of  10  (i.e., under both
neutral and stable conditions), while at distances greater than 15 km the
conventional Gaussian calculations generally agreed with observed values
while the NOAA model overpredicted center!ine concentrations by a factor
of two under stable conditions.
          These results agree at least qualitatively with the comparisons
made by Smith and Anderson (1974), in that the Gaussian models show greater
overestimation near the plant, while being within a factor of two at
greater distances.  In both works (by Niemann, and by Smith and Anderson)
the authors attribute the initial overestimation to enhanced initial
dilution from plume momentum and buoyancy.  In one of the three stable
cases examined by Smith and Anderson, and in the two cases examined by
Niemann, the observed centerline concentrations at larger downwind dis-
tances remained less than the model values, by factors ranging from 2 to 5.
Niemann suggested that this was a result of increased horizontal plume
meander and oscillation, and vertical undulation over the complex terrain
in the vicinity of the Four Corners Plant.  Smith and Anderson have
suggested that observed differences in turbulence dissipation rates
accounted for the variations which they observed  in downwind plume
behavior under similar stability conditions (i.e., stable) as defined
by the vertical temperature gradient.
          In the  February 19, 1974 case, near the stack (0.8 km), both
the width and height of the plume exceeded the model values for both
stability categories (i.e., a  by almost a factor of 3 for F stability).
This effect was probably caused by rapid initial  dilution of the plume
by buoyancy and turbulent mechanisms which may or may not have been
terrain induced.  At 8.85 km downwind the observed  lateral spread was
still much greater than the model values  (about a factor of 2), but  the

observed az became less than either the model E or F values.  The observed
a  dimension was found to lie between the model E and F values at 29 km;
the observed a  remained much less than the model value for either cate-
gory (i.e., a factor of 3 less for E stability).  Therefore, rapid growth
of the plume occurred initially followed by much slower growth than pre-
dicted by the model for either E or F stability.
          Assuming that ay and az are power functions of downwind distance
from the source, the following exponent powers were found to be applicable
at downwind distances of 8.8 to 29 km compared to the powers assumed in
the NOAA model for February 19, 1974:

                            For  the  relation:
                               a(x)  = xp
                          x  =  downwind distance
NOAA model E
Model F Stability
p = exponent
          These data indicate that the downwind lateral spread was much
less than predicted by standard techniques and the vertical spread (oz)
was somewhat less than suggested by the observed temperature lapse rate.
In retrospect, had the additional  time and financial resources been
available, certain supplemental data would have been extremely helpful
for further insights into the behavior of the plume.  The NAWC study was
carried out with limited meteorological observations, with one vertical
temperature sounding being taken near the plant before each plume tracking
flight and no upper level winds in the vicinity of the plant.  Each of the

MRI flights consisted of more frequent temperature soundings at various
distances downwind, and were supplemented by upper-level winds.  With
regard to the NAWC study, an additional downwind vertical temperature
measurement would have been useful in at least one case, when the plume
seemed to be fumigating to the surface after the lone early morning
sounding had indicated a low level inversion.  In neither study were
sufficient wind data obtained to accurately determine flow characteristics
over the entire area being sampled (e.g., the frequent upper level wind
soundings taken in the MRI study were at one location, about 5 km north
of the plant).
          One of the two major objectives of the program of study conducted
by Smith and Anderson (1974) at the Four Corners Power Plant was to investigate
the dynamics of plume impingement on obstacles in the plume path.  However,
these investigators soon learned that only limited knowledge of the plume's
impact on the surface could be gained without a ground-level sampling system.
An important factor that affects the ground-level concentration is whether the
plume remains in the drainage flow or is able to penetrate it into the synoptic
flow above.  Smith and Anderson concluded that for drainage flows of less than
1.5 m s~^ the plume would penetrate and rise above the drainage flow but
absence of a ground sampling system prevented verification of this conclusion.
The analysis of data was a bit more detailed in the MRI study; both observed
horizontal and vertical plume dimensions (standard deviations) and normalized
concentration data were compared to values predicted by standard Gaussian model
values.  However, the comparisons were only for a very limited range of meteor-
ological conditions (stable lapse rate and light drainage winds).  Although the
NAWC study compared only observed and calculated center!ine concentrations, the
comparisons were for a greater (although not appreciably wide) range of meteor-
ological conditions (neutral stability with mode&ate winds and a stable lapse
rate with light winds).  Neither study encompassed more than a few days.
          The Navajo Plant, the largest electric generating plant in the State
of Arizona, has been the subject of the greatest number of studies of plants

operating in complex terrain.   The  research  performed  to  date  include  daytime
and nighttime tracer studies  by North  American  Weather Consultants  (NAWC 1974,
Hovind et al.  1973b),  extensive ground-level  and  aircraft monitoring of S02
(Rockwell International,  MRI  and SAI,  1975)  and model-to-model  comparisons
of Navajo data (INTERA 1975).
          The Navajo station  is located at 1326 m MSL  in  a large natural
basin with the Colorado River cutting  across  the  center.   Flat mesas rise
up to 1850-2450 m MSL  within  40 km  of  the  plant,  and Navajo Mountain
(3166 m MSL) is located 48 km to the east.   The two most  significant terrain
elements for plume impaction  are Vermilion Cliffs 22.5 km to the west  and
Leche-e Rock 8 km to the southeast. The Vermilion Cliffs are  part  of  a
larger elevated landform (Paria Plateau) which  rises somewhat  abruptly
in the vicinity of the Cliffs, while Leche-e Rock is a relatively narrow
landform with a flat top; thus, these  features  represents two  distinct
types of elevated terrain which could  conceivably alter the plume direction
in different ways (i.e.,  the  plume  could flow around Leche-e Rock much more
easily than around the Paria  Plateau).  The  two locations also represent
areas whose elevations are close to that of  the predicted plume centerline
under stable conditions.
          The daytime  tracer  study  (NAWC 1974)  was designed for the
purpose of evaluating  the quantitative impact of  fluorescent particles
(FP), smoke, and equivalent SO^ impact upon  surrounding terrain as  well
as the documentation of possible unfavorable meteorological-topographic
effects on plume rise, transport, and  diffusion during conditions other
than those postulated  as  'worst case1  (i.e..  stable, light-wind) conditions
in the NOAA (Van der Hoven 1972) Southwest Energy Study.   The  nighttime
tracer study (Hovind et al.  1973b)  had as  its objective the simulation of
plume transport and diffusion under postulated  worst case (plume impingement
          In both studies, FP tracer was released from the 236 m stack
and from aircraft simulating  an effective  stack height of 210  to 250 meters
above the stack.  The  period  of the nighttime tracer program was characterized
by nocturnal inversions extending above stack height,  but not as high  as

the simulated effective stack height.  Continuous recording of winds at
stack top and numerous pibal and temperature soundings at various locations
near the plant site were taken during the releases.  The nighttime tracer
study was supplemented by six continuously recording wind stations, most
of which were located on elevated terrain, 8 to 40 km from the plant, which
equaled or exceeded the effective stack height under stable conditions.
Both the daytime and nighttime tracer studies were part of a larger diffusion
climatology program conducted by NAWC at the Navajo site from May to September
1973.  The meteorological data included pibal and temperature soundings,
and surface and stack top wind measurements.  The extensive meteorological
data were used to construct time cross-sections of the wind flow fields for
periods including the tracer releases.  No attempt was made to quantify the
tracer behavior in terms of model parameters which could use this data as
input (i.e., plume geometry as a function of downwind distance, or various
types of terrain).  However, a Rotorod network strategically distributed
around the Navajo Plant allowed for a quantitative evaluation of the impact
of FP tracer upon the most prominent elevated terrain features at critical
elevations between stack top and effective stack height.
          The FP releases did not support the theory of direct center!ine
impingement on elevated terrain.  In the night case of June 5-6, 1973,
the maximum impact from a stack top release was on elevated terrain to
the south and southwest of the plant within 24 km, but there was no
distinct maximum impact zone.  High FP counts were distributed over a large
sector of elevations.  On June 6-7, 1973, the FP plume was initially trans-
ported toward elevated terrain, but the plume never reached the surface.
The authors have hypothesized that the plume may have become entrained in
a downdraft associated with strong wind shear induced by the rising terrain,
since the maximum impact was at an elevation lower than the release point.
This phenomenon is evidence that strong vertical transport can occur near
elevated terrain even in stable conditions.   FP tracer releases showed
greatest impact on the sampling network under light wind looping conditions
on summer days.   No quantitative information on the degree of turbulence
enhancement by elevated terrain was given, however, the effect was expected
to be less than for nighttime stable conditions.

          The possibility exists, of courses  that the plume centerline in
the FP experiments may have reached the surface,  but not directly over the
network.  Conditions in wintertime may be more stable and similar experi-
ments may show even further enhancement of plume  meandering.  In the day-
time study, plume impingement was investigated under limited mixing
conditions and during inversion "break-up" conditions.  Visual smoke
plumes showed downwash within 1.6 km of the plant with strong winds.
Smoke releases upwind of elevated terrain showed  no direct plume center-
line impingement as predicted by the NOAA model,  as the plume was trans-
ported either over or around obstacles.  The greatest impact on elevated
terrain occurred with turbulent downward transport of the plume during
transitional fumigation periods between stable morning conditions and
neutral/unstable afternoon conditions.  Plume meandering occurred fre-
quently at Navajo under stable, light wind conditions due to interaction
between the gradient flow and the diurnal thermal circulations induced
by terrain.
          Oil smoke was also released just upwind of Leche-e Rock and
Ka1parow1ts Plateau, two prominent terrain features in the vicinity of
the Navajo Plant,  There was no evidence of direct centerline impinge-
ment on Leche-e Rock.  However, later in the morning increased mixing
associated with a transitional fumigation period allowed transport of
the smoke into the rills of Leche-e Rock.  At Kaiparowits Plateau, down-
slope drainage flow caught some of the smoke, but the remainder rose
305 m over the plateau and there was very little diffusion to the surface.
          Hovind et al. (1973b) have made comparisons of NOAA model calculations
with equivalent $03 ground concentrations determined from measurement of FP
tracer concentrations resulting from releases from the Navajo stack (or by air-
craft at the estimated effective plume height prior to the beginning of the
plant's operation).  The comparisons were for nighttime tracer releases under
stable conditions, and for maximum hourly concentrations resulting from releases
of 1 to 3 hours duration.  For both the aerial and stack top releases, the NOAA
model values ranged from a factor of about 20 to a factor close to 300 times
greater than the measured equivalent $63 concentrations.  The possibility

of less than TOO percent dispersing efficiency was discussed in the NAWC
report describing these comparisons; however, the point was made that even
if an extreme value of 50 percent reduction in dispensing efficiency is
assumed, the maximum S02 measured would still be nearly two orders of
magnitude below the calculations.  Their comparison between equivalent
maximum hourly S02 concentration values and values predicted with the
NOAA Impaction Model in 7 tracer releases show the model over-predicting
by factors of 20 to close to 300.
          INTERA Consultants (1975) have made comparisons between calculated
S02 values, using the NOAA, EPA "VALLEY" and INTERA models, and maximum
measured concentrations collected in the vicinity of the Navajo Plant.
The S02 data representing Vermilion Cliffs were taken from five monitoring
sites located in a line atop the Cliffs which are approximately crosswind
when the wind is blowing from the plant toward the Paria Plateau.  Hourly
average S02 data from these five sites for the three days on which the
highest S02 hourly averages occurred atop the Cliffs were compared with
models.  The highest hourly average concentration atop Leche-e Rock was
also compared to model calculations.  Aerial plume centerline measurements
for each of these four days were additionally compared to values calculated
by the standard Gaussian model (as presented in the EPA workbook, Turner
1970) and the INTERA model values.
          The model input parameters for wind speed and direction were
specified from pibal data near the plant site (Page Airport) and surface
wind data (combined to estimate likely speed and direction at time of
high concentration).  Temperature soundings made mostly near the plant
provided the basis for stability estimates.  Comparisons are made for
the range of stabilities and windspeeds thought to be appropriate for the
travel time to Vermilion Cliffs.  Limited mixing was assumed when appro-
priate, as in the Leche-e Rock case.  The wind direction which provided
the "best fit" of values calculated by the INTERA model to the observed
data was used for all three models.  The effective plume height was
obtained from aerial S02 measurements on each day.  The comparisons for
the three Vermilion Cliffs cases and the Leche-e Rock case are shown in
Table 12.

