EPA-450/4-88-010
Screening Procedures for Estimating the
Air Quality Impact of Stationary Sources
by
Roger W. Brode
Source Receptor Analysis Branch
Technical Support Division
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
August 1988 -, 0 _
a : S. Erujror.ncrfV
n Sti-aet, Hooa
60604
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DISCLAIMER
This report has been reviewed by the Office of Air Quality Planning and Standards, EPA, and approved for
publication. Mention of trade names or commercial products is not intended to constitute endorsement or
recommendation for use.
The following trademarks appear in this document'
IBM is a registered trademark of International Business Machines Corp.
Microsoft is a registered trademark of Microsoft Corp.
AFFILIATION
The author, Roger W. Brode, is on assignment from the National Oceanic and Atmospheric Administration,
U.S. Department of Commerce.
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PREFACE
This document presents current EPA guidance on the use of screening
procedures to estimate the air quality impact of stationary sources. The
document is an update and revision of the original Volume 10 of the
"Guidelines for Air Quality Maintenance Planning and Analysis", and the
later Volume 10 (Revised), and is intended to replace Volume 10R as the
standard screening procedures for regulatory modeling of stationary sources
An important advantage of the current document is the availability of the
SCREEN model as a computerized version of the short-term procedures.
While EPA encourages use of the current document for making screening
estimates, it is being issued as a draft for public comment until such time
as a final version can be incorporated into a future supplement to the
"Guideline on Air Quality Models (Revised)."
Although attempts are made to thoroughly check computer programs with
a wide variety of input data, errors are occasionally found. Any suspected
errors and technical questions regarding the use of the SCREEN model should
be directed to (919) 541-5681 or (FTS) 629-5681. Copies of the SCREEN
model in diskette form may be obtained from the National Technical Informa-
tion Service (NTIS), Springfield, VA 22161. Purchasers of the SCREEN model
from NTIS may obtain future revisions to the model from NTIS. Revisions
will also be made available on the UNAMAP Electronic Bulletin Board, which
may be accessed through (919) 541-1325 or (FTS) 629-1325.
m
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ACKNOWLEDGMENTS
Special credit and thanks are due to Mr. Thomas E. Pierce, EPA-AREAL,
for his assistance with developing the FORTRAN code for the SCREEN model
and for his technical suggestions on improving the procedures. Credit
is due Mr. Russell F. Lee, who served as EPA Project Officer on the
preparation of the original version of the Volume 10 procedures, and who
continued to provide valuable technical assistance for this document, and
to Mr, Laurence J. Budney, author of the revised version of Volume 10,
which served as a foundation for development of the current document.
The author also acknowledges those who reviewed the document and provided
many valuable comments, including the EPA Regional Modeling Contacts,
several State meteorologists, and meteorologists within EPA-OAQPS. Final
thanks are due to Messrs. James L. Dicke and Joseph A. Tikvart of EPA-OAQPS
for their support and insight, and to Mrs. Phyllis Wright for her excellent
secretarial support.
iv
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TABLE OF CONTENTS
Page
Preface iii
Acknowledgments . iv
List of Tables vi
List of Figures vi i
List of Symbols ix
1. Introduction 1-1
2. Source Data 2-1
2.1 Emissions 2-1
2.2 Merged Parameters for Multiple Stacks 2-3
2.3 Topographic Considerations 2-4
2.4 Source Building Complex 2-4
3. Meteorological Data 3-1
3.1 Wind Speed and Direction 3-1
3.2 Stability 3-3
3.3 Mixing Height 3-5
3.4 Temperature . 3-6
4. Estimating Source Impact on Air Quality 4-1
4.1 Simple Screening Procedure 4-2
4.2 Estimating Maximum Short-Term Concentrations 4-7
4.3 Short-term Concentrations at Specified Locations 4-18
4.4 Annual Average Concentrations 4-22
4.4.1 Annual Average Concentration at a Specified
Location 4-22
4.4.2 Maximum Annual Average Concentration 4-25
4.5 Special Topics 4-26
4.5.1 Building Downwash 4-26
4.5.2 Plume Impaction on Elevated Terrain 4-29
4.5.3 Fumigation 4-31
4.5.4 Estimated Concentrations from Area Sources .... 4-36
4.5.5 Contributions from Other Sources 4-38
4.5.6 Long Range Transport 4-42
5. References 5-1
Appendices
A. SCREEN Model User's Guide
Al. Introduction A-l
A2. Tutorial A-7
A3. Technical Description A-29
A4. Note to Programmers A-43
A5. References A-45
B. UNAMAP Dispersion Models B-l
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LIST OF TABLES
Table Page
3-1 Wind Profile Exponent as a Function of Atmospheric
Stability for Rural and Urban Sites 3-2
3-2 Key to Stability Categories ,3-4
4-1 Calculation Procedures to Use with Various Release Heights 4-12
4-2 Stability-Wind Speed Combinations that are Considered in
Estimating Annual Average Concentrations 4-24
4-3 Wind Speed Intervals Used by the National Climatic Data
Center for Joint Frequency Distributions of Wind Speed,
Wind Direction and Stability 4-24
4-4 Downwind Distance to the Maximum Ground-Level Concentration
for Inversion Break-up Fumigation as a Function of Stack
Height and Plume Height 4-33
4-5 Downwind Distance to the Maximum Ground-level Concentration
for Shoreline Fumigation as a Function of Stack Height and
Plume Height 4-34
VI
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LIST OF FIGURES
Figure Page
4-1 Maximum xu/Q as a Function of Plume Height, H
(for use only with the Simple Screening Procedure). 4-5
4-2 Downwind Distance to Maximum Concentration and
Maximum xu/Q as a Function of Stability Class and
Plume Height (m); Rural Terrain. 4-45
4-3 Downwind Distance to Maximum Concentration and
Maximum xu/Q as a Function of Stability Class and
Plume Height (m); Urban Terrain. 4-46
4-4 Stability Class A; Rural Terrain x^/Q Versus
Distance for Various Plume Heights (H), Assuming Very
Restrictive Mixing Heights (L). 4-47
4-5 Stability Class B; Rural Terrain xu/Q Versus
Distance for Various Plume Heights (H), Assuming Very
Restrictive Mixing Heights (L). 4-48
4-6 Stability Class C; Rural Terrain xu/Q Versus
Distance for Various Plume Heights (H), Assuming Very
Restrictive Mixing Heights (L). 4-49
4-7 Stability Class D; Rural Terrain xu/Q Versus
Distance for Various Plume Heights (H), Assuming Very
Restrictive Mixing Heights (L). 4-50
4-8 Stability Class E; Rural Terrain yu/Q Versus
Distance for Various Plume Heights (H), Assuming Very
Restrictive Mixing Heights (L). 4-51
4-9 Stability Class F; Rural Terrain xu/Q Versus
Distance for Various Plume Heights (H), Assuming Very
Restrictive Mixing Heights (L). 4-52
4-10 Stability Classes A and B; Urban Terrain xu/Q
Versus Distance for Various Plume Heights (H), Assuming
Very Restrictive Mixing Heights (L). 4-53
4-11 Stability Class C; Urban Terrain xu/Q Versus
Distance for Various Plume Heights (H), Assuming Very
Restrictive Mixing Heights (L). 4-54
VII
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LIST OF FIGURES (CONT.)
4-12 Stability Class D; Urban Terrain xu/Q Versus
Distance for Various Plume Heights (H), Assuming Very
Restrictive Mixing Heights (L). 4-55
4-13 Stability Class E; Urban Terrain xu/Q Versus
Distance for Various Plume Heights (H), Assuming Very
Restrictive Mixing Heights (L). 4-56
4-14 Vertical Dispersion Parameter (az) as a Function
of Downwind Distance and Stability Class; Rural
Terrain 4-57
4-15 Isopleths of Mean Annual Afternoon Mixing Heights. 4-58
4-16 Isopleths of Mean Annual Morning Mixing Heights. 4-59
4-17 24 Hour x/Q Versus Downwind Distance, Obtained
from the Valley Model. 4-60
4-18 Horizontal Dispersion Parameter (ay) as a Function
of Downwind Distance and Stability Class; Rural
Terrain 4-61
4-19 Maximum xu/Q as a Function of Downwind Distance and
Plume Height (H), Assuming a Mixing Height of 500
meters; D Stability. 4-62
4-20 Maximum xu/Q as a Function of Downwind Distance and
Plume Height (H); E Stability. 4-63
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LIST OF SYMBOLS
Symbol Definition
A Parameter used in building cavity calculations and TIBL height factor
Ap Cross-sectional area of building normal to the wind (m2)
B Parameter used in building cavity calculations
C Contribution to pollutant concentration (g/m3)
Fb Bouyancy flux parameter (m4/s3)
H Total heat release rate from flare (cal/s)
L Alongwind horizontal building dimension (length) (m)
Lb Lesser of building height or maximum projected width (m)
M Merged stack parameter
Q Pollutant emission rate (g/s)
QH Sensible heat release rate from flare (cal/s)
R Net rate of sensible heating by the sun (67 cal/m^/s)
S Length of side of square area source (m)
Ta Ambient temperature (K)
Ts Stack gas exit temperature (K)
V Stack gas volume flow rate (m3/s)
W Crosswind horizontal building dimension (width) (m)
Cp Specific heat of air at constant pressure (0.24 cal/gK)
ds Stack inside diameter (m)
f Frequency of occurrence of a wind speed and stability category
combination
g Acceleration due to gravity (9.806 m/s2)
h Height of release above terrain = hs - ht (m)
hb Building height (m)
he Plume (or effective stack) height (m)
ix
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LIST OF SYMBOLS (CONT.)
Symbol Definition
h-j Height of the top of the plume (he + 2az) (in)
hs Physical stack height (m)
hj Height of the Thermal Internal Boundary Layer (TIBL) (mi)
ht Height of terrain above stack base (m)
hse Effective stack release height for flare (m)
he' Plume height modified for stack tip downwash (m)
m Multiplicative factor to account for effects of limited mixing
p Wind speed power law profile exponent
r Factor to adjust 1-hour concentration to longer averaging time
tm Time required for inversion break-up to extend from stack top
to top of plume (s)
u Wind speed (m/s)
uc Critical wind speed (m/s)
us Wind speed at stack height (m/s)
uj Wind speed at a height of z\ (m/s)
u* Friction velocity (m/s)
UIQ Wind speed at a height of 10m (m/s)
uAh Normalized plume rise (m^/s)
vs Stack gas exit velocity (m/s)
x Downwind distance (m)
xmax Downwind distance to maximum ground-level concentration (m)
xr Length of cavity recirculation region (m)
xs Distance from source to shoreline (m)
Xy Virtual point source distance (m)
Zj Mixing height (m)
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LIST OF SYMBOLS (CONT.)
Symbol Definition
zm Mechanically driven mixing height (m)
Ah Plume rise (m)
A6/AZ Potential temperature gradient with height (K/m)
Ax Length of side of urban area (m)
TT pi = 3.14159
ay Horizontal (lateral) dispersion parameter (m)
Oy0 Initial horizontal dispersion parameter for area source (in)
oz Vertical dispersion parameter (in)
-3
XB Concentration contributions from other (background) sources (g/m )
O
Xf Maximum ground-level concentration due to fumigation (g/m )
Xmax Maximum ground-level concentration (g/m^)
Xp Maximum concentration for period greater than 1 hour (g/m )
xi Maximum 1-hour ground-level concentration (g/m3)
X24 Maximum 24-hour ground-level concentration (g/m )
X/Q Relative concentration (s/m^)
xu/Q Normalized relative concentration (m~2)
XI
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1. INTRODUCTION
This document is an update and revision of an earlier guideline1'2
for applying screening techniques to estimate the air quality impact of
stationary sources. The application of screening techniques is addressed
in Section 4.2.1 of the Guideline on Air Quality Models (Revised).3 The
current document incorporates changes and additions to the technical
approach. The techniques are applicable to chemically stable, gaseous or
fine particulate pollutants. An important advantage of the current
doucment is that the single source, short-term techniques can be easily
executed on an IBM-PC compatible microcomputer with at least 256K of RAM
using the SCREEN model provided with the document. As with the earlier
versions, however, many of the techniques can be applied with a pocket or
desk calculator.
The techniques described in this document can be used to evaluate the
air quality impact of sources pursuant to the requirements of the Clean Air
Act,^ such as those sources subject to the prevention of significant
deterioration regulations (PSD - addressed in 40 CFR 52.21). The techniques
can also be used, where appropriate, for new major or minor sources or modi-
fications subject to new source review regulations, and existing sources
of air pollutants, including toxic air pollutants. This document presents
a three-phase approach that is applicable to the air quality analysis:
Phase 1. Apply a simple screening procedure (Section 4.1) to
determine if either (1) the source clearly poses no
air quality problem or (2) the potential for an air
quality problem exists.
Phase 2. If the simplified screening results indicate a potential
threat to air quality, further analysis is warranted,
and the detailed screening (basic modeling) procedures
described in Sections 4.2 through 4.5 should be applied.
1-1
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Phase 3. If the detailed screening results or other factors
indicate that a more refined analysis is necessary,
refer to the Guideline on Air Quality Models (Revised).3
The simple screening procedure (Phase 1) is applied to determine if
the source poses a potential threat to air quality. The purpose of first
applying a simple screening procedure is to conserve resources by elimi-
nating from further analysis those sources that clearly will not cause or
contribute to ambient concentrations in excess of short-term air quality
standards or allowable concentration increments. A relatively large degree
of "conservatism" is incorporated in that screening procedure to provide
reasonable assurance that maximum concentrations will not be underestimated.
If the results of the simple screening procedure indicate a potential
to exceed allowable concentrations, then a detailed screening analysis is
conducted (Phase 2). The Phase 2 analysis will yield a somewhat conserva-
tive first approximation (albeit less conservative than the simple screening
estimate) of the source's maximum impact on air quality. If the Phase 2
analysis indicates that the new source does not pose an air quality problem,
further modeling may not be necessary. However, there are situations in
which analysis beyond the scope of this document (Phase 3) may be required;
for example when:
1. A more accurate estimate of the concentrations is needed
(e.g., if the results of the Phase 2 analysis indicate a
potential air quality problem).
2. The source configuration is complex.
3. Emission rates are highly variable.
4. Pollutant dispersion is significantly affected by nearby terrain
features or large bodies of water.
1-2
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In most of those situations, more refined analytical techniques, such as
computer-based dispersion models,3 can be of considerable help in estimating
ai r quality impact.
In all cases, particularly for applications beyond the scope of this
guideline, the services of knowledgeable, well-trained air pollution
meteorologists, engineers and air quality analysts should be engaged.
An air quality simulation model applied improperly can lead to serious
misjudgments regarding the source impact.
1-3
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2. SOURCE DATA
In order to estimate the impact of a stationary point or area source
on air quality, certain characteristics of the source must be known. The
following minimum information should generally be available:
0 Pollutant emission rate;
0 Stack height for a point source and release height for an area
source;
0 Stack gas temperature, stack inside diameter, and stack gas exit
velocity (for plume rise calculations);
0 Location of the point of emission with respect to surrounding
topography, and the character of that topography;
0 A detailed description of all structures in the vicinity of
(or attached to) the stack in question. (See the discussion
of aerodynamic downwash in Section 4.5.1); and
° Similar information from other significant sources in the
vicinity of the subject source (or dir quality data or
dispersion modeling results that demonstrate the air quality
impact of those sources).
At a minimum, impact estimates should be made with source character-
istics representative of the design capacity (100 percent load). In
addition, the impacts should be estimated based on source character-
istics at loads of 50 percent and 75 percent of design capacity, and
the maximum impacts selected for comparison to the applicable air quality
standard. Refer to Section 9.1.2 in the Guideline on Air Quality
Models (Revised)-^ for a further discussion of source data.
2.1 Emissions
The analysis of air quality impact requires that the emissions from
each source be fully and accurately characterized. If the pollutants
2-1
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are not emitted at a constant rate (most are not), information
should be obtained on how emissions vary with season, day of the week,
and hour of the day. In most cases, emission rates vary with the
source production rate or rate of fuel consumption. For example, for a
coal-fired power plant, emissions are related to the kilowatt-hours of
electricity produced, which is proportional to the tonnage of coal used
to produce the electricity. Fugitive emissions from an area source are
likely to vary with wind speed and both atmospheric and ground moisture
content. If pollutant emission data are not directly available, emissions
can be estimated from fuel consumption or production rates by multiplying
the rates by appropriate emission factors. Emission factors can be
determined using three different methods. They are listed below in
decreasing order of confidence:
1. Stack-test results or other emission measurements from an
identical or similar source.
2. Material balance calculations based on engineering knowledge
of the process.
3. Emission factors derived for similar sources or obtained from a
compilation by the U.S. Environmental Protection Agency.5
In cases where emissions are reduced by control equipment, the
effectiveness of the controls must be accounted for in the emissions anal-
ysis. The source operator should be able to estimate control effectiveness
in reducing emissions and how this effectiveness varies with changes in
plant operating conditions.
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2.2 Merged Parameters for Multiple Stacks
Sources that emit the same pollutant from several stacks with similar
parameters that are within about 100 meters of each other may be analyzed by
treating all of the emissions as coming from a single representative stack.
For each stack compute the parameter M:
M = (hsVTs)/Q (2.1)
where M = merged stack parameter which accounts for the relative influence
of stack height, plume rise, and emission rate on concentrations
hs = stack height (m)
V = (ir/4) dg vs = stack gas volume flow rate (rrr/s)
ds = inside stack diameter (m)
vs = stack gas exit velocity (m/s)
Ts = stack gas exit temperature (K)
Q = pollutant emission rate (g/s)
The stack that has the lowest value of M is used as a "representative"
stack. Then the sum of the emissions from all stacks is assumed to oe
emitted from the representative stack; i.e., the equivalent source is
characterized by hsi, Vj, Tsj and Q, where subscript 1 indicates the
representative stack and Q = Qi + 0,2 + ... + Qn-
The parameters from dissimilar stacks should be merged with caution.
For example, if the stacks are located more than about 100 meters apart,
or if stack heights, volume flow rates, or stack gas exit temperatures
differ by more than about 20 percent, the resulting estimates of concen-
trations due to the merged stack procedure may be unacceptably high.
2-3
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2.3 Topographic Considerations
It is important to study the topography in the vicinity of the source
being analyzed. Topographic features, through their effects on plume
behavior, will sometimes be a significant factor in determining ambient
ground-level pollutant concentrations. Important features to note are
the locations of large bodies of water, elevated terrain, valley config-
urations, and general terrain roughness in the vicinity of the source.
Section 4.5.2 provides a screening technique for estimating ambient
concentrations due to plume impaction at receptors located on elevated
terrain features above stack height. The effects of elevated terrain below
stack height can be accounted for in Sections 4.2 and 4.3. A screening
technique for estimating concentrations under shoreline fumigation
conditions is presented in Section 4.5.3. Any other topographic consider-
ations, such as terrain-induced plume downwash and valley stagnation,
are beyond the scope of this guideline.
2.4 Source Building Complex
The downwash phenomenon caused by the aerodynamic turbulence induced
by a building may result in high ground-level concentrations in the vicin-
ity of an emission source. It is therefore important to characterize the
height and width of structures nearby the source. For purposes of
these analyses, "nearby" includes structures within a distance of five
times the lesser of the height or width of the structure, but not
greater than 0.8 km (0.5 mile).6 The screening procedure for building
downwash is described in Section 4.5.1.
