United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park. NC 27711
EPA-450/4-92-006
September 1992
Air
& EPA SCREEN! Model User's Guide
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EPA-450/4-92-006
-1
o
SCREEN2 Model User's Guide
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air Quality Planning and Standards
Technical Support Division
Research Triangle Park, North Carolina 27711
September 1992 U.S. Enviro.rr' ' V:ction Agency
Region 5,!.: "j)
77 West Jac-. .vard, 12th Floor
Chicago, IL t.oc-3590
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NOTICE
The information in this document has been reviewed in its
entirety by the U.S. Environmental Protection Agency (EPA), and
approved for publication as an EPA document. Mention of trade
names, products, or services does not convey, and should not be
interpreted as conveying official EPA approval, endorsement, or
recommendation.
The following trademarks appear in this guide: IBM, are
registered trademarks of International Business Machines Corp.,
Microsoft and MS-DOS are registered trademarks of Microsoft Corp,
and Lahey F77L-EM/32 is a registered trademark of Lahey Computer
Systems, Inc.
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PREFACE
The SCREEN2 Model User's Guide is the PC-oriented
documentation for the SCREEN2 model. The SCREEN2 model includes
several modifications and enhancements to the original SCREEN
model, including updates to the code to ensure consistency with
the dispersion algorithms in the Industrial Source Complex (ISC2)
model (EPA, 1992). The SCREEN2 model has been included in the
"Guideline on Air Quality Models (Revised)" as part of Supplement
B.
Copies of the SCREEN2 model may be obtained from two
sources. They are the National Technical Information Service
(NTIS), U.S Department of Commerce, 5285 Port Royal Road,
Springfield, VA 22161, telephone (703) 487-4650, and the Support
Center for Regulatory Models (SCRAM) Bulletin Board System (BBS).
The SCRAM BBS may be accessed at (919) 541-5742.
iii
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ACKNOWLEDGEMENTS
Roger W. Erode, Pacific Environmental Services, Inc. (PES),
is the principal contributer to the SCREEN2 Model User's Guide.
This document was performed by the U.S. Environmental Protection
Agency under Contract No. 68D00124 with Dennis G. Atkinson as
Work Assignment Manager. In addition, this document was reviewed
and commented upon by Dennis G. Atkinson* , James L. Dicke*, John
S. Irwin*, and Joseph A. Tikvart (EPA, OAQPS).
*0n assignment from the National Oceanic and Atmospheric
Administration, U.S. Department of Commerce.
IV
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CONTENTS
PREFACE iii
ACKNOWLEDGEMENTS iv
FIGURES vi
TABLES vii
1. INTRODUCTION 1
1.1 Overview of User's Guide I
1.2 Purpose of SCREEN2 1
1.3 What is needed in order to use SCREEN2? 1
1.4 What will SCREEN2 do? 2
1.5 What will SCREEN2 not do? 2
1.6 How will SCREEN2 results compare to hand
calculations? 3
1.7 What changes have been incorporated into SCREEN2? . 4
1.8 How does SCREEN2 differ from PTPLU, PTMAX-and
PTDIS? 5
2. TUTORIAL 7
2.1 What is needed? 7
2.2 Setup on the PC 7
2.3 Executing the Model 7
2.4 Point Source Example 8
2.5 Flare Release Example 14
2. 6 Area 'Source Example 15
2.7 Volume Source Example 16
3. TECHNICAL DESCRIPTION 33
3.1 Basic Concepts of Dispersion Modeling 33
3.2 Worst Case Meteorological Conditions 34
3.3 Plume Rise for Point Sources 36
3.4 Dispersion Parameters 37
3.5 Buoyancy Induced Dispersion 37
3.6 Building Downwash 37
3.7 Fumigation • 39
3.8 Complex Terrain 24-hour Screen 42
4. NOTE TO PROGRAMMERS 43
5. REFERENCES • 45
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FIGURES
Figure Page
1. Point Source Options in SCREEN2 18
2. SCREEN2 Point Source Example for Complex Terrain .... 19
3. SCREEN2 Point Source Example with Building Downwash . . 20
4. Flow Chart of Inputs and Outputs for SCREEN2 Point
Source 22
5. SCREEN2 Flare Release Example 24
6. Flow Chart of Inputs and Outputs for SCREEN2 Flare
Release 26
7. SCREEN2 Area Source Example 28
8. Flow Chart of Inputs and Outputs for SCREEN2 Area
Source 30
9. SCREEN2 Volume Source Example 31
10. Flow Chart of Inputs and Outputs for SCREEN2 Volume
Source 32
VI
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TABLES
Table Page
1. Summary of Suggested Procedures for Estimating Initial
Lateral Dimensions (cryo) and Initial Vertical Dimensions
(aw} for Volume Sources 17
2. Wind Speed and Stability Class Combinations Used by the
SCREEN2 Model 35
VI1
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1. INTRODUCTION
l.l Overview of User's Guide
It will be easier to understand this user's guide and the
SCREEN2 model by being familiar with the "Screening Procedures
for Estimating the Air Quality Impact of Stationary Sources,
Revised" (EPA, I992a). The SCREEN2 Model User's Guide is PC-
oriented instruction and application of this document.
This introduction should answer most general questions about
what the SCREEN2 model can (and cannot) do, and explain its
relationship to the Screening Procedures Document (SPD) above.
Section 2 provides several examples of how to run the
SCREEN2 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. Being familiar with
personal computers and with the screening procedures will prevent
excessive difficulties running SCREEN2 and "experimenting" with
it. It runs interactively, and the prompts should be self
explanatory.
Section 3 provides background technical information as a
reference for those who want to know more about how SCREEN2 makes
certain calculations. The discussion in Section 3 is intended to
be as brief as possible, with reference to other documents for
more detailed descriptions.
1.2 Purpose of SCREEN2
The SCREEN2 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 availability and use of personal
computers (PCs), the SCREEN2 model makes screening calculations
accessible to a wide range of users.
1.3 What is needed in order to use SCREEN2?
SCREEN2 will run on an IBM-PC compatible personal computer
with at least 256K of RAM. You will need at least one 5 1/4 inch
double-sided, double-density (360K), a 5 1/4 inch high density
(1.2MB), or a 3.5 inch high density (1.4MB) 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. SCREEN2 will write a
date and time to the output file, provided that a real time clock
is available.
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1.4 What will SCREEN2 do?
SCREEN2 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. SCREEN2 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, SPD),
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
recirculation 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 of simple elevated
terrain on maximum concentrations (Section 4.2), and can also
estimate 24-hour average concentrations 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 SCREEN2 using a finite line segment approach, consistent
with the ISCST2 model (Section 4.5.4). The SCREEN2 model can
also be used to model the effects of simple volume sources using
a virtual point source procedure (Section 4.5.5). The volume
source algorithm is .described at length in Volume II of- the ISC2
model user's guide (EPA, 1992). The SCREEN2 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 100km for long-range
transport (Section 4.5.7).
