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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