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3. METEOROLOGICAL DATA
The computational procedures given in Section 4 for estimating the
impact of a stationary source on air quality utilize information on
the following meteorological parameters:
0 Wind speed and direction
0 Stability class
0 Mixing height
0 Temperature
A discussion of each of these parameters follows.
3.1 Wind Speed and Direction
Wind speed and direction data are required to estimate short-term peak
and long-term average concentrations. The wind speed is used to determine
(1) plume dilution, and (2) the plume rise downwind of the stack. These
factors, in turn, affect the magnitude of and distance to the maximum
ground-level concentration.
Most wind data are collected near ground level. The wind speed at
stack height, us, can be estimated from the following power law equation:
us= Ul(hs/Zl)P (3.1)
where:
us = the wind speed (m/s) at stack height, hs,
ui = the wind speed at a reference height, zi (such as the anemometer
height), and
p = the stability-related power law exponent from Table 3-1.
3-1
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Table 3-1. Wind Profile
Stability Class
A
B
C
D
E
F
Exponent as a Function of Atmospheri
for Rural and Urban Sites*
Rural Exponent Urban
0.07
0.07
0.10
0.15
0.35
0.55
c Stability
Exponent
0.15
0.15
0.20
0.25
0.30
0.30
The power law equation may be used to adjust wind speeds over a
height range from about 10 to 300 meters. Adjustments to heights above 300
meters should be used with caution. For release heights below 10 meters the
reference wind speed should be used without adjustment. For the procedures
in Section 4 the reference height is assumed to be at 10 meters.
The wind direction is an approximation to the direction of transport
of the plume. The variability of the direction of transport over a period
of time is a major factor in estimating ground-level concentrations averaged
over that time period.
Wind speed and direction data from National Weather Service, Air Weather
Service, and Naval Weather Service stations are available from the National
Climatic Data Center (NCDC), Federal Building, Asheville, North Carolina,
704-259-0682 (FTS 672-0682). Wind data are often also recorded at existing
* The classification of a site as rural or urban should be based on one of the
procedures described in Section 8.2.8 of the Guideline on Air Quality
Models (Revised).3
3-2
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plant sites and at air quality monitoring sites. It is important that the
equipment used to record such data be properly designed, sited, and maintained
to record data that are reasonably representative of the direction and
speed of the plume. Guidance on collection of on-site meteorological
data is contained primarily in Reference 7, but also in References 3 and 8.
3.2 Stability
Stability categories, as depicted in Tables 3-1 and 3-2, are indicators
of atmospheric turbulence. The stability category at any given time will
depend upon static stability (related to the change in temperature wit'n
height), thermal turbulence (caused by heating of the air at ground level),
and mechanical turbulence (a function of wind speed and surface roughness).
It is generally estimated by a method given by Turner^, which requires
information on solar elevation angle, cloud cover, cloud ceiling height,
and wind speed (see Table 3-2). Opaque cloud cover should be used if
available, otherwise total cloud cover may be used. The solar elevation
angle is a function of the time of year and the time of day, and is
presented in charts in the Smithsonian Meteorological Tables.10 The
hourly weather observations of the National Weather Service include
cloud cover, ceiling height, and wind speed. These data are available
from the NCDC. Methods for estimating atmospheric stability categories
from on-site data are presented in Reference 7. For computation of
seasonal and annual concentrations, a joint frequency distribution of
stability class, wind direction, and wind speed (stability wind rose)
is needed. Such distributions, called STAR summaries, can be obtained
from the NCDC for National Weather Service stations.
3-3
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Table 3-2. Key To Stability Categories
Surface Wind
Speed at a
Height of 10m
(m/s)
< 2
2-3
3-5
5-6
> 6
Day
Incoming Solar Radiation**
(Insolation)
Strong
A
A-B
B
C
C
Moderate
A-B
B
B-C
C-D
D
Slight
B
C
C
D
D
Night*
Thinly Overcast
or > 4/8 Low
Cloud Cover
F
E
D
D
D
<_ 3/8
Cloud
Cover
F
F
E
D
D
The neutral class (D) should be assumed for all overcast conditions during day
or night.
*Night is defined as the period from 1 hour before sunset to 1 hour after
sunrise.
**Appropriate insolation categories may be determined through the use of sky
cover and solar elevation information as follows:
Sky Cover (Opaque
or Total )
4/8 or Less or
Any Amount of
High Thin Clouds
5/8 to 7/8 Middle
clouds (7000 feet to
16,000 foot base
5/8 to 7/8 Low
Clouds (less than
7,000 foot base)
Solar Elevation
Angle > 60°
Strong
Moderate
Slight
Solar Elevation
Angle < 60°
But > 15°
Moderate
Slight
Slight
Solar Elevation
Angle < 35°
But > T5°
SI i ght
Slight
Slight
3-4
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3.3 Mixing Height
The mixing height is the distance above the ground to which relatively
unrestricted vertical mixing occurs in the atmosphere. When the mixing height
is low (but still above plume height) ambient ground-level concentrations will
be relatively high because the pollutants are prevented from dispersing
upward. For estimating long-term average concentrations, it is generally
adequate to use an annual-average mixing height rather than daily values.
Mixing height data are generally derived from surface temperatures
and from upper air soundings which are made at selected National Weather
Service stations. The procedure used to determine mixing heights is one
developed by Holzworth.H Tabulations and summaries of mixing height data
can be obtained from the NCDC.
For the purposes of calculations made in Section 4.2 and for use in
the SCREEN model, a mechanically driven mixing height is estimated to provide
a lower limit to the mixing height used during neutral and unstable conditions.
The mechanical mixing height is calculated from:12
zm = 0.3 u*/f (3.2)
where: u* = friction velocity (m/s)
f = Coriolis parameter (9.374 x 10-5$-! at 40° latitude)
Using a log-linear vertical profile for the wind speed, and assuming a sur-
face roughness length of about 0.3m, u* may be estimated from the 10 meter
wind speed, UIQ, as
u* = 0.1 UIQ
Substituting for u* in (3.2) yields
zm = 320 UIQ (3.3)
If the plume height is calculated to be above the mixing height determined
3-5
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from Equation 3.3, then the mixing height is set at 1 meter above the
plume height for conservatism in the SCREEN model.
3.4 Temperature
Ambient air temperature must be known in order to calculate the amount
of rise of a buoyant plume. Plume rise is proportional to a fractional
power of the temperature difference between the stack gases and the ambient
air (see Section 4.2). Ambient temperature data are collected hourly at
National Weather Service stations, and are available from the NCDC. For
the procedures in Section 4, a default value of 293K is used for ambient
temperature if no data are available.
3-6
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4. ESTIMATING SOURCE IMPACT ON AIR QUALITY
A three-phase approach, as discussed in the Introduction, is recommended
for estimating the air quality impact of a stationary source:*
Phase 1. Simple screening analysis
Phase 2. Detailed screening (basic modeling) analysis
Phase 3. Refined modeling analysis
The Phase 3 analysis is beyond the scope of this guideline, and the user is
referred to the Guideline on Air Quality Models (Revised).3 This section
presents the simple screening procedure (Section 4.1) and the detailed
screening procedures (Sections 4.2 through 4.5). All of the procedures,
with the partial exception of the procedures in Sections 4.5.2 and 4.5.3,
are based upon the bi-variate Gaussian dispersion model assumptions
described in the Workbook of Atmospheric Dispersion Estimates.9 A
consistent set of units (meters, grams, seconds) is used throughout:
Distance (m)
Pollutant Emission Rate (g/s)
Pollutant Concentration (g/m^)
Wind Speed (m/s)
To convert pollutant concentration to micrograms per cubic meter
for comparison with air quality standards, multiply the value in
by 1 x 106.
*The techniques described in this section can be used, where appropriate,
to evaluate sources subject to the prevention of significant deterioration
regulations (PSD - addressed in 40 CFR 52.21), new major or minor
sources subject to new source review regulations, and existing sources
of air pollutants, including toxic air pollutants.
4-1
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4.1 Simple Screening Procedure
The simple screening procedure is the "first phase" that is recommended
when assessing the air quality impact of a new point source. The purpose of
this screening procedure is to eliminate from further analysis those sources
that clearly will not cause or contribute to ambient concentrations in excess
of short-term air quality standards.
The scope of the procedure is confined to elevated point sources with
plume heights of 10 to 300 meters, and concentration averaging times of 1
to 24 hours. The procedure is particularly useful for sources where the
short-term air quality standards are "controlling"; i.e., in cases
where meeting the short-term standards provides good assurance of meeting
the annual standard for that pollutant. Elevated point sources (i.e.,
sources for which the emission points are well above ground level) are
often in that category, particularly when they are isolated from other
sources.
When applying the screening procedure to elevated point sources, the
following assumptions must apply:
1. No aerodynamic downwash of the effluent plume by nearby buildings
occurs. (Refer to Section 4.5.1 to determine if building
downwash is a potential problem.)
2. The plume does not impact on elevated terrain. (Refer to Section
4.5.2 to determine if elevated terrain above stack height may
be impacted.)
If the potential for building downwash exists, then the SCREEN model should
be used to estimate air quality impact and the simple screening procedure
is not applicable. If the potential for plume impaction on elevated terrian
4-2
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exists, then the calculation procedure described in the indicated
section should also be applied, and the higher concentration from the
terrain impaction procedure and the simple screening procedure should be
selected to estimate the maximum ground-level concentration. The
effects of elevated terrain below stack height should also be accounted
for by reducing, the computed plume heights by the maximum terrain height
above stack base.
The screening procedure utilizes the Gaussian dispersion equation to
estimate the maximum 1-hour ground-level concentration for the source
in question (Computations 1-6 below). To obtain concentrations for
other averaging times up to 24 hours, multiply the 1-hour value by an
appropriate factor (Computation 7). Then account for background concen-
trations (Computation 8) to obtain a total concentration estimate.
That estimate is then used, in conjunction with any elevated terrain
estimates, to determine if further analysis of the source impact is
warranted (Computation 9):
Step 1. Estimate the normalized plume rise (uAh) that is applicable
to the source during neutral and unstable atmospheric conditions. (Stable
atmospheric conditions are not treated explicitly since this simple
screening procedure does not apply to stack heights less than 10 meters
or cases with terrain intercepts.) First, compute the buoyancy flux
parameter, Ft>:
Fb = (9/4)vsds2[(Ts-Ta)/Ts] (4.1)
= 3.12 V [(Ts-Ta)/Ts]
4-3
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where: g = acceleration due to gravity (9.806 m/s^)
v$ = stack gas exit velocity (m/s)
ds = stack inside diameter (m)
TS = stack gas exit temperature (K)
Ta = ambient air temperature (K) (If no ambient temperature data are
available, assume that Ta = 293K.)
p o
V = (ir/4)ds vs = actual stack gas volume flow rate (m/s)
Normalized plume rise (uAh) is then given by:
uAh = 21.4Fh3/4 when Fh < 55 m4/s3
(4-2)
uAh = 38.7Fb3/5 when Fb >_ 55 m4/s3
Step 2. Divide the uAh value obtained from Equation 4.2 by each
of five wind speeds (u = 1.0, 2.0, 3.0, 5.0 and 10 m/s) to estimate the
actual plume rise (Ah) for each wind speed:
Ah = (uAh)/u
Step 3. Compute the plume height (he) that will occur during each
wind speed by adding the respective plume rises to the stack height (hs):
he = hs + Ah
If the effects of elevated terrain below stack height are to be accounted for,
then reduce each plume height by the maximum terrain height above stack base.
Step 4. For each plume height computed in (3), estimate a xu/Q value
from Figure 4-1.14
*If stack gas temperature or exit velocity data are unavailable, they
may be approximated from guidelines that present typical values for those
parameters for existing plants.*3
4-4
-------
10-3 \
10-4
Cxi
'E
a"
x
10'!
10'6
10
20
50 100 200
PLUME HEIGHT, m
500
1000
Figure 4-1. Maximum xu/Q as a function of plume height, H (for use only
with the simple screening procedure).
4 "j
-------
Step 5. Divide each xu/Q value by the respective wind speed to
determine the corresponding x/Q values:
x./Q = (xu/Q)/u
Step 6. Multiply the maximun x/Q value obtained in (5) by the
emission rate Q (g/s), and incorporate a factor of 2 margin of safety,
to obtain the maximum 1-hour ground-level concentration xi (9/m ) due
to emissions from the stack in question:
XI = 2Q(X/Q)
The margin of safety is incorporated in the screening procedure to account
for the potential inaccuracy of concentration estimates obtained through
calculations of this type.
If more than one stack is being considered, and the procedure
for merging parameters for multiple stacks is not applicable (Section 2.2),
(1) through (6) must be applied for each stack separately. The maximum
values (xi) found for each stack are then added together to estimate
the total maximum 1-hour concentration.
Step 7. To obtain a concentration estimate (xp) for an averaging
time greater than one hour, multiply the one-hour value by an appropriate
factor, r. (See the discussion in Step 5 of Section 4.2 which addresses
multiplication factors for averaging times longer than 1 hour).
Xp = rxi
Step 8^ Next, contributions from other sources (XB) should be taken
into account, yielding the final screening procedure concentration estimate
%ax (3/m3):
Xmax = xp + XB-
4-6
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Procedures on estimating concentrations due to other sources are provided
in Section 4.5.5.
Step 9. Based on the estimate of xmax and (^ applicable) estimate
of concentrations due to terrain impaction problems, determine if further
analysis of the source is warranted. If any of the estimated concentrations
exceeds the air quality level of concern (e.g., an air quality standard),
proceed to Section 4.2 for further analysis. If the concentrations are
below the level of concern, the source can be safely assumed to pose no
threat to that air quality level, and no further analysis is necessary.
4.2 Estimating Maximum Short-Term Concentrations
The basic modeling procedures described in the remainder of this
document comprise the recommended "second phase" (or detailed screening)
that may be used in assessing air quality impacts. The procedures
are intended for application in those cases where the simple screening pro-
cedure (first phase) indicates a potential air quality problem.
As with the first phase (simple screening) analysis in Section 4.1, if
elevated terrain above stack height occurs within 50 km of the source, then
the procedure in Section 4.5.2 should be applied in addition to the procedures
in this section. The highest concentration from all applicable procedures
should then be selected to estimate the maximum ground-level concentration.
Even if the plume is not likely to impact on elevated terrain, the user
should account for the effects of elevated terrain below stack height. If
the terrain is relatively uniform around the source, then a procedure to
account for terrain effects is to reduce the computed plume height, he (for
all stabilities), by the maximum terrain elevation above stack base within
4-7
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a 50 km radius from the source. The adjusted plume height can then be used
in conjunction with the "flat terrain" procedures described in this section.
If there are only a few isolated terrain features in otherwise flat
terrain, then the flat terrain estimates from this section should be expanded
to include the procedures of Section 4.3 applied to the locations with
elevated terrain. For the additional calculations the computed plume
height, he, should be reduced by the terrain height above stack base corre-
sponding to the specific terrain features.
The procedures in this section can be applied without the aid of a
computer (a pocket or desk calculator will suffice). However, they are subject
to the same limitations as the simple screening procedure, i.e., no building
downwash occurs (see Section 4.5.1), no terrain impaction occurs (Section
4.5.2), and plume heights do not exceed 300m. An alternative approach is
to use the SCREEN computer program that has been made available by EPA for
use on an IBM-PC compatible microcomputer with at least 256K of RAM. The
SCREEN model replaces the PTPLU, PTMAX, and PTDIS codes previously used in
conjunction with Volume 10R.2 It is applicable to all of the procedures
contained in this section and Section 4.3, but also includes calculations
for the special cases of building downwash, fumigation, elevated terrain,
area sources and long-range transport described in Section 4.5. A complete
user's guide for the SCREEN model is provided in Appendix A.
This section (4.2) presents the basic procedures for estimating
maximum short-term concentrations for specific meteorological situations.
If building downwash occurs (see Section 4.5.1), then the SCREEN model
must be used in lieu of these procedures. In Steps 1-3, plume risers,16,17
4-8
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and a critical wind speed are computed. In Step 4, maximum 1-hour
concentrations are estimated. In Step 5, the 1-hour concentrations are
used to estimate concentrations for averaging times up to 24 hours.
Contributions from other sources are accounted for in Step 6.
Step 1. Estimate the normalized plume rise (uAh) that is applicable
to the source during neutral and unstable atmospheric conditions. First,
compute the buoyancy flux term, Fb, using Equation 4.1 (repeated here for
convenience):
Fb = (9/4)vsds2[(Ts-Ta)/Ts] (4.1)
= 3.12 V [(Ts-Ta)/Ts]
where: g = acceleration of gravity (9.806 m/s^)
vs = stack gas exit velocity (m/s)
ds = inside stack diameter (m)
TS = stack gas temperature (i<)
Ta = ambient air temperature (K) (If no ambient temperature data
are available, assume that Ta = 293 K.)
p O
V = (ir/4)ds vs = actual stack gas flow rate (irr/s)
Normalized plume rise is then given by Equation 4.2:
UAh = 21.4Fb3/4 when Fb < 55 m4/s3
'
A -3 (4-2)
UAh = 38.7Fb when Fb _> 55 m4/sj
If stack gas temperature or exit velocity data are unavailable, they may
be approximated from guidelines that present typical values for those
parameters for existing plants.13
4-9
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If the emissions are from a flare, then the normalized plume rise and
an effective release height may be determined with the following procedure:
(a) Calculate the total heat release rate, H (cal/s), of the flared gas
based on the heat content and the gas consumption rate.
(b) Calculate the buoyancy flux term, F^, for the flare:*
Fb = 1.66 x 10~5 x H (4.3)
(c) Calculate the normalized plume rise (uAh) from Equation 4.2.
(d) Calculate the vertical height of the flame, hf (m), assuming
the flame is tilted 45° from the vertical:^
hf = 4.56 x 10"3 x H0-478 (4.4)
(e) Calculate an effective release height for the tip of the flame:
hse = hs + hf.
Use hse in place of hs along with the value of uAh calculated from (c)
in determining plume heights in the following procedures.
Step 2. Estimate the critical wind speed (uc) applicable to the source
during neutral and near-neutral atmospheric conditions. The critical wind
speed is a function of two opposing effects that occur with increasing
wind speed; namely, increased dilution of the effluent as it leaves the
stack (which tends to decrease the maximum impact on ground-level concen-
tration) and suppression of plume rise (tending to increase the impact).
The wind speed at which the interaction of those opposing effects results
in the highest ground-level concentration is the critical wind speed.
This formula was derived from: F^, = (gQH)/UpcpTa) (Eqn. 4.20,
Briggs15), assuming Ta = 293 K, p = 1205 g/m3, and cp = 0.24 cal/gK,
and that the sensible heat release rate, QH = (0.45)H.18
4-10
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The critical wind speed can be estimated through the following
approximation:
uc = (uAh)/hs (4.5)
Assume that the value of uc from Equation 4.5 corresponds to the
stack height wind speed. If the value of uc calculated from Equation 4.5 is
less than 1.0 m/s, then use uc = 1.0 m/s. If the value of uc calculated
from Equation 4.5 is greater than 15.0 m/s, then use uc = 15.0 m/s.
