United States
Environmental Protection
Agency
Atmospheric Sciences
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S8-88/082 July 1988
v°/EPA Project Summary
User's Guide for Executing
OZIPM-4 with CBM-IV or
Urban and Regional Modeling
M. W. Gery, G. Z. Whitten, and J. P. Killus
In a recent study, Systems
Applications developed a new
chemical mechanism called the
Carbon-Bond Mechanism-IV
(CBM-IV), which provides a
complete and verified description of
urban smog chemistry. In this study,
the CBM-IV has been incorporated
into a new computer program called
Ozone Isopleth Plotting with Option
Mechanisms -- Version 4 (OZIPM-
4). This program is designed to be
used with EKMA to calculate the
emission reductions needed to
achieve the air quality standard for
ozone. The OZIPM-4 can accept as
input chemical mechanism other
than the CBM-IV. Recent updates
and improvements to the OZIPM-4
are discussed along with the CBM-
IV mechanism. OZIPM-4 expands on
earlier codes by providing a wider
compatibility between computers, an
improved isopleth plotting package,
expanded user interaction with
control strategy calculations, and a
new option for determining credits
for carbon monoxide emissions
reductions. Volume 1 serves as the
User's Manual for OZIPM-4. It
contains both a detailed description
of OZIPM-4 and a discussion of the
input and output requirements and
options available for exercising
either the default CBM-IV
mechanism or an optional
mechanism. Five examples of
OZIPM-4 input and output files are
also included. Volume 2 contains the
listing of the FORTRAN computer
code. A magnetic tape or floppy disk
of this code is also available from
Systems Applications.
This Project Summary was
developed by EPA's Atmospheric
Sciences Research Laboratory,
Research Triangle Park, NC, to
announce key findings of the research
project that is fully documented In two
separate volumes of the same title
(see Project Report ordering
information at back).
Introduction
This project consisted of the
development of a new version of the
OZIPM (Ozone Isopleth Plotting with
Optional Mechanisms) computer
program, which is recommended by the
U.S Environmental Protection Agency
(EPA) for formulating State
Implementation Plans (SIPs) for
attainment of the ozone National Ambient
Air Quality Standard (NAAQS). OZIPM
utilizes the Empirical Kinetics Modeling
Approach (EKMA) to relate levels of
ozone to levels of nonmethane organic
compounds (NMOC) and oxides of
nitrogen (NOX). The current version is
known as OZIPM-4 because the
Carbon-Bond Mechanism-IV (CBM-
IV) is the default photochemical kinetics
mechanism (though alternate chemical
mechanisms may be used). In addition to
development of the OZIPM-4 computer
code, this project involved creation of a
user's manual containing (1) a technical
description of the model and the various
input and output options, (2) guidance on
the selection of input options, (3) a quick
reference section, and (4) example
simulations that demonstrate certain
model features.
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Description of OZIPM-4
OZIPM-4 consists of two distinct
components: the first is a trajectory-
based photochemical kinetics simulation
model that mathematically simulates
physical and chemical processes in the
atmosphere; these results are then used
as part of the EKMA procedure to
calculate emission control requirement
for a specific test case or to construct an
ozone isopleth diagram.
In the OZIPM-4 photochemical
kinetics model a column of air containing
ozone and precursors is transported
along an assumed trajectory. As the
column moves, it encounters fresh
precursor emissions that are uniformly
mixed within the column, which is
assumed to extend from the earth's
surface through the mixed layer. The
assumed horizontal dimensions of this
column are such that the concentration
gradients are small enough to make the
horizontal exchange of air between the
column and its surroundings insignificant.
The air within the column is assumed to
be uniformly mixed at all times.
At the beginning of a simulation, the
column is assumed to contain some
specified initial concentrations of NMOC
and NOX- As it moves along the assumed
trajectory, the height of the column can
change due to temporal and spatial
variations in mixing height; it is assumed
to change with time during a user-
selected period, and to be constant
before and after that period. As the
height of the column increases, its
volume increases, and air from the
inversion layer above is mixed in.
Pollutants above the mixed layer are
described as "transported above the
surface layer" or "transported aloft." Any
ozone or ozone precursors above the
mixed layer that are mixed into the
column as it expands are assumed to be
rapidly mixed throughout the column.
The photochemical kinetics model in
OZIPM-4 considers emissions of VOC,
NOX, and CO into the column as it moves
along its trajectory. The concentrations of
these species within the column are
physically decreased by dilution due to
the inversion rise, and physically
increased by both entrainment of
pollutants transported aloft and fresh
emissions. All species react chemically
according to the kinetic mechanism
selected. The photolysis rates within the
mechanism are functions of the intensity
and spectral distribution of sunlight and
they vary diurnally according to time of
year and location.
The EKMA Procedure
The EKMA procedure was developed
to relate levels of photochemical oxidants
(expressed as ozone) to levels of NMOC
and oxides of nitrogen NOX. It utilizes a
set of isopleths that depict maximum
afternoon concentrations of ozone as a
function of the following parameters:
Morning concentrations of NMOC and
NOX (which may include precursors
transported from upwind sources);
Emissions of volatile organic
compounds (VOC), NOX, and other
species (such as carbon monoxide)
occurring during the day;
Meteorological conditions; and
The reactivity of different VOC and
NMOC mixtures.
The EKMA procedure utilizes multiple
computer simulations with different levels
of NMOC and NOX concentrations to
predict the resulting maximum hourly
ozone concentrations. These ozone
concentrations are then used to generate
ozone concentration isolines that are
plotted as a function of initial precursor
concentrations. These isopleths are used
to compute the percent reduction in
emissions that is needed to lower peak
ozone to the NAAQS of 0.12 ppm. It is
not necessary to use isopleth diagrams
to perform EKMA calculations because
the EKMA option in OZIPM-4 will do
this internally and report a control value.