                       NAVAJO GENERATING STATION
Site -Date
Vermillion Cliffs

Vermillion Cliffs

Vermillion Cliffs

Leche-e Rock
Model Calculations (ppm)
0. 14
0.09 '


Measured Peak
Hourly SO2
  Note:  The EPA "VALLEY" model was not designed for the calculation of hourly
        averages, hence the results shown here for "VALLEY" are of limited relevance.

          It is seen that for the input values specified, the NOAA model
overpredicts by a factor of 3-15, while the VALLEY and INTERA models are
generally within a factor of three.  For the Vermilion Cliffs cases, the
VALLEY model performs the best if E stability is assumed, while the
INTERA model performs the best if F stability is assumed.
          The comparisons with aerial measurements were made in each case
for three or four downwind distances, generally between 3 and 22 km from
the plant.  The model calculations were expected to be somewhat lower than
the measured values since the former corresponded to a one-hour average
at a particular point and the latter to an "instantaneous" value.   However,
this was not the case for the aerial data collected on the high concentration
days at Vermilion Cliffs.  At closer distances to the plant (4-8 km), the
INTERA model overpredicted the plume centerline concentration on all three
days by a factor of 2 to 3 for the meteorological conditions under which
it performs best with respect to ground level concentrations (F stability,
1.5 m/s); while approximately equaling the centerline values for E
stability and 1.5 m/s.  The INTERA model calculations for either condition
at 5 km were generally within 20 percent of observed values but low by a
factor of 2 to 4 at 22 km.  The Gaussian calculations for either E or F
stability (without sector averaging as employed by the EPA model]  were
somewhat higher than the INTERA model predictions (by up to a factor of
1.5) at close distances to the plant (about 8 km), while the calculations
were of about equal value at greater distances.
          Extensive ground-level and aircraft monitoring of S02 was under-
taken near the Navajo Generating Station and the results were presented in
a report assembled by Rockwell International, MRI, and SAI (1975).  Since
the purpose of the project was to determine if additional SO,, removal
would be necessary at the plant, field measurements were conducted during
the season of the greatest occurrence of stable conditions (fall and
winter), as determined from climatological records.

          The  principal  measurements obtained  from the field program

included three-hour  average stack emissions, ambient S02 concentrations,

surface winds  from a wide range of terrain elevations (including those
potentially affected by  plume impingement), pibal  soundings at least four

times daily (increased to 12 times daily during  intensive study), and

radiosonde and  aircraft  temperature soundings  (once and twice daily,

respectively).   Particular to this study among all  of those reviewed

were the following:

               Classification by terrain location  and meteoro-
                logical conditions of the highest measured ground-
                level  concentrations.

               Comparison of S02 peak (five minute) to mean
                (3 hour)  ratios for elevated terrain near the
                Navajo Plant (high enough to be impacted by the
                plume) to equivalent ratios obtained by Montgomery
                et al. (1972) at TVA's Paradise Plant located in
                relatively flat terrain.
               Spatial interpolation of three-hourly SO? con-
                centrations for samples located on  elevated
                terrain (at or near plume impingement height) to
                estimate  daily three-hour SC^ maxima.

               Utilization of results from several  previous field
                programs* conducted at the same site in the design
                of the field sampling program.

          Vermilion  Cliffs was the area most significantly affected, with
direct impingement being the dominant mechanism.   The study looked at three

peak cases, and  compared these high concentration  days to 23 other non-zero

low concentration days.   It was concluded that the  peak concentrations of

S02, determined  with  respect to Q, resulted from:   (1) the plume centerline
* Two of these studies were the daytime and nighttime tracer studies conducted by Hovind et al. which

  were previously discussed; the other two were background measurements obtained by Dames and Moore

  (1973), and another six-day field study conducted by Smith and Anderson (1975) which was not

  available at the time of this report but is summarized in the Rockwell report.

being near the top of the cliffs; (2) a steady plume direction over at
least a 3-hour period; and (3) light winds (1 to 4 m/s) at plume level.
The major factor separating cases with slightly lower S02 values from
the peak cases was variable wind direction.  Cases with the greatest S02
impingement on the cliffs usually were characterized by the plume being
forced down in front of the cliff.
          The prime requirement for significant S02 concentrations on
Leche-e Rock was steady wind direction toward this area for several  hours.
This condition was met only twice during the program.  Plume hetght and
wind speed were then critical  for determining the actual  concentrations.
Monitoring sites were located on top of each element of elevated terrain
to insure interception of the plume if impingement occurred.
          Several independent tracer studies have been carried out in
Huntington Canyon, Utah, a very steep-walled canyon with generally moun-
tainous terrain.
          A study by the Air Resources Laboratory of NOAA (Start et al.
1973) was conducted in March and April of 1973, with the purposes of
(1) determining the nature and extent of plume impaction on elevated ter-
rain and (2) comparing dilution within rough terrain to that expected
over flat, open terrain.  The instrumentation network was of appreciable
density, consisting of (1) 40 SFs tracer gas surface samplers located at
various points on the canyon walls and floor (sampling averaging time of
about one hour), primarily up-canyon from the stack release point, and
within 10 km of the latter; (2) nine surface wind speed and direction
recording stations, six of which were up-canyon from the stack release point;
(3) aspirated resistance thermometers at three levels on the 183 meter stack
of a power plant which was under construction at the site; and (4) a Bell
Helicopter which collected one minute plume samples.  The number of SFs
tracer releases was limited to 11, with 6 of the releases being from the
elevated stack;  The latter were made exclusively during daytime lapse
conditions.  One elevated release was made during inversion conditions,
that being from a point of elevated terrain which jutted into the canyon.

Comparisons were made between observed center!ine values and corresponding
values calculated by the standard Gaussian plume model and stratified  by
stability categories.*  Calculated versus observed plume center  con-
centrations were found to range from minimal differences during  moderate
to strong temperature lapse, to canyon dilutions of five times that of
"standard" flat terrain curves, to values about fifteen times more dilute
than standard curves for strong inversions.  The phenomenon of enhanced
mechanical turbulence is believed to be responsible for the greater
effluent dilutions with increasing stability in this study.
          The data summarizing the results of the elevated release tests
for D stability* are presented in Figures 14a and 14b from Start et al.
(1973).   Aerial  centerline samples are represented by 0, ground-level
samples  are depicted by X; Figure 14a includes both helicopter and ground
samples, while 14b represents helicopter samples only.  Figures  15a and
15b are  comparable to Figures 14a and 14b but are for ground-level releases
for conditions of stable down-canyon flow.  The solid curves represent
the expected flat terrain concentrations.
* See Table 11 for category definitions.



 Distance (m)
        Figure 14a.  Helicopter and Ground Samples for D stability.

                    0   Aerial samples
                    X - Canyon wall and floor samples

      "3-   10-s
IO3           IO4
     Distance (m)
Figure 14b.  Helicopter Samples only for D Stability Elevated Release Tests

                             0 - Aerial samples

     X   10"
                              Distance (m)
   Figure 15a.  Helicopter and Ground Samples for F Stability Release at
           Ground-Level in Conditions of Down-Canyon Flow
                    0 - Aerial Samples
                    X   Canyon Wall and Floor Samples

               IO2           IO3            IO4           IO5
                              Distance (m)
Figure 15b.  Helicopter Samples only for F Stability Release at Ground-Level
                  in Conditions of Down-Canyon Flow

                          0 - Aerial Samples

          North American Weather Consultants (Hovind et al. 1973a) con-
ducted a series of three separate tracer experiments, each of one week's
duration, in order to provide a quantitative description of the air
quality impact from a 430 MW power plant site in Huntington Canyon, and
also to evaluate the applicability of the NOAA and Standard Gaussian
plume centerline models.
          Tracer Program III, the most extensive of the three tracer
experiments, consisted of FP tracer and smoke releases from the estimated
effective stack height as well  as helicopter smoke releases near elevated
terrain.  The FP tracer concentrations were subsequently converted to
equivalent S02 concentrations.   Six surface stations monitored temperature
and winds at various locations within the canyon, while pibal  and aircraft
temperature soundings were made up to three times a day.  Included in the
sampling network was a special  sampling grid on one of the canyon walls
aligned in a principally crosswind direction.
          Aircraft measurements of the turbulence dissipation parameter
(e) were made with a Universal  Indicated Turbulence System.  This param-
eter, which is actually a measure of the turbulence dissipation rate in the
inertial subrange of eddy sizes, indicates the rate of energy flow from
larger to smaller eddies, and has been related to a turbulence magnitude
scale.  Values of e were recorded that indicated moderate to heavy turbu-
lence even when stabilities were classified as stable or extreme:ly stable.
Greater values of e were found over Huntington Canyon than over Castle
Valley, a nearby terrain feature characterized by less roughness.
          In the plume tracer studies by Hovind et al. (1973a), the plume
tended to follow a meandering path during up-canyon transport along a
mean direction outlined by the elevated boundaries of the main and side
canyon.  Persistent plume transport in the stable air mass across Hunting-
ton Canyon toward the major topographic features was never observed,
although the plume would at times move briefly toward that direction only
to be deflected into an up-canyon direction while approaching the canyon
walls.  Therefore, the NOAA model assumption of plume transport across
canyon onto elevated terrain was in this case unjustified.