Step 3. Stable atmospheric conditions may be critical if the emission
height is less than 50 meters. The stable case plume rise (Ah) should
be estimated as follows:
Ah = 2.6[(FbTa)/(ugAe/Az)]1/3 (4.6)
The value Afi/Az is the change in potential temperature with height.
Values of 0.02 K/m for E stability (applicable to urban sites), and 0.035 K/m
for F stability (rural sites) should be used. The classification of a
site as rural or urban should be based on one of the procedures described
in Section 8.2.8 of the Guideline on Air Quality Models (Revised).3
Step 4. Estimate maximum 1-hour concentrations that will occur
during various dispersion situations. First, using Table 4-1 as a guide,
determine the dispersion situations and corresponding calculation procedures
applicable to the source being considered. Then apply the applicable
calculation procedures, which are described on the following pages, in
order to estimate maximum 1-hour concentrations. Then proceed to Step 5.
As discussed earlier and as noted in Table 4-1, the hand calculation
procedures presented in this step are limited by certain assumptions,
4-11
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Table 4-1. Calculation Procedures To Use With
Various Release Heights
Height of Release
Above Terrain, h
Applicable Calculation
Procedures
h >^ 50 meters
10 < h < 50 meters
h < 10 meters and
ground-level sources
NOTE:
(a) Unstable/Limited Mixing
(b) Near-neutral/High Wind
(a) Unstable/Limited Mixing
(b) Near-neutral/High Wind
(c) Stable
(b) Near-neutral/High Wind
(c) Stable
If hs < ht) + 1.5L5, refer to Section 4.5.1 on building downwash and
use the SCREEN Model.
If elevated terrain above stack height occurs within 50 km, refer to
Section 4.5.2.
If fumigation is potentially a problem (for rural sources with hs _>. 10m),
refer to Section 4.5.3.
If the plume height, he = hs + (uAh/us) is greater than 300m, then
the procedures in this section are not applicable (the SCREEN model may be
used without this restriction).
= hs - ht
= stack height
= terrain height above stack base
= height of nearby structure
= lesser of height or maximum projected width of nearby structure
4-12
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namely that no building downwash occurs (Section 4.5.1), no terrain
impaction occurs (Section 4.5.2), and that plume heights are belovj
300m. For cases involving building downwash or plume heights above
300m, the SCREEN model should be used. A detailed user's guide for the
SCREEN model is provided in Appendix A.
Procedure (a): Unstable/Limited Mixing
During very unstable conditions, the plume from a stack will be mixed to
ground level relatively close to the source, resulting in high short-term
concentrations. These concentrations can be significantly increased when
the unstable conditions occur in conjunction with a limited mixing condition.
Limited mixing (also called plume trapping) occurs when a stable layer
aloft limits the vertical mixing of the plume. The highest concentrations
occur when the mixing height is at or slightly above the plume height.
Calculation Procedure:
1. Compute the plume height, he, that will occur during A stability
and 10-meter wind speeds of 1 and 3 m/s. Adjust the wind speeds from 10
meters to stack height using Equation 3.1 and the exponent for stability
class A. Use the uAh value computed in Step 1.
he = hs + (uAh/us)
= hs + Ah
If vs < 1.5us, account for stack tip downwash as follows:
he = hs + Ah + 2(vs/us-1.5)ds (4.7)
If elevated terrain is to be accounted for, then reduce the computed
plume height for each wind speed by the maximum terrain elevation above
stack base.
4-13
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2. For both wind speeds considered in (1), determine the maximum
1-hour xti/Q using the curve for stability A on Figure 4-2 (rural)9 or
A-B on Figure 4-3 (urban).20
3. Compute the maximum 1-hour concentration, xi> for both cases using:
XI- mQ(xu/Q)/us (4.8)
where m is a conservative factor to account for the increase in
concentration expected due to reflections of the plume off the top of
the mixed layer. The value of m depends on the plume height as follows:*
m = 2.0 for 290m _< he
m = 1.8 for 270m <_ he < 290m
m = 1.5 for 210m £ he < 270m
m = 1.2 for 180m _< he < 210m
m = 1.1 for 160m <_ he < 180m
m = 1.0 for he < 160m
Select the highest concentration computed.
Procedure(b): Near-neutral/High Wind
Some buoyant plumes will have their greatest impact on ground-level
concentrations during neutral or near-neutral conditions, often in conjunction
with high wind speeds.
Calculation procedure:
1. Compute the plume height, he, that will occur during C stability
with a stack height wind speed of us = uc, the value of the critical
* The values of m are based on an assumed minimum daytime mixing height
of about 320m (see Section 3.3).
4-14
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wind speed computed in Step 2. If uc < 10 m/s, then also compute the plume
height that will occur during C stability with a 10-meter wind speed of
10 m/s. Adjust the 10 m/s wind speed from 10 meters to stack height using
Equation 3.1 and the exponent for stability class C. Use the uAh value
computed in Step 1.
he = hs + (uAh)/us
If vs < 1.5us, account for stack tip downwash using Equation 4.7. If elevated
terrain is to be accounted for, then reduce the computed plume height for
each wind speed by the maximum terrain elevation above stack base.
2. For the wind speed(s) considered in (1), determine the maximum 1-hour
yu/Q using the curve for stability C on Figure 4-2 (rural)^ or Figure 4.3
(urban).20
3. Compute the maximum 1-hour concentration xi f°r each case
using:
xi = Q(xu/Q)/us
and select the highest concentration computed.
Procedure (c): Stable
Low-level sources (i.e., sources with stack heights less than about
50m) sometimes produce the highest concentrations during stable atmos-
pheric conditions. Under such conditions, the plume's vertical spread is
severely restricted and horizontal spreading is also reduced. This results
in what is called a fanning plume.
Calculation procedures:
A. For low-level sources with some plume rise, calculate the
concencration as follows:
4-15
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1. Compute the plume height (he) that will occur during F
stability (for rural cases) and 10-meter wind speeds of 1, 3, and 4 m/s,*
or E stability (for urban cases) and 10-meter wind speeds of 1, 3, and 5
m/s. Adjust the wind speeds from 10 meters to stack height, using Equation
3.1 and the appropriate exponent. Use the stable plume rise (Ah)
computed from Equation 4.6 in Step 3:
he = hs + Ah
If vs < 1.5us, account for stack tip downwash using Equation 4.7. If
elevated terrain is to be accounted for, then reduce the computed plume
height for each wind speed by the maximum terrain elevation above stack base.
2. For each wind speed and stability considered in (1), find
the maximum 1-hour xu/Q from Figure 4-2 (rural)9 or 4-3 (urban).20
Compute the maximum 1-hour concentration for each case, using
Xi = Q(xu/Q)/us
and select the highest concentration computed.
B. For low-level sources with no plume rise (he = hs), find the
maximum 1-hour xu/Q from Figure 4-2 (rural case—assume F stability)
or 4-3 (urban case—assume E stability). Compute the maximum 1-hour con-
centration, assuming a 10-meter wind speed of 1 m/s. Adjust the wind speed
from 10 meters to stack height using Equation 3.1 and the appropriate
exponent.
xl = Q(xu/Q)/us
*Refer to the discussion on worst case meteorological conditions in Appendix
A, Section A3, for an explanation of the use of F stability with a 4 m/s
wind speed.
4-16
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Step 5. Obtain concentration estimates for the averaging times of
concern. The maximum 1-hour concentration (xi) is the highest of the
concentrations estimated in Step 4, Procedures (a) - (cj. For averaging
times greater than 1-hour, the maximum concentration will generally be
less than the 1-hour value. The following discussion describes how the
maximum 1-hour value may be used to make an estimate of maximum concentra-
tions for longer averaging times.
The ratio between a longer-term maximum concentration and a
1-hour maximum will depend upon the duration of the longer averaging time,
source characteristics, local climatology and topography, and the meteoro-
logical conditions associated with the 1-hour maximum. Because of the many
ways in which such factors interact, it is not practical to categorize all
situations that will typically result in any specified ratio between the
longer-term and 1-hour maxima. Therefore, ratios are presented here for a
"general case" and the user is given some flexibility to adjust those
ratios to represent more closely any particular point source application
where actual meteorological data are used. To obtain the estimated maximum
concentration for a 3, 8, or 24-hour averaging time, multiply the 1-hour
maximum (yj) by the given factor:
Averaging Time Multiplying Factor
3 hours 0.9 (±0.1)
8 hours 0.7 (±0.2)
24 hours 0.4 (±0.2)
The numbers in parentheses are recommended limits to which one may diverge
from the multiplying factors representing the general case. For example,
if aerodynamic downwash or terrain is a problem at the facility, or if the
4-17
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emission height is very low, it may be necessary to increase the factors
(within the limits specified in parentheses). On the other hand, if the
stack is relatively tall and there are no terrain or downwash problems,
it may be appropriate to decrease the factors. Agreement should be reached
with the Regional Office prior to modifying the factors.
The multiplying factors listed above are based upon general
experience with elevated point sources. The factors are only intended
as a rough guide for estimating maximum concentrations for averaging
times greater than one hour. A degree of conservatism is incorporated
in the factors to provide reasonable assurance that maximum concentrations
for 3, 8, and 24 hours will not be underestimated.
Step 6. Add the expected contribution from other sources to the
concentration estimated in Step 5. Concentrations due to other sources
can be estimated from measured data, or by computing the effect of
existing sources on air quality in the area being studied. Procedures
for estimating such concentrations are given in Section 4.5.5.
At this point in the analysis, a first approximation of maximum
short-term ambient concentrations (source impact plus contributions from
other sources) has been obtained. If concentrations at specified locations,
long-term concentrations, or other special topics must be addressed, refer
to applicable portions of Sections 4.3 to 4.5.
4.3 Short-Term Concentrations at Specified Locations
In Section 4.2, maximum concentrations are generally estimated without
specific attention to the location(s) of the receptor(s). In some cases,
however, it is particularly important to estimate the impact of a source
4-18
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on air quality in specified (e.g., critical) areas. For example, there may be
nearby locations at which high pollutant concentrations already occur due to
other sources, and where a relatively small addition to ambient concentrations
might cause ambient standards to be exceeded. Another example would be
where an isolated terrain feature occurs in otherwise flat terrain, and
concentrations at the elevated terrain location may exceed those estimated
for flat terrain. These procedures assume that no building downwash occurs
(Section 4.5.1), no terrain impaction occurs (Section 4.5.2), and that plume
heights do not exceed 300m.
Each of the sources affecting a given location can be expected to produce
its greatest impact during certain meteorological conditions. The composite
maximum concentration at that location due to the interaction of all the
sources may occur under different meteorological conditions than those which
produce the highest impact from any one source. Thus, the analysis of this
problem can be difficult, and may require substantial use of high-speed
computers.
Despite the potential complexity of the problem, some preliminary
calculations can be made that will at least indicate whether or not a more
detailed study is needed. For example, if the preliminary analysis indi-
cates that the estimated concentrations are near or above the air quality
standards of concern, a more detailed analysis will probably be required.
Calculation procedure: (If the SCREEN model is used, refer to the
discrete distance option described in Appendix A.)
Step 1. Compute the normalized plume rise (uAh) for neutral and
unstable conditions, utilizing the procedure described in Step 1 of Section 4.2.
4-19
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Step 2. Compute the plume rise, Ah, that will occur during C
stability (to represent neutral and unstable conditions) with 10-meter wind
speeds of 1, 3, 5, 10, and 20 m/s. Adjust the wind speeds from 10 meters
to stack height using Equation 3.1 and the exponent for stability class C.
Ah = (uAh)/us
Step 3. Compute the plume height (he) that will occur during each
wind speed by adding the respective plume rises to the stack height (hs):
he = hs + Ah
If vs < 1.5 us, account for stack tip downwash using Equation 4.7.
If elevated terrain is to be accounted for, then reduce the computed
plume height for each wind speed by the terrain elevation above stack
base for the specified location.
Step 4. For each stability class-wind speed combination listed
below, at the downwind distance of the "specified location," determine
the xu/Q value from Figures 4-4 through 4-7 (rural) or Figures 4-10
through 4-12 (urban). Note that in those figures (see the captions) very
restrictive mixing heights are assumed, resulting in trapping of the
entire plume within a shallow layer.
Stability Class 10 Meter Wind Speed (m/s)
A 1, 3
B 1, 3, 5
C 1, 3, 5, 10
D 1, 3, 5, 10, 20
Step 5. (If the physical stack height is greater than 50 meters and
flat terrain is being assumed, Steps 5 and 6 may be skipped.) Compute plume
4-20
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heights (he) that will occur for stability class E and 10-meter wind speeds
of 1, 3, and 5 m/s, and for stability class F (rural sources only) and
10-meter wind speeds of 1 and 3 and 4 m/s.* Adjust the wind speeds from
10 meters to stack height using Equation 3.1 and the appropriate exponent.
Use the stable plume rise (Ah) computed from Equation 4.6 in Step 3
of Section 4.2:
he = hs + Ah
If vs < 1.5us, account for stack tip downwash using Equation 4.7. If ele-
vated terrain is to be accounted for, then reduce the computed plume height
for each case by the terrain elevation above stack base for the specified
location.
Step 6. For each stability class-wind speed combination considered
in Step 5, at the downwind distance of the specified location, determine
a xu/Q value from Figures 4-8 and 4-9 (or Figure 4-13 for the urban
case).
Step 7. For each yu/Q value obtained in Step 4 (and Step 6 if
applicable), compute x/Q:
x/Q = (xu/Q)/us
Step 8. Select the largest x/Q ancl multiply by the source emission
rate (g/s) to obtain a 1-hour concentration value (g/m3):
xi = Q(x/Q)max
Step 9. To estimate concentrations for averaging time greater
than 1 hour, refer to the averaging time procedure described earlier
(Step 5 of Section 4.2). To account for contributions from other sources,
see Section 4.5.5.
* Refer to the discussion on worst case meteorological conditions in Appendix
A, Section A3, for an explanation of the use of F stability with a 4m/s wind
speed.
4-21
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4.4 Annual Average Concentrations
This section presents procedures for estimating annual average ambient
concentrations caused by a single point source. The procedure for estimating
the annual concentration at a specified location is presented first, followed
by a suggestion of how that procedure can be expanded to estimate the
overall "tiaxiTiun annual concentration (regardless of location).
The procedures assume that the emissions are continuous and at a
constant rate. The data required are emission rate, stack height, stack
gas volume flow rate (or diameter and exit velocity), stack gas tempera-
ture, average afternoon mixing height, and a representative stability
wind rose. Refer to Sections 2 and 3 for a discussion of such data.
4.4.1 Annual Average Concentration at a Specified Location
Calculation procedure:
Step 1. (Applicable to stability categories A through D). Using
the procedure described in Step 1 of Section 4.2 (Equations 4.1 and 4.2)
obtain a normalized plume rise value, uAh.
Step 2. (Applicable to stability categories E and F). Use Equation
4.6 from Step 3 of Section 4.2 to estimate the plume rise (Ah) as a
function of wind speed for both stable categories (E and F) using values of
AO/Az = 0.02 K/m for category E and AQ/Az = 0.035 K/m for category F.
*The stability wind rose is a joint frequency distribution of wind speed,
wind direction and atmospheric stability for a given locality. Stability
wind roses for many locations are available from the National Climatic Data
Center, Asheville, North Carolina.
4-22
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Step 3. Compute plume rise (Ah) for each stability-wind speed
category in Table 4-2 by (1) substituting the corresponding wind speed for
u in the appropriate equations referenced in Step 1 or 2 above and (2)
solving the equation for Ah. The wind speeds listed in Table 4-2
are derived from the wind speed intervals used by the National Climatic
Data Center (Table 4-3) in specifying stability-wind roses. The wind
speeds may be adjusted from 10 meters to stack height using Equation 3.1.
Step 4. Compute plume height (he) for each stability-wind speed
category in Table 4-2 by adding the physical stack height (hs) to each of
the plume rise values computed in Step 3:
he = hs + Ah
Step 5. Estimate the contribution to the annual average concentration
at the specified location for each of the stability-wind speed categories
in Table 4-2. First, determine the vertical dispersion coefficient (oz)
for each stability class for the downwind distance (x) between the source
and the specified location, using Figure 4-14. (Note: For urban F stability
cases, use the cz for stability E.) Next, determine the mixing height
(ZT ) applicable to each stability class. For stabilities A to D, use the
average afternoon mixing height for the area (Figure 4-15). For urban sta-
bility E use the average morning mixing height (Figure 4-16). For rural
stabilities E and F, mixing height is not applicable. Then, use that
information as follows: For all stability-wind conditions when the plume
height (he) is greater than the mixing height (z-j), assume a zero contribution
to the annual concentration at the specified location. For each condition
when cz <_ O.Sz-j, and for all rural stability E and F cases, apply
the following equation^ to estimate the contribution C (g/m^):
4-23
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Table 4-2. STABILITY-WIND SPEED COMBINATIONS THAT ARE
CONSIDERED IN ESTIMATING ANNUAL AVERAGE CONCENTRATIONS
Atmospheric
Stability Categories
A
B
C
D
E
F
Wind Speed (m/s)
1.5
*
*
*
*
*
*
2.5
*
*
*
*
*
*
4.5
*
*
*
*
7
*
*
9.5
*
*
12.5
*
*It is only necessary to consider the stability-wind speed conditions
marked with an asterisk.
Table 4-3. WIND SPEED INTERVALS USED BY THE NATIONAL CLIMATIC DATA CENTER
FOR JOINT FREQUENCY DISTRIBUTIONS OF WIND SPEED,
WIND DIRECTION AND STABILITY
Class
1
2
3
4
5
6
Speed Interval ,
0 to 1.8
1 .8 to 3.3
3.3 to 5.4
5.4 to 8.5
8.5 to 11.0
>n.o
m/s (knots)
(0 to 3)
(4 to 6)
(7 to 10)
(11 to 16)
(17 to 21)
(>21)
Representative Wind Speed
m/s
1.5
2.5
4.5
7.0
9.5
12.5
4-24
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C = [(2.032 Q f)/(oz u x)] Gxp[-l/2[he/az]2l (4.9)
For each condition during which az > O.Bz^, the following equation'^ is
applied:
C = (2.55 Q f)/(z-j u x) (4.10)
In these equations:
Q = pollutant emission rate (g/s)
u = wind speed (in/s)
f = frequency of occurrence of the particular wind speed-stability
combination (obtained from the stability-wind rose (STAR) sumnary
available from the National Climatic Data Center) for the wind
direction of concern. Only consider the wind speed-stability
combinations for the wind direction that vill bring the plir.ie
closest to the specified location.
Step 6. Sun the contributions (C) computed in Step 5 to estimate
the annual average concentration at the specified location.
4.4.2 Maximum Annual Average Concentration
To estimate the overall maximum annual average concentration (the
maximum concentration regardless of location) follow the procedure Tor
the annual average concentration at a specified location, repeating the
procedure for each of several receptor distances, and for all directions.
Because of the large number of calculations required, it is recommended
that a computer model such as ISCLT be used.^1 The ISCLT model is a part
of the UNAMAP series, which is discussed in Appendix B.
