United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Laboratory
Research Triangle Park NC 27711
o'Y-
-
Research and Development
EPA/600/S3-89/020 Aug. 1989
4MEPA Project Summary
A Review of Current
Methods for Measuring
Particulate Matter Including
Condensablesfrom Stationary
Sources
Joseph D. McCain and Ashley D. Williamson
The PM-io ambient air participate
concentration standard has created a
need for updating measurement
methods for PM-io emissions
(nominally 10 nm aerodynamic dia-
meter and smaller) from stationary
sources. Condensable emissions
can be a significant portion of stack
emissions. Further, since these sub-
stances primarily condense to par-
ticles less than 10 pm in diameter,
they form a greater percentage of the
PM-to fraction than of the total par-
ticulate matter emissions. Therefore,
the need arises for developing a
source test method which includes
the condensable component of e-
missions. A review of possible tech-
niques was conducted to determine
current methodology and to make
recommendations for research. Re-
search is recommended on two ap-
proaches. One is a dilution method
which simulates plume formation by
mixing stack gases with conditioned
ambient air; the other is an adapta-
tion of utilizing the Method 5 back-
half catch.
This Project Summary was
developed by EPA's Atmospheric
Research and Exposure Assessment
Laboratory, Research Triangle 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
Stationary sources contribute to the
ambient particulate burden through three
distinct mechanisms. Two are normally
considered together as the formation of
"primary" particulate emissions from
sources, and the third is the formation of
"secondary" aerosols, such as sulfates
formed from SC>2 and organic smogs
formed from photochemical processes.
Primary emissions are composed of (1)
materials that are in particulate form
(solid or liquid) in the gas stream before
and after discharge to the atmosphere
and (2) materials that are in the vapor
phase before discharge but that rapidly
condense to the particulate form when
they are discharged into and cooled by
mixing with ambient air.
Because condensation takes place
preferentially on small particles,
condensable matter is concentrated pri-
marily in the PM-io fraction (particulate
matter less than 10 pm in diameter) of
source emissions. Since the basis of the
standard for ambient air particulate con-
centrations has been changed from total
particulate concentration to PM-|0 con-
centration, quantitative data on conden-
sable emissions rates will be needed to
set up State Implementation Plans for
compliance with ambient air PM10 stan-
dards. However, current methods for
particulate emissions measurement usu-
ally exclude the condensables fraction.
Efforts are now being made to develop
a reference method to quantify the
condensables fraction separately from
measurements of the particulate portion
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of primary emissions from stationary
sources. In addition, a working definition
for stationary sources condensable e-
missions must be established to develop
a reference method. A review of pos-
sible techniques was conducted from
which recommendations are made for
the optimum approach for development
of routine field sampling procedures for
measuring condensable emissions.
Approaches for Measuring
Condensable Matter
To explore the possible options for
measuring condensable matter, a
working definition of condensable matter
is needed. In particular, the quantity of
condensable matter that is present can
vary because equilibrium vapor pres-
sures and condensation and evaporation
rates vary significantly with changes in
temperature and other conditions inc-
luding concentrations. Consequently, the
partitioning between the vapor and
particulate phases of condensable matter
will exhibit seasonal variations. From a
regulatory point of view, however, the
reference method(s) used for measuring
condensable matter should provide re-
sults that are not dependent on local
temperatures. Thus some standard tem-
perature for sample collection is needed,
such as 0, 5, 20, or 25°C. Whatever
temperature is designated to be
standard, the operational definition of
condensable emissions should be that
material collected by the selected refer-
ence method(s). This type of definition
is now used for particulate matter collect-
ed by Method 5.
Adaptations of Method 5
In considering the back-half catch as
described in Method 5 for further
development as a vehicle for collecting
condensable matter, certain problem
areas must be addressed. A protocol
must be devised for carrying out the
evaporative process to remove the large
volumes of water from the impmger
solutions while reducing to acceptable
levels any losses of the condensable
materials that are to be measured.
Because impingers used in conjunction
with Method 5 result in vigorous contact
between sample gases and impmger
solutions, the potential for reactions with
gases that could cause positive
measurement biases must be eliminated
or minimized. Also, impingers may
enhance uptake of gases when sampling
for condensable materials with Method 5.
Research should be performed to
determine if these effects occur at a
significant level and to eliminate or
minimize them if necessary Use of a
coil-type condenser may reduce these
effects. A filter downstream of the
impmger/condenser could be used, if
necessary, to ensure that no aerosolized
portion of the condensate escapes with
the spent sample gas.
Dilution Method
In principle, no practical method can
be envisioned that would precisely
duplicate the mixing process of flue gas
with ambient air for all conditions that
actually occur However, methods de-
signed to reproduce the important
features of the mixing process for some
typical conditions have been devised. All
involve the dilution of a sample gas
stream that has been maintained at or
near stack conditions with ambient air
that has been conditioned to varying
extents. In some cases, the dilution air is
simply filtered to remove existing
particles. In others, its temperature and
humidity are controlled, and in some
cases, scrubbing of vapor phase
components from the dilution air is done.