          During a week of observations in January 1973, all except one
of the days were characterized by stable conditions, and the remaining
day was neutral.  Model-to-measurement comparisons by Hovind et al. (1973c)
indicated that the NOAA model overestimated centerline concentrations by
10 times at 2.5 km downwind, but was closer to unity beyond 10 km from the
plant site under stable, light wind conditions.  No information was given
regarding ay and az, except that the plume influence on the sampling grid was
rather uniform for stable conditions.   This could either mean that a  was
much greater than the lateral extent of the sampling grid (400 m) or that
the plume was non-Gaussian.  There is  also serious question as to whether the
aircraft release was equivalent to a point source, thus making comparisons
to model calculations unjustified.
          In another analysis effort by NAWC, Hovind et al. (1974) described
studies of FP and oil fog dispersion that were undertaken at three sites
with different roughness characteristics in the southwestern U.S. to deter-
mine the effect of terrain roughness upon plume dispersion  from an elevated
source.  The three sites were characterized as follows:  (1) a canyon with
gradually rising canyon floors and steep walls; (2) a plant site located
at relatively high elevation compared  with surrounding terrain, with the
general area being characterized by considerable ground roughness; and
(3) relatively smooth terrain but with some low bluffs and  cliffs in the
direction of rising terrain.  The authors do not disclose the names of the
three sites in the report, although the first site seems representative
of Huntington Canyon.  Figure 16, from the report, provides a depiction
of cross-section profiles at the three sites.

                    '^-" PLAN
                    I.'OJ -

                    9 CO -
                        PLANT SITE  B
                        PLANT SITE C
                        25  20  15  10  5  0   5   10   15  20  25
                               HORIZONTAL P'STAHCE [KILCUETERSI

               Figure 16.  Terrain Cross-Sections at Three Sites of Varying Degrees
                         of Roughness (from Hovind et aL 1974)

          Aircraft FP  tracer releases upwind of selected elevated terrain
areas were employed  at the first site.   Six  such  releases were studied  in
January 1973,  under  stagnant atmospheric conditions with temperature
inversions existing  immediately above the release altitude.  Oil fog  was
used as a tracer  at  the latter two sites.   Data representing four cases
characterized  by  neutral stability with  moderate winds were summarized  for
the second site,  while nine cases having a stable atmosphere were investi-
gated for the  site representing the smoothest terrain.

          Hovind's et al.  (1974) comparison  study of three sites with
different roughness characteristics  in  the southwest U.S.  provided ratios
of calculated centerline concentrations  to observed  values using a stan-
dard Gaussian model with dispersion  coefficients  as  defined in Turner
(1971).  The average ratios for each of  the  three sites  were 10.2 for the
canyon site, 6.0 for the rugged open terrain  site, and 1.2 for the rela-
tively flat, open terrain  site  (see  Table  13).  The  authors concluded that
average departures of observed values from model  calculations were signif-
icantly high for the two sites with  rougher  terrain, but minimal for the
open,  level terrain.  The  departures were attributed to  increased turbu-
lence  in the rough terrain.
               et al. 1974)

Confined Canyon
(Site A)
Rugged open
terrain (Site B)
Relatively flat,
open terrain
(Site C)
y ' /Y'
cal/X obs
6.0 (5;53)
1-2 J>
No . of
          For the canyon site the authors used  a   and  a   values correspond-
ing to stability classes* C and D as inputs  for the  model,  while observed
meteorological conditions indicated an  F stability condition.   Since
tracer releases were made below the inversion  layer, the plumes, at
least initially, were not in an atmosphere characterized by F stability.
          Three mechanisms were hypothesized for  the enhanced mechanical
turbulence:   (1) gradient flow momentum transport into the  canyon;
(2) drainage winds from feeder canyons  which, when combined with additional
slope drainage have enough momentum to  be carried up the other side of
the canyon;  (3) turbulence effects created by  the plume  winding about
* See Table 11 for stability class definitions.

protrusions or bluffs into the canyon center.  However, there was no
analysis of wind observations and no turbulence measurements to substan-
tiate these flow hypotheses.
          The objectives of the study, to observe impaction and dilution
within the canyon were met.  It was concluded that transient impactions
on the order of a few minutes may occur at any point during lapse condi-
tions.  The results are somewhat limited in significance because the topog-
raphy of the release points varied greatly for the differing meteorological
conditions and because sampling was only conducted for flow to the steep
canyon terrain (the latter fact was acknowledged by the authors), i.e., no
sampling was conducted to the northwest for flows which carried the plume
toward the main valley to the east, away from the mountains.
          Looking back upon the series of Huntington Canyon tracer programs
conducted by NAWC, certain supplemental information gathering would have
proven helpful with respect to evaluating the tracer impact under stable or
very stable light wind conditions (e.g., those consistent with hypothesized
worst case conditions).  An extension of the study sampling period could
have allowed for investigation of such phenomena as fumigation (observed
in the NOAA study) or the possibility of lower level coupling with the
gradient flow and subsequent cross-canyon flow.  The aircraft FP tracer
and turbulence measurements could also have been related in a systematic
way to plume behavior (e.g., attempt to assess plume geometry from com-
bined surface and aircraft FP data, and to relate plume centerline con-
centrations to turbulence measurements).  An additional point to be made
is that both the NOAA and NAWC Huntington Canyon programs involved tracer
releases less than or equal to one hour in duration.  Had these release
time lengths been of longer duration, concentrations for longer averaging
times might have been calculated, or peak to mean ratios (assuredly appli-
cable for complex terrain) might have been utilized.

          An investigation by NOAA ARL  (Start et  al.  1974)  involved a
short canyon near Garfield, Utah, in a  mountain range  along  the  south
shore of the Great Salt Lake.  The diurnal cycling of  the  lake-valley
winds made this site more complex than  Huntington Canyon.  The  tracer
diffusion tests in this mountainous terrain  involved  the  122 meter Garfield
Smelter stack and had the following objectives:   (1)  to measure  ground-
level and elevated centerline concentrations to quantify  the plume dilu-
tion, if any, attributable to rough terrain; (2)  to examine  the  degree of
impaction against the mountain slopes;  and (3) to establish  a modest data
base as an aid to mathematical analysis of diffusion  in complex  terrain.
          Seven SFg tracer releases were made in  as many  days from the
elevated stack.  Forty samplers were positioned on the mountain  slopes
and canyon floor; in addition, 10 continuous wind speed and  direction
recorders were placed within the testing area, and pibals  were  taken both
before and during the release period.   Radiosonde ascents  were  also made
while each test was in progress.  The seven  elevated  releases were all
made under similar estimated stability  conditions*  (B  or  C); two ground-
level nighttime tracer releases (no visible  tracer was released  with the
SF5) were made under inversion conditions, but their  discussion  was limited
in the report because of difficulties in locating a defined  plume centerline.
          Model-to-measurement comparisons of centerline  concentrations
and lateral plume dimensions were made  for all of the  elevated  releases;
for three of the releases, the ay values from the data were  not  derived
from samplers positioned in a crosswind direction but  rather from esti-
mated plume widths or second moment** calculations.   Similarly,  az values
were derived from transformations of the Gaussian equation or with cross-
wind integrated concentrations; no actual measurements of vertical con-
centration gradients were made in the study.  Plume measurements were not
taken during early morning inversion conditions and so the effect of the
 * See Table 11 for stability definition.
** Second moment of the lateral distribution of tracer mass about the center of gravity of the mass

drainage wind flowing out toward the lake could not be documented.  Start

et al. state in their report that "the plume impacted significantly" against

the steep terrain on the west side of the canyon in one test case, while

in other tests the plume conformed more or less to the terrain undulations,

without significant impingement.

          Based on visual observations during the tests, the authors sug-

gested several mechanisms which are believed to contribute to the enhanced

lateral spreading and lower center!ine concentrations.  These are sum-
marized as follows:

          e    A plume approaching steeply rising terrain can
               experience lateral deflection in an attempt to
               flow around the blocking obstacle.  This is
               particularly true during plume looping conditions
               when descending segments neared the ground.

          9    Mechanical turbulence, and vertical shear,
               believed to arise over and around the peaks
               and ridges of mountainous terrain results in
               an enhanced turbulent state (one visual
               observation of the actual plumes emitted
               from two of the smelter stacks revealed that
               the plume from the lower stack was being
               carried up-canyon while the plume from the
               higher stack was moving in a direction 90
               from this, across a ridge in response to the
               near gradient flow aloft).

          The results of Garfield aerial center!ine measurements for sta-

bility classes B and C are exhibited in Figure !7a, b from Start et al.  (1974)

A least-squares, first-order curve fitting of the data points is repre-

sented by the dashed line in both graphs.  Plume measurements conducted

over  level terrain are denoted by the 0 symbols in Figure 17b.  The solid

lines are the expected curves over flat terrain.

x  10
               10        10
              Distance (Meters)
  Figure 17a.  Results of Garfield Aerial Sampling
      Test with Stability Class "B" Conditions
                                            10        10       10
                                                    Distance (Meters)
                                        Figure 17b. Results of Garfield Aerial Sampling
                                           Test with Stability Class "C" Conditions
             The researchers  who  conducted the Garfield  SF6 study (Start et
   al.  1974) made comparisons of  observed normalized  (xu/Q) plume centerline
   concentrations with calculations  from standard  curves presented in the
   EPA  Workbook (Turner  1970).  Observed and calculated  lateral  plume spread-
   ing  were also compared.  Xu/Q  values of the seven  elevated releases of
   SFg  conducted in lapse  conditions were two to four times less than pre-
   dicted by the standard  curves.   However, data from four of the tests were
   not  analyzed because  of complicated plume geometry.   In the three tests
   that did have a reasonably Gaussian shaped plume,  a  exceeded the expected
   value by a factor of  two.   The enhanced lateral  spreading may be due to
   avoidance of terrain  by the plume.  There was a tendency for the plumes
   to be deflected laterally  in an attempt to flow out and around blocking
   obstacles.  Values of oz however, were in general  less than those for
   flat terrain.  The aerial  plume centerline comparisons were essentially
   the  same as those described in the next paragraph, made by INTERA for the

NOAA model (since the latter is based on the same curves), and thus gave
the same results.  Lateral spreading was examined in a quantitative manner
in the Start et al .  (1974) study by (1) selecting slices across the iso-
pleth patterns which were normal to the observed direction of plume travel;
(2) extracting analyzed concentration values along each slice to obtain
reasonable approximations of the concentration distributions; and (3) cal-
culating a  values by both the plume "width" method and the second moment
method (both methods resulted in a  values which were approximately the
same).  A comparison of these observed values with standard a  values for
the appropriate stability classes (B or C) showed the average ratio of
observed a  to Pasquill-Gifford a  to be 1.79.
          The data from these three NOAA Garfield tests were also compared
with the NOAA, EPA "VALLEY," and INTERA model calculations (Intera
Consultants 1975).
          The input data were determined as follows:

              The plume rise was obtained by extrapolating the plume
               centerline as determined from helicopter observations,
               back to the source.
              The INTERA model calculations were performed using wind
               profiles (1) from pibal data at the site and (2) from a
               standard power law for unstable conditions.
              The stability class was determined from the objective
               criteria suggested by Turner*  (1970).

          The models were compared by  INTERA Consultants (1975) by using
two different statistical measures.  One method, involving the ratio of
the calculated mean value to the observed mean value ground-level concen-
tration, tends to give a greater weight to the larger measured and calcu-
lated values.  This ratio (Rl) can be mathematically stated as:
                               Rl =
* See Table 11 for criteria used.