4-25
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4.5 Special Topics
4.5.1 Bui 1ding Downwash
In some cases, the aerodynamic turbulence induced by a nearby building
will cause a pollutant emitted from an elevated source to be mixed rapidly
toward the ground (downwash), resulting in higher ground-level concentration
immediately to the lee of the building than would otherwise occur. Thus, when
assessing the impact of a source on air quality, the possibility of downwash
problems should be investigated. For purposes of these analyses, "nearby"
includes structures within a distance of five times the lesser of the
height or width of the structure, but not greater than 0.8 km (0.5 mile).6
if downwash is found to be a potential problem, its effect on air quality should
be estimated. Also when Good Engineering Practice (GEP) analysis indicates
that a stack is less than the GEP height, the following screening procedures
should be applied to assess the potential air quality impact.
The best approach to determine if downwash will be a problem at a
proposed facility is to conduct observations of effluent behavior at a simi-
lar facility. If this is not feasible, and if the facility has a
simple configuration (e.g., a stack adjacent or attached to a single
rectangular building), a simple rule-of-thumb22 may be applied to
determine the stack height (hs) necessary to avoid downwash problems:
hs _> hb + 1.5 Lb (4.11)
where !% is building height and L^ is the lesser of either building height
or .naximun projected building width. In other words, if the stack
height is equal to or greater than h^ + 1.5 L^, downwash is unlikely to
be a problem.
4-26
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If there is more than one stack at a given facility, the above rule must
be successively applied to each stack. If more than one building is involved
the rule must be successively applied to each building. Tiered structures
and groups of structures should be treated according to Reference 6. For
relatively complex source configurations the rule may not be applicable,
particularly when the building shapes are much different from the simple
rectangular building for which the above equation was derived. For these
cases, refined modeling techniques-^ or a wind tunnel study is recommended.
If it is determined that the potential for downwash exists, then the
SCREEN model should be used to estimate the maximum ground-level pollutant
concentrations that occur as a result of the downwash. The building downwash
screening procedure is divided into the following two major areas of concern:
A. Cavity Region; and
B. Wake Region
Generally, downwash has its greatest impact when the effluent is caught
in the cavity region. However, the cavity may not extend beyond the
plant boundary, and, in some instances, impacts in the wake region nay
exceed impacts in the cavity region. Therefore, impacts in both regions
must be considered if downwash is potentially a problem.
When the SCREEN model is run for building downwash calculations, the
program prompts the user for the building height, the minimum horizontal
building dimension, and the maximum horizontal building dimension.
A. Cavity Region
The cavity calculations are made using methods described by Hosker.23
Cavity calculations are based on the determination of a critical (i.e.,
minimum) wind speed required to cause entrainment of the plume in the
4-27
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cavity (defined as being when the plume center!ine height equals the
cavity height). Two cavity calculations are made, the first using the
minimum horizontal dimension alongwind, and the second using the maximum
horizontal dimension alongwind. The SCREEN output provides the cavity
concentration, cavity length (measured from the lee side of the building),
cavity height and critical wind speed for each orientation. The highest
concentration value that potentially affects ambient air should be used
as the maximum 1-hour cavity concentration for the source.
A more detailed description of the cavity effects screening proce-
dure is contained in Appendix A, Section A3. For situations significantly
different from the worst case, and for complex source configurations, a
more detailed analysis is required.24,25 if this estimate proves unaccept-
able, one may also wish to consider a field study or fluid modeling
demonstration to show maintenance of the NAAQS or PSD increments within
the cavity. If such options are pursued, prior agreement on the study
plan and methodology should be reached with the Regional Office.
B. Make Region
Wake effects screening can also be performed with the SCREEN model.
The SCREEN model uses the downwash procedures contained in the Industrial
Source Complex (ISC) Model, Second Edition (Revised)21, of UNAHAP, and
applies them to the full range of meteorological conditions described
in Appendix A. The SCREEN model accounts for downwash effects within
the "near" wake region (out to ten times the lesser of the building
height or projected building width, lOL^), and also accounts for the
effects of enhanced dispersion of the plume within the "far" wake region
4-28
-------
(beyond lOL^,). The same building dimensions as described above for the
cavity calculations are used, and SCREEN calculates the maximum projected
width from the values input for the minimum and maximum horizontal dimensions
The wake effects procedures are described in more detail in the ISC manual.21
4.5.2 Plume Impaction on Elevated Terrain
There is growing acceptance of the hypothesis that greater concentra-
tions can occur on elevated than on flat terrain in the vicinity of an ele-
vated source.* That is particularly true when the terrain extends well
above the effective plume height.
A procedure is presented here to (1) determine whether or not an
elevated plume may impact on elevated terrain and, (2) estimate the maximum
24-hour concentration if terrain impaction is likely. The procedure is
based largely upon the 24-hour mode of the EPA VALLEY model.26 A similar
procedure that accounts for terrain heights above plume height using the
VALLEY model, and compares results from the VALLEY model to simple terrain
calculations for terrain between stack height and plume height, is included
in the SCREEN program (see Appendix A). A concentration estimate obtained
through the procedure in this section will likely be somewhat greater
than provided by the VALLEY model or by the SCREEN program, primarily due
to the relatively conservative plume height that is used in Step 1:
Step 1. Determine if the plume is likely to impact on elevated terrain
in the vicinity of the source:
An exception may be certain flat terrain situations where building
downwash is a problem. (See Section 4.5.1).
4-29
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(1) Compute one-half the plume rise that can be expected
during F stability and a stack height wind speed (us) of 2.5 m/s. (The
reason for using only one-half the normally computed plume rise is to
provide a margin of safety in determining both if the plume may intercept
terrain and the resulting ground-level concentration. This assumption is
necessary because actual plume heights will be lower with higher stack
height wind speeds, and because impacts on intervening terrain above
stack height but below the full plune height might otherwise be missed.)
Ah = 2.6[(FbTa)/(usgA6/Az)]1/3/2 (4.12)
Refer to Steps 1 and 3 of Section 4.2 for a definition of terms.
(2) Compute a conservative plume height (he) by adding the
physical stack height (hs) to Ah:
he = hs + Ah
(3) Determine if any terrain features in the vicinity of the
source are as high as he. If so, proceed with Step 2. If that is not
the case, the plume is not likely to intercept terrain, and Step 2 is
not applicable.*
*Even if the plume is not likely to impact on elevated terrain (and for all
concentration averaging times of concern) the user should account for the
effects of elevated terrain on maximum concentrations. A procedure to
account for elevated terrain below stack height is described in Section
4.2 and consists of reducing the computed plume height, he (for all stabi-
lities), by the elevation difference between stack base and location of the
receptor(s) in question. The adjusted plume heights can then be used in
conjunction with the "flat-terrain" modeling procedures described earlier.
4-30
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Step 2. Estimate the maximum 24-hour ground-level concentration on
elevated terrain in the vicinity of the source:
(1) Using a topographic map, determine the distance from the
source to the nearest ground-level location at the height he.
(2) Using Figure 4-17 and the distance determined in (1),
estimate a 24-hour x/Q value.
(3) Multiply the (x/Q)24 value by the emission rate Q
(g/s) to estimate the maximum 24-hour concentration, x24> due to plume
impaction on elevated terrain:
X24 = Q(x/Q)24
4.5.3 Fumigation
Fumigation occurs when a plume that was originally emitted into a
stable layer is mixed rapidly to ground-level when unstable air below the
plume reaches plume level. Fumigation can cause very high ground-level
concentrations.^^ Typical situations in which fumigation occurs are:
1. Breaking up of the nocturnal radiation inversion by solar
warming of the ground surface;
2. Shoreline fumigation caused by advection of pollutants
from a stable marine environment to an unstable inland
environment; and
3. Advection of pollutants from a stable rural environment
to a turbulent urban environment.
The following procedure can be used for estimating concentrations due
to inversion break-up and shoreline fumigation in rural areas. Sources
located within 3 km of a large body of water should be evaluated for
shoreline fumigation. Procedures for estimating concentrations during
the third type, rural/urban, are beyond the scope of this document.
4-31
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Calculation procedures:
Step 1. Compute the plume height (he) that will occur during F
stability and a stack height wind speed of 2.5 m/s:
he = hs + Ah
To obtain a value for Ah, use the procedure described in Step 3 of
Section 4.2 with u = 2.5 m/s. If vs < 1.5us, account for stack tip downwash
using Equation 4.7.
Step 2. Estimate the downwind distance to maximum ground-level concentra-
tion using (a) for inversion break-up and (b) for shoreline fumigation.
(a) For inversion break-up fumigation, use Table 4-4 (derived from
Equation (5.5) of Turner's Workbook)^ to estimate the downwind distance at
which the maximum fumigation concentration is expected to occur, which is
based on the time required for the mixed layer to develop from the top
of the stack to the top of the plume. If this distance is less than
about ? kilometers, then fumigation concentrations are not likely to
exceed the limited mixing concentrations estimated in Step 4, Procedure (a),
of Section 4.2, and may be ignored.
(b) For shoreline fumigation, the maximum fumigation concentration
is expected to occur where the top of the stable plume intercepts the top of
the thermal internal boundary layer (TIBL). The distance to this location,
measured from the shoreline, may be estimated from Table 4-5. The distances
in Table 4-5 are based on the assumption of a parabolic TIBL shape.28 Subtract
the distance from the source to the shoreline from the value in Table 4-5
in order to obtain the downwind distance to the maximum from the source.
If the distance obtained is less than 0.2 km, then the shoreline fumigation
screening procedure should not be applied since the plume/TIBL interaction
4-32
-------
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4-34
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may be influenced by transitional plume rise effects.
Step 3. At the distance estimated in (2), determine the value of av
from Figure 4-18 and of az from Figure 4-14 for F stability. Since the
effects of buoyancy-induced dispersion (BID) have been incorporated in the
distances determined in (2) above, it is recommended that the values for ay
and az be adjusted for BID effects as follows:
a/ = [a2 + (Ah/3.5)2]i/2 ,
y y (4.13)
oz' = [az2 + (Ah/3.5)2]1/2
where Ah is the plume rise determined in (1) above. The maximum fumigation
estimate, particularly for shoreline fumigation, is sensitive to the inclusion
of BID since it effects the distance to the maximum as well as the actual
concentration calculation.
Step 4. Compute the maximum fumigation concentration (xf). using the
following equation:9
xf = Q/[/27u(ayl+he/8)(he+2az1)] (4.14)
For the inversion break-up case, the concentration xf can be expected to
persist for about 30 to 90 minutes. For shoreline fumigation, the high
ground-level concentrations can persist as lonq as the stable onshore flow
persists, up to several hours, although the location may shift as the direction
of the onshore flow shifts.
Step 5. If the estimated fumigation concentration, xf> "is less
than the maximum 1-hour concentration, xl» estimated from Step 4 of
Section 4.2, then the effects of fumigation may be ignored. If the estimated
fumigation concentration exceeds the maximum 1-hour concentration estimated
from Step 4 of Section 4.2, then the effect of fumigation on longer averaging
periods may be accounted for as follows. The value of x used with the
4-35
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multiplying factors in Step 5 (Section 4.2) should be adjusted using a
weighted average of xi and xf> assuming that xf persists for 90
minutes. The weighted average should be calculated as follows:
Averaging Time Adjustment of x^ for Fumigation
3 hours Xl' = (xi + Xf)/2
8 hours Xl' = (13xi + 3Xf)/16
24 hours Xl' = (15x1 + Xf)/16
The adjusted value, xi'» should then be used with the multiplying factors
in Step 5 of Section 4.2.
4.5.4 Estimated Concentrations from Area Sources
Fugitive emissions from simple area sources may be modeled as virtual
point sources in order to obtain pollutant concentration estimates,9 using
the procedure in this section. This procedure should only be applied to
approximately square area sources of at least 50 meters on a side and
with effective release heights of less than 10 meters. The SCREEN model
may also be used to estimate concentrations for area sources without
these restrictions on size and height (refer to Appendix A). Because
of the simplifying assumptions used in this procedure, the results
should be used with extreme caution, especially for receptors close to
the area source where there may be a bias toward over prediction. An
area source approximation for estimating contributions from multiple
point sources is presented in Section 4.5.5(C).
Step _!. Define the area source by approximating it as a square area.
(For complex area sources that cannot be approximated by a square, the
Industrial Source Complex (ISC) model 21 of the UNAMAP series may be used
if the area can be broken down into a group of adjacent squares).
4-36
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Step 2. Determine the distance to the virtual point source corre-
sponding to stability classes C and F for rural sources and classes C and
E for urban sources.
(1) Estimate the initial horizontal dispersion parameter,
ay0, by dividing the length of the side of the area source, S, by 4.3:
ayo = S/4.3 (4. IS)
(2) For rural sites, use Figure 4-18 to determine the virtual
point source distance, Xy, that corresponds with the value of ay0 for
both stability classes (C and E or F).
For urban sites, calculate the virtual point source
distance, Xy, that corresponds with the value of ay0 from the following:
xy = [0.0004ayoMl.6xlO-7ay0H4a2oyo2)1/2]/(2a?-) (4.16)
with a = 0.22 for stability class C and a = 0.11 for stability class E.
Step 3. Determine the effective release height, he. In general, this
will be the physical height of the source for fugitive emissions. For a
slag pile, use one half the height of the pile. If the effective release
height cannot be determined, assume a release height of 0 m.
Step 4. Estimate maximum short term (1-hour) concentrations by following
the procedure for point sources outlined in Step 4 of Section 4.2, assuming
no plume rise, Ah = 0. Do not use the multiplying factors in Step 5 of
Section 4.2 to correct for averaging times greater than 1-hour. Concen-
trations close to an area source will not vary as much as those for point
sources in response to varying wind directions, and the meteorological
conditions which are likely to give maximum 1-hour concentrations (Procedures
4-37
-------
(b) and (c) of Section 4.2) can persist for several hours. Therefore it
is recommended that the maximum 1-hour concentration be conservatively
assumed to apply for averaging periods out to 24 hours.
Step 5. Determine the downwind distance to the maximum concentration,
meaji'red from the downwind edge of the area source, by subtracting the
virtual point source distance, Xy, from the distance obtained from Figure
4-2 (rural) or Figure 4-3 (urban) in Step 4 of Section 4.2. For ground-
level sources (he = Om), the maximum concentration will be at the downwind
edge of the source.
4.5.5 Contributions from Other Sources
To assess the significance of the air quality impact of a proposed
source, the impact of nearby sources and "background" must be specifically
determined. (Background includes those concentrations due to natural
sources, and distant or unspecified man-made sources.) The impact of
the proposed source can be separately estimated, applying the techniques
presented elsewhere in Section 4, and then superimposed upon the impact of
the nearby sources and background to determine total concentrations in
the vicinity of the proposed source.
This section addresses the estimation of concentrations due to nearby
sources and background. Three situations are considered:
A. A proposed source relatively isolated from other sources.
B. A proposed source in the vicinity of a few other sources.
C. A proposed source in the vicinity of an urban area or other
large number of sources.
4-38
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It must be noted that in all references to air quality monitoring in
the following discussion, it is assumed that the source in question is not
yet operating. If the source is emitting pollutants during the period of
air quality data collection, care must be taken not to use monitoring data
influenced by the impact of the source. Additional guidance on determining
background concentrations is provided in Section 9.2 of the Guideline
on Air Quality Models (Revised).3
A. Relatively Isolated Proposed Source
A proposed source may be considered to be isolated if it is expected
that background will be the only other significant contributor to ambient
pollutant concentrations in its vicinity. In that case, it is recommended
that air quality data from monitors in the vicinity of the proposed source
be used to estimate the background concentrations. If monitoring data are
not available from the vicinity of the source, use data from a "regional"
site; i.e., a site that characterizes air quality across a broad area,
including that in which the source is located.
Annual average concentrations should be relatively easy to determine
from available air quality data. For averaging times of about 24 hours
or less, meteorology should be accounted for; i.e., the combined source/
background concentration must be calculated for several meteorological
conditions to ensure that the maximum total concentration is determined.
B. Proposed Source in the Vicinity of a Few Other Sources
If there already are a few sources in the vicinity of the proposed
facility, the air quality impact of these sources should be accounted for.
As long as the number of nearby sources is relatively small, the reco.n-
4-39
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mended procedure is to use (1) air quality monitoring data to estimate
background concentrations and (2) dispersion modeling to estimate
concentrations due to the nearby source(s). Then superimpose those estimates
to determine total concentrations in the vicinity of the proposed source.
To estimate background concentrations, follow the same basic procedure
as in the case of an isolated source. In this case, however, there is one
added complication. Wind direction must be accounted for in order to single
out the air quality data that represent background only (i.e., data that
are not affected by contributions from nearby sources).
Concentrations due to the nearby sources will normally be best
determined through dispersion modeling. The modeling techniques presented in
this guideline may be used. If the user has access to UNAMAP, the modeling
effort can be considerably simplified. If UNAMAP can not be used, the user
should model each source separately to estimate concentrations due to each
source during various meteorological conditions and at an array of receptor
locations (e.g., see Sections 4.3 and 4.4.1) where interactions between the
effluents of the proposed source and the nearby sources can occur. Signi-
ficant locations include (1) the area of expected maximum impact of the
proposed source, (2) the area of maximum impact of the nearby sources, and
(3) the area where all sources will combine to cause maximum impact. It may
be necessary to identify those locations through a trial and error analysis.
C. Proposed Source Within an Urban Area or in the Vicinity of a Large
Number of Sources
For more than a very small number of nearby sources, it may be
impractical to model each source separately. Two possible alternatives
for estimating ambient concentrations due to the other sources are to use
air quality monitoring data or a multisource dispersion model.
4-40
-------
If data from a comprehensive air monitoring network are available, it
may be possible to rely entirely on the measured data. The data should be
adequate to permit a reliable assessment of maximum concentrations, par-
ticularly in (1) the area of expected maximum impact of the proposed source,
(2) the area of maximum impact of the existing sources and (3) the area
where all sources will combine to cause maximum impact.
In some cases, the available air quality monitor data will only be
adequate to estimate general area-wide background concentrations. In such
cases, there is no choice but to use dispersion modeling to estimate concen-
trations due to the nearby sources. If possible, a multisource dispersion
model should be used. If the user has access to UNAMAP the ISCLT model can
be applied for long-term concentration estimates, and the MPTER or
ISCST model for short-term estimates (MPTER can handle up to 250 point
sources but cannot handle building downwash effects).
If it is not feasible to apply a multisource model, and there is a
considerable number of nearby sources, a rough estimate of maximum concen-
trations due to those sources can be made by arbitrarily grouping the
sources into an area source through the following equation.29 (The esti-
mate is primarily applicable to receptor locations near the center of the
area source, defined below, although it may be considered a reasonable
first-approximation for any location within the area):
C = 18 Q (Ax)1/1+/u (4.17)
where:
C = maximum short term (1 - 24 hours) contribution to ground-level
concentrations from the area source (g/m^)
4-41
-------
Q = average emission rate (g/m^/s) within the area
defined by Ax
u = assumed average wind speed (m/s) for the averaging
time of concern (use 2 m/s if no data are available)
Ax = length (n) of one side of the smallest square area that
will contain the nearby sources, ignoring relatively
small outlying sources or any source that is considerably
removed from the other sources.
The best results will be obtained with the above equation when emissions
are uniformly distributed over the defined area. Any large point sources
in the vicinity should be modeled separately, and the estimated concentra-
tions manually superimposed upon that computed for the area source.