Some particulate matter losses occur
during transport of stack samples
through sampling probes Because the
sample must be extracted and trans-
ported through a sampling probe to a
location outside the stack for a dilution
sampling system, the initial size
distribution of the particles in the flue gas
cannot be duplicated precisely. How-
ever, in systems designed to reproduce
the important features of mixing the
plume with ambient air, these losses are
low enough for sufficient quantities of
particles in the critical size range (a few
hundredths of a micrometer to a few
micrometers) to be transported to allow
the use of a method involving dilution of
an extracted stack gas sample
Research Needs
To help ensure that the most
appropriate and acceptable method was
recommended, a number of people in
regulatory agencies at the state and
federal level, experts in source
measurement and characterization,
experts in the field of pollutant transport
and fate, and experts in the field of
ambient sampling and analysis were
contacted for advice and ideas. The
approach preferred by a majority was
that of air dilution cooling rather than
condensation in impingers or conden-
sers. However, from the standpoint of
ease of sampling it was generally agreed
that the Method 5 back-half approach
would be preferable. Research would be
necessary to resolve the potential
difficulties posed by the large volumes of
condensed water and possible reactions
of dissolved gases in aqueous solution to
form artifacts that could erroneously be
counted as condensable matter.
Research also would be necessary to
develop hardware and establish
operational parameters for the dilution
tram approach. Hence, it is recom-
mended that both the air dilution and the
impmger catch approaches be further
developed as EPA methods for measur-
ing condensable source emissions. This
would not set any precedents in emission
sampling methodology because the use
of air dilution techniques is already
standard in quantifying emissions from
mobile sources and from wood-burning
stoves, and Method 5 back-half ap-
proaches are used in some states.
Working Definition of
Condensables
Because the split of any condensable
component of emissions from a source
between the vapor and condensed
phases depends on temperature (and for
some compounds, the amount of dilution
that has taken place and background
concentrations of the material), it is rec-
ommended that condensable emissions
be defined as the material measured by
the sampling tram selected by EPA for
collecting condensable matter. Primary
emissions that include condensable mat-
ter would be defined by the catch of the
sampling train, inclusive of the nozzle
through the filter.
Suggested Dilution Sampling
Method
The use of low mixing rates to
preserve, insofar as possible, the detailed
size distribution characteristics that would
develop in the actual plume was not con-
sidered to be an important factor by most
of the experts who provided advice. By
foregoing any attempt to preserve the
detailed particle size distribution of the
final aerosol, rapid mixing of the in-
coming sample stream and the dilution
air can be used. This permits the design
of a compact diluter and keeps the
weight and size of the device at a
minimum.
Conditioning recommended for the
dilution air includes filtration to remove
background particulate matter and drying
to a dewpoint of 35°F (1 5°C), with a final
temperature of 68°F (20°C). The low
dewpoint and moderately high dilution
ratio should prevent problems of moisture'
condensation for most flue
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3ases that might be encountered.
Because the sample flow is only a
small part of the total flow, measurement
of the sample flow at the exhaust end of
the system, as in Method 5, is not
possible in the recommended setup.
Instead, a flow-metering element may
be installed upstream of the sample inlet
to the diluter. A venturi-type flow meter
is recommended, but other types might
be used
Sampling Protocol
The suggested sampling protocol for a
measurement of total emissions including
condensable matter parallels that of
Method 5 in most respects. A nozzle of
appropriate size for the design sampling
rate of the system and the gas velocities
in the stack would be utilized. A
standard Method 5-type traverse pat-
tern would be used in sampling, and the
sampling rate would be set according to
the venturi meter readings and adjusted
as needed to maintain isokmetic sam-
pling conditions. This protocol does not
maintain a fixed dilution ratio, but the
variability induced will not pose a
problem. A minimum acceptable dilution
factor should be specified (which would
in turn set a maximum sampling rate);
the nozzle size to be used for a traverse
would then be selected to ensure that the
minimum dilution specification is not
violated.
The dilution train will not provide a
direct measure of the split between
condensable matter and preexisting
particulate material in the flue gas unless
use of a filter in the tram can be devel-
oped. However, by running a parallel
Method 17 sample, the split could be
found by difference
Conclusions and Recom-
mendations
The dilution method appears to be one
of two suitable approaches for research
and development for measuring total
primary emissions including condensable
matter from stationary sources. This
approach forms condensed particulate
matter by the same physical mechanism
that occurs in actual plumes. Construc-
tion of a system with traversing capability
that is suitable for field use appears
feasible, consequently, this approach is
recommended for development. The
other suitable method is the im-
pmger/condenser approach. This ap-
proach requires the least investment in
terms of methods development, operator
training, and capital equipment costs
(because existing equipment may be
adequate). Research and coincidental
testing should be designed to reveal the
relative merits of the dilution and im-
pmger/condenser approaches
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Joseph D. McCain and Ashley D. Williamson are with the Southern Research
Institute, Birmingham, AL 35255-5305.
Thomas E. Ward is the EPA Project Officer (see below).
The complete report, entitled "A Review of Current Methods for Measuring
Particulate Matter Including Condensables from Stationary Sources," (Order No.
PB 89-169 9731 AS; Cost: $13.95, 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:
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S3-89/020
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