United States
Environmental Protection
Agency
Research and Development
Atmospheric Research and Exposure
Assessment Laboratory
Research Triangle Park NC 27711
EPA/600/S8-90/083 April 1991
«rEPA Project Summary
The Regional Oxidant Model
(ROM) User's Guide
L. Milich, L. Bender, T. Boehm, C. Coats, J. Eichinger, S. Fudge,
S. Hallyburton, D. Jordan, D. Jorge, C. Maxwell, D. Olerud, R. Tang,
A. Van Meter, R. Wayland, J. Young, O. Bullock, J. Novak,
T. Pierce, S. Roselle and K. Schere,
The Regional Oxidant Model (ROM)
determines hourly concentrations and
fates of ozone and 34 other chemical
species over a scale of 1000 km x 1000
km for ozone "episodes" of up to one
month's duration. The model structure,
based on phenomenological concepts,
consists of 31/2-layers. The surfaces
separating the layers respond to varia-
tions in space and time of the meteo-
rological phenomena simulated in each
layer. The model simulates many
physical and chemical processes that
affect the motion and distribution of
chemical concentrations: among these
are horizontal transport, photochemis-
try, nighttime wind shear and noctur-
nal jet, cumulus cloud effects and me-
soscale vertical motion, terrain and
mesoscale eddy effects, subgrid scale
chemistry processes, natural sources
of hydrocarbon, and dry deposition.
The ROM is a complex model that re-
quires users to have expertise in pho-
tochemical grid modeling. Meteorolo-
gists, engineers, and computer scien-
tists familiar with this type of modeling
will find this User's Guide relevant and
helpful for running the ROM.
This Project Summary was developed
by EPA's Atmospheric Research and
Exposure Assessment Laboratory, Re-
search Triangle Park, NC, to announce
key findings of the research project
that Is fully documented In a three-part
report of the same title (see Project
Report ordering information at back).
Introduction
The Regional Oxidant Model (ROM) is
a three-dimensional photochemical
Eulerian grid model designed to simulate
concentrations of ozone and related spe-
cies. ROM is a 3 1/2-layer model with a
horizontal resolution of approximately 19
km; each grid cell has dimensions of
1/6° latitude by 1/4° longitude. The typi-
cal horizontal extent of the modeling do-
main is 1000 km. The model is designed
to simulate hourly regional concentrations
of ozone during largely stagnant summer-
time conditions that are associated with
elevated smog episodes. ROM is also
intended to simulate the effect of alterna-
tive emission control strategies that might
be used to mitigate harmful levels of ozone
pollution.
Development of the ROM began in the
middle 1970's. Research versions of the
model were tested and modified during
the 1980's. The model described in this
user's guide (version 2.1) became opera-
tional in late 1989 and has been exten-
sively used in applications by the EPA.
The model simulates many physical and
chemical processes that affect the motion
and distribution of chemical concentrations.
These processes include horizontal trans-
port using a refined objective analysis
scheme, photochemistry using the Car-
bon Bond 4 mechanism, cumulus cloud
effects and mesoscale vertical motion,
nighttime wind shear and nocturnal jets,
terrain and mesoscale eddy effects,
subgrid scale chemistry processes, bio-
Printed on Recycled Paper
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genie emissions of hydrocarbons, and dry
deposition.
The purpose of this user's guide is to
provide potential users with sufficient in-
formation to execute the ROM on a com-
bination VAX and IBM computer system.
Readers are referred to other publications
to obtain details on the model's technical
background. Because of the model's
complexity, the user's guide is divided into
three parts. Part 1 discusses the prepro-
cessors, which manipulate the raw data.
Part 2 contains information on the many
processors that are used to generate four
data files for input to the core model. Part
3 discusses operation of the core model
on the IBM computer.
ROM Preprocessors (Part 1)
This portion of the user's guide dis-
cusses the programs that are used to
convert raw data into a format acceptable
for use in the processor network. Raw
data that are handled by the preprocessors
include the following:
(1) meteorological data from buoys,
(2) surface meteorological data (both
U.S. and Canada),
(3) upper-air meteorological data (both
U.S. and Canada),
(4) anthropogenic emissions,
(5) biogenic emissions,
(6) ozone boundary conditions,
(7) chemistry initial conditions, and
(8) line source information.