Because this is an area source approximation, the adjustment factors for
averaging times greater than an hour should not be used.
4.5.6 Long Range Transport
In certain instances it will be necessary to estimate the air quality
impact of a proposed source at locations beyond its vicinity (beyond roughly
30-50 km). To estimate seasonal or annual average concentrations (out to
about 100 km) the procedures of Section 4.4 provide a rough estimate. The
procedures are limited to plume heights greater than 50m, and should not be
applied beyond 100 km.
For short-term estimates (concentration averaging times up to about
24 hours) beyond the vicinity of the source and out to 100 km downwind, the
following procedure is recommended. The procedure accounts for the meteoro-
logical situations with the greatest persistence that are likely to result
in the highest concentrations at large distances; viz., neutral/high wind
conditions (Steps 1-4) and stable conditions (Steps 5-7):
4-42
-------
Step 1. Estimate the normalized plume rise (uAh) applicable to
neutral and unstable atmospheric conditions. Use the procedure described
in Step 1 of Section 4.2.
Step 2. Compute plume height, he, that will occur during D stability
with a 10-meter wind speed of 5 m/s. Adjust the wind speed from 10 meters
to stack height, using Equation 3.1 and the exponent for stability class D.
he = hs + (uAh)/us
Step 3. Using Figure 4-19, obtain a yU/Q value for the desired
downwind distance (D stability case). (If the plume height is greater than
300m, then the value corresponding to he = 300m may be used for conservatism.)
Step 4. Compute the maximum 1-hour D stability concentration, xmax»
using the yu/Q value obtained in Step 3.
>max = Q(xu/Q)/us
For Q, substitute the source emission rate (g/s), and use the value of us
determined in Step 2.
Step 5. Compute the plume height he = hs + Ah that will occur
during E stability with a 10-meter wind speed of 2 m/s. Adjust the wind
speed from 10 meters to stack height using Equation 3.1 and the exponent
for stability class E. Use the stable plume rise (Ah) computed
from Equation 4.6 in Step 3 of Section 4.2.
he = hs + Ah
Step 6. From Figure 4-20, obtain a yu/Q value for the same distance
considered in Step 3 above. (If the plume height is greater than 300m, then
the value corresponding to he = 300m may be used for conservatism).
4-43
-------
Step 7. Compute the maximum 1-hour E stability concentration, xmax>
using the xu/Q value obtained in Step 6:
Xmax = Q(xu/Q)/us
where us was determined in Step 5.
Step 8. Select the higher of the xmax values computed in Steps 4
and 7. The selected value represents the highest 1-hour concentration
likely to occur at the specified distance.
Step 9. To estimate concentrations for averaging times up to 24 hours,
multiply the 1-hour value by the factors presented in Step 5 of Section 4.2.
4-44
-------
QNIMNMOQ
4-45
-------
0.1
10
-6
10-4
2 5 1Q-5 2 5
MAXIMUMxu/Q.m'2
Figure 4-3. Downwind distance to maximum concentration and maximum xu/Q as a function
of stability class and plume height (m); urban terrain.
10-'
4-45
-------
0.1 0.2
0.5 1 2 5 10 20
DOWNWIND DISTANCE, km
50 100
Figure 4-4. Stability class A; rural terrain xu/Q versus distance for various
pmme heights (H), assuming very restrictive mixing heignts (U: L = bO m
for H s= 50 m; L = H for H > 50 m
-------
10'3
0.1
0.2
0.5
12 5 10
DOWNWIND DISTANCE, km
20
100
Figure 4-5 Stability class B; rural terrain xu/Q versus distance for various
plume heights (H), assuming very restrictive mixing heights (L): L = 50 m
for H ^ 50 m; L = H for H > 50 m.
4
-------
10-7-
0.1 0.2
0.5 1
10 20
50 100
DOWNWIND DISTANCE, km
Figure 4-6. Stability class C; rural terrain xu/Q versus distance for various
plume heights (H), assuming very restrictive mixing heights (L): L = 50 m
for H < 50 m; L = H for H > 50 m.
•i 49
-------
0.1
0.2
0.5
12 5 10
DOWNWIND DISTANCE, km
20
50
100
Figure 4-7. Stability class D; rural terrain xu/Q versus distance for various
plume neights (H), assuming very restrictive mixing heights (L): L = 50 m
for H < 50 m; L = H for H > 50 m.
SO
-------
ID'6
0.1
0.5
20
50
100
12 5 10
DOWNWIND DISTANCE, km
Figure 4-8 Stability class E; rural terrain xu/Q versus distance for various plume
heights (HI, assuming very restrictive nrxing ne'ghts (L): L = 50 m for H < 50 m;
I = H for H > 50 m
-------
ID'2 —
10
0.1 0.2
0.5
12 5 10
DOWNWIND DISTANCE, km
20
50
Figure 4-9 Stability class F; rural terrain xu/Q versus distance for various
piun-e tie'yhts (H), assuming very restrictive mixing heights (L): L = 5Qrr\
for H < 50 m; L = H for H > 50 m.
-------
0.1
0.5
2 5 10
DOWNWIND DISTANCE, km
20
50
100
Figure 4-10. Stability classes A and B; urban terrain xu/Q versus distance for various plume
heights (H), assuming very restrictive mixing heights (L): L = 50 m for H < 50 m; L = H
for H > 50 m.
-------
0.1
0.2
0.5
1
20
50
2 5 10
DOWNWIND DISTANCE, km
ciaurp 4-11. Stability class C; urban terrain xu/Q versus distance for various plume heights (H),
assuming very restrictive mixing heights (L): L = 50 m for H < 50 m; L = H for H > 50 m.
100
4-54
-------
0.2
0.5
2 5 10
DOWNWIND DISTANCE, km
20
50
100
Figure 4-12. Stability class D; urban terrain xu/Q versus Distance for various plume h : jhts
m), assuming very restrictive mixing heights (LI i_ = ou m for H ^ 50 m; L = H for
H >50m
a v.
-------
0.1 0.2
0.5
2 5 10
DOWNWIND DISTANCE, km
20
50 100
Figure 4-13. Stability class E; urban terrain xu/Q versus distance for various plume heights
ini. dbsunmg very restrictive mixing heights (L): L = bO m for H < 50 m; L = H for
H •> 50 rr,
56
-------
5,000
2,000
1,000
7H
500
200
100
50
20
10
X
/
r xx
0.1 0.2
0.5 1 2 5 10 20
DOWNWIND DISTANCE, km
50 100
Figure 4-14. Vertical dispersion parameter (az) as a function of downwind distance and
class; rural terrain.
4-57
-------
.c
O)
'CU
JC
O5
c
'x
'E
c
o
o
c
CD
4-»
H—
CD
"CD
3
C
C
to
c
CD
0)
E
03
+-»
CD
E
Q.
O
en
in
5
CU
t_
D
_O)
IT
4-58
-------
O)
'cu
.c
O)
c
'x
'E
en
c
'c
1_
O
E
c
c
n:
c
CD
QJ
•+-<
OJ
E
M—
O
a
o
ISI
CO
*j
CD
u.
,?
L
4-59
-------
0.1
0.2
0.5
1 2 5
DOWNWIND DISTANCE, km
20
50
100
Figure 4-17. 24 hour x/Q versus downwind distance, obtained from the valley model
Asbumpuuiib include stability class F, a wind speed of 2.5 m/sec, and plume height lO
meters above ter^a^n.
4-60
-------
10,000
5,000
2.000
1,000
50
:oo
E
>
100
50
X
x /
/
X X
'xx —
X ' x x
X x x x_
x' ' / .^ x'
x x x x x
XXX X .x
,x x- x x x
x'' X x x x
^XX/ xX/ x""
x X x ^x
x' x x
'' / ''
x x / s*
XX X
X
V X ' X
XXX
Xxx
XX x
>;/
X
X
X
20
10
PC
^7
/ ' x
,>>x
X
0.1 0.2
0.5 1 2 5 10 20
DOWNWIND DISTANCE, km
50 100
Figure 4-18. Horizontal dispersion parameter (cry) as a function of downwind distance and
stability class; rural terrain.
4-61
-------
DOWNWIND DISTANCE, km
Figure 4-19. Maximum xu/Q as a function of downwind distance and plume
height (H), assuming a mixing height of 500 meters; D stability.
4-h?
-------
10
20 50
DOWNWIND DISTANCE, km
Figure 4-20. Maximum XU/Q as a function of downwind distance and p'ume
height (H); E stability.
4 63
-------
5. REFERENCES
1. U. S. Environmental Protection Agency, September 1974. Guidelines for
Air Quality Maintenance Planning and Analysis, Volume 10: Reviewing
New Stationary Sources. EPA-450/4-74-011 (OAQPS Number 1.2-029),
Research Triangle Park, N. C. 27711.
2. U. S. Environmental Protection Agency, October 1977. Guidelines for
Air Quality Maintenance Planning and Analysis, Volume 10 (Revised):
Procedures for Evaluating Air Quality Impact of New Stationary
Sources. EPA-450/4-77-001 (OAQPS Number 1.2-029R), Research
Triangle Park, N. C. 27711.
3. U. S. Environmental Protection Agency, 1986. Guideline on Air Quality
Models (Revised) and Supplement A (1987). EPA-450/2-78-027R. U. S.
Environmental Protection Agency. Research Triangle Park, N. C. 27711.
4. U. S. Congress, August 1977. Clean Air Act Amendments of 1977 - Public
Law 95-95, Section 302 (j).
5. U. S. Environmental Protection Agency, 1985. Compilation of Air
Pollution Emission Factors, Volume I: Stationary Point and Area
Sources. Publication No. AP-42, Fourth Edition, Research Triangle
Park, N. C. 27711.
6. U. S. Environmental Protection Agency, 1985. Guideline for Determination
of Good Engineering Practice Stack Height (Technical Support Document
for the Stack Height Regulations), (Revised), EPA-450/1-80-023R. U. S.
Environmental Protection Agency, Research Triangle Park, N. C. 27711.
7. U. S. Environmental Protection Agency, 1987. On-site Meteorological
Program Guidance for Regulatory Modeling Applications,
EPA-450/8-87-013. U.S. Environmental Protection Agency. Research
Triangle Park, NC 27711.
8. U. S. Environmental Protection Agency, 1987. Ambient Monitoring
Guidelines for Prevention of Significant Deterioration (PSD).
EPA-450/4-87-007. U. S. Environmental Protection Agency, Research
Triangle Park, N. C. 27711.
9. Turner, D. B., 1970. Workbook of Atmospheric Dispersion Estimates.
Revised, Sixth printing, Jan. 1973. Office of Air Programs Publication
No. AP-26. U. S. Environmental Protection Agency. U. S. Government
Printing Office, Washington, D. C. 20402.
10. List, R. J., 1966. Smithsonian Meteorological Tables. Sixth Revised
Edition (Third Reprint).Smithsonian Institution, Washington, D. C.
5-1
-------
11. Holzworth, G. C., 1972. Mixing Heights, Wind Speeds, and Potential for
Urban Air Pollution Throughout the Contiguous United States. Office
of Air Programs Publication No. AP-101, U. S. Environmental Protection
Agency. U. S. Government Printing Office, Washington, D. C. 20402.
12. Randerson, D., 1984. Atmospheric Boundary Layer. In Atmospheric Science
and Power Production. Randerson, D. (ed.), DOE/TIC-27601, U. S. Department
of Energy, Washington, D.C.
13. U. S. Environmental Protection Agency, 1971. Exhaust Gases from
Combustion and Industrial Sources, APTD-0805. Pub. No. PB203-861,
NTIS, Springfield, Virginia 22151.
14. Turner, D. B. and E. L. Martinez, 1973. A Simple Screening Technique
for Estimating the Impact of a Point Source of Air Pollution Relative
to the Air Quality Standards. (NOAA manuscript) U. S. Environmental
Protection Agency, Research Triangle Park, N. C. 27711.
15. Sriggs, G. A., 1969. Plume Rise. USAEC Critical Review Series
TID-25075, National Technical Information Service, Springfield,
Virginia 22151.
16. Briggs, G. A., 1971. Some Recent Analyses of Plume Rise Observation
Pages 1029-1032 of the Proceedings of the Second International Clean
Air Congress, edited by H. M. Englund and H. T. Berry. Academic
Press, N. Y.
17. Briggs, G. A., 1975. Plume Rise Predictions. In: Lectures on Air
Pollution and Environmental Impact Analysis, D. A. Haugen, ed,, American
Meteorological Society, Boston, Massachusetts, pp. 59-111.
18. Leahey, D.M. and M.J.E. Davies, 1984. Observations of Plume Rise from
Sour Gas Flares. Atmospheric Environment, 18, 917-922
19. Beychok, M., 1979. Fundamentals of Stack Gas Dispersion, Irvine, CA.
20. McElroy, J. L. and Pooler, F., December 1968. St. Louis Dispersion
Study, Volume II - Analyses. AP-53, National Air Pollution Control
Administration, Arlington, Virginia 22203.
21. U. S. Environmental Protection Agency, 1987. Industrial Source
Complex (ISC) Dispersion Model User's Guide - Second Edition
(Revised), EPA-450/4-88-002a. U. S. Environmental Protection
Agency, Research Triangle Park, N. C. 27711
22. Snyder, W. H., and R. E. Lawson, Jr., 1976. Determination of a
Necessary Height for a Stack Close to a Building--A Rind Tunnel Study.
Atmospheric Environment, 10, 683-691.
23. Hosker, R. P., 1984. Flow and Diffusion Near Obstacles. In Atmospheric
Science and Power Production. Randerson, D. (ed.), DOE/TIC-27601, U. S.
Department of Energy, Washington, D.C.
5-2
-------
24. Huber, A. H., and W. H. Snyder, October 1976. Building Wake Effects
on Short Stack Effluents. Preprint volume: Third Symposium on
Atmospheric Turbulence, Diffusion and Air Quality. Published by
American Meteorological Society, Boston, Massachusetts, pp. 235-242.
25. Huber, A. H., 1977. Incorporating Building/Terrain Wake Effects on
Stack Effluents. Preprint volume: AMS-APCA Joint Conference on
Applications of Air Pollution Meteorology, November 29 - December 2,
1977, Salt Lake City, Utah.
25. Burt, E. W., September 1977. Valley Model User's Guide. EPA-450/2-
77-018. U. S. Environmental Protection Agency, Research Triangle
Park, N. C. 27711.
27. Lyons, U. A., and H. S. Cole, 1973. Fumigation and Plume Trapping on
the Shores of Lake Michigan During Stable Onshore Flow. J. of Applied
Meteorology, 12_, pp. 494-510.
28. Stunder, M. and S. SethuRaman, 1986. A Statistical Evaluation of Coastal
Point Source Dispersion Models. Atmospheric Environment, 20, 301-315.
29. Hanna, S. R. 1971. A Simple Method of Calculating Dispersion from
Urban Area Sources. Journal of the Air Pollution Control Association, 12,
774-777.
5-3
-------
APPENDIX A
SCREEN Model User's Guide
-------
-------
Al. INTRODUCTION
Overview of User's Guide
It will be easier to understand this user's guide and the SCREEN
model if you are already familiar with the screening procedures, especially
those described in Section 4.2.
This introduction should answer most of your general questions about
what the SCREEN model can (and cannot) do, and explain its relationship to
the screening procedures document.
Section A2 provides several examples of how to run the SCREEN model
and will also help the novice user get started. The point source example
provides the most detailed description and should be read before the
other examples. If you are already familiar with personal computers and
with the screening procedures, you probably won't have much trouble
simply running SCREEN and "experimenting" with it. It runs interactively,
and the prompts should be self explanatory.
Section A3 provides background technical information as a reference
for those who want to know more about how SCREEN makes certain calculations.
The discussion in Section A3 is intended to be as brief as possible,
with reference to other documents for more detailed descriptions.
Purpose of SCREEN
The SCREEN model was developed to provide an easy-to-use method of
obtaining pollutant concentration estimates based on the new screening
procedures document. By taking advantage of the rapid growth in the
A-l
-------
availability and use of personal computers (PCs) the SCREEN model makes
screening calculations accessible to a wide range of users.
What is needed in order to use SCREEN?
SCREEN will run on an IBM-PC compatible personal computer with at
least 256K of RAM. You will need at least one 5 1/4" double-sided, double-
density (360K) or a 5 1/4" high density (1.2MB) disk drive. The program
will run with or without a math coprocessor chip. Execution time will be
greatly enhanced with a math coprocessor chip present (about a factor of
5 in runtime) and will also benefit from the use of a hard disk drive.
SCREEN will write a date and time to the output file, provided that a
real time clock is available.
What will SCREEN do?
SCREEN runs interactively on the PC, meaning that the program asks the
user a series of questions in order to obtain the necessary input data, and
to determine which options to exercise. SCREEN can perform all of the
single source, short-term calculations in the screening procedures document,
including estimating maximum ground-level concentrations and the distance
to the maximum (Step 4 of Section 4.2), incorporating the effects of building
downwash on the maximum concentrations for both the near wake and far wake
regions (Section 4.5.1), estimating concentrations in the cavity recircu-
lation zone (Section 4.5.1), estimating concentrations due to inversion
break-up and shoreline fumigation (Section 4.5.3), and determining plume
rise for flare releases (Step 1 of Section 4.2). The model can incorporate
the effects on maximum concentrations of elevated terrain below stack
height (Section 4.2), and can also estimate 24-hour average concentrations
A-2
-------
due to plume impaction in complex terrain using the VALLEY model 24-hour
screening procedure (Section 4.5.2). Simple area sources can be modeled
with SCREEN using a virtual point source procedure (Section 4.5.4). The
SCREEN model can also calculate the maximum concentration at any number of
user-specified distances in flat or elevated simple terrain (Section 4.3),
including distances out to 100 km for long-range transport (Section 4.5.6).
Uhat will SCREEN not do?
SCREEN can not explicitly determine maximum impacts from multiple
sources, except for the procedure to handle multiple nearby stacks by
merging emissions into a single "representative" stack (Section 2.2).
The user is directed to the MPTER or ISCST models in the UNAMAP series to
model short-term impacts for multiple sources. With the exception of the
24-hour estimate for complex terrain impacts, the results from SCREEN are
estimated maximum 1-hour concentrations. To handle longer period averages,
the screening procedures document contains recommended adjustment factors
to estimate concentrations out to 24 hours from the maximum 1-hour value
(Section 4.2, Step 5). For seasonal or annual averages, Section 4.4 of
the screening procedures document contains a procedure using hand calcu-
lations, but the use of ISCLT or another long-term model of UNAMAP is
recommended.
How will SCREEN results compare to hand calculations from the document?
The SCREEN model is based on the same modeling assumptions that are
incorporated into the screening procedures and nomographs, and for many
sources the results will be very comparable, with estimated maximum concen-
A-3
-------
trations differing by less than about 5 percent across a range of source
characteristics. However, there are a few differences that the user should
be aware of. For some sources, particularly taller sources with greater
buoyancy, the differences in estimated concentrations will be larger, with
the hand calculation exceeding the SCREEN model result by as much as 25
percent. These differences are described in more detail below.
