United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-85/027 Jan. 1986
Project Summary
TRS-80 In-Stack Opacity
Computer Programs: User and
Programmer Manual
S. J. Cowen, D. S. Ensor, and L E. Sparks
The manual describes a microcom-
puter program written to estimate in-
stack opacity from ducted sources.
Input data required to run the program
are the particle size distribution, particle
refractive index, mass emission concen-
tration, wavelength of light, particle
density, and stack diameter. The particle
size distribution may be entered either
as a histogram of particle diameter and
fraction-greater-than-stated diameter
or as log normal particle size distribu-
tion. The program calculates and dis-
plays the in-stack opacity. The program
is written in the BASIC computer lan-
guage and is specifically designed for
the TRS-80 Model I, III, and IV com-
puters. A moderate effort will be re-
quired to convert the programs to the
IBM-PC and similar computers.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park. NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Most particulate regulations set a limit
on both the mass of the particulate matter
being emitted and the opacity of the
plume due to particulate emissions. Al-
though in the past plume opacity was
measured by a trained observer, the trend
is to measure the opacity in the stack with
a transmissometer. Considerable empir-
ical effort has been spent relating the
mass and opacity sta ndards to each other
to ensure that they are compatible. These
efforts have not always been successful
because they neglected the effects of
particle size distribution and other im-
portant factors.
A model was developed to predict in-
stack opacity from a knowledge of the
important particulate properties and the
stack diameter. The model is based on
verified physics and is rigorous for spher-
ical particles. The output from the model
is in-stack opacity as measured by a
transmissometer. The model has been
implemented in the Radio Shack TRS-80
Models I, III, and IV computers. Complete
details of the models and the computer
program are included in the full manual.
Opacity Theory
The transmission of light through a
volume containing an aerosol is described
by the Beer-Lambert law:
Opacity = 1 - transmittance = 1-I/I0 =
1 -exp(-B.L)
where
I = transmitted light,
I0 = incident light,
B, = the light extinction coefficient,
and
L = the illumination pathlength (the
stack diameter in this case).
The aerosol mass concentration is related
to the optical transmittance through a
modified form of the Beer-Lambert law:
l/l0=exp[-(MLS,/p)]
where
' M = the particle mass concentration
(actual conditions).
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Sv = the ratio of the light extinction
coefficient to the specific panic-
ulate volume, and
p - the average particle density.
Sv is a function of the particle size
distribution, particle index of refraction,
wavelength of light, and particle mass.
Parameter K, the reciprocal of Sv, can
be defined and used to relate the trans-
mittance and the mass by:
M = 1 n(l/l0) K p/L
Parameter K can be calculated from the
Mie theory of light extinction.
Error Analysis of the Computed
Results
Two main areas which introduce error
into the opacity prediction are:
1. Inherent errors in the programs
caused by roundoff errors, numer-
ical truncation, numerical app.ox-
imations, and program limitations.
2. Sensitivity of the opacity prediction
to errors in the input data.
The full manual represents a detailed
error analysis of these two sources of
error.
The major source of error in the opacity
prediction is in the measurement of the
input data—particularly the particle size
distribution and the particulate mass con-
centration. The inherent error is general-
ly less than 4 percent, much less than the
error in the measured input data. The
error in the opacity prediction is about the
same as the errors in the measured input
data. For example, if the particulate mass
is in error by 10 percent, the error in the
calculated in-stack opacity will also be 10
percent. If the opacity is much greater
than 20 percent, the error in calculated
opacity is no longer linear with the error
in mass concentration.
If proper care is taken in making the
measurements, the error in the input data
can be held to less than 30 percent. Thus
the error in the predicted opacity should
also be less than 30 percent in most cases
of interest for air pollution control.
Computer Program
Two computer programs were written
to predict opacity. The difference between
the two programs is the type of particle
size distribution used as data input: one
requires a log normal particle size distri-
bution; the other, a histogram particle
size distribution.
The log normal size distribution pro-
gram was developed to allow prediction
of opacity when the only data available
are the log normal parameters of mass
mean diameter and the geometric stand-
ard deviation. The log normal model is
also useful for estimating the effects of
various factors on in-stack opacity.
The histogram model was developed to
allow use of data from cascade impactor
measurements. The histogram model can
also be used in conjunction with partic-
ulate control device models developed by
EPA for electrostatic precipitators, fabric
filters, and venturi scrubbers.
Data for both the histogram and the log
normal models are entered using a menu
format. The menu for the log normal
model is shown in Figure 1. The histogram
has two menus: one for entering general
data; the other for entering size distribu-
tion data. These two menus are shown in
Figures 2 and 3, respectively.
System Requirements
The programs are written in Microsoft
BASIC as implemented on the Radio
Shack TRS-80 Model I, III, and IV family.
The programs require at least 48K RAM,
1 disk drive, and disk BASIC. A printer is
useful but not required. The programs
can also be compiled by the Microsoft
BASIC compiler for the TRS-80 Model I.
If the data input module is rewritten,
the programs can run on a CP/M-based
microcomputer with 64K RAM, 1 disk
drive, and microsoft BASIC 5.x or the
IBM-PC and other MS-DOS computers
with 128K RAM and Microsoft BASIC.
Complete documentation, including
program listing and user instructions, is
contained in the full manual.
Conclusion and Results
Programs for predicting the in-stack
opacity due to particulate emissions have
been developed and documented. The
programs provide a rapid means of esti-
mating the opacity from particulate emis-
sions if the particle size distribution, mass
emissions, and stack diameter are known.
The models can be used with either log
normal or histogram particle size distribu-
tion data.
OPACITY DATA ENTRY PAGE 1
REAL PART OF INDEX OF REFRACTION
IMAGINARY PART OF INDEX OF REFRACTION
WA VELENGTH OF LIGHT
MASS CONCENTRATION
PARTICLE DENSITY
STACK DIAMETER
MASS MEAN DIAMETER
GEOMETRIC STD DEVIA TION
1.50
0.0001
0.55 MICRONS
0.010 G/M3
2.4 G/CC
6.9 METERS
1.000 MICRONS
2.000
n ARE ACTIVE
USE * TO INITIATE CALCULA TIONS. USE H FOR HELP.
Figure 1. Log normal size distribution program data input menu.
OPACITY DATA ENTER PAGE 1
- REAL PART OF INDEX OF REFRACTION
IMA GINARY PART OF INDEX OF REFRACTION
WAVELENGTH OF LIGHT
MASS CONCENTRATION
PARTICLE DENSITY
STACK DIAMETER
1.50
0.0001
0.55 MICRONS
0.010 G/M3
2.4 G/CC
5.00 METERS
tl ARE ACTIVE. USE > TO GO TO NEXT PAGE.
USE * TO INITIATE CALCULATIONS.
USE H FOR HELP.
Figure 2. Histogram size distribution program input menu for entering general data.
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DIAMETER MICRONS CUMULATIVE MASS ( TO GO TO NEXT PAGE, < TO GO TO PREVIOUS PAGE.
Figure 3. Histogram size distribution program input menu for entering size distribution data.
S. J. Cowen is with Atmospheric Research Group. Altadena, CA 91001; the EPA
author L. F. Sparks (also the EPA Project Officer, see below) is with the Air and
Energy Engineering Research Laboratory, Research Triangle Park, NC 27711;
andD. S. Ensoris with Research Triangle Institute, Research Triangle Park, NC
27709.
The complete report, entitled "TRS-80 In-Stack Opacity Computer Program: User
and Programmer Manual," (Order No. PB 86-130 218/AS; Cost: $11.95.
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 Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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