Much of the initial quality assurance of
the data is performed during preprocess-
ing. Other operations that are performed
include merging and sorting the databases
and converting them into appropriate for-
mats. All preprocessor programs, except
for the ozone boundary-condition proce-
dure, are FORTRAN programs that reside
on the VAX computer. The ozone bound-
ary-condition procedure is an ad hoc pro-
cess that is performed using a spread-
sheet program on a desktop computer.
ROM Processor Network
(Part 2)
Figure 1 shows the ROM 2.1 processor
network. Processing occurs in several
stages. The initial data files are entered
into processors in Stage 0 and processing
continues through Stage 8. The proces-
sor network transforms the raw data into
four core mode input files: ICON (initial-
concentration data); BCON (boundary-
condition concentration data); BTRK
[diffusivity and backtrack (advection trans-
port) information]; and BMAT (parameter-
ization for vertical fluxes, meteorological
parameters necessary for chemistry rate
constant adjustments, and parameterized
emissions source strengths).
All of the processors have been written
in FORTRAN-77 and have been executed
on EPA's cluster of VAX computers. Data
processing for a typical three-day simula-
tion of the northeastern U.S. requires 12
hours of CPU on a VAX 8650.
Core Model (Part 3)
Unlike other components of the ROM
modeling system, the core model resides
on an IBM 3090 computer. The core
model takes data from the four files gen-
erated by the processor network (ICON,
BCON, BTRK, and BMAT) and computes
concentrations of ozone and 34 other
chemical species.
There are two principal components of
the core model: BIGGAM and LILGAM.
BIGGAM solves the horizontal transport
for each grid cell in 30-minute time steps.
LILGAM solves the chemistry in time steps
that are allowed to vary according to the
"stiffness" of the solution. Vertical mass
fluxes, including emissions injection, are
also accounted for in LILGAM. The pri-
mary output of the core model is a large
concentration file consisting of gridded 30-
minute average concentrations for all
chemical species. A typical three-day simu-
lation of the core model for the northeast-
ern U.S. uses 9.5 hours of CPU on an
IBM 3090.
Summary
This three-part user's guide provides
the information necessary to execute ver-
sion 2.1 of the Regional Oxidant Model
(ROM). Potential users of the system
should be forewarned that the modeling
system is complex and requires extensive
computer resources. The services of en-
gineers, meteorologists, or computer sci-
entists experienced in photochemical grid
modeling are required. Although the code
has been designed and executed on VAX
and IBM computers, it should be adapt-
able to other computer systems.
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STAGE 3 STAGE 4 STAGE 5
STAGE 6 STAGE 7 STAGE •
Figure 1. Structure and final output files of the ROM 2.1 Processor Network.
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L. Milich, L. Bender, T. Boehm, C. Coats, J. Eichinger, S. Fudge, S. Hallyburton,
D. Jordan, D. Jorge, C. Maxwell, D. Olerud, R. Tang, A. Van Meter, R. Way/and,
and J. Young are with Computer Sciences Corporation, NC 27709; the EPA
authors, O. Bullock, J. Novak (also the Project Officer, see below), T. Pierce,
S. Roselle, and K. Schere are on assignment to the Atmospheric Research and
Exposure Assessment Laboratory, Research Triangle Park, NC 27711, from the
National Oceanic and Atmospheric Administration.
The complete report, entitled "The Regional Oxidant Model (ROM) User's Guide,"
Part 1. The ROM Preprocessors (Order No. PB91-171 926/AS; Cost: $39.00,
subject to change)
Part 2. The ROM Processor Network (Order No. PB91-171 934/AS; Cost: $45.00,
subject to change)
Part 3. The Core Model (Order No. PB91-171 942/AS; Cost: $31.00, and the
Complete Set. (Order No. PB 91-171 918/AS; Cost: $98.00, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S8-90/083
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