= calculated concentration
= observed concentration.
The second method gives an average of the calculated  to  observed  ratio
at every specific sample point.  This logarithmic mean ratio  (R2)  is
mathematically described as:
                          R2 = exp
                           1n (XCALC/XOBS)
          N = number of points.
          The log mean ratio gives approximately  equal weight  to  large
and small measured and calculated values.  Model-to-measurement compart
sons for ground-level concentrations are summarized  in Table 14.



Estimated Pasquill Stability



INTERA - Pibal
INTERA Standard
INTERA - Pibal
INTERA Standard
INTERA - Pibal
INTERA - Standard

          Analysis of these three tests, using R1,  show the INTERA model

ground concentration results to be within a factor of 2.5 and the results

of the NOAA model to be within a factor of 3.9.  For Test 7, the NOAA node!
performs as well as the INTERA model when the standard profile was input to

the latter (Rl = 1.50), and better than the INTERA model with a pibal wind


          Additional comparisons were made with observed data in the

three tests for predicted plume centerline concentrations as a function

of downwind distance, and for how well the observed concentration pat-

terns were reproduced spatially.

          The helicopter samples, corresponding to an averaging time of
the order of one minute, were converted to one hour values by the EPA

Workbook technique  (Turner 1970) to correspond to the model calculations,

which represent one hour averages.  The results of the comparisons for
the aerial centerline data are 35 follows:

              The  INTERA model calculations using standard
               wind profile data were lower than observed
               values by factors from 1.3 to 4.0 in two of
               the  cases and were within a factor of 1.5 in
               the  last test.

              The  INTERA model values calculated using
               pibal wind data were within a factor of
               1.5  in two of the three tests, but were
               higher than plume centerline values by a
               factor of 2 to 4 at distances beyond 1 km
               in the last test.

              The NOAA model calculations were greater
               than observed centerline values by a factor
               of 2 to 5 at distances within 4 km of the
               plant in two of the three tests and for all
               distances in the last test; calculated values
               approached observed values at distances
               greater than 4 km in Tests 2 and 3.

The results of the model comparisons for accuracy of reproduction of the

observed concentration pattern showed the INTERA model predicting the

location of the maximum concentrations accurately in two of the three
tests, while the NOAA model was accurate in this regard in only one of
the tests.  The NOAA model predicted the location of the maximum concen-
tration in a valley in two of the three cases.
          Comparison of the heights of the maximum in-plumes concentrations
indicate that the NOAA model assumption of parallel to terrain plume center-
line flow in complex terrain under unstable conditions is invalid for the
unstable conditions characterizing the days evaluated.  For these days,
the heights of the maximum in-plume concentrations over the ridges was
in general half those over the valleys.  The INTERA model usually predicted
the heights with good accuracy, although it did not show quite as much con-
formance to the terrain features as actually observed.
          A recent FP and oil fog tracer study has been conducted by
North American Weather Consultants (1974) in the vicinity of the proposed
Kaiparowits Generating Station which was to be located in the rugged canyonland
of southern Utah.  Some of the details of this study were not available at
the time of this report.   However, it is known that the study was fairly
limited in duration, consisting of 10 FP tracer releases in May of 1974,
7 at one location in the  area and 3 at another.  Each of the releases was
supplemented by measurements of the vertical temperature profile, vertical
wind profile, and turbulence measurements.   FP recoveries from four ele-
vated tracer releases made by aircraft, two of which were at one proposed
site (Fourmile Bench), and two of which were at the Nipple Bench site,
were chosen for evaluation.  One of the Fourmile Bench tests was character-
ized by early morning stable conditions, while the other three tests were
characterized by unstable conditons.  The principal interest in the study
lies in the subsequent use of the data in model-to-measurement comparisons
by Hoffnagle et al.  (1975).
          Initial model calculations were made using the stability cate-
gory observed at the time of each test, and pibal wind profiles constructed
for each test.   Once the  initial model calculations had been compared to

the measured data, the models were adjusted individually to provide the
best possible simulation within the limits of model  flexibility.
          Hoffnagle et al. (1975) have tested the EPA "VALLEY," NOAA, TVA
coning model and INTERA models against fluorescent particle tracer data
obtained by North American Weather Consultants at two proposed sites for
the Kaiparowits Generating Station.  It is important to note that the TVA
model (which, like the NOAA model, is actually a set of Gaussian  calcula-
tional techniques, with each technique being appropriate to a different
meteorological condition) was not specifically designed for application
in complex terrain situations; however, the comparison here is of interest
because the model differs from the other standard Gaussian models (EPA
"VALLEY," NOAA) in that the diffusion coefficients used (a  and a ) are
not the same as the standard coefficients as described in Turner  (1969),
and were essentially derived from observations of power plant plumes.  A
different set of equations is used for computing maximum S02 concentra-
tions from power plants under coning (neutral stability), inversion breakup,
and limited mixing conditions; the INTERA comparisons were based  on TVA
"coning" model calculations in each case.
          Initial model calculations were made using the stability cate-
gory, observed at the time of each test, and pibal wind profiles  made
during each test (for determination of wind speed in the case of  the
Gaussian models, and wind profile in the case of the INTERA model).  Once
the initial model calculations had been compared to the measured  data,
the models were adjusted individually to provide the best possible simu-
lation within the limits of model flexibility.
          Table  15 shows the results of the comparison of initial model
calculations with the FP data.

Tracer Test HI
No. of Receptors
Tracer Test 12
No. of Receptors
Tracer Test #3
No. of Receptors
Tracer Test #4
No. of Receptors
              Of  the  3  to  20  receptors  evaluated in each case, the NOAA
               model had the best mean ratio of calculated to observed
               concentrations  in  three of the four cases, and its mean
               ratio was within 30 percent of unity in all four cases.

              None of the  remaining three models had consistently better
               mean ratios  than the other two.  The TVA coning model
               generally underestimated  (three of the four cases); the
               EPA "VALLEY" model  had mean ratios from 0.8 to 2.3; and
               the INTERA model had mean ratios from 0.9 to 1.9.

              None of the  four models had consistently good correlation
               coefficients, and  thus did not accurately calculate plume
               behavior  as  a whole.   The INTERA model had the highest
               single  case  correlation of 0.8.  The INTERA, TVA and
               NOAA models  had correlations exceeding 0.5 in only one
               case, while  the "VALLEY"  model  always gave correlations
               below 0.5.  (But it should be noted that the "VALLEY"
               model was never intended  for use in short-term

          The "plume"  recoveries  in  at least one of the cases (the release

under assumed stable conditions)  suggest that inversion breakup may have

been occurring; the fact that no  meteorological data were available to

confirm this (as had been the case in the comparisons for the Navajo

Generating Station) points  out the need  for better documentation.  It also

suggests that application of TVA's "inversion breakup" Gaussian equation

might have been more appropriate  in  this case.  The results of the other

 cases  imply that the  terrain  in  the  Kaiparowits  area  is  characterized  by
 more enhanced  dispersion  for  the given  situation  than would be expected
 from conventional  Pasquill-Gifford measures  of stability.
 Description of the Site
           The  Large Power Plant  Effluent  Study (LAPPES)  was initiated
 during  1967, and conducted  during a  subsequent five-year period,  to evalu-
 ate the extent and effects  of air pollution  resulting from three  coal
 burning generating stations with tall stacks  (Conemaugh, Keystone, and
 Homer  City) in rolling  to mountainous terrain 1n  Western Pennsylvania.
 The four-volume  report  on the LAPPES program by Schiermeier et al. (1970-
 1972) dealt mainly with data  presentation and was not concerned for the most
 part with  any  data analysis,  other than to qualitatively describe a few
 obvious cases  of terrain  influence on dispersion  from the Conemaugh Station
 (located in the  roughest  terrain of  any of the plants) as evidenced from
 airborne monitoring near  that plant  during April  and  October of 1971,
 The terrain in the vicinity of the Keystone, Homer  City  and Conemaugh
 Plants  is  composed of rolling hills  rising 100 -  200  meters above
 valley floors  and ridges  rising  200  - 450 meters  above valley floors.
 The major  features are  Chestnut  Ridge,  oriented  NE-SW between the Homer
 City and Conemaugh stations,  and Laurel Ridge which is considerably
 higher and located to the SE  of  Conemaugh.
           The  Keystone  Station is situated in a  shallow  rural valley with two
 244 m  stacks the base of  which are at 305 m  MSL.  Except for this valley, the
 surrounding terrain within 5  km  is hilly, with the  highest peak reaching no
 more than  mid-stack height, i.e., about 120  m above the  plant.  The Keystone
 Power  Station  is about  25 km  to  the  northwest of  the  closest ridge (Chest-
 nut Ridge). So  the influence of topography  was  not evident from  ground-
 level measurements near Keystone Plant.
          The Homer City Station, with twin stacks at a height of 244  m,  is
located on a plateau,  with the surrounding terrain falling  off as  much  as
100 m  from the  stack  base  height  of  366  m  MSL.   The  highest peaks  within  5  km

are those of Chestnut Ridge to the SE,  which range slightly higher than
midstack height, i.e.,  about 170 m above the plant.   East of the ridge
is another plateau which  received higher S02 concentrations at ground
level  than were found at  a similar distance in any other direction.   This
phenomenon may have been  a lee effect of Chestnut Ridge.
          The Conemaugh Station is the most susceptible to terrain influ-
ences.  Separating this plant from Johnstown to the SE is Laurel Ridge,
which  has peaks reaching  180 meters above the stack top of 305 meters
within 10 km of the plant.  These hills along with the slightly lower
Chestnut Ridge to the west may cause channeling of the plume.   Schiermeier
(1972) observed that under neutral conditions flow from the SE quadrant
(passing over Laurel Ridge before reaching the plant) brought the plume
to the surface very quickly.  Ground-level concentrations then diminished
with further distance,  but then increased again on the lea side of Chestnut
Ridge.  Downwash on the lee side of Laurel Ridge, confirmed by subsidence
of pilot balloons in the vicinity of the plant, was responsible for
bringing the plume to the surface near the plant.  Surface heating on
sunny days precluded downwash.  However, under northwest flow the plume
rose over Laurel Ridge and mixed in a deep layer in the lee of the ridge.
Only low concentrations were measured at ground level.  No lee waves were
detected downwind of Laurel Ridge.  This lack of downwash supports the
idea that roughness fetch plays a large role with regard to plume transport
and dispersion characteristics.  It is known from previous studies (Egan
1975)  that flow separation in complex terrain may either take the form of
large, reverse, stationary eddies, or "shed" vortices.  It is conceivable
that the former was being observed near the Conemaugh Plant with southeast
winds  (the downwash conditions), while upwind roughness characteristics
favored the second type of separation flow with northwest winds, since down-
wash was then absent.