1.5 What will SCREEN2 not do?
SCREEN2 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 (Pierce,
et al, 1980) or ISC2 (EPA, 1992) models on EPA's Support Center
for Regulatory Air Models (SCRAM) Bulletin Board System (BBS) to
model short-term impacts for multiple sources. With the
exception of the 24-hour estimate for complex terrain impacts,
the results from SCREEN2 are estimated maximum l-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 calculations, but the use of ISCLT2 or
another long-term model on the SCRAM BBS is recommended.
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1.6 How will SCREEN2 results compare to hand calculations?
The SCREEN2 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 concentrations differing by
less than about 5 percent across a range of source
characteristics. However, there are a few differences of which
the user should be aware. For some sources, particularly taller
sources with greater buoyancy, the differences in estimated
concentrations will be larger, with the hand calculation
exceeding the SCREEN2 model result by as much as 25 percent.
These differences are described in more detail below.
The SCREEN2 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 SCREEN2 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, SCREEN2 examines a full range of meteorological
conditions, including all stability classes and wind speeds (see
Section 3) 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 a full set of
meteorological conditions is required in SCREEN2 because maximum
concentrations are also given as a function of distance, and
because A, C, and E or F stability may not be controlling for
sources with building downwash (not included in the hand
calculations). SCREEN2 explicitly calculates the effects of
multiple reflections of the plume off the elevated inversion and
off the ground when calculating concentrations under limited
mixing conditions. To account for these reflections, the hand
calculation screening procedure (Procedure (a) of Step 4 in
Section 4.2, SPD) 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 SCREEN2 using the
multiple reflections, depending on the source. Also, SCREEN2
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. In contrast, 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. 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
controlling.
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The SCREEN2 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 SCREEN2 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
calculations, 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.
1.7 What changes have been incorporated into SCREEN2?
The SCREEN2 model (dated 92245) includes several
modifications relative to the original release of SCREEN (dated
88300). These changes were made in order for the SCREEN2 model
to be more consistent with the ISCST2 model (dated 92062),
especially for the downwash algorithms. Significant portions of
the ISCST2 model code have been incorporated into the SCREEN2
model both to ensure consistency of calculations and to
facilitate any future revisions that potentially affect both
models.
The following SCREEN2 enhancements were made to ensure that
the SCREEN2 model gives conservative concentration estimates
relative to the ISCST2 model. These changes include
modifications to the iteration procedure used to locate the peak
concentration, the addition of wind speeds in 0.5 m/s increments
for 10-meter wind speeds less than 5.0 m/s, and the addition of F
stability with a 0.035 K/m lapse rate for the urban dispersion
option.
The virtual point source algorithm used for area sources in
the original SCREEN model has been replaced with a finite line
segment approach for consistency with ISCST2 (version 92062) .
The emission rate input units have been changed to g/(s-m2) for
consistency with ISCST2, and the distances are now measured from
the center of the area source.
A new source type option has been added to SCREEN2 for
modeling volume sources. The SCREEN2 volume source algorithm is
based on a virtual point source approach, consistent with the
ISCST2 model. This option has been added to give the user
greater flexibility in modeling various source types,
particularly for certain types of air toxic releases.
An option to input volumetric flow rate in lieu of stack gas
exit velocity has been incorporated in SCREEN2 for point sources.
The flow rate can be input in either English units, Actual Cubic
Feet per Minute (ACFM), or metric units (m3/s).
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1.8 -How does SCREEN2 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
SCREEN2 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
SCREEN2 model also requires less manual "postprocessing" than the
earlier models by listing the maximum concentrations in the
output. However, many of the algorithms in SCREEN2 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. SCREEN2 also incorporates the option to
estimate concentrations at discrete user-specified distances,
which was available with PTDIS, but is not included in PTPLU.
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2. TUTORIAL
2.1 What is needed?
• IBM-PC compatible with at least 256K bytes of RAM, and a 5
1/4 inch double-sided, double-density or 5 1/4 inch high
density, or a 3.5 inch high density disk drive.
• Diskette provided with SCREEN2 software.
• Hard or floppy disk drive (minimum of 55OK memory
available).
• Math coprocessor chip (optional but recommended).
• Blank diskette for use in making a backup copy of software.
2.2 Setup on the PC
Using the DISKCOPY command of DOS (Disk Operating System) -or
similar routine, make a backup copy of the SCREEN2 software.
Store the original SCREEN2 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 and the "pkunzip" decompression
program resident on the hard disk drive. The "pkunzip" program
can be obtained via the Support Center for Regulatory Air Models
(SCRAM) Bulletin Board System (BBS) by accessing the
archivers/dearchivers option under system utilities on the top
menu.
Insert the SCREEN2 diskette in floppy drive A: and enter the
following command at the DOS prompt from drive C: (either from
the root directory or a subdirectory):
PKUNZIP A:SCREEN2
This command will decompress the six-files from the SCREEN2
diskette and place them on the hard disk. The hard disk will now
contain the executable file of SCREEN2, called SCREEN2.EXE, as
well as the FORTRAN source files, SCREEN2.FOR and MAIN.INC, an
example input file, EXAMPLE.DAT, an associated output file
EXAMPLE.OUT, and this document, the SCREEN2 Model User's Guide
(in WordPerfect 5.1 format), SCREEN2.WPF.
2.3 Executing the Model
The SCREEN2 model is written as an interactive program for
the PC, as described earlier. Therefore, SCREEN2 is normally
executed by simply typing SCREEN2 from any drive and directory
that contains the SCREEN2.EXE file, and responding to the prompts
provided by the program. However, a mechanism has been provided
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to accommodate the fact that for some applications of SCREEN2 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:
SCREEN2
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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) or
flow rate (ACFM or nr/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/rural option (U = urban, R = rural)
The SCREEN2 model uses free format to read the numerical
input data, with the exception of the exit velocity/flow rate
option. The default choice for this input is stack gas exit
velocity, which SCREEN2 will read as free format. However, if
the user precedes the input with the characters VF= in columns 1-
3, then SCREEN2 will interpret the input as flow rate in actual
cubic feet per minute (ACFM). Alternatively, if the user inputs
the characters VM= in columns 1-3, then SCREEN2 will interpret
the input as flow rate in m3/s. The user can input either upper
or lower case characters for VF and VM. The flow rate values are
then converted to exit velocity in m/s for use in the plume rise
equations, based on the diameter of the stack.
SCREEN2 allows for the selection of urban or rural
dispersion coefficients. The urban dispersion option is selected
by entering a 'U' (lower or upper case) in column 1, while the
rural dispersion option is selected by entering an 'R' (upper or
lower case) in column 1. For compatibility with the previous
version of the model, SCREEN2 also allows for an input of '!' to
select the urban option, or a '2' to select the rural option.
Determination of the applicability of urban or rural dispersion
is based upon land use or population density. For determination
by land use, (1) circumscribe a 3km radius circle, A,,, about the
source using the meteorological land use typing scheme and (2) if
land use types II, 12, Cl, R2, and R3 account for 50 percent or
more of A,,, select the urban option, otherwise use the rural
option. Using the population density criteria, (1) compute the
average population density, "p", per square kilometer with A,, as
defined above and (2) if "p" is greater than 750 people/km2, use
the urban option, otherwise select the rural option. Of the two
methods, the land use procedure is considered more definitive.
