United States
Environmental Protection
Agency
Atmospheric Sciences
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-87/021 Sept. 1987
Project Summary
Development of Computer
Modules of Particulate
Processes for Regional
Particulate Model
A. Belle Hudischewskyj, Pradeep Saxena, and Christian Seigneur
The development of an aerosol model
for inclusion in the EPA Regional
Participate Model is described. Existing
computer models of particulate pro-
cesses developed under contract to the
EPA are compared to determine effi-
cient and accurate methods of simu-
lating particulate behavior. These
methods are then incorporated into an
aerosol model, which is both accurate
and efficient in its treatment of the
dynamics, thermodynamics, and
chemical composition of atmospheric
aerosols.
This Project Summary was devel-
oped by EPA's Atmospheric Sciences
Research Laboratory, Research Tri-
angle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
In the past, air pollution monitoring and
modeling studies have generally focused
on the study of photochemical smog
formation and related impacts. Recently,
however, more attention has been paid
to such concerns as high levels of
particulate matter with diameters less
than 10 fjm (PM10), visibility impair-
ment, and acid deposition. A knowledge
of the concentration, chemical composi-
tion, and size distribution of atmospheric
aerosols over the entire range of relative
humidities is required to model these
phenomena.
During the course of this work, we
installed and evaluated numerous com-
puter models of Articulate processes
developed under contract to the E PA to
select efficient and accurate models for
incorporation into Ihe regional model.
These models were developed to treat the
dynamics, thermodynamics, and chemis-
try of atmospehric particulate matter. The
evaluation took into consideration the
computational requirements, predictive
accuracy, and application range of the
models.
Aerosol Dynamics
For our study of the treatment of
aerosol dynamics, we compared four
models: COAGUL and CONFEMM, devel-
oped at the University of Texas by
Professor J. R. Brock and co-workers;
AGRO, developed at the University of
Minnesota by Professor K. T. Whitby, Mr.
E. E. Whitby, and co-workers; and
ESMAP, developed at the California
Institute of Technology by Professor J.
H. Seinfeld and co-workers. These four
models represent the three major
approaches to solving the General
Dynamic Equation (GDE) that governs the
treatment of aerosol coagulation and
condensation. COAGUL and CONFEMM
are examples of a continuous represen-
tation of the GDE for coagulation and
condensation, respectively. ESMA P is an
example of a discrete representation in
which the size distribution is sectional-
ized. AGRO represents a parameterized
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approach in which the size distribution
is assumed to be lognormal.
Coagulation
COAGUL, AGRO, and ESMAP were
used to simulate aerosol coagulation
over 12 hours for atmospheric aerosol
concentrations typical of clear, hazy, and
urban conditions. ESMAP was applied
with two different size resolutions, 12
and 39 sections, over the 0.001 (jm. to
10 A
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coated aerosols; and formation of small
sulfate and organic aerosols.
The gas-phase chemistry is treated by
means of the Carbon-Bond Mechanism
IV (CBM-IV) developed by Whitten and
Gery of Systems Applications, Inc. The
mechanism describes the chemistry of
oxidants, nitrogen oxides, and anthropo-
genic and natural hydrocarbons. The
Carbon-Bond Mechanism X (CBM-X),
developed by Whitten and co-workers,
was also examined for incorporation into
the regional paniculate model, and the
number of reactions was condensed
through variational sensitivity analysis.
Evaluation
To evaluate the aerosol model, we
simulated' both a regional environment
and an urban plume, using a plume
trajectory model, PLMSTAR, developed
by Godden and Lurmann of ER&T, into
which our aerosol model was incorpo-
rated. This trajectory/aerosol model,
which also employs the Carbon-Bond
Mechanism for the treatment of gas-
phase chemistry, was developed under
contract to Southern California Edison
Company.
Two simulations were conducted for
36-hour periods (23-24 August 1987) to
simulate both daytime and nighttime
chemistries. The first simulation, for
Columbus, Ohio, was selected to repre-
sent a regional environment. The second,
for St. Louis, Missouri, was selected to
represent an urban plume. In addition to
the two base case studies, six sensitivity
studies were conducted. Five of these
studies were based on the data for the
regional environment and consisted of
simulations performed with (1) the base
case S02 emissions and initial S02
concentrations reduced by 50 percent, (2)
the base case NOX emissions and initial
NOx concentrations reduced by 50 per-
cent, (3) the base case NH3 emissions
and initial NH3 concentrations reduced
by 50 percent, (4) the base case reactive
hydrocarbon (RHC) emissions and initial
RHC concentrations reduced by 50
percent, and (5) the season changed from
summer to winter. (Modification to the
summer base case input parameters to
represent winter conditions included a
change in date, a decrease in temper-
ature, lowering the H2O2 and 03 initial
concentrations, lowering the mixing
height, and shortening the daylight
period.) The sensitivity study based on
the data from the St. Louis urban plume
consisted of increasing the relative
humidity from 60 percent to 85 percent.
Conclusions
Results for all the studies were com-
pared and evaluated, and it was con-
cluded that the aerosol model performs
well under a variety of atmospheric and
meteorological conditions. These results
indicate that the aerosol model is a useful
tool for studies of PM10, visibility, and
acid deposition.
A. Belle Hudischewskyj, Pradeep Saxena, and Christian Seigneur are with
Systems Applications, Inc.. San Rafael, CA 94903.
Harold M. Barnes is the EPA Project Officer (see below).
The complete report, entitled "Development of Computer Modules of Paniculate
Processes for Regional Paniculate Model," (Order No. PB 87-227 278/AS;
Cost: $24.95, 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 Officer can be contacted at:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S3-87/021
60604
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