The SCREEN model can provide estimated concentrations for distances
less than 100 meters (down to one meter as in other regulatory models),
whereas the nomographs used in the hand calculations are limited to distances
greater than or equal to 100 meters. The SCREEN model is also not limited
to plume heights of 300 meters, whereas the nomographs are. In both cases,
caution should be used in interpreting results that are outside the range
of the nomographs.
In addition, SCREEN examines a full range of meteorological conditions,
including all stability classes and wind speeds (see Section A3) to find maximum
impacts, whereas to keep the hand calculations tractable only a subset of
meteorological conditions (stability classes A, C, and E or F) likely to
contribute to the maximum concentration are examined. The use of full
meteorology is required in SCREEN because maximum concentrations are also
given as a function of distance, and because A, C, and E or F may not be
controlling for sources with building downwash (not included in the hand
calculations). SCREEN explicitly calculates the effects of multiple reflec-
tions of the plume off the elevated inversion and off the ground when
calculating concentrations under limited mixing conditions. To account for
A-4
-------
these reflections, the hand calculation screening procedure (Procedure (a)
of Step 4 in Section 4.2) increases the calculated maximum concentrations
for A stability by a factor ranging from 1.0 to 2.0. The factor is intended
to be a conservative estimate of the increase due to limited mixing, and
may be slightly higher (about 5 to 10 percent) than the increase obtained
from SCREEN using the multiple reflections, depending on the source. Also,
SCREEN handles the near neutral/high wind speed case (Procedure (b)) by
examining a range of wind speeds for stability class C and selecting the
maximum, whereas the hand calculations are based on the maximum concentration
estimated using stability class C with a calculated critical wind speed and
a 10 meter wind speed of 10 m/s. stability class C. This difference
should result in differences in maximum concentrations of less than about 5
percent for those sources where the near neutral/high wind speed case is
control 1 ing.
The SCREEN model results also include the effects of buoyancy-induced
dispersion (BID), which are not accounted for by the hand calculations (except
for fumigation). The inclusion of BID in SCREEN may either increase or
decrease the estimated concentrations, depending on the source and distance.
For sources with plume heights below the 300 meter limit of the hand calcu-
lations, the effect of BID on estimated maximum concentrations will usually
be less than about +_ 10 percent. For elevated sources with relatively
large buoyancy, the inclusion of BID may be expected to decrease the estimated
maximum concentration by as much as 25 percent.
A-5
-------
How does SCREEN differ from PTPLU, PTMAX and PTDIS?
The PT-series of models have been used in the past to obtain results
for certain screening procedures in Volume 10R. The SCREEN model is designed
specifically as a computerized implementation of the revised screening
procedures, and is much more complete than the earlier models, as described
above. The SCREEN model also requires less manual "postprocessing" than
the earlier models by listing the maximum concentrations in the output.
However, many of the algorithms in SCREEN are the same as those contained
in PTPLU-2.0. For the same source parameters and for given meteorological
conditions, the two models will give comparable results. SCREEN also
incorporates the option to estimate concentrations at discrete user-specified
distances, which was available with PTDIS, but is not included in PTPLU.
A-6
-------
A2. TUTORIAL
What is needed?
o IBM-PC compatible with at least 256K bytes of RAM, and a 5 1/4" double-
sided, double-density or high density disk drive.
o DisKette provided with SCREEN software.
o Hard disk drive (Optional but recommended).
o Math coprocessor chip (Optional but recommended).
o Blank diskette for use in making a backup copy of software.
Setup on the PC
Using the DISKCOPY command of DOS (Disk Operating System) or similar
routine, make a backup copy of the SCREEN software. Store the original
SCREEN software diskette in a safe location. The DISKCOPY command will also
format the blank disk if needed.
The following set-up instructions assume that the user has a system with
a hard disk drive. Examine the contents of the READ.ME file on the SCREEN
diskette (e.g., by using the DOS TYPE command) for instructions on the set-up
of SCREEN for a system with no hard disk drive.
Insert the SCREEN diskette in floppy drive A: and enter the following
commands at the DOS prompt from drive C: (either from the root directory or
a subdirectory):
COPY A:*-*
ARC521
ARC E SCREEN
A-7
-------
These commands will copy the three files from the SCREEN diskette, SCREEN.ARC,
ARC521.COM, and READ.ME, to the hard disk; "unpack" the archiving program,
ARC521; and extract the SCREEN files from archive. The hard disk will now
contain the executable file of SCREEN, called SCREEN.EXE, as well as the
FORTRAN source file, SCREEN.FOR, a listing file, SCREEN.1ST, an example input
file, EXAMPLE.DAT, and associate output file EXAMPLE.OUT.
Executing the Model
The SCREEN model is written as an interactive program for the PC, as
described earlier. Therefore, SCREEN is normally executed by simply
typing SCREEN from any drive and directory that contains the SCREEN.EXE
file, and responding to the prompts provided by the program. However, a
mechanism has been provided to accommodate for the fact that for some
applications of SCREEN the user might want to perform several runs for the
same source changing only one or a few input parameters. This mechanism
takes advantage of the fact that the Disk Operating System (DOS) on PCs
allows for the redirection of input that is normally provided via the
keyboard to be read from a file instead. As an example, to run the sample
problem provided on the disk one would type:
SCREEN
-------
model, SCREEN has been programmed to write out all inputs provided to a
file called SCREEN.DAT during execution. Therefore, at the completion of a
run, if the user types SCREEN
-------
will identify either upper or lower case letters and will repeat the prompt
until a valid response is given).
For a point source, the user will be asked to provide the following inputs:
Point Source Inputs
Emission rate (g/s)
Stack height (m)
Stack inside diameter (m)
Stack gas exit velocity (m/s)
Stack gas temperature (K)
Ambient temperature (K) (use default of 293K if not known)
Receptor height above ground (may be used to define flagpole
receptors) (m)
Urban/rurdl option (l=urban, 2=rural)
The SCREEN model uses free format to read the numerical input data.
Figure A-l presents the order of options within the SCREEN model for
point sources and is annotated with the corresponding sections from the
screening procedures document. In order to obtain results from SCREEN
corresponding to the procedures in Step 4 of Section 4.2, the user should
select the full meteorology option, the automated distance array option,
and, if applicable for the source, the simple elevated terrain option.
These, as well as the other options in Figure A-l, are explained in more
detail below.
Building Downwash Option
Following the basic input of source characteristics SCREEN will first
ask if building downwash is to be considered, and if so, asks for the
building height, minimum horizontal dimension, and maximun horizontal
dimension in meters. The downwash screening procedure assumes that the building
A-10
-------
Order of Options
in SCREEN
Corresponding Section in
Screening Procedures Document
Input Source
'Characteristics
Building
Downwash
Option
Complex
Terrain
Option
Simple Elevated
or Flat Terrain
Option*
Choice
of
Meteorology*
Automated
Distance Array
Option*
Discrete
Distance
Option*
Fumigation
Option
(Rural Only)
Section 4.5.1
Section 4.5.2
Section 4.2
Section 4.2, Step 4
Section 4.2, Step 4
Section 4.3 for Distances < 50km
Section 4.5.6 for Distances > 50km
Figure A—1
Section 4.5.3
*These options also apply to
Area Sources, Section 4.5.4
Point Source Options in SCREEN
A-ll
-------
can be approximated by a simple rectangular box. Wake effects are included
in any calculations made using the automated distance array or discrete
distance options (described below). Cavity calculations are made for two
building orientations - first with the minimum horizontal building dimension
alongwind, and second with the maximum horizontal dimension alongwind.
The cavity calculations are summarized at the end of the distance-dependent
calculations.
Complex Terrain Option
The complex terrain option of SCREEN allows the user to estimate
impacts for cases where terrain elevations exceed stack height. If the
user elects this option, then SCREEN will calculate and print out a final
stable plume height and distance to final rise for the VALLEY model 24-hour
screening technique. This technique assumes stability class F (E for
urban) and a stack height wind speed of 2.5 m/s. For complex terrain,
maximum impacts are expected to occur for plume impaction on the elevated
terrain under stable conditions. The user is therefore instructed to enter
minimum distances and terrain heights for which impaction is likely, given
the plume height calculated, and taking into account complex terrain closer
than the distance to final rise. If the plume is at or below the terrain
height for the distance entered, then SCREEN will make a 24-hour concentration
estimate using the VALLEY screening technique. If the terrain is above
stack height but below plume centerline height for the distance entered,
then SCREEN will make a VALLEY 24-hour estimate (assuming E or F and 2.5
m/s), and also estimate the maximum concentration across a full range of
meteorological conditions using simple terrain procedures with terrain
A-12
-------
"chopped off" at physical stack height. The higher of the two estimates is
selected as controlling for that distance and terrain height (both estimates
are printed out for comparison). The simple terrain estimate is adjusted
to represent a 24-hour average by multiplying by a factor of 0.40, while
the VALLEY 24-hour estimate incorporates the 0.25 factor used in the VALLEY
model. Calculations continue for each terrain height/distance combination
entered until a terrain height of zero is entered. The user will then have
the option to continue with simple terrain calculations or to exit the
program. It should be noted that SCREEN will not consider building downwash
effects in either the VALLEY or the simple terrain component of the complex
terrain screening procedure, even if the building downwash option is selected,
SCREEN also uses a receptor height above ground of 0.0m (i.e. no flagpole
receptors) in the complex terrain option even if a non-zero value is entered.
The original receptor height is saved for later calculations. Refer to
Section A3 for more details on the complex terrain screening procedure.
Simple Elevated or Flat Terrain Option
The user is given the option in SCREEN of modeling either simple
elevated terrain, where terrain heights exceed stack base but are below
stack height, or simple flat terrain, where terrain heights are assumed not
to exceed stack base elevation. If the user elects not to use the option
for simple terrain screening with terrain above stack base, then flat
terrain is assumed and the terrain height is assigned a value of zero. If
the simple elevated terrain option is used, SCREEN will prompt the user to
enter a terrain height above stack base. If terrain heights above physical
stack height are entered by the user for this option, they are chopped off
at the physical stack height.
A-13
-------
The simple elevated terrain screening procedure assumes that the plume
elevation above sea level is not affected by the elevated terrain. Concen-
tration estimates are made by reducing the calculated plume height by the
user-supplied terrain height above stack base. Neither the plume height
nor terrain height are allowed to go below zero. The user can model simple
elevated terrain using either or both of the distance options described
below, i.e., the automated distance array or the discrete distance option.
When the simple elevated terrain calculations for each distance option
are completed, the user will have the option of continuing simple terrain
calculations for that option with a new terrain height. (For flat terrain
the user will not be given the option to continue with a new terrain height).
For conservatism and to discourage the user from modeling terrain heights
that decrease with distance, the new terrain height for the automated
distances cannot be lower than the previous height for that run. The user
is still given considerable flexibility to model the effects of elevated
terrain below stack height across a wide range of situations.
For relatively uniform elevated terrain, or as a "first cut" conservative
estimate of terrain effects, the user should input the maximum terrain
elevation (above stack base) within 50 km of the source, and exercise the
automated distance array option out to 50 km. For isolated terrain features
a separate calculation can be made using the discrete distance option for
the distance to the terrain feature, with the terrain height input as the
maximum height of the feature above stack base. Where terrain heights vary
with distance from the source, then the SCREEN model can be run on each of
several concentric rings using the minimum and maximum distance inputs of
the automated distance option, to define each ring, and using the maximum
A-14
-------
terrain elevation above stack base within each ring for terrain height
input. As noted above, the terrain heights are not allowed to decrease
with distance in SCREEN. If terrain decreasing with distance (in all
directions) can be justified for a particular source, then the distance
rings would have to modeled using separate SCREEN runs, and the results
combined. The overall maximum concentration would then be the controlling
value. The optimum ring sizes will depend on how the terrain heights vary
with distance, but as a "first cut" it is suggested that ring sizes of
about 5 km be used (i.e., 0-5km, 5-10km, etc.). The application of SCREEN
to evaluating the effects of elevated terrain should be done in consultation
with the permitting agency.
Choice of Meteorology
For simple elevated or flat terrain screening, the user will be given
the option of selecting from three choices of meteorology: (1) full meteorology
(all stability classes and wind speeds); (2) specifying a single stability
class; or (3) specifying a single stability class and wind speed. Generally,
the full meteorology option should be selected. The other two options were
originally included for testing purposes only, but may be useful when
particular meteorological conditions are of concern. See Section A3 for more
details on the determination of worst case meteorological conditions by SCREEN.
Automated Distance Array Option
The automated distance array option of SCREEN gives the user the
option of using a pre-selected array of 50 distances ranging from 100m out
to 50 km. Increments of 100m are used out to 3,000m, with 500m increments
from 3,000m to 10 km, 5 km increments from 10 km to 30 km, and 10 km increments
A-15
-------
out to 50 km. When using the automated distance array, SCREEN prompts the
user for a minimum and maximum distance to use, which should be input in
free format, i.e., separated by a comma or a space. SCREEN then calculates
the maximum concentration across a range of meteorological conditions for
the minimum distance given (_>_ 1 meter), and then for each distance in the
array larger than the minimum and less than or equal to the maximum. Thus,
the user can input the minimum site boundary distance as the minimum distance
for calculation and obtain a concentration estimate at the site boundary
and beyond, while ignoring distances less than the site boundary.
If the automated distance array is used, then the SCREEN model will use
an iteration routine to determine the maximum value and associated distance
to the nearest meter. Note: SCREEN assumes that the overall maximum
concentration occurs for the same stability class that is associated with
the maximum concentration from the automated distance array, and begins
interating from that value, examining a range of wind speeds for that
stability (unless Option 3 for choice of meteorology is selected). If the
minimum and maximum distances entered do not encompass the true maximum
concentration, then the maximum value calculated by SCREEN may not be the
true maximum. Therefore, it is recommended that the maximum distance be
set sufficiently large initially to ensure that the maximum concentration
is found. This distance will depend on the source, and some "trial and
error" may be necessary, however, the user can input a distance of 50,000m
to examine the entire array. The iteration routine stops after 50 iter-
ations and prints out a message if the maximum is not found. Also, since
there may be several local maxima in the concentration distribution associated
A-16
-------
with different wind speeds, it is possible that SCREEN will not identify
the overall maximum in its iteration. This is not likely to be a frequent
occurrence, but will be more likely for stability classes C and D due to
the larger number of wind speeds examined.
Discrete Distance Option
The discrete distance option of SCREEN allows the user to input specific
distances. Any number of distances (>_ 1 meter) can be input by the user
and the maximum concentration for each distance will be calculated. The
user will always be given this option whether or not the automated distance
array option is used. The option is terminated by entering a distance of
zero (0). SCREEN will accept distances out to 100 km for long-range transport
estimates with the discrete distance option. However, for distances greater
than 50 km, SCREEN sets the minimum 10 meter wind speed at 2 m/s to avoid
unrealistic transport times.
Fumigation Option
Once the distance-dependent calculations are completed, SCREEN will
give the user the option of estimating maximum concentrations and distance
to the maximun associated with inversion break-up fumigation, and shoreline
fumigation. The option for fumigation calculations is applicable only
for rural sites with stack heights greater than or equal to 10 meters
(within 3,000m of a large body of water for shoreline.)
Once all calculations are completed, SCREEN summarizes the
maximum concentrations for each of the calculation procedures considered.
Before execution is stopped, whether it is after complex terrain calculations
A-17
-------
are completed or at the end of the simple terrain calculations, the user is
given the option of printing a hardcopy of the results. Whether or not a
hardcopy is printed, the results of the session, including all input data
and concentration estimates, are stored in a file called SCREEN.OUT. This
file is opened by the model each time it is run. If a file named SCREEN.OUT
already exists, then its contents will be overwritten and lost. Thus, if
you wish to save results of a particular run, then change the name of the
output file using the DOS RENAME command, e.g., type 'REN SCREEN.OUT
SAMPLE1.0UT', or print the file using the option at the end of the program.
If SCREEN.OUT is later printed using the DOS PRINT command, the FORTRAN
carriage controls will not be observed. (Instructions are included in
Section A4 for simple modifications to the SCREEN code that allow the
user to specify an output filename for each run.)
Figure A-2 shows an example using the complex terrain screen only.
Figure A-3 shows an example for an urban point source which uses the
building downwash option. In the DWASH column of the output, 'NO1 indicates
that no downwash is included, 'HS1 means that Huber-Snyder downwash is
included, 'SS1 means that Schulman-Scire downwash is included, and 'NA1
means that downwash is not applicable since the downwind distance is less
than 31^. A blank in the DWASH column means that no calculation was made
for that distance because the concentration was so small.
Figure A-4 presents a flow chart of all the inputs and various options
of SCREEN for point sources. Also illustrated are all of the outputs from
SCREEN. If a cell on the flow chart does not contain the words "Enter" or
"Print out", then it is an internal test or process of the program, and
is included to show the flow of the program.
A-18
-------
10-25-36
12:00:00
*** SCREEN-1.1 MODEL RUN ***
*** VERSION DATED 88300 ***
POINT SOURCE EXAMPLE WITH COMPLEX TERRAIN
COMPLEX TERRAIN INPUTS:
SOURCE TYPE = POINT
EMISSION RATE (G/S) = 100.0
STACK HT ;M) = 100.00
STACK DIAMETER 'Ml = 2.50
STACK VELOCITY (M/S'= 25.00
STACK GAS TEMP tK ! = 450.00
AMBIENT AIR TEMP ( K > = 293.00
RECEPTOR HEIGHT iM) = .00
IOPT ( 1=URB.2 = RUR ) = 2
BUOY. FLUX = 133.54 M**4/S**c: MOM. FLUX = 635.35 M**4.S**2.
FINAL STABLE PLUME HEIGHT = 132.9
DISTANCE TO FINAL RISE (M) = 151.3
*VALLEV 24-HR CAL
TERR
HT
( M )
150
200 .
2CO.
200.
GIST
(M)
1000.
2000.
5000.
10000.
MAX 24-HR
CONC
( UG/M**3 )
243.4
284. 3
91 . 39
37 . 36
CONC
! UG/'M**3 !
243 .4
284.3
91.29
37. 3c
PLUME
ABOVE
BASE
192
1 32
192
1 92
CS*
HT
STK
;M)
.9
_ 9
_ 9
.9
**SIMPLE
CONC
( UG/M**3 I
161.1
.0000
. 0000
.OCOO
TERRAIN 24-HR CALCS**
PLUME HT
ABOVE STK
HGT (M)
C2 . 9
.0
.0
. 0
sc
4
0
c
0
U10M
USTK
(M/S )
15.0
_ o
. 0
. V
21
_;
r\
. 'J
, J
fc******,*.************.*******************
*** SUMMARY OF SCREEN MODEL RESULTS ***
****************************»:*********«
:ALCULATION
PROCEDURE
COMPLEX TERRAIN
MA> CONC
:UG/M**3 i
DIST TO
MAX (M)
2000.
