United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
vvEPA
Research and Development
EPA-600/S2-81-104 Aug. 1981
Project Summary
Data Reduction
Techniques for Aerosol Size
Distribution Measuring
Instruments
Abde Kapadia
Data reduction methods for the
electrical aerosol analyzer (EAA) and
the diffusion battery+condensation
nuclei counter (DB+CNC) are pre-
sented. Both the EAA and DB+CNC
can be modeled by the Fredholm
Integral Equation of the First Kind.
Thus, the data reduction methods for
both the instruments are similar.
For the EAA, four data reduction
methods are presented. First, an
optimized EAA channel method is pre-
sented, in which the channel bound-
aries are chosen such that the
response matrix can be approximated
by an identity matrix. This method is
applicable only for specialized applica-
tions of the EAA. The next two
methods are based on two non-linear
algorithms (NLIA). When using the
NLIA's, no assumption regarding the
form of the aerosol size distribution
must be made. Finally, a curve-fitting
procedure based on a simplex minimi-
zation algorithm is investigated. This
method gives the parameters of
unimodal or bimodal log-normal
distribution which best fits the data.
The data reduction methods for
both the instruments were analyzed
with simulated and experimental data.
For the EAA, the comparison between
the different data reduction methods
for the number distribution is excel-
lent. However, for the surface and
volume distributions, the agreement
was only satisfactory in the size range
of 0.316 to 1.0 fjm. The agreement
between the number distribution re-
trieved by the three data reduction
methods for the DB+CNC was found
to be good.
This Project Summary was develop-
ed by EPA's Environmental Sciences
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
ings 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 recent years, considerable interest
and concern has been expressed
regarding submicron aerosols. Automo-
bile exhaust and photochemical con-
version of gaseous pollutants in the
atmosphere usually produce aerosols in
the submicron range. These aerosols
affect human health, visibility, and
climate As a first step in understanding
the various phenomena associated with
submicron aerosols, it is essential to
know their size distribution and concen-
tration
Various methods and instruments are
available for measuring the concentra-
tion and size distribution of aerosols.
The diffusion battery (DB) and the
condensation nuclei counter (CDC) and
US GOVERNMENT PRINTING OFFICE. 1961 -757-012/7263
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the electrical aerosol analyzer (EAA)
have been used for measuring the
aerosol size distribution for some time
now, but no systematic comparison of
their measurement •capabilities has
been carried out to date, due to lack of a
generalized data reduction procedure
which could be applied to such instru-
ments
The objectives of this thesis are to
make a systematic study of the several
procedures which can be used for data
reduction for aerosol size measurement
instruments that can be modeled math-
ematically and to compare the various
data reduction techniques using simu-
lation and experimental data for the
diffusion battery and the EAA. To
achieve the objectives, data reduction
techniques were developed both for the
diffusion battery system and the EAA,
and the utility of these data reduction
methods was determined
During this investigation, a non-
linear iterative algorithm was develop-
ed, which was faster than previous
methods Another method, developed
for solving the set of linear equations,
consists of fitting either a unimodal or a
bimodal log-normal aerosol size distri-
bution to the measured data using a
simplex minimization method. This
method has also been adapted to solve
the DB and EAA data reduction problem
For the EAA, an optimized channel
method was also developed, but it can
be used only for specialized applications
of the EAA, specifically only when the
particle diameter is between 0.0075/jm
to 0 1 9 fjm for the aerosol.
These data reduction procedures
were tested in two simulation studies.
For the first, the data reduction
procedures for the EAA were tested
with several simulated unimodal and
log-normal distributions For the
second, normal random noise (mean 0,
and a standard deviation of 5%, 10%,
and 1 5%) to simulate the measurement
error and the instability of the aerosol
being measured was added to the
expected response of the instruments
for the simulated aerosol This modified
response was then used as input to the
EAA and DB data reduction procedures.
The retrieved distributions for the
second set were compared with results
obtained from the first set of simula-
tions and were found to be within +1 0%
Finally, submicron aerosols of di-octyl
phthalate (OOP) and NaCI, generated
using a Collison atomizer, were simul-
taneously measured by the EAA and
DB+CNC The data thus obtained were
analyzed using the data reduction
methods developed during the course of
this project For the EAA, the agreement
between the various data reduction
techniques for the number distribution
was good For the surface and volume
distributions, however, a non-linear
iteration logarithm and the monodis-
perse sensitivity method of Liu and Pui
consistently overestimated the surface
and volume concentration in the last
two channels The simplex minimiza-
tion curve-fitting procedure, however,
gave satisfactory results for all of the
three weightings
Abde Kapadia is with the Mechanical Engineering Department, University of
Minnesota, Minneapolis, MN
Tom Dzubay is the EPA Project Officer fsee below)
The complete report, entitled "Data Reduction Techniques for Aerosol Size
Distribution Measuring Instruments," /Order No. PB 81-214 298, Cost
$21 50, 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
Environmental Sciences Research Laboratory
U S Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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