Terrain Roughness Parameters
          In the course of preparing this present report GEOMET undertook
special analyses of data from the LAPPES and other studies to assess the
impact of terrain-induced turbulence on the diffusion parameters a  and
az in a Gaussian dispersion model.  In order to quantitatively measure
the terrain variation, ground elevations beneath several plume center!ine
paths were plotted from USGS topographic maps.  The standard deviations of
the elevations along the plume center!ine paths out to various distances
were computed.  A space interval of 200 m was used for plotting elevations.
Calculated Standard Deviation of Elevations (SDE's) are tabulated for com-
parison (Table 17) with the differences between plume parameters measured
in the plume and conventional values for the same plume estimated by the
methods of Turner's Workbook (1970).
          Figure 18 shows the terrain cross-sections of 14 plume paths,
plotted in various compass directions from the Keystone plant out to 16 km
distance, together with the corresponding SDE values.  The abscissa shows
downwind distance in kilometers; the ordinate shows elevation above sea
level in meters.  (Note that the vertical to horizontal scale ratio is
0.06).  The figure shows that larger SDE numbers correspond to more com-
plex terrain.  For example, the highest calculated SDE value, 58.2 m, is
noted for the direction toward the east; the smallest calculated SDE value,
24.3 m, occurs to the south-southwest.  The elevation profile to the south-
southwest contains smaller variations than that of the profile toward the
east.  Figure 18 is included as an example of the technique for characterizing
terrain cross-sections.  Similar calculations were made for the other SDE
values shown in Tables  16 and 17.
Plume Cross-Sections and Meteorological Data
          Standard deviations (a  and a ) of the observed S02 concentrations
in LAPPES plume cross-sections were statistically computed by GEOMET through
integration of the vertical concentrations and crosswind concentrations

TABLE 16. (Continued)


Wind Sector







From Plant













1807. 3


TABLE 16.  (Concluded)
Wind Sector
From Plant

                                          STABILITY CLASS FOR COMBINED KEYSTONE AND CONEMAUGH DATA





16.8- 19.8
25.2- 27.2
30.5- 34.7
40.8- 43.1
23.1- 24.3
31.0- 33.7
37.3- 40.0
58.2- 66.8
28.5- 30.7
36.5- 42.5
58.2- 65.0
ay (m)






             * Estimate from Workbook for Atmospheric Dispersion Estimates (Turner 1970).

            ** KY and KZ are the approximate Pasquill Stability Class (i.e., A = 1, B = 2, etc. ) required to represent the observed value.








                   394   _
                   333     _


                                                                                                                     SDE = 33.5 (m)

                                                                                                                     Wind Sector 1

                                                                                                                                        SDE = 28.3 (m)

                                                                                                                                        Wind Sector 2

                                 SDE = 37.1 (m)

                                 Wind Sector 3

                                                                                                                      SDE= 37.7 (m)

                                                                                                                     Wind Sector 4
                                                                     Down Wind Distance (km)
                         Figure 18 ,  Profile* of Elevation Toward 14 Directions from Keysto".: Power Plant.  Standard deviation of

                                    elevation rcai.1 by an increment of 200 m horizontally arc also indicated. (Continued)





455 _


                                         I      I      I      1  	I      I      I      I      I      I      I      I      I      I      I
                                        H	1	j	1	1	1	1	1	1	1	1	1	1	1	h
                                         1	1H	1	1	1	1	1	K-
                                                                            H	1	1	1	H
                                               I	1	1	1	1	1H	1	1	1
                                             I      I      I      I      I      I      I      I      I      I
                                             67      8     9      10     11    12     13    14      15

                                                 Down Wind Distance (km)
                                                                                                                                              SDE = 57.8 (m)

                                                                                                                                              Wind Sector  5

                                                                                                                 SDE = 32. 2 (m)

                                                                                                                 Wind Sector 6


                                                                                                                 SDE = 36. 2 (m)

                                                                                                                 Wind Sector 7

                                                                                                                                             SDE = 27.0(m)

                                                                                                                                             Wind Sector 8
                             Figure ^   Profiles of Elevation Toward 14 Directions from Keystone Power Plant. Standard deviation of

                                         elevation read by an increment of 200 in horizontally are also indicated.   (Continued)


                                           Down Wind Distance (km)

                                                                                                        SDE = 24.2 (m)

                                                                                                        Wind Sector 9

                                                                                                        SDE = 30.4 (m)

                                                                                                        Wind Sector 10

                                                                                                        SDE = 31.6 (m)

                                                                                                        Wind Sector 11


                                                                                                        SDE =42.4 (m)

                                                                                                        Wind Sector 12
  Figure 18 .  Profiles of Elevation Toward 14 Directions from Keystone Power Plant. Standard deviation of
              elevation read by increment of 200 m horizontally are also indicated. (Continued)



                                      I     I      1     I



                                                                 6     78     9    10    11

                                                                    Down Wind Distance (km) 

13    14


                        SDE = 29.9 (m)

                        Wind Sector 13


                        SDE = 33.5 (m)

                        Wind Sector 14
                             Figure 18 . Profiles of Elevation Toward 14 Directions from Keystone Power Plant.  Standard deviation of

                                          elevation read by an increment of 200 m horizontally are also indicated.  (Concluded)

respectively.  Because the statistical method used is valid for Gaussian
distribution curves only, 436 plume cross-sections were examined manually
and 28 percent (122), which appeared to be near the Gaussian bell shape,
were selected for further study.  Wind speed and solar radiation, measured
at Jimmy Stewart Airport in Indiana, Pennsylvania in the LAPPES program,
were used to determine the stability classes* for each measurement period.
          Skewness was calculated for horizontally integrated concentra-
tions measured at the Conemaugh Power Plant.  Although the plume cross-
sections used were selected to be nearly Gaussian in shape, vertical
concentrations (horizontally integrated) were generally skewed toward the
upper half of the plume.  Seventy-two percent of the cross-sections were
skewed toward the upper half of the plume, 17 percent were skewed toward
the lower half of the plume, and 11 percent had no skewness.  It is our
speculation that these results indicate more rapid mixing in the lower
portions of the plume than in the upper portions, perhaps due to a terrain-
induced turbulence effect or due to thermally induced turbulence due to
heating of the ground surface.  A stronger possibility may be that the
skewness was caused by a shearing-off of plume remnants as the main part
of the plume rose to its buoyant level or into an inversion aloft.
          Dispersion parameters, a  and a   in a Gaussian dispersion model
are considered to be a function of downwind distance and atmospheric sta-
bility.  Conventionally, atmospheric stability is treated as a function of
wind speed and solar radiation or lapse rate.  This primarily represents
the effects of thermally-induced turbulence; but the terrain-induced
turbulence, which is very important in a complex terrain area, is not
accommodated by the Gaussian dispersion model.  If terrain-induced turbu-
lence has no effect on plume dispersion, then we would expect that the
differences between observed ay and az and the values calculated by con-
ventional methods (i.e.. Turner's Workbook) will on the average be zero.
If significant differences are observed, the deviation should correlate
with terrain characteristics such as the SDE values.

* See Table 11 for category definitions.

          Plume measurements were sorted by their center!ine direction
into 16 compass directions.  Observed values of a  and a  were averaged
for each stability class, plume travel direction and distance.  All cases
selected were for neutral conditions  (class D).  Homer City data were
omitted because of the small number of observations.  Table 16 shows
observed a  and a  values and SDE values for each plume-centerline direc-
tion and distance from the plant.  In order to see the influence of SDE
on a  and a , we grouped the data by  ranges of SDE values and downwind
distances (4, 10 and 16 km) and computed the mean ay and az for each
group in Table 17.  Also tabulated are ay and az values which have been
measured, values estimated from Turner's Workbook (1970), and their dif-
ferences.  The measured ay and az values were used to determine equivalent
stability classes, KY and KZ, based upon the observed horizontal and
vertical concentration distributions, respectively.  These values are
also tabulated in Table 17.  From this table one can observe that the
impact of terrain on the horizontal dispersion parameter (ay) is more
significant than on the vertical dispersion parameter (az).  If one
examines the average of KY values for a fixed travel distance, an increase
in the average KY value with distance is noted.  At 4 km distance, the
average KY is 2.5, while out to 16 km distance, the average KY is 3.6;
this is closer to the actual stability class of 4.  This indicates that
the terrain influences on ay are more significant at closer distances
from the plant; the terrain influence on az is more important at further
distances from the plant.  With increasing distance the influence of
terrain on the plume becomes smaller.  The correlation between SDE and KZ
is not recognizable.  It should be recognized that these calculated SDE's
depend to some extent on downwind distance and AX (the distance increment)
as well as the nature of the terrain; instead of a specific direction,
consideration of a sector may be warranted.
          The TVA's Kingston Power Plant has been the focal point for
several intensive field programs.  These programs exceed the magnitude of
the Navajo and LAPPES studies in scope of data collections.  A computer

analysis of Kingston Plant data similar to the analysis of LAPPES data was
performed by GEOMET to examine terrain-influenced dispersion within the plume;
this work is described below.
Description of the Site and Monitoring Program
          The Kingston Steam Plant is situated in eastern Tennessee about
56 km west-southwest of Knoxville and 3.2 km northeast of Kingston.  The
plant lies on a peninsula formed by the junction of the Emory and Clinch
Rivers.   Flowing southward from the plant site, the Clinch River combines
with the Tennessee River some 4.8 km downstream.  Within a radius of
1.6 to 4.8 km, the plant is almost totally encompassed by ridges 107 to
122 m higher than the plant grade.  The terrain continues to be hilly
outside the immediate area, with ridges aligned northeast-southwest and
extending to elevations about 244 m higher than the plant grade.
          Intensive field studies of plumes were conducted in the
vicinity of TVA's Kingston Power Plant for three two-to-three month peri-
ods in the winter and early spring of 1973 - 1975.   Only preliminary
analyses of data had been made at the time of this  report and these were
essentially limited to calculations of ay.  The most impressive aspect
of this field monitoring program compared to the others previously described
was the number of different modes of S02 monitoring used, and more impor-
tantly, the coordination between these modes which  resulted in use of each
to its optimal advantage.
          For example, in the 1975 sampling period, a fixed-wing aircraft,
van, helicopter, and 11 fixed surface monitors were used on a daily basis,
in addition to plume photography.  The van and helicopter were both equipped
with S02 monitors and served to locate the portable monitoring in areas of
high S02 concentrations.  Airborne crosswind plume  measurements were made
at fixed distances downwind.  Thuss the analyses of plume geometry could
be made for this two-month period in late winter-early $pring,  The three
data collection periods featured intense collection (from the standpoint
of temporal resolution) of upper air meteorological data, especially with
respect to temperature soundings, which were made on an hourly basis by

aircraft.  In the LAPPES program four to six helicopter  temperature  pro-
files plus two radiosondes were taken each day.  However,  it was  evident
from the discussion of the Navajo results that spatial resolution in
temperature soundings may be more important than temporal  resolutions  in
complex terrain.
          In a series of experimental studies at the TVA Kingston and
Johnsonville Steam Plants plume S02 concentration data taken from flights
of fixed-wing aircraft were used by Nilsson (1975)  in a  preliminary  anal-
ysis, to calculate a values, employing three different methods.   The first
method is a statistical approach in which the Gaussian curve is approximated
by a series of straight lines by taking several points on  the graph.   The
second method is the area under a curve approach, where  a  (area)  is  obtained
by integrating the Gaussian curve equation.  The third method is  a peak-based
approach whereby the curve peak is measured and the standard deviation is
obtained by dividing the calculated width between the points where the ordin-
ates of the graph are a certain fraction of the peak.  Linear regression is
performed on the a  values calculated by one method versus  the a   values
                  J                                             J
produced by another.  For the Kingston Power Plant  a  (stat) is greater
than a  (area) in all cases, but when the S02 data  taken near the Johnsonville
Plant are adjusted to account for instrument time lag (this data  adjustment
procedure is not done for the Kingston graphs), the resulting regression
showed a slope much closer to unity.  These results are  summarized in  Table  18
The study did not focus on plume-terrain effects at all  in  the program, but
was primarily concerned with the application of different  statistical  tests
on plume location and dimensions.  An analysis of the Kingston data  by TVA
is in progress.