TERRAIN
HT (Mi
200. (24-HR CONG)
***************************************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
Figure A-2. SCREEN Point Source Example for Complex Terrain
A-19
-------
10-26-33
12.00:00
*** SCREEN-1.1 MODEL RUN
*** VERSION DATED 88300
***
***
POINT SOURCE EXAMPLE WITH BUILDING DOWNWASH
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = POINT
EMISSION RATE (G/S) = 100.0
STACK HEIGHT (M: = 100.00
STK INSIDE DIAM !M) = 2. CO
STK EXIT VELOCITY !M/S)= 15.00
STK GAS EXIT TEMP (K) = 450.03
AMBIENT AIR TEMP (K) = 293.00
RECEPTOR HEIGHT 'Ml = .00
IOPT [ 1=URB.2=RUR ) = 1
BUILDING HEIGHT (M) = 30.00
MIN HORIZ BLDG DIM (M) = 30.00
MAX HORIZ BLDG DIM |M) = 100.00
BUOY. FLUX = 51.32 M**4/S**3: MOM. FLUX = 145.50 M**4/S**2.
*** FULL METEOROLOGY ***
*** SCREEN AUTOMATED DISTANCES ***
**********************************
*** TERRAIN HEIGHT OF
0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES ***
DIST
(M )
100.
200.
300.
400.
500.
600.
700.
800.
900.
1000.
MAXIMUM
274 .
CONC
(UG/M**3 )
.0000
.0000
601
479
412
403
459
547
549
547
1-HR
61 1
. 1
.9
.5
.8
.3
.9
-7
.5
STAB
0
0
1
1
3
5
c
5
5
5
CONCENTRATION
.3
1
U10M
(M/S )
.0
.0
2.0
2.0
2.0
2.0
1 .0
1 .0
1 .0
1 .0
AT OR
2.0
USTK
(M/S )
2 .
2
3.
4.
i_ .
2 ,
2 .
2 ,
.-\
. L/
0
.8
.a
o
.0
.0
.0
.0
.0
BEVQND
2 _
.8
MIX HT
I M !
640,
640
640
5000
5000
5000
5000
5000
100
640
.0
_ Q
.0
.0
.0
.0
.0
.0
. 0
.0
. M:
.0
PLUME
HT l M )
.0
.0
111.5
119.5
133.1
110.1
121.5
121.5
121.5
1 2' . 5
103.3
SIGMA
• (M)
90.
118.
100.
59.
58.
76.
84
93.
S3,
.0
,0
, 7
3
.4
2
, 1
.6
.9
,0
,5
SIGMA
Z (M)
32,
113.
100
59.
58.
64
67
70,
74.
.0
.0
. 1
.6
.0
.2
.3
. 5
.4
. 2
r
DWASH
NA
NA
SS
SS
SS
SS
SS
SS
C £
SS
SS
DWASH= MEANS NO CALC MADE (CONC = 0.0)
DWASH=NO MEANS NO BUILDING DOWNWASH USED
DWASH-HS MEANS HUBER-SNYDER DOWNWASH USED
DWASH^SS MEANS SCHULMAN-SCIRE DOWNWASH USED
DWASH=NA MEANS DOWNWASH NOT APPLICABLE, X-3*LB
*«* CAVITY CALCULATION - 1 ***
CONC
-------
"igure A-4. Flow Chart of Inputs and Outputs for SCREEN Point Source
A-21
-------
Flare Release Example
By answering "F" or "f" to the question on source type the user selects the
flare release option. This option is similar to the point source described above
except for the inputs needed to calculate plume rise. The inputs for flare
releases are as follows:
Flare Release Inputs
Emission rate (g/s)
Flare stack height (m)
Total heat release rate (cal/s)
Receptor height above ground (m)
Urban/rural option (1 = urban, 2 = rural)
The SCREEN model calculates plume rise for flares based on an effective
buoyancy flux parameter. An ambient temperature of 293K is assumed in this
calculation and therefore none is input by the user. It is assumed that 55
percent of the total heat is lost due to radiation. Plume rise is calculated
from the top of the flame, assuming that the flame is bent 45 degrees from
the vertical. SCREEN calculates and prints out the effective release
height for the flare. SCREEN provides the same options for flares as de-
scribed earlier for point sources, including building downwash, complex
and/or simple terrain, fumigation, and the automated and/or discrete dis-
tances. The order of these options and the user prompts are the same as
described for the point source example.
While building downwash is included as an option for flare releases,
it should be noted that SCREEN assumes an effective stack gas exit velocity
(vs) of 20 m/s and an effective stack gas exit temperature (Ts) of 1,273K,
and calculates an effective stack diameter based on the heat release rate.
These effective stack parameters are somewhat arbitary, but the resulting
buoyancy flux estimate is expected to give reasonable final plume rise
estimates for flares. However, since building downwash estimates depend on
A-22
-------
transitional momentum plume rise and transitional buoyant plume rise calcu-
lations, the selection of effective stack parameters could influence the
estimates. Therefore, building downwash estimates should be used with
extra caution for flare releases. If more realistic stack parameters can
be determined, then the estimate could alternatively be made with the point
source option of SCREEN. In doing so, care should be taken to account for
the vertical height of the flame in specifying the release height (see Section
A3). Figure A-5 shows an example for a flare release, and Figure A-6 shows
a flow chart of the flare release inputs, options, and output.
Area Source Example
The third source type option in SCREEN is for area sources. The area
source algorithm in SCREEN is a simple virtual point source procedure
that assumes that the area source can be approximated by a simple square
area. The inputs requested for area sources are as follows:
Area Source Inputs
Emission rate (g/s)
Source release height (m)
Length of side of the square area (m)
Receptor height above ground (m)
Urban/rural option (1 = urban, 2 = rural)
The user has the same options for handling distances and the same choices
of meteorology as described above for point sources, but no complex terrain,
elevated simple terrain, building downwash, or fumigation calculations are
made for area sources. Figure A-7 shows an example of SCREEN for an area
source, using both the automated and discrete distance options. Figure A-8
provides a flow chart of inputs, options, and outputs for area sources.
A-23
-------
*** SCREEN-1.1 MODEL RUN ***
*** VERSION DATED 88300 ***
FLARE RELEASE EXAMPLE
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = FLARE
EMISSION RATE (G/S) = t000.
FLARE STACK HEIGHT IMI = 100.00
TOT HEAT RLS (CAL/S) = .1000E+08
RECEPTOR HEIGHT (M) ; .00
IOPT ( 1= URB,2 = RUR ) = 2
EFF RELEASE HEIGHT (M) = 110.11
BUILDING HEIGHT IM) = .00
MIN HORI2 BLDG DIM (M) = .00
MAX HORIZ 8LDG DIM (M) = .30
10-26-88
12:00:00
BL'Cr. FLUX - 165.80 M**4/S**2. MOM. FLU'»
*«* FULL METEOROLOGY ***
101.10 M**4/S**2.
«** SCREEN AUTOMATED DISTANCES ***
**************************A*******
«** TERRAIN HEIGHT OF 0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES ***
U10M USTK
STAB (M/S) iM/S)
CIST CONC
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1 24-1 . 1 1 . C 1.2
pwaSH= MEANS NO CALC MADE (CONC = 0.0'
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DrVASH = SS MEANS SCHULMAN-SCIRE DOWNWASH USED
C'WASH = NA MEANS DOWNWASH NOT APPLICABLE. • 3*LB
*** SUMMARY OF SCREEN MODEL RESULTS ***
•JC
CALCULATION
PROCEDURE
MAX CCNC DIST TO TEFPAIN
( UG,'M**3 ' MAx. (Mi NT M )
SIMPLE TERRAIN
1244.
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
Figure A-5. SCREEN
A-24
-------
Figure ' --. Flow Chart of Inputs -nd Outputs for SCREEN Flare Release
A-25
-------
10-26-88
1 2:00.00
»** 3CREEN-1.1 MODEL RUN *»*
*** VERSION DATED 88300 ***
AREA SOURCE EXAMPLE
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = AREA
EMISSION RATE iG/S) = 1 GO.G
SOURCE HEIGHT (M) = 5.00
LENGTH OF SIDE !M) = 200.00
RECEPTOR HEIGHT (M) = .00
IOPT (1=URB.2=RUR) = 1
BUOr. FLUX = .00 M**4/S**3: MOM. FLU" =
*** FULL METEOROLOGY ***
*** SCREEN AUTOMATED DISTANCES ***
.30 M**4/S**2.
**» TERRAIN HEIGHT OF
3. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES *«*
CIST
( M )
C ,~J
1CO.
200.
3QC.
4CO.
500.
500.
700.
800
900.
1000.
CONC
(UG/M**3) STAB
.6957E^05 5
.6121E+C5 5
.3235E+05 5
. 21 14E+05 5
.1512E+05 5
. 1157E+05 5
9258. 5
7654. 5
6483. 5
5597. 5
4906. 5
Ul DM
i M/S
1 . j
1 .0
' . C
1 . 0
1 .0
1 .0
1 .0
1 .0
1 .0
1 0
1 .0
LISTh
( M 'S i
1 .0
; .0
• o
• i
1 .~i
1 ^
', . D
' . 0
1 . D
1 ~\
1 .0
MIX HT PLUME
' M ! HT ( M )
5000.
5000.
5000.
5000.
5 COO.
5000.
5000.
5000.
5DOO.
5000.
= 000
G
.0
.0
.0
. 0
0
. 0
0
. 0
. 0
.0
5.0
5.0
5 .0
5.0
5 .0
5 . 0
5.0
5 . 0
5.0
5 . 0
5 .0
SIGMA
Y (M)
51 .
55.
64.
73.
31 ,
89.
97 .
105.
113.
1 20.
127 ,
, 1
. 7
, 6
.2
.6
.8
. 7
.5
,0
4
.6
SIGMA
2 (Ml
2
7 .
1 4
19
25
30.
34
39
43
47 .
50
.9
.5
.0
.9
. 3
.2
.8
. 1
. 1
.0
.6
DWASH
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
MAXIMUM 1-HR CONCENTRAT ION AT OR BEYOND 50. M:
52. .7371E+05 5 1.0 1.0 50CC . 0
DWASH= MEANS NO CALC MADE (CONC = 0.0)
DWASH=NO MEANS NO BUILDING DOWNWASH USED
DWASH=HS MEANS HUBER-SNYDER DOWNWASH USED
DWASH^SS MEANS SCHULMAN-SCIRE DOWNWASH USED
DWASH-NA MEANS DOWNWASH NOT APPLICABLE. X<3«LB
52.3
NO
*** SCREEN DISCRETE DISTANCES »**
*** TERRAIN HEI3HT OF
o. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES ***
DIST
i M )
5000.
10000.
20000.
50000 .
CONC
( UG/M**3 1
688.8
314.8
149 . 1
71.18
STAB
5
5
5
4
U10M
( M / S )
1 .0
1 .0
1 .0
1 .0
USTK
! M/S )
1 .0
1 .0
1 .0
1 . 0
MIX HT
(M)
5000.0
5000.0
5000.0
320.0
PLUME
HT ( M !
5 .0
5 .0
5 .0
5 .0
SIGMA
Y (M )
336 .6
505.4
742.6
1751 .4
SIGMA
Z (M)
137.2
200.0
287 .4
1750.0
DWASH
NO
NO
NO
NO
DWA3H= MEANS NO GAL: MADE iCONC = G.Gi
DWASH=NO MEANS MO BUILDING DOWNWASH USED
DWASH=HS MEANS HUBER-SNYDER OOWNWASH USED
DWASH=SS MEANS SCHULMAN-SCIRE DOWNWASH USED
DWASH=NA MEANS DOWNWASH NOT APPLICABLE. X'3*LB
*** SUMMARY OF SCREEN MODEL RESULTS ***
******#*****************x***** *******««
CALCULATION
PROCEDURE
MAX CONC
(UG/M«*3)
DIST TO
MAX (M)
TERRAIN
HT ( M )
SIMPLE TERRAIN
.7371E+05
62.
0.
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
Figure A-7. SCREEN Area Source Example
A-26
-------
Type SCREEN
to STflRT
Enter Title
, Enter Source
Type - fl for
3rea Source
Enter
Emission Rate
tg/s)
Enter Source
Release
Height (m)
Enter Length
of Side for
Square flrea
(m)
I Enter
Receptor
Height Hbove
Ground
(m)
Enter
Urban/Rural
Option:
1-Urban
2-Rural
Enter Choice
of Meteorology
1-Full Met
2="Slngle Stab
3-Sing Stab "
Wind Speed
Enter Mln and
Max Dlst for
flutomated
Distance
Rrray (m)
/
No
/ Print Out /
/ Maximum /
/Concentrations /
/ by Distance /
/ Prlr
/ Overa]
/ and Dls
it Out /
1 Max /
ration /
>tance /
User-
Specified
Distances?
Enter Y
or N
Enter
Distance from
Source (m)
: Print Out
Maximum
Concentration
at Specified
Distance
Print Out
Summary of
Results
Print Out
Hardcopy of
Results
Figure A-8. Flow Chart of Inputs and Outputs for SCREEN Area Source
A-27
-------
A3. TECHNICAL DESCRIPTION
Most of the techniques used in the SCREEN model are based on assumptions
and methods common to other EPA dispersion models. For the sake of brevity,
lengthy technical descriptions that are available elsewhere are not duplicated
here. This discussion will concentrate on how those methods are incorporated
into SCREEN and on describing those techniques that are unique to SCREEN.
Basic Concepts of Dispersion Modeling
SCREEN uses a Gaussian plume node! to estimate pollutant concentration
from continuous sources which incorporates source-related factors and meteor-
ological factors. It is assumed that the pollutant does not undergo any chem-
ical reactions, and that no other removal processes, such as wet or dry depo-
sition, act on the plume during its transport from the source. The Gaussian
model equations and the interactions of the source-related and meteorological
factors are described in the PTPLU user's guide (Pierce, et al, 1982), and
in the Workbook of Atmospheric Dispersion Estimates (Turner, 1970).
The basic equation for determining ground-level concentrations under
the plume center!ine is:
X = q/(2uusayaz) {exp[-l/2((zr-he)/az)2]
+ exp[-l/2((zr+he)/az)2]
k
+ I [ exP[-l/2((zr-he-2Nz-j)/az)2]
N=l
+ exp[-l/2((zr+he-2Nz-()/az)2]
+ exp[-l/2((zr-he+2Nzi)/az)2]
+ exp[-l/2((zr+he+2Nz-j)/az)2] ] } (A.I)
A-29
-------
where
x = concentration (g/m^)
Q = emission rate (g/s)
IT = 3.14159
us = stack height wind speed (m/s)
oy = lateral dispersion parameter (in)
az = vertical dispersion parameter (in)
zr = receptor height above ground (m)
he = plume centerline height (m)
z-j = inixing hei ght (m)
k = summation limit for multiple reflections of plume off of the
ground and elevated inversion, usually _<4.
Note that for stable conditions and/or mixing heights greater than or
equal to 5,000m, unlimited mixing is assumed and the summation term is
assumed to be zero.
Worst Case Meteorological Conditions
SCREEN examines a range of stability classes and wind speeds to identify
the "worst case" meteorological conditions, i.e., the combination of wind
speed and stability that results in the maximum ground level concentrations.
The wind speed and stability class combinations used by SCREEN are given in
Table A-l. The 10-meter wind speeds given in Table A-l are adjusted to
stack height by SCREEN using the wind profile power law exponents given in
Table 3-1 of the screening procedures document. For release heights of
less than 10 meters, the wind speeds listed in Table A-l are used without
adjustment. For distances greater than 50 km (available with the discrete
distance option), SCREEN sets 2 m/s as the lower limit for the 10-meter
A-30
-------
wind speed to avoid unrealistic transport times. Table A-l includes some
cases that may not be considered standard stability class/wind speed combi-
nations, namely E with 1 m/s, and F with 4 m/s. The combination of E and
1 m/s is often excluded because the algorithm developed by Turner (1964) to
determine stability class from routine National Weather Service (NWS)
observations excludes cases of E stability for wind speeds less than 4
knots (2 m/s). The combination of E and 1 m/s is included in SCREEN because
it is a valid combination that could appear in a data set using on-site
meteorological data with another stability class method. A wind speed of 6
knots (the highest speed for F stability in Turner's scheme) measured at a
typical NWS anemometer height of 20 feet (6.1 meters) corresponds to a 10
meter wind speed of 4 m/s under F stability. Therefore the combination of F
and 4 m/s has been included for conservatism.
Table A-l. Wind Speed and Stability Class Combinations
Used by the SCREEN Model
Stability
Class
A
B
C
D
E
F(rural
only)
10-m Wi nd Speed
(m/s)
1 2 3 4 5 8 10 15 20
* * *
*****
****** *
****** * * *
*****
* * * *
A-31
-------
The user has three choices of meteorological data to examine. The
first choice, which should be used in most applications, is to use "Full
Meteorology" which examines all six stability classes (five for urban
sources) and their associated wind speeds. Using full meteorology with the
automated distance array (described in Section A2), SCREEN prints out the
maximum concentration for each distance, and the overall maximum and
associated distance. The overall maximum concentration from SCREEN represents
the controlling 1-hour value corresponding to the result from Procedures (a) -
(c) in Step 4 of Section 4.2. Full meteorology is used instead of the A,
C, and E or F subset used by the hand calculations because SCREEN provides
maximum concentrations as a function of distance, and stability classes A,
C and E or F may not be controlling for all distances. The use of A, C, and
E or F may also not give the maximum concentration when building downwash
is considered. The second choice is to input a single stability class (1 =
A, 2 = B, ..., 6 = F). SCREEN will examine a range of wind speeds for that
stability class only. Using this option the user is able to determine the
maximum concentrations associated with each of the individual procedures,
(a) - (c), in Step 4 of Section 4.2. The third choice is to specify a
single stability class and wind speed. The last two choices were originally
put into SCREEN to facilitate testing only, but they may be useful if
particular meteorological conditions are of concern. However, they are not
recommended for routine uses of SCREEN.
The mixing height used in SCREEN for neutral and unstable conditions
(classes A-D) is based on an estimate of the mechanically driven mixing
height. The mechanical nixing height, zm (m), is calculated (Randerson,
A-32
-------
1984) as
zm = 0.3 u*/f (A.2)
where: u* = friction velocity (m/s)
f = Coriolis parameter (9.374 x 10~5 s'1 at 40° latitude)
Using a log-linear profile of the wind speed, and assuming a surface
roughness length of about 0.3m, u* is estimated from the 10-meter wind
speed, UIQ, as
u* = 0.1 uio (A.3)
Substituting for u* in Equation A.2 we have
zm = 320 uio. (A.4)
The mechanical mixing height is taken to be the minimum daytime mixing
height. To be conservative for limited mixing calculations, if the value
of zrn from Equation A.3 is less than the plume height, he, then the mixing
height used in calculating the concentration is set equal to he + 1. For
stable conditions, the mixing height is set equal to 5000m to represent
unlimited mixing.
Plume Rise for Point Sources
The use of the methods of Briggs to estimate plume rise are discussed
in detail in the PTPLU user's guide (Pierce, et al, 1982). These methods
are also incorporated in the SCREEN model.
Stack tip downwash is estimated following Briggs (1973, p.4) for all
sources except those employing the Schulman-Scire downwash algorithm.
Buoyancy flux for non-flare point sources is calculated from
Fb = 9 vs ds2 (Ts-Ta)/(4Ts), (A.5)
which is described in Section 4 of the screening procedures document and
is equivalent to Briggs1 (1975, p. 63) Equation 12.