However, though use of the EKMA option
will provide the target VOC control
requirements, in some cases an isopleth
diagram can provide additional
diagnostic information.
The Chemical Kinetics
Mechanism
As noted earlier, the CBM-IV is
internally stored in the OZIPM-4
program. However, the program can
accept a chemical mechanism other than
the default CBM-IV. This optional
kinetic mechanism cannot contain more
than 135 reactions and/or 60 species. To
input a different kinetic mechanism, the
user must specify certain parameters:
The total number of photolysis
reactions (maximum of 20) and the
reaction numbers that identify the
photolysis reactions in the
mechanism.
The total number of organic species
included in the initial NMOC mix
(maximum of 20), the names that
identify these species, and tnl
number of carbon atoms in each.
The fraction of total carbon that eacl
organic species represents.
Mechanisms are included in thi
OZIPM-4 through the use of variou:
input options. These options and other:
are described next.
Input and Output Options
Input parameters (options) that cai
be specified by the user whe
performing an OZIPM-4 calculatio
include:
A new chemical kinetic mechanism;
The zenith-angle-dependence c
the photolytic rates for the chemic;
mechanism;
Latitude, longitude, time zone an
date;
Morning and afternoon mixing heighl
(also called mixing depths) or hour!
mixing depths;
Hourly temperature variation;
The simulation start and stop times;
Concentrations of NMOC, NOX, C(
ozone, and up to 10 other species i
the air above the mixed layer due 1
transport aloft (note that these canm
be varied in time);
Concentrations of NMOC, NOX, C(
ozone, and any other chemic
species transported in the surfac
layer;
Background concentrations of NMO
NOX, and ozone. The backgrour
represents the minimum levels in bo
the surface layer and aloft that cou
be achieved if all urban emissioi
were reduced to zero (i.e., continen
background);
VOC, NOX, and CO emissions at ea
hour;
Organic reactivity. Four reactiviti
can be specified: background, initi
aloft, and emitted. However, each ty
of reactivity is fixed in time for ea
diagram point and at every point
the diagram;
NOX reactivity (initial fraction of N
that is N02);
Surface deposition as a function
time for up to 10 species.
In addition, the user may va
individual reaction rates, alter the er
tolerance of the calculations, and in|
simulation results from previous ru
The major function of OZIPM-4 is
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_ ._ the VOC reductions needed to
achieve the ozone air quality standard.
The output depends on the option
selected by the user. Three types of
output can be requested:
(1) Perform a single calculation for a
specified set of initial concentrations.
(2) Compute VOC emission reduction
needed to achieve the 03 standard of
0.12 ppm without generating an 03
isopleth.
(3) Generate an 03 isopleth.
In addition, the user may generate
isopleths for species other than ozone,
and perform off-line (CALCOMP)
plotting.
Limitations of the
OZIPM-4/EKMA
OZIPM-4 has a limited applicability
to ozone problems within, or immediately
downwind of, large urban areas and thus
should not be applied to the following
situations unless special attention is
given to current limitations and
assumptions:
The rural ozone problem;
Situations in which transported ozone
and/or precursors are clearly
dominant (i.e., multiday transport
situations);
Cases in which the maximum ozone
concentration occurs at night or in the
early morning; and
The development of control strategies
for single or small groups of emission
sources.
The validity of an ozone isopleth
diagram generated by OZIPM-4 for a
particular city may be limited by the
following considerations:
The kinetic mechanism used to
describe the transformations of NMOC
and NOX;
The physical assumptions used to
formulate the trajectory model coded
into OZIPM-4;
The meteorological data and
assumptions used to specify required
OZIPM-4 parameters;
The availability and reliability of
current ozone data, precursor
concentration data, and VOC, NOX,
and CO emission inventories;
The mathematical assumptions
needed to integrate the differential
equations formulated within OZIPM-
4; and
The interpolations needed to generate
isopleths from the results of a number
of computer simulations.
Summary
A new version of the Ozone Isopleth
Plotting Package with optional
Mechanisms (OZIPM-4) computer code
has been developed for use in the
Empirical Kinetic Modeling Approach
(EKMA). The OZIPM-4 contains the
Carbon-Bond Kinetics Mechanism-IV
(CBM-IV) and additional capabilities not
present in earlier versions of OZIPM. The
use of the computer code is fully
described in the user's manual.
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M. W. Gery, G. Z. Whitten, and J. P. Killus are with Systems Applications, Inc., San
Rafael, CA 94903.
Marc/a C. Dodge is the EPA Project Officer (see below).
The complete report consists of two volumes and a computer tape, entitled
"User's Guide for Executing OZIPM-4 with CBM-IV or Optional Mechanisms,"
EPA/600/8-88-073a, b, and c.
"Volumel. Description of the Ozone Isopleth Plotting Package Version 4," (Order
No. PB 88-221 957/AS; Cost $25.95)
"Volume 2. Computer Code," (Order No. PB 88-221 965/AS; Cost: $19.95)
"OZIPM-4 Source Code (Computer Tape)" (Order No. PB 88-221 940/AS; Cost:
$800.00-cost of tape includes paper copy of reports)
The above reports and computer tape will be available only from: (cost subject to
change)
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric ScTenpGs'Kesearch Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
*
*
Official Business
Penalty for Private Use $300
EPA/600/S8-88/082
0000329 9$
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