Area vs Stat

Area vs Stat

10 Percent vs Stat

10 Percent vs Area


          In the GEOMEl  analysis of Kingston data,  terrain characteristics
were determined using elevations read from USGS topographic maps for 200 m
increments between the source and the six S02 monitoring stations.   Figure 19
shows elevation cross-sections from the Kingston Steam plant to six monitor-
ing stations, together with SDE values.   Ground-level  S02 measurement stations
were labeled from 1  through 6.  Data were analyzed  for the following time

          Station No. 1           1/72 to 6/72, 1/74 to 12/74
          Station No. 2           1/74 to 12/74
          Station No. 3           1/74 to 12/74
          Station No. 4           1/74 to 12/74
          Station No. 5           1/74 to 12/74
          Station No. 6           7/72 to 12/72, 1/74 to 12/74.

Wind speed, wind direction and temperature measured at about 46 m above
the  ground,  and  temperature measured at  1.22 m  above  the ground, were
available in the Kingston  data.  Wind direction was coded  in 16 compass
directions.  Stack parameters were  obtained from FPC  Form  67.   Gas  tem-
perature  and exit velocity were  calculated from daily coal  consumption
rates,  BTU  content of coal, and  BTU  rating of  the unit.  S02 emission
rates were  provided  by TVA in  tons  per day for  each unit.
          An analysis was  made by GEOMET  between measured  concentrations
and  those estimated  using  a standard Gaussian  plume dispersion  model for
point sources.   The  dispersion model is  a multiple-source  Gaussian  plume
model,  adopted  from  EPA's  UNAMAP (Users'  Network for  Applied Modeling of
Air  Pollution).  Plume rise is calculated according to Brigg's  plume rise
estimates.   The  program was modified to  use dispersion parameters c and
az,  based on the TVA curves  (TVA 1970).   Temperature  gradient  measurements
were used to determine the closest  stability class  for  the observation
period; no  unstable  condition  (less  than  -0.13K/100m) was included in
this analysis.





a   303


                                    I	1	1	1	1	1	1
           0     1
                                                                                      SDK = 7.

                                  Down Wind Distance (km)
10    11
         Figure 19.  Elevation Profile from Kingston Plant to Each Receptor

          About 125 cases of 24-hour mean S02 concentrations  were  cal-
culated by the model using hourly meteorological and emission data for
each of six observation stations.  The mean concentrations are summarized
together with SDE values in Table 19.  Fifty percent of the model  values
are in the same order of magnitude as the observed values; the other
50 percent are off by an order of magnitude or more.  The ratios of
computed concentrations to the corresponding observed  values  are  also
shown in Table 19.  The principal conclusion to  be drawn  from these
comparisons is that wind direction resolved to 16 compass directions
is not sufficient to define the  location of plume relative to the
monitoring stations.  Between adjacent elevation cross-sections there
could be hills or valleys.  This emphasizes the  short-comings of  com-
puting SDE along a small number  of specific directions.   In  reality,
a plume travels in the downwind  direction in a narrow-angle  sector; and
terrain features in the entire sector influence  the diffusion of  the
plume.  Therefore, it is logical to  compute the  SDE of  a  sector.

SDE (m)
Mean Competed
Concentration (fig/m )
Mean Observed
Concentration (^jg/m )
Computed Minus
Observed (/^g/m )
Computed Divided
by Observed

     About 125 cases were used for each station.

          Correlations between SDE values and the values of xcalc/Xobs
are not evident.  In addition to the definition of wind direction utilized,
and the deficiency in the computational method of the SDE, the reasons
for the poor correlation can be (1) the terrain induced aerodynamic effect
is not included, and (2) the small amount of data in the preliminary GEOMET
analyses suggest that a plume dispersion model for complex terrain requires
at least the following capabilities:

          1.  Inclusion of a means of categorizing terrain
              numerically by sectors and by distance from the
          2.  Inclusion of wind flows of varying pattern rather
              than just a uniform flow.
          Table 20 (Part A, Plume Sampling Characteristics and Part B,
Meteorological Data) is a compendium of the 16 field studies that were
reviewed in Section  IX.  The major objective of each of these research
efforts has been the compilation of data regarding the physical behavior
of either stack plumes or tracer material in complex terrain.  The format
of this summary includes (in Table 20A) a statement of study title and
investigators, the nature of pollutant (tracer) and source, and a brief
project comment.  The information matrix categorically depicts the nature
of the field observations for each study, describing the characteristics
of ground and airborne sampling efforts.  The details concerning ground
sampling include the number of samplers, the distance range, the terrain
characteristics of samplers and the number of sampling days.  The distance
range, number of sampling days and the sampled plume characteristics are
listed for airborne sampling.  Meteorological observations are portrayed
in Table 20B with information concerning methodology of temperature measure-
ments, type and range of aerial turbulence measurements, frequencies of
stable, neutral, or unstable stabilities and type of wind data along with
range of wind speeds and wind direction characteristics.

A. Plume and Sampling Characteristics
Study Number



Study Title and Investigators
"P articulate Diffusion Over
Irregular Terrain,
McMuLlen and Perkins 1963
"Diffusion Over Coastal
Mountains of Southern
Hinds 1970

"Plume Dispersion
Studies and Modeling
for Fossil -Fueled Power
Well 1974

Nature of Pollutant
(Tracer) and Source
particles released
from straight line
airplane flight
Releases from ZnS
from ground-level
point sources

SO plume from

Some of the earliest FP
diffusion trials ever con-
ducted in complex ter-
Diffusion comparisons
over mountains and
flat terrain show night-
time stable conditions
lead to interactions
between terrain-
induced drainage flow
and synoptic scale
flow in complex ter-
Study clearly demon-
bulence due to rough

Ground Sampling
of Samplers
=: 100


Mobile van

11-21 km

= 8 km


at Samplers
450-600 rn
above valley
30-500 m
above sea level


of Days

113 tests

Oct 1972
thru Apr
1973 (no.
of days
not known
Airborne Sampling
27 km


of Days


Downwind and
return to release


                                                                                    TABLE 20.  (CONTINUED)
A. Plume and Sampling Characteristics





Study Title and Investigators
"An Initial Evaluation of
Sulfur Dioxide Measurements
Conducted at Naughton
Power Plant,"
Sp angler et al. 1973

"Airborne SO^ Measure-
ments at Four Corners
Power Plant, '
Niemann 1973

"Analysis of Plume Data -
Four Corners Power Plant, '
Smith and Anderson 1974
"Nighttime Tracer Studies
of Power Plant Plumes at
the Navajo Generating
Station, "
Hovind et al. 1973
"Daytime Plume Simu-
lation Tracer and Clima-

tology Program at the
Navajo Generating
North American Weather
Consultants 1974

Nature of Pollutant
(Tracer) and Source
SO from power
plant stack

SC"2 from power
plant stack, com-
parison with NCAA
model results

Visible (oil fog)
, smoke and fluor-
escent particle

Visible (oil fog)
smoke released

upwind of ele-
vated terrain.
. Fluorescent
particle tracer
to simulate SO2
released by air-
craft at stack
and effective
stack heights.

During stable flow the
plume remained aloft with
no ground-level impaction
upon the elevated terrain
downwind of the plant

Turbulence dissipation
measurements indicated
enhanced dilution over
complex terrain than
that expected over flat

Two cafe* where FP relesie* under
stable nighttime condition! did not
rapport the theory of direct center-
line Impingement OB elevated ter-

Tha greatest lampllng network
bnpkcrj were noted under light
wind looping condition* on
nunmer day?

Ground Sampling

of Samplers




1-5 km


Up to
45 km

Up to

plant or

of Samplers
 100-250 km
above stack


*=s up to 10OO nr
above stack

s= up to 600 m
above stack


of Days




Airborne Sampling

0-15 km
stable day,
not known
for other
five days
Up to
45 km

Up to
18 km


of Days





Ascending spiral,
crosswlnd, along

Crosswind and




                                                                                            TABLE 20.  (CONTINUED)






A. Plume and Sampling Characteristics

Study Title and Investigators
"Navajo Generating Station
SO Field Monitoring Pro-
Rockwell Inl., MRI, SAI
"Summary Report on
Meteorological Power
Plant Plume Simulation
Tracer Studies in
Huntington Canyon, Utah,
Hovind et al. I973a

"The Influence of Rough
Mountainous Terrain Upon
Plume Dispersion from An
Elevated Source,
HovJnd et al. 1974
"Diffusion in Canyon with
Rough Mountainous Ter-
rain, '
Start et al. 1975

"Effluent Dilutions Over
Mountainous Terrain,
Start et al. 1974

Nature of Pollutant
(Tracer) and Source
SO2 from power
plant stack

FF and smoke
releases from
effective stack
height, by sky-
writer, in addi-
tion to helicopter
smoke releases
in area inacces-
sible by plane *
particles at one
site and oil fog
dispersion at two
SFg tracer from
stack, elevated
terrain, and can-
yon floor. Also
oil fog flow.
SF^ tracer released
from smelter stack

(Same aj Study
No. 8)

Extensive supplemental
observational informa-
tion including photo-
graphs of various types
of plume behavior -
much of subjective infor-
mation reported valuable
to understanding flow in
complex terrain - several
physical mechanisms for
the increase of lateral
dispersion observed

Ground Sampling

of Samplers

86 rotorod

Used at
FP site
Number not


Up to
30 km

Up to
15 km

Up to
25 km

0-10 km

0-5 km

of Samplers
= up to 600 m
above stack

Up to 850 m
above stack


Up to =350 m
above canyon

Up to =850 m
above smelter

of Days
145 days
total, 80
tion days




Airborne Sampling

Up to
28 km

was made,
but details
not discus-

Up to
25 km

10 km

Up to
6 km

of Days





Crosswlad, along


Crosswind and

Center line

Center! in e

         *  Refers to Tracer Program III,  the most extensive of seven separate field studies (each of about one

            week's duration), conducted by NAWC at the Huntington Canyon Plant Site.