This guidance is extracted from Section 8.2.8 of the "Guideline
On Air Quality Models (Revised)" (EPA, 1986) .
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Figure 1 presents the order of options within the SCREEN2
model for point sources and is annotated with the corresponding
sections from the screening procedures document. In order to
obtain results from SCREEN2 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.
The simple elevated terrain option would be used if the terrain
rises above the stack base elevation but is less than the height
of the physical stack. These, as well as the other options in
Figure 1, are explained in more detail below. A flagpole
receptor is defined as any receptor which is located above local
ground level, e.g., to represent the roof or balcony of a
building.
2.4.1 Building Downwash Option
Following the basic input of source characteristics SCREEN2
will first ask if building downwash is to be considered, and if
so, asks for the building height, minimum horizontal dimension,
and maximum horizontal dimension in meters. The downwash
screening procedure assumes that the building 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 calcinations.
Refer to Section 3.6 for more details on the building downwash
cavity and wake screening procedure.
• 2.4.2 Complex Terrain Option
The complex terrain option of SCREEN2 allows the user to
estimate impacts for cases where terrain elevations exceed stack
height. If the user selects this option, then SCREEN2 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 SCREEN2 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 SCREEN2 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
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conditions using simple terrain procedures with terrain "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 0.4, 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 SCREEN2 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. SCREEN2 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 3 for
more details on the complex terrain screening procedure.
2.4.3 Simple Elevated or Flat Terrain Option
The user is given the option in SCREEN2 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, SCREEN2 will prompt the user bo
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.
The simple elevated terrain screening procedure assumes that
the plume elevation above sea level is not affected by the
elevated terrain. Concentration 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.
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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 SCREEN2
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 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 SCREEN2. If terrain decreasing with
distance (in all directions) can be justified for a particular
source, then the distance rings would have to be modeled using
separate SCREEN2 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 SCREEN2 to evaluating the effects of elevated
terrain should be done in consultation with the permitting
agency.
2.4.4 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. Refer to Section 3 for more details on the
determination of worst case meteorological conditions by SCREEN2.
2.4.5 Automated Distance Array Option
The automated distance array option of SCREEN2 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 out to 50
km. When using the automated distance array, SCREEN2 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.
SCREEN2 then calculates the maximum concentration across a range
of meteorological conditions for the minimum distance given (a 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
12
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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 SCREEN2
model will use an iteration routine to determine the maximum
value and associated distance to the nearest meter. If the
minimum and maximum distances entered do not encompass the true
maximum concentration, then the maximum value calculated by
SCREEN2 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 iterations and prints out a message if the maximum is
not found. Also, since there may be several local maxima in the
concentration distribution associated with different wind speeds,
it is possible that SCREEN2 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.
2.4.6 Discrete Distance Option
The discrete distance option of SCREEN2 allows the user to
input specific distances. Any number of distances (a 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). SCREEN2 will accept distances out to 100 km for long-range
transport estimates with the discrete distance option. However,
for distances greater than 50 km, SCREEN2 sets the minimum 10
meter wind speed at 2 m/s to avoid unrealistic transport times.
2.4.7 Fumigation Option
Once the distance-dependent calculations are completed,
SCREEN2 will give the user the option of estimating maximum
concentrations and distance to the maximum associated with
inversion break-up fumigation, and shoreline fumigation. The
option for fumigation calculations is applicable only for rural
inland sites with stack heights greater than or equal to 10
meters (within 3,000m onshore from a large body of water.) The
fumigation algorithm also ignores any potential effects of
elevated terrain.
Once all calculations are completed,"SCREEN2 summarizes the
maximum concentrations for each of the calculation procedures
considered. Before execution is stopped, whether it is after
complex terrain calculations are completed or at the end of the
13
-------
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 ~he
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 4 for simple modifications to the SCREEN2
code that allow the user to specify an output filename for each
run.)
•
Figure 2 shows an example using the complex terrain screen
only. Figure 3 shows an example for an urban point source which
uses the building downwash option. In the DWASH column of the
output, 'NO' indicates that no downwash is included, 'HS' means!
that Huber-Snyder downwash is included, 'SS' means that
Schulman-Scire downwash is included, and 'NA' means that downwash
is not applicable since the downwind distance is less than 3L, .
A blank in the DWASH column means that no calculation was made
for that distance because the concentration was so small.
Figure 4 presents a flow chart of all the inputs and various
options of SCREEN2 for point sources. Also illustrated are all
of the outputs from SCREEN2. 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.
2.5 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 (U = urban, R = rural)
The SCREEN2 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
14
-------
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. SCREEN2 calculates and prints out the effective
release height for the flare. SCREEN2 provides the same options
for flares as described earlier for point sources, including
building downwash, complex and/or simple terrain, fumigation, and
the automated and/or discrete distances. 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 SCREEN2 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 arbitrary, but the resulting
buoyancy flux estimate is expected to give reasonable final plume
rise estimates for flares." However, since, building downwash
estimates depend on transitional momentum plume rise and
transitional buoyant plume rise calculations, 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 SCREEN2. In doing so, care
should be taken to account for the vertical height of the flame
in specifying the release height (see Section 3). Figure 5 shows
an example for a flare release, and Figure 6 shows a flow chart
of the flare release inputs, options, and output.
2.6 Area Source Example
The third source type option in SCREEN2 is for area sources.
The area source algorithm in SCREEN2 is based on a finite line
segment approach consistent with ISCST2 (dated 92062) , and
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-m2)]
Source release height (m)
Length of side of the square area (m)
Receptor height above ground (m)
Urban/rural option (U = urban, R = rural)
Note that the emission rate for area sources is input as an
emission rate per unit area in units of g/(s-m2). These units
are consistent with the ISCST2 model (version 92062), but differ
from the original SCREEN model which used input units of g/s for
a total emission rate for the area.
15
-------
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.
Distances are measured from the center of the square area. Since
this algorithm cannot estimate concentrations within the area
source, the model will give a concentration of zero for distances
less than XINIT//7T, where XINIT is the width of the area. Figure
7 shows an example of SCREEN2 for an area source, using both the
automated and discrete distance options. Figure 8 provides a
flow chart of inputs, options, and outputs for area sources.
2.7 Volume Source Example
The fourth source type option in SCREEN2 is for volume
sources. The volume source algorithm is based on a virtual point
source approach, consistent with the ISCST2 model (version
92062), and may be used for non-buoyant sources whose emissions
occupy some initial volume. The inputs requested for volume
sources are as follows:
Volume Source Inputs
Emission rate (g/s)
Source release height (m)
Initial lateral dimension of volume (m)
Initial vertical dimension of volume (m)
Receptor height above ground (m)
Urban/rural option (U = urban, R = rural)
The user must determine the initial dimensions of the volume
source plume before exercising the SCREEN2 model volume source.
Table 1 provides guidance on determining these inputs. Since the
volume source algorithm cannot estimate concentrations within the
volume source, the model will give a concentration of zero for
distances (measured from the center of the volume) of less than
2.15 ayo. Figure 9 shows an example of SCREEN2 for a volume
source, and Figure 10 provides a flow chart of inputs, options,
and outputs for volume sources.
16
-------
TABLE 1.