A-33
-------
Buoyancy flux for flare releases is estimated from
Fb = 1.66 x 10'5 x H (A.6)
where H is the total heat release rate of the flare (cal/s). This
formula was derived from Equation 4.20 of Briggs (1969), assuming Td =
293K, P = 1205 g/m, cp = 0.24 cal/gK, and that the sensible heat release
rate, QH = (0.45) H. The sensible heat rate is based on the assumption
that 55 percent of the total heat released is lost due to radiation
(Leahey and Davies, 1984). The buoyancy flux for flares is calculated in
SCREEN by assuming effective stack parameters of vs = 20 m/s, Ts = 1,273K,
and solving for an effective stack diameter, ds = 9.88 x 10'^Q^.
The momentum flux, which is used in estimating plume rise for building
downwash effects, is calculated from,
Fm = vs2 ds2Ta/(4Ts) (A.7)
The PTPLU-2.0 user's guide (Pierce, et al 1982) describes the equations
used to estimate buoyant plume rise and momentum plume rise for both
unstable/neutral and stable conditions. Also described are transitional plume
rise and how to estimate the distance to final rise. Final plume rise is
used in SCREEN for all cases with the exception of the complex terrain screening
procedure and for building downwash effects.
The buoyant line source plume rise formulas that are used for the Schulman-
Scire downwash scheme are described in Section 2.3.12 of the revised ISC manual
(EPA, 1987a). These formulas apply to sources where hs _< h^ + 0.5Lb. For sources
subject to downwash but not meeting this criterion, the downwash algorithms of
Huber and Snyder (EPA, 1987a) are used, which employ the Briggs plume rise
formulas referenced above.
A-34
-------
Dispersion Parameters
The formulas used for calculating vertical (oz) and lateral (
-------
L = alongwind dimension of the building (m)
Using the plume height based on momentum rise at two building heights downwind,
including stack tip downwash, a critical (i.e. minimum) stack height wind speed
is calculated that will just put the plume into the cavity (defined by plume
centerline height = cavity height). The critical wind speed is then adjusted
from stack height to 10-meter using a power law with an exponent of 0.2 to
represent neutral conditions (no attempt is made to differentiate between
urban or rural sites or different stability classes). If the critical wind
speed (adjusted to 10-meters) is less than or equal to 20 m/s, then a cavity
concentration is calculated, otherwise the cavity concentration is assumed to
be zero. Concentrations within the cavity, xc> are estimated by the following
approximation (Hosker, 1974):
Xc = Q/(1.5 Ap u) (A.10)
where: Q = emission rate (g/s)
o
Ap = h(j»W = cross-sectional area of the building normal to the wind (m )
W = crosswind dim ension of the building (m)
u = wind speed (m/s).
For u, a value of one-half the _stack_ height critical wind speed is used, but not
greater than 10 m/s and not less than 1 m/s. Thus, the calculation of xc
is linked to the determination of a critical wind speed. The concentration,
Xc» is assumed to be uniform within the cavity.
The cavity length, xr, measured from the lee side of the building, is
estimated by the following (Hosker, 1984):
(1) for short buildings (L/hfc < 2);
xr = (A)(H) (A.11)
1.0 + B(U/hb)
A-36
-------
(2) for long buildings (L/h^ >_ 2);
xr = 1.75 (W) (A.12)
1.0 + 0.25(W/hb)
Where: hb - building height (m)
L = alongwind building dimension (m)
W = crosswind building dimension (m)
A = -2.0 + 3.7 (L/hb)-1/3, and
B = -0.15 + 0.305 (L/hb)-1/3
The equations above for cavity height, concentration and cavity length
are all sensitive to building orientation through the terms L, W and Ap.
Therefore, the entire cavity procedure is performed for two orientations,
first with the minimum horizontal dimension alongwind and second with the
maximum horizontal dimension alongwind. For screening purposes, this is
thought to give reasonable bounds on the cavity estimates. The first
case will maximize the cavity height, and therefore minimize the critical
wind speed. However, the Ap term will also be larger and will tend to
reduce concentrations. The highest concentration that potentially effects
ambient air should be used as the controlling value for the cavity procedure.
Wake Region
The calculations for the building wake region are based on the revised
ISCST model, UNAMAP 6 Change 7 (EPA, 1987a). The wake effects are divided
into two regions, one referred to as the "near wake" extending from 3Lb
to lOL^ (Lb is the lesser of the building height, hb, and maximum projected
width), and the other as the "far wake" for distances greater than 10Lb.
For the SCREEN model, the maximum projected width is calculated from the
input minimum and maximum horizontal dimensions as (L2 + W2)1/2. The
A-37
-------
remainder of the building wake calculations in SCREEN are based on the
ISC manual (EPA, 1987a).
It should be noted that, unlike the cavity calculation, the comparison
of plume height (due to momentum rise at two building heights) to wake
height to determine if wake effects apply does not include stack tip
downwash. This is done for consistency with the ISC model.
Fumigation
Inversion Break-up Fumigation
The inversion break-up screening calculations are based on procedures
described in Turner's Workbook of Atmospheric Dispersion Estimates (Turner,
1970). The distance to maximum fumigation is based on an estimate of the
time required for the mixing layer to develop from the top of the stack to
the top of the plume, using Equation 5.5 of Turner (1970):
xmax = u tm
= (u Pa Cp/R) (A6/AZ) (hi - hs) [(hi + hs)/2] (A.13)
where
xmax = downwind distance to maximum concentration (m)
tm = time required for mixing layer to develop from top of stack
to top of plume (s)
u = wind speed (2.5 m/s assumed)
pa = ambient air density (1205 g/m3 at 20°C)
Cp = specific heat of the air at constant pressure (0.24 cal/gK)
R = net rate of sensible heating of an air column by solar radiation
(about 67 cal/m2/s)
Ae/Az = vertical potential temperature gradient (assume 0.035 K/m for
F stability)
A-38
-------
h-j = height of the top of the plume (m) = he + 2oz (he = plume
centerline height)
hs = physical stack height (in).
az' = vertical dispersion parameter (m)
The values of u and A6/Az are based on assumed conditions of stability
class F and stack height wind speed of 2.5 m/s for the stable layer above
the inversion. The value of hi incorporates the effect of buoyancy
induced dispersion on az. The equation above is solved by iteration,
starting from an initial guess of xmax = 5,000m.
The maximum ground-level concentration due to inversion break-up
fumigation, yf» is calculated from Equation 5.2 of Turner (1970).
Xf = Q/[/27u(ay1+h8/8)(he+2az1)] (A.14)
where Q is the emission rate (g/s), and other terms are defined above.
i i
The dispersion parameters, cr and az , incorporate the effects of buoyancy
induced dispersion. If tne distance to the maximum fumigation is less
than 2000m, then SCREEN sets xf = ^ since for such short distances the
fumigation concentration is not likely to exceed the unstable/limited
mixing concentration estimated by the simple terrain screening procedure.
Shoreline Fumigation
For rural sources within 3000m of a large body of water, maximum shoreline
fumigation concentrations can be estimated by SCREEN. A stable onshore flow
is assumed with stability class F (AG/Az = 0.035 K/m) and stack height
wind speed of 2.5 m/s. Similar to the inversion break-up fumigation case,
the maxinum ground-level shoreline fumigation concentration is assumed to
occur where the top of the stable plume intersects the top of the well-mixed
thermal internal boundary layer (TIBL).
A-39
-------
An evaluation of coastal fumigation models (EPA, 1987b) has shown
that the TIBL height as a function of distance inland is well -represented
in rural areas with relatively flat terrain by an equation of the form:
hT = A [x] 1/2 (A. 15)
where: hj = height of the TIBL (m)
A = TIBL factor containing physics needed for TIBL parameterization
(including heat flux) (m1/2)
x = inland distance from shoreline (m).
Studies (e.g. Misra and Onlock, 1982) have shown that the TIBL factor, A,
ranges from about 2 to 6. For screening purposes, A is conservatively
set equal to 6, since this will minimize the distance to plume/TIBL
intersection, and therefore tend to maximize the concentration estimate.
As with the inversion break-up case, the distance to maximum ground-
level concentration is determined by iteration. The equation used for
the shoreline fumigation case is:
xmax = e + ^z - xs A
where: xmax = downwind distance to maximum concentration (m)
xs = shortest distance from source to shoreline (m)
he = plume centerline height (m)
az' = vertical dispersion parameter (m)
Plume height is based on the assumed F stability and 2.5 m/s wind speed, and
the dispersion parameter (oz') incorporates the effects of buoyancy induced
dispersion. If xmax is less than 200m, then no shoreline fumigation calcula-
tion is made, since the plume may still be influenced by transitional rise
and its interaction with the TIBL is more difficult to model.
A-40
-------
The maximum ground-level concentration due to shoreline fumigation,
xf, is also calculated from Turner's (1970) Equation 5.2:
xf = Q/E/^utay'+he/SMhe+Zaz1)] (A.14)
with ay1 and oz' incorporating the effects of buoyancy induced
dispersion.
Even though the calculation of xmax above accounts for the distance
from the source to the shoreline in xs, extra caution should be used in
interpreting results as the value of xs increases. The use of A=6 in
Equations A.15 and A.16 may not be conservative in these cases since there
will be an increased chance that the plume will be calculated as being
below the TIBL height, and therefore no fumigation concentration estimated.
Hhereas a smaller value of A could put the plume above the TIBL with a
potentially high fumigation concentration. Also, this screening procedure
considers only TIBLs that begin formation at the shoreline, and neglects
TIBLs that begin to form offshore.
Complex Terrain 24-hour Screen
The SCREEN model also contains the option to calculate maximum 24-
hour concentrations for terrain elevations above stack height. A final
plume height and distance to final rise are calculated based on the VALLEY model
screening technique (Burt, 1977) assuming conditions of F stability (E for
urban), and a stack height wind speed of 2.5 m/s. Stack tip downwash is
incorporated in the plume rise calculation.
The user then inputs a terrain height and a distance (m) for the nearest
terrain feature likely to experience plume impaction, taking into account
complex terrain closer than the distance to final rise. If the plume height
A-41
-------
is at or below the terrain height for the distance entered, then SCREEN will
make a 24-hour average concentration estimate using the VALLEY screening
technique. If the terrain is above stack height but below plume center!ine
height, then SCREEN will make a VALLEY 24-hour estimate (assuming F or E and
2.5 m/s), and also estimate the maximum concentration across a full range of
meteorological conditions using simple terrain procedures with terrain "chopped
off" at physical stack height, and select the higher estimate. Calculations
continue until a terrain height of zero is entered. For the VALLEY model
concentration SCREEN will calculate a sector-averaged ground-level concentration
with the plume centerline height (he) as the larger of 10.0m or the difference
between plume height and terrain height. The equation used is
X = 2.032 Q exp[-0.5(he/az')2]. (A.17)
oz'u x
Note that for screening purposes, concentrations are not attenuated for
terrain heights above plume height. The dispersion parameter,
-------
A4. NOTE TO PROGRAMMERS
The SCREEN model provided on the diskette was compiled on an IBM PC/AT
compatible microcomputer using the Microsoft FORTRAN 4.1 Optimizing Compiler.
It was compiled with the emulator library, meaning that the executable file
(SCREEN.EXE) will run with or without a math coprocessor chip. A minimum of
256 KB of RAM is required to execute the model. Provided in an archive file
on the diskette are the executable file, SCREEN.EXE, the FORTRAN source file,
SCREEN.FOR, the listing file, SCREEN.LST, a sample input file, EXAMPLE.DAT,
and associated output file, EXAMPLE.OUT. Also included on the diskette is a
READ.ME file with instructions on extracting SCREEN, and the archiving program
ARC521.COM. The listing file contains 99 pages.
The SCREEN model provided was complied with the following Microsoft
FORTRAN options:
/4I2 Defines all integer variables as INTE6ER*2
/FPi Causes floating point operations to be processed
using in-line instructions rather than library
CALLs (used for faster execution)
/Fs Causes source listing file to be generated
/St"SCREEN-l.l PROGRAM" Causes title to be printed at the top of each
page of the .LST file
It was also compiled with the following METACOMMAND included in the source file:
$PAGE Causes new page in .LST file, used at end of
each SUBROUTINE or FUNCTION
The $PAGE METACOMMAND has been commented out in the source file provided on
the diskette in order to facilitate recompiling SCREEN with a different
compiler. SCREEN uses the FORTRAN default unit number of 5 (five) for reading
input from the keyboard and 6 (six) for writing to the screen. The unit
number for the disk output file, SCREEN.OUT, is set internally to 9, and
A-43
-------
the unit number for writing to the input data file, SCREEN.DAT, is set to 7.
These unit numbers are assigned to the variables IRD, IPRT, IOUT, and IDAT,
respectively, beginning on line 86 of the source file. The Microsoft
version of SCREEN also uses the GETDAT and GETTIM system routines for
retrieving the date and time. These routines require the variables to be
INTEGER*2, and they may differ on other compilers.
The following simple change can be made to the SCREEN source file,
SCREEN.FOR, in order to create a version that will accept a user-speci^ien
output filename, instead of automatically writing to the file SCREEN.OUT.
An ASCII editor or a wordprocessor that has an ASCII or nondocument mode may
be used to edit the source file. Delete the letter C from Column 1 on lines
128 to 131. They should read as follows:
WRIT£(IPRT,*) ' '
94 WRITE(IPRT,*) 'ENTER NAME FOR OUTPUT FILE1
READ(IRD,95) OUTFIL
95 FORMAT(A12)
With this change, if the user-specified filename already exists, it will be
overwritten. If desired, the OPEN statement on line 133 may also be changed
to read as follows:
OPEN(IOUT,FILE=OUTFIL,STATUS='NEW',ERR=94)
With this additional change, the program will continue to prompt for the input
filename until a filename that doesn't already exist is entered by the user.
Before recompiling, make any other changes that may be necessary for the
particular compiler being used, and use the appropriate compile option for
defining all integer variables as INTEGER*2. It should be noted that without
optimization, the source file may be too large to compile as a single unit.
In this case, the SCREEN.FOR file may need to be split up into separate modules
that can compiled separately and then linked together.
A-44
-------
A5. REFERENCES
Briggs, G.A., 1969. Plume Rise. USAEC Critical Review Series, TID-25075,
National Technical Information Service Springfield, Virginia 22151.
Briggs, G.A , 1973. Diffusion Estimation for Small Emissions. NOAA ATDL,
Contribution File No. 79 (Draft). Oak Ridge, TN.
Briggs, G.A., 1975. Plume Rise Predictions. In: Lectures on Air Pollution
and Environmental Impact Analysis, Haugen, D.A. (ed.),American Meteor-
ological Society, Boston, MA, pp. 59-111.
Burt, E.W., 1977. Valley Model User's Guide. EPA-450/2-77-018. U.S.
Environmental Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1983. Regional Workshops on Air
Quality Modeling: A Summary Report - Addendum. EPA-450/4-82-015. U.S.
Environmental Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1987a. Industrial Source Complex (ISC)
Dispersion Model User's Guide - Second Edition (Revised). EPA-450/4-88-002a.
U.S. Environmental Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1987b. Analysis and Evaluation of
Statistical Coastal Fumigation Models. EPA-450/4-87-002. U.S. Environ-
mental Protection Agnecy, Research Triangle Park, NC.
Hosker, R.P., 1984. Flow and Diffusion Near Obstacles. In: Atrnospheric Sc ience
and Power Production. Randerson, D. (ed.), DOE/TIC-27601, U.S. Department
of Energy, Washington, D C.
Leahey, D.M. and M J.E. Davies, 1984. Observations of Plume Rise from Sour
Gas Flares. Atmospheric Environment, 18, 917-922.
Misra, P.K. and S. Onlock, 1982. Modelling Continuous Fumigation of Nanticoke
Generating Station Plume. Atmospheric Environment, 16, 479-482.
Pierce, T.E., D.B. Turner, J.A. Catalano, and F.V. Hale, 1982. PTPLU - A
Single Source Gaussian Dispersion Algorithm User's Guide. EPA-600/8-82-014.
U.S. Environmental Protection Agency, Research Triangle Park, NC.
Randerson, D., 1984. Atmospheric Boundary Layer. In Atmospheric Science and
Power Production. Randerson, D. (ed.), DOE/TIC-27601, U.S. Department of
Energy, Washington, D.C.
Turner, D. B , 1964. A Diffusion Model for t,n Urban Area. Journal of Applied
Meteorology, 3, 83-91.
Turner, D.B , 1970. Workbook of Atmospheric Dispersion Estimates, Revised,
Sixth printing, Jan. 1973. Office of Air Programs Publication No. AP-26.
U.S. Environmental Protection Agency. U.S. Government Printing Office,
Washington, D.C.
A-45
U. S. ODVEIWMEMT PROTTING OFFICE 1988/627-090/87009
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APPENDIX B
UNAMAP Dispersion Models
UNAMAP is an acronym for User's Network for Applied Modeling of Air
Pollution. Since 1973, UNAMAP has served as a source for air quality
simulation models in computer compatible form. UNAMAP has grown from an
original six models in 1973 to 23 models as of July 1986 with UNAMAP
Version 6. UNAMAP includes the source codes and test cases for the
Appendix A models from the Guideline on Air Quality Models (Revised), as
well as other models and processors.
The UNAMAP versions are created and maintained by:
Applied Modeling Research Branch
Atmospheric Sciences Modeling Division (MD-80)
Atmospheric Research and Environmental Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
(919) 541-4564; FTS 629-4564
A magnetic tape containing the current UNAMAP is available from:
Computer Products
National Technical Information Service
U.S. Department of Commerce
Springfield, VA 22161
(703) 487-4763; FTS 737-4763
A more detailed description of UNAMAP (Version 6) including abstracts for
all of the models, is provided in the publication Description of UNAMAP
(Version 6), by D. B. Turner and L. W. Bender, EPA/600/M-86/027, U. S.
Environmental Protection Agency, Research Triangle Park, NC (Dec. 1986).
B-l
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/4-88-010
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Screening Procedures for Estimating the Air
Quality Impact of Stationary Sources
5. REPORT DAT
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Roger W. Brode
8. PERFORMING ORGANIZATION REPORT NO.
PORT DATE
August 1988
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
Office of Air Quality Planning and Standards
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
This document is a revision of Volume 10R of the Guidelines for Air Quality
Maintenance Planning and Analysis series, EPA-450/4-77-001.
16. ABSTRACT
This document presents current EPA guidance on the use of screening procedures
to estimate the air quality impact of stationary sources. It is an update and
revision of Volume 10R of the GAQMPA series, and is intended to replace Volume
10R as the standard screening procedures for regulatory modeling of stationary
sources. It is being issued as a draft for public comment until such time as
a final version can be incorporated into a future supplement to the Guideline
on Air Quality Models (Revised). An important advantage of the current document
is the availability of the SCREEN model for executing the single source, short-
term procedures on a personal computer.
7.
DESCRIPTORS
KEY WORDS AND DOCUMENT ANALYSIS
h.IDENTIFIERS/OPEN ENDED TERMS
Air Pollution
Atmospheric Diffusion
Atmospheric Models
Meteorology
8 DISTRIBUTION STATEMtNT
Unlimited
New Source Review
19. SECURITY CLASn /7' c'_ ASb I This pti'fej
; None
c. COSAT! Held/Group
21 NO OF'PAGES
145
~2~ "ppTcE,
2220-1 (Rev. 4—77} PREVIOUS FICTION is OBSOLETE
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