A. Plume and Sampling Characteristics

Study Title and Investigators
"Elevated FP Tracer Releases
from Kaiparowits Power Plant
Site, "
North American Weather
Consultants 1974
"Large Power Plant Effluent
Study - Vol. 4, "
Schiermeler 1971

TVA Field Smelters in the
Vicinity of Kingston Power

Nature of Pollutant
(Tracer) and Source
FP tracer released
from aircraft at
two sites supple-
mented by oil fog
SOT from power
plant stack

SO from power
plant stack

Vicinity of proposed plant
site subject of tracer
studies and model simu-

Airborne sampling data
provide large data base
for future studies of ter-
rain influences

Ground Sampling

of Samplers
Not stated

Up to 14

11 fixed
sites, plus


Variable -
op to
27 km

Up to

of Samplers

Up to mid-
stack height

Up to 250 m
above the
plant grade

of Days
Not stated
but total of
10 tracer

1973, Mar-
Apr 1974,
Airborne Sampling


Up to
16 kjn

Up to
21 km

of Days




Crosswind at
several altitudes

Crosswind at
several altitudes

                                                                                      TABU 20.  (CONTINUED)
S tudy N um ber





B. Meteorological Data

Tpmpe nature
Aircraft Profiles
Sampling at ground
and tower
Hourly radiosondes
Sampling at surface
and 100 m
Aircraft Profiles
2 to 3 Radiosondes
Per Day

Aircraft Profiles

Types of


Lateral (ff )


Range of Aerial




Observed Stability Conditions
of Stable




of Neutral




of Unstable




Other Stability

Not known, precisely,
but mostly neutral and
Not precisely knowna but
majority of sampling
was probabhy conducted
under neutral or unstable
conditions (between H)am
and 4pm only)
Not exactly known, but
stated that plume track-
ing over 6-day period
covered a variety of
meteorological condi-
tions including 1 day
with extremely stable
air mass.

Types of Wind Data
Radiosonde, tower,
plbal, surface

Radiosonde,, tower,

Radiosonde, tower,

Pibal, surface

RanRe of Wind Speeds
Light (3)
Strong (1)



Not known

Wind Direction Characterise! cs
Predominantly SSE,



Not known, but both easterly
and westerly flow sampled


Study Num
B. Meteorological Data
Aircraft Profiles
Aircraft Profiles
Aircraft ProflUs
Ground Sampling
Aircraft Profiles
Aircraft Profiles
1 Radiosonde Per
Aircraft Profiles
Ground Sampling
A Ircraf t Profiles
Sampling at 3 levels
on 183 m stack
Ground Sampling
1 Radiosonde Per
Some vertical temp-
erature profiles
taken, but number
and mediod unknown
Types of
Dissipation Rate
Dissipation Rate
Dissipation Rate
Dissipation Rate
Range of Aerial
Yes, sfc. to plume
Yes, sfc. to plume
Not precisely known
Yes to top of plume
Observed Stability Conditions
of Stable

of Neutral

of Unstable

Other Stability
1/2 (Transitory inver-
sion breakup)
Not known precisely, but
majority of cases stable
or neutral
Not precisely known, but
testa during neutral,
stable, and slightly
unstable conditions
Types of Wind Data
Radiosonde, surface
Pibal, stack top,
Pibal, stack top
Radiosonde, plbal,
stack top, surface
Plbal, stack top,
Tower, stack top,
Radiosonde, pibal,
Range of Wind Speeds
Nov. cases moderate
Jan, cases calm to
very light
2 days light,
2 days moderate
Very light
Moderate to strong
Wide range
0 to 4 m/sec
Light to moderate
Light to moderate
Wind Direction Characteristics
Steady easterly variable
Generally easterly near surface
Great variability
Mostly southwest
Observations divided Into 3 cate-
gories - 2 distinct directions and
Mostly east-southeast, westerly
on one occasion
Mostly southeast and north at
stack top
All between northwest and
east- northeast

                                                                                         TABLE 20.  (CONCLUDED)
B. Meteorological Data
Aircraft Profiles
Ground Sampling
2 Radiosondes Per
Aircraft Profiles
Sampling at 1 , 2,
and 48 m levels
Types of
Lence measure-
ments by NtRI as
part of LAPPES
LQ spring and
fall of 1968
Dissipation Rate
Range of Aerial

Yes, up to 5000 m
Observed Stability Conditions
of Stable
of Neutral
of Unstable
Odier Stability
Measurements made during stable morning and inversion breakup
for each date
Types of Wind Data
Radiosonde, pibal,
Tower, plbal,
Range of Wind Speeds
Light to moderate
Wind Direction Characteristics
Southwest and west dominant

                               Section X

          The analysis of the scope of previous studies of plume (or
simulated plume) behavior in complex terrain, and its relationship to
meteorological, emission, and topographical factors has revealed that
a modest data base, of both theoretical and observational information has
been gathered relative to important phenomena associated with flow in com-
plex terrain.  Financial  restraints in conjunction with other practical
considerations have dictated that field measurement programs  each focus
on a small number of specific objectives.   The diversity of geographic
sites selected, the variety in the experimental methods utilized, and
the differences in the analysis of results present a formidable under-
taking if the goal is to consolidate the outcomes of each of  these pro-
grams into a flexible, yet coherent, universal set of rules for plume
diffusion in complex terrain.  However, certain common denominators have
been found to link the diversity of research projects in the literature,
thus allowing a number of qualitative generalizations regarding plume
diffusion and transport in complex terrain to be presented.
          Plume studies have indicated that an expected increase in turbu-
lence exists in complex terrain over that found over relatively flat sur-
faces.  This conclusion has been achieved through analyses of wind direction
fluctuations, comparison of ay and az measured values to the Pasquill-
Gifford values applicable to flat terrain, and by model-to-measurement
comparisons of effluent or tracer concentrations.  As earlier references
have made clear, a major purpose of many field investigations has been
the collection of plume geometry data from which inferences can be made
concerning the levels of turbulence present near power plants located in
complex terrain.  It appears from a study of this literature that in
general, aircraft measurements of plume cross-sections yield the best
information about plume geometry.  When aircraft measurements are not

available, comparisons of measured  ground-level  concentrations  to model
calculations of ground-level  concentrations in flat terrain may be  used
to estimate turbulence enhancement  due to the complex terrain.
          One of the important  questions  to be approached is how stability
affects the proximity of the  plume  to  the surrounding complex terrain.
For those studies in which  the  stability  of the  atmosphere was reported
in detail, the stable conditons  most frequently  characterized the cases
studied, principally because  study  objectives often were to examine the
validity of hypothesized NOAA model plume impingement on elevated terrain
under these conditions.  The  Navajo studies (Rockwell, MRI and SRI, 1975)
contained two cases where the few FP releases under stable nighttime  con-
ditions did not support the theory  of  direct centerline impingement on
elevated terrain.  Even though  the  tracer was initially transported towards
critical elevations (between  stack  top and effective stack height), no
distinct maximum impact zones were  indicated, except for one case,  and  that
was for a location below the  release elevation (however, the highest  S02
ground concentrations occurred  on the  cliffs).  Evidently, strong vertical
mixing was occurring near the elevated terrain even with the stable con-
ditions, probably as a result of strong wind shear induced by the rising
terrain.  Direct impingement  upon elevated terrain was also not evident  in
the Huntington Canyon studies for stable  conditions;* when the  plume  was
directed toward the canyon  walls, the  observations indicate that it was
deflected away from the wall  before impingement.*  During lapse conditions
at Huntington Canyon it was concluded  that transient impactions on  the
order of several minutes may  indeed occur at any point, however the results  are
limited in significance; one  reason being because the topography of the  release
points varied greatly for the differing meterorological conditions.   Direct
impingement of a plume against  steep canyon walls was observed  by Start  et al.
 *  The lone stable release from an elevated position on a natural prominence visually showed the plume
   to impinge on the canyon wall, however,  it moved up the slope, away from the samplers, so ao
   quantitative data were obtained. Kinematically produced deformation effects may have been responsible.

in one Stability B test case near the Garfield Smelter.   In the Navajo
studies, oil smoke releases during transitional fumigation conditions
allowed transport of the smoke into the rills of one of the elevated
terrain features (Leche-e Rock) 8 km downwind; earlier stable conditions
had presented no evidence of direct centerline impingement.  The turbulent
downward transport of the plume was expected to result in the greatest
impact on elevated terrain during transitional fumigation periods between
stable morning and neutral unstable afternoon conditions.  The greatest
Navajo sampling network impacts were noted under light wind looping con-
ditions on summer days.  Most of the field studies have been of limited
duration (generally less than two weeks, and in most cases of the order
of one week), and as a result have examined dispersion over a relatively
limited range of atmospheric stability conditions.  However, plume behavior
in complex terrain during documented transitory conditions (especially
inversion breakup) has been investigated and discussed in detail (i.e.,
over periods greater than one week) in the six-month Navajo study by
Rockwell International, Meteorology Research, Inc., and Systems Applica-
tions, Inc. (1975).  Many of the observed impingement events occurred
during unstable conditions and primarily at the initiation of unstable
conditions.  Temperature soundings atop a relatively flat, elevated ter-
rain feature for the days on which the plume passed close to or inter-
sected that terrain (resulting in the highest observed ground concentrations)
were not conducted, but soundings near the plant suggested that fumigation
rather than stable conditions may have resulted in the high concentrations
          There is some evidence from the LAPPES program (Schiermeier 1970,
1972), GEOMET's analyses of the LAPPES data  (1976), and the Four Corners
studies  (Niemann 1973, Smith and Anderson 1974) that horizontal spreading
(i.e., a ) is amplified to a greater extent than vertical spreading in
complex terrain, particularly under stable conditions.  The resultant
increase of a  has been attributed primarily to plume separation processes

and plume meandering which  occur when the higher terrain elevations are
confronted by the plume.  Plume meandering was frequent in the Navajo region
under stable light conditions due to gradient flow interaction with the
nocturnal thermal  circulations induced by terrain.   Both Smith and Anderson
and Niemann concluded that  significant differences  in plume dimension and
dilution could occur without any major change in the stability category
as determined by turbulence variations at the plume level.  This indicates
that perhaps a more concise way of characterizing dispersion other than
atmospheric stability may be needed in complex terrain.   At Huntington
Canyon, moderate to heavy turbulence conditions have been documented with
stable conditions, with enhanced dilution as  stabilities increased.  Recent
acoustic sounding data shows extensive waves  and breaking waves in stable
layers, thus indicating that stable layers are not quiescent.   The cooling
and subsequent development  of radiation inversions  in irregular topography
cause drainage of air down  the slopes, and this acceleration of air has to
set off compensating circulations.  Thus, inversions and their possible
subsequent anti-mountain circulations can be  said to enhance turbulence
in this complex terrain situation.  Studies have also shown turbulence
levels in the down-valley and downslope flow  to increase as a function of
the inversion intensity, probably due to the  role of inversions in the
production of katabatic winds.  Lee wave phenomena have also been pointed
out as responsible for increased turbulent effects, and mechanical tur-
bulence and vertical shear  are postulated to  arise over and around peaks
and ridges of mountainous terrain.  As was evident in the Navajo program,
significant interactions between terrain-induced drainage flow and the
prevailing gradient flow aloft may occur near elevated features.
          A comparison study of measured aerial plume centerline S0? con-
centrations to the concentrations predicted by the Gaussian plume model
on one test day characterized by stable conditions  near the Naughton Plant
site showed results similar to those obtained near the Four Corners and
Navajo plants for stable conditions.  Within  2 km of Naughton for the one
case situation described by Spangler et al. (1973)  model S0? centerline