Summary of Suggested Procedures for Estimating
Initial Lateral Dimensions { 0) on or am = building height divided
Adjacent to a Building by 2.15
Elevated Source (he > 0) not on am = vertical dimension of
or Adjacent to a Building source divided by 4.3
17
-------
Order of Options
i n SCREEN2
Input Source
Character i sti cs/
Bu i Id i ng
Downwash
Opt ion
CompI ex
Terra i n
Opt ion
Simple Elevated
or FI at Terra i n
Opt i on*
Cho i ce
of
MeteoroIogy*
Automated
Distance Array
Option*
D i screte
Distance
Option*
Fumigation
Opt i on
CRural On Iy}
Corresponding Section in
Screening Procedures Document
Sect ion A 5 1
Sect i on 4.5 2
Sect ion 4.2
Sect ion 4 2^ Step 4
Section 4.2, Step 4
Section 4.3 for Distances < 50km
Section 4 . 5 . 7 for Distances >> 50km
Sect i on 4.5.3
*These options also apply to
Area Sources, Section 454
Figure 1. Point Source Options in SCREEN2
18
-------
*** SCREEN2 MODEL RUN ***
*** VERSION DATED 92245 ***
POINT SOURCE EXAMPLE WITH COMPLEX TERRAIN
COMPLEX TERRAIN INPUTS:
SOURCE TYPE
EMISSION RATE (G/S)
STACK HT (M)
STACK DIAMETER (M)
STACK VELOCITY (M/S)
STACK GAS. TEMP (K)
AMBIENT AIR TEMP (K)
RECEPTOR HEIGHT (M)
URBAN/RURAL OPTION
POINT
100.000
100.0000
2.5000
25.0000
450.0000
293.0000
.0000
RURAL
09/01/92
12:00:00
BUOY. FLUX = 133.643 M**4/S**3; MOM. FLUX = 635.851 M**4/S**2.
FINAL STABLE PLUME HEIGHT (M) = 192.9
DISTANCE TO FINAL RISE (M) = 151.3
TERR
HT
(M)
150.
200.
200.
200.
DIST
(M)
1000.
2000.
5000.
10000.
MAX 24-HR
CONC
(UG/M**3)
243.4
284.3
91.39
37.36
*VALLEY 24- HR CALCS*
PLUME HT
CONC ABOVE STK
(UG/M**3) BASE (M)
243.4
284.3
91.39
37.36
192.9
192.9
192.9
192.9
**SIMPLE
CONC
(UG/M**3)
161.1
.0000
.0000
.0000
TERRAIN 24-HR CALCS**
PLUME HT
ABOVE STK U10M USTK
HGT (M) SC (M/S)
32.9
.0
.0
.0
4
0
0
0
15.0
.0
.0
.0
21.2
.0
.0
.0
***************************************
*** SUMMARY OF SCREEN MODEL RESULTS ***
***************************************
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
DIST TO
MAX (M)
TERRAIN
HT (M)
COMPLEX TERRAIN
284.3
2000.
200. (24-HR CONC)
***************************************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
Figure 2. SCREEN2 Point Source Example for Complex Terrain
19
-------
09/01/92
13:00:00
*** SCREEN2 MODEL RUN ***
*** VERSION DATED 92245 ***
POINT SOURCE EXAMPLE WITH BUILDING DOWNUASH .
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = POINT
EMISSION RATE (G/S) = 100.000
STACK HEIGHT (M) = 100.0000
STK INSIDE DIAM (M) = 2.0000
STIC EXIT VELOCITY (M/S)= 15.0000
STK GAS EXIT TEMP (K) = 450.0000
AMBIENT AIR TEMP (K) - 293.0000
RECEPTOR HEIGHT (M) = .0000
URBAN/RURAL OPTION = URBAN
BUILDING HEIGHT (M) = 80.0000
MIN HORIZ BLDG DIM (M) = 80.0000
MAX HORIZ BLDG DIM (M) = 100.0000
BUOY. FLUX = 51.319 M**4/S**3; MOM. FLUX = 146.500 M**4/S**2.
*** FULL METEOROLOGY ***
**********************************
*** SCREEN AUTOMATED DISTANCES ***
**********************************
*** TERRAIN HEIGHT OF 0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES ***
DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA
(M) (UG/M**3) STAB (M/S) (M/S) (M) HT
-------
*** CAVITY CALCULATION - 1 ***
CONC (UG/M**3) = 3168.
CRIT WS 31 OH (M/S) = 3.32
CRIT US a HS (M/S) = 5.26
DILUTION WS (M/S) - 2.63
CAVITY HT CM) = 114.88
CAVITY LENGTH (M) = 142.41
ALONGWIND DIM (M) - 80.00
*** CAVITY CALCULATION - 2 ***
CONC (UG/M**3) = 1691.
CRIT WS 310M (M/S) = 7.77
CRIT WS 3 HS (M/S) = 12.32
DILUTION WS (M/S) = 6.16
CAVITY HT (M) = 105.20
CAVITY LENGTH (M) = 101.30
ALONGWIND DIM (M) = 100.00
***************************************
*** SUMMARY OF SCREEN MODEL RESULTS ***
***************************************
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
DIST TO
MAX (M)
TERRAIN
HT (M)
SIMPLE TERRAIN 715.3
BUILDING CAVITY-1 3168.
BUILDING CAVITY-2 1691.
800.
142.
101.
0.
(DIST = CAVITY LENGTH)
(DIST = CAVITY LENGTH)
***************************************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
Figure 3. SCREEN2 Point Source Example with Building Dounwash (Page 2 of 2)
21
-------
Type SCREENS
to START
Enter Title
, Enter Source
Type - P for
Point Source
I Enter
Emission Rate
C9's]
Enter Stack
Height (m)
Enter Stack
inside
Diame t er (m)
I Enter Exit
Veloclty
(mis) or Flow
Rate (ACFM
or m»*3/s)
Enter Stack
Gas Exit
Temperature
Enter Ambient
Temper at ure
I Enter
Receptor
Height Above
Ground
(m)
Enter
Urban/Rural
Op tion.
U=Urban
RsRural
Enter
BuiIding
Height (m)
Enter Mm
Horizontal
BuiIding
Dimension
Cm)
Enter Max
Horizon taI
QuiIding
Dimension
(m)
Print Out
Plume Height
and Dist to
Final Rise
(m)
: Enter Terrain
Heignt (m)
and Distance
to Terrain
(m)
Print Out
Complex
Terrain
24-hr
Concentrat i on
Figure 4. Flow Chart of Inputs and Outputs for SCREEN2 Point Source (Page 1 of 2)
22
-------
/Print Out /
Ovtrsll Uax /
*J Concentration /
/ ind Dlcianca /
Print Owl / / Enter MM
M*«l»wn / / Olstanca
hor«l In* M ••"' y fro* Sourc*
Punigaiion / /
>ne ft Dist / /
Figure 4. Flow Chart of Inputs and Outputs for SCREEN2 Point Source (Page 2 of 2)
23
-------
*** SCREEN2 MODEL RUN ***
*** VERSION DATED 92245 ***
FLARE RELEASE EXAMPLE
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = FLARE
EMISSION RATE (G/S) = 1000.00
FLARE STACK HEIGHT (M) = 100.0000
TOT HEAT RLS (CAL/S) = .100000E+08
RECEPTOR HEIGHT (M) = .0000
URBAN/RURAL OPTION = RURAL
EFF RELEASE HEIGHT (M) = 110.1150
BUILDING HEIGHT (M) = .0000
MIN HORIZ BLDG DIM (M) = .0000
MAX HORIZ BLDG DIM (M) = .0000
09/01/92
12:00:00
BUOY. FLUX = 165.803 M**4/S**3; MOM. FLUX = 101.103 M**4/S**2t
*** FULL METEOROLOGY ***
**********************************
*** SCREEN AUTOMATED DISTANCES ***
**********************************
*** TERRAIN HEIGHT OF 0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES ***
DIST
(M)
250.
300.
400.
500.
600.
700.
800.
900.
1000.
1100.
1200.
1300.
1400.
1500.
1600.
1700.
1800.
1900.
2000.
CONC
(UG/M**3)
.7733E-04
.2501E-03
1.283
66.54
407.0
741.2
944.9
1303.
1449.
1448.
1387.
1315.
1248.
1187.
1132.
1082.
1036.
993.9
957.5
STAB
5
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
U10M
(M/S)
1.0
3.0
3.0
3.0
3.0
3.0
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.0
USTK
(M/S)
MIX HT
(M)
2.3 10000.0
3.5
3.5
3.5
3.5
3.5
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.2
960.0
960.0
960.0
960.0
960.0
579.5
579.5
579.5
579.5
579.5
579.5
579.5
579.5
579.5
579.5
579.5
579.5
813.6
PLUME
HT (M)
233
344
344
344
344
344
578
578
578
578
578
578
578
578
578
578
578
578
812
.54
.28
.28
.28
.28
.28
.45
.45
.45
.45
.45
.45
.45
.45
.45
.45
.45
.45
.62
SIGMA
Y (M)
38.
78.
100.
121.
142.
162.
210.
231.
247.
263.
279.
295.
310.
326.
342.
358.
374.
390.
432.
05
46
36
51
09
21
37
47
92
50
21
03
90
80
72
64
55
43
95
SIGMA
Z (M)
36.05
57.07
80.87
113.75
161.96
220.50
308.17
386.36
473.16
571.19
680.86
802.07
934.77
1078.93
1234.58
1401.74
1580.46
1770.78
1978.42
DUASH
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
MAXIMUM 1-HR CONCENTRATION AT OR BEYOND
. 1046. 1461. 1 1.5 1.8
250. M:
579.5 578.45 254.91 515.82
DWASK= MEANS NO CALC MADE (CONC = 0.0)
DUASH=NO MEANS NO BUILDING DOUNWASH USED
DWASH=HS MEANS HUBER-SNYDER DOWNUASH USED
DWASH=SS MEANS SCHULMAN-SCIRE DOWNWASH USED
DWASH=NA MEANS DOWNUASH NOT APPLICABLE, X<3*LB
NO
Figure 5. SCREEN2 Flare Release Example (Page 1 of 2)
24
-------
*** SUMMARY OF SCREEN MODEL RESULTS ***
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
DIST TO
MAX (M)
TERRAIN
HT (M)
SIMPLE TERRAIN 1461. 1046. 0.
***************************************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
Figure 5. SCREEN2 Flare Release Example (Page 2 of 2)
25
-------
Type SCREENS
to START
Enter Title
Enter Source
Type - F for
Flare Release
Enter
Emi s s i o n Rate
Cg/s)
Enter Flare
Release
Height Cm)
EntQr Total
Heat Released
(ca I /5 )
Enter
Receptor
He ignt Above
Ground
Cm)
Enter
Urban/Rural
Op t io n
U=Urban
R=Ru r a I
Mate
Complex Ter
21 - hour Ca I c
enter Y
or N
Enter
Bui I d i ng
Height Cm)
Enter Mi
Horizontal
Bui Iding
Dimension
Cm)
\ f
Enter Max
HorizontaI
Bui IdIng
D i me n sio n
Cm)
Print Ou t
PIume Heign t
and Dis t to
Final Rise
Cm)
Enter Te r r ai
Height (m)
and Distance
t o Te r r ai n
Cm)
Print Out
Compiex
Terrain
24-hr
Concentration
Figure 6. Flow Chart of Inputs and Outputs for SCREEN2 Flare Release (Page 1 of 2)
26
-------
Enter Terrain / / Enter um in
H« iflfii AbO¥« / / Max Dltc for
Stick 8as* / W Automata*)
/ / DUtance
/ / Array [m)
Print Out
Maxiffin
Conc«ntraiion»
Bi> Distance
nter Ternin / /
• IBM Abo»« / / Enlt
tick Bait / ™' *T Dutine*
/ / Source
Figure 6. Flow Chart of Inputs and Outputs for SCREEN2 Flare Release (Page 2 of 2)
27
-------
*** SCREEN2 MODEL RUN ***
*** VERSION DATED 92245 ***
AREA SOURCE EXAMPLE
SIMPLE TERRAIN INPUTS:
SOURCE TYPE
EMISSION RATE (G/(S-M**2))
SOURCE HEIGHT (M)
LENGTH OF SIDE (M)
RECEPTOR HEIGHT (M)
URBAN/RURAL OPTION
09/01/92
12:00:00
AREA
.250000E-02
5.0000
200.0000
.0000
URBAN
BUOY. FLUX = .000 M**4/S**3; MOM. FLUX
*** FULL METEOROLOGY ***
**********************************
*** SCREEN AUTOMATED DISTANCES ***
**********************************
.000 M**4/S**2.
*** TERRAIN HEIGHT OF 0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES ***
DIST
(M)
150.
200.
300.
400.
500.
600.
700.
800.
900.
1000.
CONC
(UG/M**3)
.2070E+05
.1780E+05
.1406E+05
.1176E+05
.1017E+05
8894.
7804.
6867.
6068.
5394.
STAB
5
5
5
5
5
5
5
5
5
5
U10M
(M/S)
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
USTK
(M/S)
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
MIX HT
(M)
10000.0
10000.0
10000.0
10000.0
10000.0
10000.0
10000.0
10000.0
10000.0
10000.0
PLUME
HT (M)
5
5
5
5
5
5
5
5
5
5
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
SIGMA
Y (M)
4.'06
9.42
19.86
29.92
39.63
49.02
58.12
66.95
75.51
83.84
SIGMA
Z (M)
16
19
24
29
34
38
42
46
50
53
.29
.21
.63
.62
.25
.58
.64
.49
.14
.62
DUASH
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
MAXIMUM 1-HR CONCENTRATION AT OR BEYOND 150. M:
150. .2070E+05 5 1.0 1.0 10000.0 5.00
DWASH= MEANS NO CALC MADE (CONC = 0.0)
DWASH=NO MEANS NO BUILDING DOWNUASH USED
DWASH=HS MEANS HUBER-SNYDER DOWNUASH USED
DWASH=SS MEANS SCHULMAN-SCIRE DOWNWASH USED
DWASH=NA MEANS DOWNWASH NOT APPLICABLE, X<3*LB
4.06 16.29
NO
Figure 7. SCREEN2 Area Source Example (Page 1 of 2)
28
-------
*********************************
*** SCREEN DISCRETE DISTANCES ***
*********************************
*** TERRAIN HEIGHT OF 0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES ***
DIST
(M)
5000.