concentrations were greater than seven times those observed; while beyond
7 km the calculations were within a factor of 2 of the measured values.  At
Four Corners  (Smith and Anderson 1974) 11 data points representing three
test days were overpredicted by factors of 5 to 30 at 1 km from the stack;
the measured/calculated values were within a factor of 2 beyond 12 km,
and results were similar at 18 km from the plant.  Niemann's (1973) com-
parison of Four Corners measured instantaneous S02 plume centerline con-
centrations for six flights under neutral and very stable conditions in two
different seasons support the Spang!er et al. (1973) and the Smith and
Anderson (1974) results.  For the neutral condition data, the conventional
plume model for centerline dispersion was used for comparison, and for the
stable data,  the NOAA model predictions were used.  Both models overesti-
mated the measured concentrations by a factor of 10 under both stability
conditions close to the plant.  At distances greater than 15 km, the con-
ventional Gaussian calculations generally agreed with the observed values,
while the NOAA model over-predicted centerline concentrations by a factor
of 2 under stable conditions.  Seven comparisons of equivalent maximum
hourly ground concentrations obtained from airborne and stacktop FP releases
and the calculations of the NOAA centerline  prediction equation were made
at Navajo (Hovind et al. 1973 draft report).  Under stated stable conditions,
model overestimations ranged from 20 to 300  times the actual observed S02
values.  At Huntington Canyon, 11 test comparisons between observed plume
centerline concentrations and corresponding  values calculated by the standard
Gaussian plume model showed minimal differences during moderate to strong
temperature lapse; canyon dilutions of 5 times to 15 times that of
"standard" curves were evident for strong inversions (Start et al. 1975).
In the Hovind et al.  (1973c) study in the same region, the NOAA model
overestimated centerline concentrations by 10 times at 2.5 km downwind,
but approached actual  measured values beyond 10 km during one week of
observations in which all  except one of the days were characterized by
stable conditions; the remaining day was neutral.  The Hovind et al. (1974)
study, compared the ratio of calculated standard Gaussian plume centerline
concentrations to observed values at three sites with different roughness

characteristics.  These ratios ranged from 10.2 for the Huntington Canyon
site under F stability for six cases, to 6.0 for four cases of D stability
in the rugged open canyon site, to 1.2 for nine cases of E stability in
flat open terrain.  Near the Garfield Smelter, Start et al. (1974) found
that for this location, characterized by complex air circulations due to
the presence of the nearby Great Salt Lake, measured xu/Q values were 2
to 4 times less than predicted by standard curves in seven elevated FP
releases in lapse conditions.  INTERA (1975) verifies these results in
three tests which found NOAA model concentrations to be greater than
observed centerline values by factors of 2 to 5 (for stability categories
of B and C) at distances within 4 km of the plant in two of the three tests,
and for all distances in the last test.   Beyond 4 km, calculated values
approached observed values.  Hoffnagle et al. (1975) compared the measured
data of four FP tests at two proposed plant sites in complex terrain to
NOAA model  calculations where one test was characterized by stable condi-
tions, and the other three characterized by unstable conditions.  The
mean ratio of calculated to observed values in all  four cases (7 to 20
receptors evaluated in each case) was within 30 percent of unity.
          Comparisons of the NOAA, EPA, and INTERA models systematically
show greater overestimation with respect to plume centerline values close
to the Navajo, Garfield, and Kaiparowits sites than at greater distances,
suggesting that neither the Gaussian nor INTERA models in these cases
adequately take into account the initial dilution due to emission-related
parameters (buoyancy and turbulence generated by stack exit velocity and
possible immediate terrain effects).  The validity of the comparisons for
aerial data may be limited because of the different averaging times repre-
senting the model calculations (one hour, 24 hours for Valley) and measure-
ments (one minute).  The effective plume height used in the model calculations
was determined from aerial data, rather than from plume rise formula; thus,
the true predictive capability of these differing formulae could not be
realistically assessed for the given meteorological and topographical con-

          Comparisons of measured plume dimensions to the Pasquill-Gifford
diffusion parameters (a  and a ) in complex terrain indicate that, for
both E and F stabilities, rapid growth of the plume occurs initially
followed by slower growth than predicted by the standard Gaussian plume
model.  The model values in general underestimate initial lateral spread,
and overestimate vertical spread at greater distances.
          Several studies have revealed that greater discrepancies between
modeled/observed concentrations occur under stable conditions than under
neutral conditions.  The NOAA Huntington Canyon study, the Niemann 1973
study at Four Corners, and the NOAA model/measurement comparisons made by
INTERA (1975), for Navajo (under stable conditions), Kaiparowits (unstable
conditions) and Garfield (unstable conditions) support this conclusion.
          Analysis of the available numerical models developed or
adapted for use in complex terrain from the literature reveal no evidence
of validation for the Environmental Research and Technology (Egan 1975)
modified Gaussian model or the Aerovironment (MacCready et al. 1974)
modified Gaussian model.  Research has been done in the past on effects of
topography on airflow (with two outstanding examples being drainage-
counter-drainage winds and hydraulic "jump" flow) but nothing surfaced
during this review that revealed an attempt to develop and validate a
point source air quality model to incorporate these effects.  Current
models are incapable of simulating plume behavior when the lower part of
the plume is caught in drainage flow and the upper part of the plume is
in the counter flow.  There exists a need to determine how severely down-
wash conditions affect the performance of the available models.  Presently
available models represent the influences of terrain by a receptor height
adjustment procedure, or in the case of the INTERA model, by means of a
wind speed profile.  The detailed turbulence influences of terrain
characteristics and terrain obstructions are required for reliable esti-
mations of air quality impact; future emphasis must be placed on relating
terrain roughness to dispersion in complex terrain in a quantitative

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                               Appendix B

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Lester, P.P. and W.A. Fingerhut, 1974.  "Lower Turbulent Zones Associated
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Niemann, B.L.,  1974.  Plume Simulation Smoke Tracer Studies at  the Navajo
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Raymond, D.J., 1972.  "Calculation of Airflow Over an Arbitrary Ridge
  Including Diabatic Heating and Cooling." J. Atmos. Sci. 29:837-843.

Record, F.A., 1962.   Comparison of Sulphur Dioxide Diffusion Trials
  Geophysics Corporation of America GCA Technical Report 62-11-G.
  19 November 1962.

Roberts, J.J., E.J.  Croke, A.S. Kennedy, J.E. Norco, and L.A. Conley, 1970.
  A Multiple-Source Urban Atmospheric Dispersion Model. Argonne National
  Laboratory ANL/ES-CC-007.   May 1970.

Rockwell International, Inc., Meteorology Research, Inc., Systems Applications,
  Inc., 1975.  Navajo Generating Station Sulfur Dioxide Field Monitoring
  Program.  Vol. 1, Final Report, Sept. 1975.     

Roffman, A. and R.Grimble, 1974,  "A Time-Dependent Air Quality Model with
  Terrain Corrections,"  Preprints A.M.So  Symposium on Atmospheric Diffusion
  and Air Pollution, September 9-13, 1974, Santa Barbara, Calif, pp. 311-316.

Sagendorf,  J.F. and C.  Ray Dickson, 1974.   Diffusion Under Low Windspeed,
  Inversion Conditions. NOAA Technical Memorandum ERL ARL-52, December 1974.

Schiermeier, F.A., 1971.  "Study of Effluents from Large Power Plants."
  Paper presented at American Industrial Hygiene Assoc. Conf., May 1971,

Schiermeier, F.A. and I.E. Niemeyer, 1970.  Large Power Plant Effluent
  Study (LAPPES) Volume 1  - Instrumentation, Procedures and Data Tabula-
  tions (1968).  U.S. Dept. of Health. Education, and Welfare.APTD 70-2.

Schiermeier, F.A., 1970.  Large Power Plant Effluent Study (LAPPES)
  Volume 2 - Instrumentation, Procedures, and Data Tabulations (1967 and
  1969).U.S. Dept. of Health, Education, and Welfare.APTD 0589.

Schiermeier, F.A., 1972.  Large Power Plant Effluent Study (LAPPES) Volume  3 -
  Instrumentation. Procedures, and Data Tabulations (1970).Environmental
  Protection Agency APTD NO. 0735.

Schiermeier, F.A., 1972.  Large Power Plaht Effluent Study (LAPPES) Volume  4 -
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Settari,  A.  and  R.B.  Lantz,  1974.   "A Turbulent  Flow Model for Use in
  Numerical  Evaluation  of Air  Quality."   Paper presented  at the 25th
  Annual  Technical  Meeting of  the  Petroleum Society of CIM in Calgary,
  May  7-10,  1974.

Shum,  Y.S.,  W.D.  Loveland,  and E.W.  Hewson, 1975.   "The Use of Artificial
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                                  TECHNICAL REPORT DATA
                           (Please read Instructions on the reverse before completing)
                                                          3. RECIPIENT'S ACCESSION1 NO.
  An Appraisal of  Current Research
                                                          5. REPORT DATE
                                                            March 1977
  AUTHOR(s)Robert C.  Koch,  W.  Gale Biggs, Paul H. Hwang,
  Irving Leichter,  Kenneth E.  Pickering, Eric R. Swadey,
  and John I  . Swift	.	_
                                                          10. PROGRAM ELEMENT NO.
  GEOMET, Incorporated
  15 Firstfield  Road
  Gaithersburg,  MD  20760
              11. CONTRACT/GRANT NO.

  Environmental  Sciences Research Laboratory -  RTP,  NC
  Office of Research  and Development
  U. S. Environmental  Protection Agency
  Research Triangle  Park, North Carolina  27711	
                 Interim   11/75 - 10/76
              14. SPONSORING AGENCY CODE
  This report  reviews  the literature of scientific studies of  the  behavior of stack
  plumes from  fossil-fueled electric power plants in complex  (hilly  or mountainous)
  terrain.  Non-conservative chemical transformation and depletion,  and conservative
  transport and  diffusion of pollutants are considered.  Studies of  S02 oxidation
  rates in power plant plumes are described and the primary mechanisms for conversion
  to sulfate are detailed.   Scavenging of S02 from plumes by precipitation is reviewed
  along with surface contact and deposition as important plume depletion processes.
  Current theories  of  airflow, turbulence and diffusion phenomena  in complex terrain
  are described, and are exemplified through the review of sixteen field observation
  programs of  the physical  behavior of plumes from continuous  elevated sources in
  complex terrain.   The review discusses program objectives, data  sampling methodolo-
  gies, model-to-measurement comparisons associated with the field program conclusions,
  The types of models  available to simulate plume behavior numerically are discussed
  in the contexts of these programs.  In addition, results are reported of an indepen-
  dent GEOMET  analysis of ay and CTZ relationships in the Gaussian  plume model over
  complex terrain,  using data from LAPPES and TVA field measurement  programs.
                               KEY WORDS AND DOCUMENT ANALYSIS
                                             b.lDENTIFIERS/OPEN ENDED TERMS
                              cos AT I Field/Group
 *Air pollution          *Mountains
 *Reviews                *Atmospheric diffusion
 *Electric power  plants  *Transport properties
 *Plumes                 *Chemical reactions
 *Sulfur dioxide         *Field tests

  19. SECURITY CLASS (This Report)
                                              20. SECURITY CLASS (This page)

                            22. PRICE
EPA Form 2220-1 (9-73)