10000.
20000.
50000.
CONC
(UG/M**3)
718.6
321.3
150.6
71.45
STAB
5
5
5
4
U10M
(M/S)
1.0
1.0
1.0
1.0
USTK MIX HT
(M/S) (M)
1.0 10000.0
1.0 10000.0
1.0 10000.0
1.0 320.0
PLUME SIGMA SIGMA
HT (M) Y (M) Z (M)
5.00 312.74 138.53
5.00 488.59 200.92
5.00 731.03 288.01
5.00 1743.68 1751.62
DUASH
NO
NO
NO
NO
DUASH= MEANS NO CALC MADE (CONC = 0.0)
DWASH=NO MEANS NO BUILDING DOWNWASH USED
DUASH=HS MEANS HUBER-SNYDER DOUNUASH USED
DWASH=SS MEANS SCHULMAN-SCIRE DOWNUASH USED
DUASH=NA MEANS DOWNWASH NOT APPLICABLE, X<3*LB
***************************************
*** SUMMARY Of SCREEN MODEL RESULTS ***'
***************************************
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
DIST TO
MAX (M)
TERRAIN
HT (M)
SIMPLE TERRAIN
.2070E+05
150.
0.
A**************************************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
Figure 7. SCREEN2 Area Source Example (Page 2 of 2)
29
-------
Type SCREENS
to START
Enter Title
Enter Sou rce
Type - A for
Area Sou red
Enter
£mis sion Ra t e
Enter Source
Re I ease
He igh t Cm)
Enter Length
of Side for
Square Area
Cm)
En t«r Cno(ce
o f Me taoroIogy
1=FuI I M«t
2=Single Stab
3=5 Ing Stab &
W t rid Speed
Enter Min
Ma x Ois t
Au t oma t 9(3
D i stance
Array Cm]
Print Out
Ma x imum
by Distance
Pr,nt Oit
Overa M Ma x
Con central ion
and Distance
/ Enter
^Y Distance f r
IP r in t Ou 1
Ma x imum
Co ncentrat ion
a t Spec i f i ed
D 1 stance
Figure 8. Flow Chart of Inputs and Outputs for SCREEN2 Area Source
30
-------
09/01/92
12:00:00
*** SCREEN2 MODEL RUN ***
*** VERSION DATED 92245 ***
VOLUME SOURCE EXAMPLE
SIMPLE TERRAIN INPUTS:
SOURCE TYPE = VOLUME
EMISSION RATE (G/S) = 1.00000
SOURCE HEIGHT (M) = 10.0000
INIT. LATERAL DIMEN (M) = 50.0000
INIT. VERTICAL DIMEN (M) - 20.0000
RECEPTOR HEIGHT (M) = .0000
URBAN/RURAL OPTION = RURAL
BUOY. FLUX = .000 M**4/S**3; MOM. FLUX = .000 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.
CONC
(UG/M**3)
.0000
239.5
224.1
209.1
195.7
183.8
173.0
163.2
154.4
146.3
STAB
0
6
6
6
6
6
6
6
6
6
U10M
(M/S)
.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
USTK
(M/S)
.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
MIX HT
(M)
10000
10000
10000
10000
10000
10000
10000
.0
.0
.0
.0
.0
.0
.0
.0
10000.0
10000
.0
PLUME
HT (M)
.00
10.00
10.00
10.00
10.00
10.00
10.00
10.00
10.00
10.00
SIGMA
Y (M)
.00
55.68
58.61
61.51
64.41
67.28
70.15
73.00
75.84
78.66
SIGMA
Z (M)
21
21
22
22
23
24
24
25
25
.00
.40
.82
.40
.96
.52
.06
.60
.12
.64
DUASH
NO
NO
NO
NO
NO
NO
NO
NO
NO
MAXIMUM 1-HR CONCENTRATION AT OR BEYOND 100. M:
109. 257.5 6 1.0 1.0 10000.0 10.00
DWASH= MEANS NO CALC MADE (CONC = 0.0)
DWASH=NO MEANS NO BUILDING DOWNUASH USED
DWASH=HS MEANS HUBER-SNYDER DOUNWASH USED
DWASH=SS MEANS SCHULMAN-SCIRE DOWNWASH USED
DWASH=NA MEANS DOWNWASH NOT APPLICABLE, X<3*LB
***************************************
*** SUMMARY OF SCREEN MODEL RESULTS ***
***************************************
53.04 20.78
NO
CALCULATION
PROCEDURE
MAX CONC
(UG/M**3)
DIST TO
MAX (M)
TERRAIN
HT (M)
SIMPLE TERRAIN
257.5
109.
0.
***************************************************
** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **
***************************************************
Figure 9. SCREEN2 Volume Source Example
31
-------
1-Full M«t
2»Stngi* St«b
3«Slng Stab ft
Wind Sp«»d
Figure 10. Flow Chart of Inputs and Outputs for SCREEN2 Volume Source
32
-------
3. TECHNICAL DESCRIPTION
Most of the techniques used in the SCREEN2 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
SCREEN2 and on describing those techniques that are unique to
SCREEN2.
3.1 Basic Concepts of Dispersion Modeling
SCREEN2 uses a Gaussian plume model that incorporates
source-related factors and meteorological factors to estimate
pollutant concentration from continuous sources. It is assumed
that the pollutant does not undergo any chemical reactions, and
that no other removal processes, such as wet or dry deposition,
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 Volume
II of the ISC2 user's guide (EPA, 1992), and in the Workbook of
Atmospheric Dispersion Estimates (Turner, 1970).
The basic equation for determining ground-level
concentrations under the plume centerline is:
X = Q/(27rus]
+ exp[-*((zr+he+2NZj)/az)2]- ] } (1)
where
X = concentration (g/m )
Q = emission rate (g/s)
TT = 3.141593
us = stack height wind speed (m/s)
cry = lateral dispersion parameter (m)
crz = vertical dispersion parameter (m)
zr = receptor height above ground (m)
he = plume centerline height (m)
Zj ~ mixing height (m)
k = summation limit for multiple reflections of plume
off of the ground and elevated inversion, usually s4.
33
-------
Note that for stable conditions and/or mixing heights greater
than or equal to 10,000m, unlimited mixing is assumed and the
summation term is assumed to be zero.
Equation I is used to model the plume impacts from point
sources, flare releases, and volume releases in SCREEN2. The
SCREEN2 volume source option uses a virtual point source
approach, as described in Volume II (Section 1.2.2) of the ISC2
model user's guide (EPA, 1992). The user inputs the initial
lateral and vertical dimensions of the volume source, as
described in Section 2.7 above.
The SCREEN2 model uses a finite line segment algorithm for
modeling impacts from area sources, as described in Volume II
(Section 1.2.3) of the ISC2 model user's guide (EPA, 1992). The
area source is assumed to be a square shape, and the model cannot
be used to estimate concentrations within the area.
3.2 Worst Case Meteorological Conditions
SCREEN2 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 SCREEN2 are given in Table
2. The 10-meter wind speeds given in Table 2 are adjusted to
stack height by SCREEN2 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 2 are used without adjustment. For
distances greater than 50 km (available with the discrete
distance option), SCREEN2 sets 2 m/s as the lower limit for the;
10-meter wind speed to avoid unrealistic transport times. Table; 2
includes some cases that may not be considered standard stability
class/wind speed combinations, namely E with winds less than 2
m/s, and F with winds greater than 3 m/s. The combinations of E
and winds of 1 - 1.5 m/s are 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) .
These combinations are included in SCREEN2 because they are valid
combinations 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.
34
-------
Stability
Class
A
B
C
D
F
Table 2. Wind Speed and Stability Class Combinations
Used by the SCREENS Model
10-m Wind Speed
(m/s)
1 1.5 2 2.5 3 3.5 4 4.5 5 8 10 15 20
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 2), SCREEN2 prints out the maximum
concentration for each distance, and the overall maximum and
associated distance. The overall maximum concentration from
SCREEN2 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 SCREEN2 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). SCREEN2 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 SCREEN2 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 SCREEN2.
The mixing height used in SCREEN2 for neutral and unstable
conditions (classes A-D) is based on an estimate of the
mechanically driven mixing height. The mechanical mixing height,
zm (m), is calculated (Randerson, 1984) as
0.3 u*/f
(2)
35
-------
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, u10, as
u* - 0.1 u10 (3)
Substituting for u* in Equation 2 we have
zm = 320 u10. (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 zm from Equation 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 10,000m to represent unlimited
mixing.
3.3 Plume Rise for Point Sources
The use of the methods of Briggs to estimate plume rise are
discussed in detail in Section 1.1.4 of Volume II of the ISC2
user's guide (EPA, 1992). These methods are also incorporated in
the SCREEN2 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 = gvsds'(Ts-TJ/(4T8), (5)
which is described in Section 4 of the screening procedures
document and is equivalent to Briggs' (1975, p. 63) Equation 12.
Buoyancy flux for flare releases is estimated from
Fb = 1.66 x 10'5 x H, (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 Ta = 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 SCREEN2 by assuming
effective stack parameters of vs = 20 m/s, T, = 1,273K, and
solving for an effective stack diameter, d, = 9.88 x 10"4(QH)°-5.
36
-------
The momentum flux, which is used in estimating plume rise
for building downwash effects, is calculated from,
Fm = v.'d.'T./UT.) . (7)
m
The ISC2 user's guide (EPA, 1992) 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 SCREEN2 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
1.1.4.11 of Volume II of the ISC2 user's guide (EPA, 1992).
These formulas apply to sources where h, s E^ + 0.5Lb. For
sources subject to downwash but not meeting this criterion, the
downwash algorithms of Huber and Snyder (EPA, 1992) are used,
which employ the Briggs plume rise formulas referenced above.
3.4 Dispersion Parameters
The formulas used for calculating vertical (<7Z) and lateral
(ay) dispersion parameters for rural and urban sites are
described in Section 1.1.5 of Volume II of the ISC2 user's guide
(EPA, 1992) .
3.5 Buoyancy Induced Dispersion
Throughout the SCREEN2 model, with the exception of the
Schulman-Scire downwash algorithm, the dispersion parameters, cry
and az, are adjusted to account for the effects of buoyancy
induced dispersion as follows:
aye = (
-------
If non-zero building dimensions are input to SCREEN2 for
either point or flare releases, then cavity calculations will be
made as follows. The cavity height, hc (m) , is estimated based
on the following equation from Hosker (1984) :
hc = hb (l.O + 1.6 exp (-1.3L/hb)), (9)
where: hb = building height (m)
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.=.,
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, 1984):
Xc = Q/(1.5 A,, u) ' (10)
where: Q = emission rate (g/s)
Ap = Hb-W = cross-sectional area of the building normal
to the wind (ma)
W = crosswind dimension 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 l 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, x^, measured from the lee side of the
building, is estimated by the following (Hosker, 1984) :
(1) for short buildings (L/hb s 2) ,
x, = (A) (W) (11)
1.0 + B(W/hb)
(2) for long buildings (L/hb a 2) ,
^ - 1.75 (W) (12)
1.0 + 0.25(W/hJ
38
-------
where: hb = building height (m)
L = alongwind building dimension (m)
W = crosswind building dimension (m)
A = -2.0 + 3.7 (L/hbrl73, 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 A,,. 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. However, the
higher concentration that potentially effects ambient air should
be used as the controlling value for the cavity procedure. The
cavity heights estimated by Equation (9) for tall narrow
buildings can exceed the-GEP height. In these situations use of
Equation (9) to calculate cavity concentrations may not be
accurate and use of other techniques should be investigated.
3.6.2 Wake Region
The calculations for the building wake region are based on
the ISC2 model (EPA, 1992). The wake effects are divided into
two regions, one referred to as the "near wake" extending from
3Lb to lOLb (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 SCREEN2 model, the maximum
projected width is calculated from the input minimum and maximum
horizontal dimensions as (L2 + W2)0-5. The remainder of the
building wake calculations in SCREEN2 are based on the ISC2
user's guide (EPA, 1992).
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 ISC2 model.
3.7 Fumigation
3.7.1 Inversion Break-up Fumigation
The inversion break-up screening calculations are based on
procedures described in the 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):
= u tm
= (u pa c./R) (Ae/Az) (h; - hs) [(hj + hs)/2] (13)
39
-------
where:
x^ = 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)
A0/Az =» vertical potential temperature gradient (assume
0.035 K/m for F stability)
hj = height of the top of the plume (m) = he + 20^ (he =
plume centerline height)
ns = physical stack height (m).
a^. = vertical dispersion parameter incorporating buoyancy
induced dispersion (m)
The values of u and A9/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 h; incorporates
the effect of buoyancy induced dispersion on az, however,
elevated terrain effects are ignored. The equation above is
solved by iteration, starting from an initial guess of x,^ =
5,000m.
The maximum ground-level concentration due to inversion
break-up fumigation, Xf, is calculated from Equation 5.2 of
Turner (1970) .
X, = Q/[(27T)°-5u(ffye+he/8) (lv-2ffj] (14)
where Q is the emission rate (g/s), and other terms are defined
above. The dispersion parameters, aye and o^, incorporate the
effects of buoyancy induced dispersion. If the distance to the
maximum fumigation is less than 2000m, then SCREEN2 sets Xf = 0
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.
3.7.2 Shoreline Fumigation
For rural sources within 3000m of a large body of water,
maximum shoreline fumigation concentrations can be estimated by
SCREEN2. A stable onshore flow is assumed with stability classs F
(A9/Az = 0.035 K/m) and stack height wind speed of 2.5 m/s.
Similar to the inversion break-up fumigation case, the maximum
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).
40
-------
An evaluation of coastal fumigation models (EPA, 1987) 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:
A [x]
°-3
(15)
where:
A
x
height of the TIBL (m)
TIBL factor containing physics needed for TIBL
parameterization (including heat flux) (m1/4)
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:
[(he 4-
- x,
(16)
where:
= downwind distance to maximum concentration (m)
x, = shortest distance from source to shoreline (m)
he = plume centerline height (m)
au = vertical dispersion parameter incorporating
buoyancy induced dispersion (m)
Plume height is based on the assumed F stability and 2.5 m/s wind
speed, and the dispersion parameter (<;„) incorporates the effects
of buoyancy induced dispersion. If x,^ is less than 200m, then
no shoreline fumigation calculation is made, since the plume may
still be influenced by transitional rise and its interaction with
the TIBL is more difficult to model.
The maximum ground- level concentration due to shoreline
fumigation, Xf, is also calculated from Turner's (1970) Equation
5.2:
Xf = Q/[(27r)°-5u(aye+he/8) (he+2aj] " (14)
with (Tye and a^ incorporating the effects of buoyancy induced
dispersion.
Even though the calculation of x,^ above accounts for the
distance from the source to the shoreline in x,, extra caution
should be used in interpreting results as the value of x,
increases. The use of A=6 in Equations 15 and 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.
41
-------
Whereas 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.
3.8 Complex Terrain 24-hour Screen
The SCREEN2 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 is at or below the terrain
height for the distance entered, then SCREEN2 will make a 24-hour
average concentration estimate using the VALLEY screening
technique. If the terrain is above stack height but below plume
centerline height, then SCREEN2 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 SCREEN2 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 0 exp [-0.5 (hs/a^) 2] . (17)
a^ u x
Note that for screening purposes, concentrations are not
attenuated for terrain heights above plume height. The
dispersion parameter, a^, incorporates the effects of buoyancy
induced dispersion (BID). For the simple terrain calculation
SCREEN2 examines concentrations for the full range of
meteorological conditions and selects the highest ground level
concentration. Plume heights are reduced by the chopped off
terrain height for the simple terrain calculation. To adjust the
concentrations to 24-hour averages, the VALLEY screening value is
multiplied by 0.25, as done in the VALLEY model, and the simple
terrain value is multiplied by the 0.4 factor used in Step 5 of
Section 4.2.
42
-------
4. NOTE TO PROGRAMMERS
The SCREEN2 model was compiled on an IBM PC/AT compatible
microcomputer using the Microsoft FORTRAN Compiler, Version 5.1.
It was compiled with the emulator library, meaning that the
executable file (SCREEN2.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 a compressed file on the diskette
are the executable file, SCREEN2.EXE, the FORTRAN source code
files, SCREEN2.FOR and MAIN.INC, a sample input file,
EXAMPLE.DAT, an associated output file, EXAMPLE.OUT, and this
document, the SCREEN2 Model User's Guide (in WordPerfect 5.1
format), SCREEN2.WPF. Also included on the diskette is a READ.ME
file with instructions on extracting SCREEN2.
The SCREEN2 model provided was compiled with the following
Microsoft FORTRAN compile command:
FL /FPi SCREEN2.FOR
where the /FPi compile option specifies the emulator library and
causes floating point operations to be processed using in-line
instructions rather than library CALLs (used for faster
execution). SCREEN2 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 the unit number for
writing inputs to the data file, SCREEN.DAT, is set to 7. These
unit numbers are assigned to the variables IRD, IPRT, IOUT, and
IDAT, respectively, and are initialized in BLOCK DATA at the end
of the SCREEN2.FOR source file. The Microsoft version of SCREEN2
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 SCREEN2
source file, SCREEN2.FOR, in order to create a version that will
accept a user-specified output filename, instead of automatically
writing to the file SCREEN.OUT. An ASCII text 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 199 to 202. They should read as follows:
WRITE(IPRT,*) ' '
94 WRITE(IPRT,*) 'ENTER NAME FOR OUTPUT FILE'
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
204 may also be changed to read as follows:
OPEN(IOUT,FILE=OUTFIL,STATUS='NEW',ERR=94)
43
-------
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. It should be noted that without optimization, the source
file may be too large to compile as a single unit. In this case,
the SCREEN2.FOR file may need to be split up into separate
modules that can be compiled separately and then linked together.
The SCREEN2 model code has also been successfully compiled
with the Lahey F77/EM-32 Fortran compiler, with the following
compile command:
F77L3 SCREEN2.FOR /NO /NW /D1LAHEY
where the /NO option suppresses the printing of compile options,
/NW suppresses certain warning messages, and /D1LAHEY defines
LAHEY for implementing the conditional compile block of Lahey-
specific statements for retrieving the system date and time for
the output file. Follow the instructions with the Lahey compiler
for linking the model to create an executable file.
44
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5. 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 Meteorological 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, 1986. Guideline On Air
Quality Models (Revised). EPA-450/2-78-027R. U.S.
Environmental Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1987. Analysis and
Evaluation of Statistical Coastal Fumigation Models.
EPA-450/4-87-002. U.S. Environmental Protection Agency,
Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1992a. Screening
Procedures for Estimating the Air Quality Impact of
Stationary Sources, Revised. EPA-450/R-92-019. U.S.
Environmental Protection Agency, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 1992. Industrial Source
Complex (ISC2) Dispersion Model User's Guide. EPA-450/4-92-
008. U.S. Environmental Protection Agency, Research
Triangle Park, NC.
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.
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.
45
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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.
Pierce, T.E., 1986. Addendum to PTPLU - A Single Source Gaussian
Dispersion Algorithm. EPA/600/8-86-042. U.S. Environmental
Protection Agency, Research Triangle Park, NC. (Available
only from NTIS.. NTIS Accession Number PB87-145 363.)
Pierce, T.E. and D.B. Turner, 1980. User's Guide for MPTER - A
Multiple Point Gaussian Dispersion Algorithm With Optional
Terrain Adjustment.. EPA-600/8-80-016. 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 an Urban Area.
Journal of Applied Meteorology. 3, 83-91.
p
Turner, D.B., 1970. Workbook of Atmospheric Dispersion
Estimates. Revised, Sixth printing, Jan. 1973. Office cf
Air Programs Publication No. AP-26.
46
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INSTRUCTIONS
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/4-92-006
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
5. REPORT DATE
Model User's Guide
September 1992
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Pacific Environmental Services, Inc.
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14. SPONSORING AGENCY CODE-
IS. SUPPLEMENTARY NOTES
16. ABSTRACT
This document presents current EPA guidance on the use of the SCREEN2 screening
model. The SCREEN2 model is supported by the "SCREEN2 Model User's Guide," which
previously was Appendix A of "Screening Procedures for Estimating the Air Quality
Impact of Stationary Sources - Draft for Public Comment". SCREEN2 is a PC-driven,
Gaussian atmospheric dispersion model which calculates maximum 1-hour, downwind
concentrations of non-reactive pollutants. Major changes in this version of
SCREEN2 are the finite line segment method for area sources, addition of wind
speeds in the wind speed-stability matrix for calculating concentrations, and the
inclusion of a single volume source option. The structure of the computer cxxJe was
modified to aid in any future revisions to
17.
KEY WORDS AND DOCUMENT ANALYSIS
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b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Air Pollution
Atmospheric Diffusion
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EPA Form 2220-1 (9-73)
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