United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-83-073 Sept. 1983
Project Summary
Development Design, and
Operation of a Cascade Impactor
to Collect Aerosol Samples for
Wavelength-Dispersive X-Ray
Fluorescence Analysis
L G. Felix, D. H. Hussey, and J. D. McCain
The goal of this research project was
to design and construct a particle-sizing
device that will collect and size source-
emitted aerosols on 47-mm diameter
substrates for subsequent wavelength-
dispersive x-ray fluorescence analysis.
A five-stage slit impactor was de-
signed to accomplish this goal. The
impactor uses an oscillating drum
beneath each jet to collect the sample
evenly over a 31- x 34-mm area. The
impactor is constructed from 316
stainless steel and will fit through a 4-
in. sampling port. A right-angle pre-
impactor is used at the inlet to reduce
inlet losses and to provide a 15-^m
aerodynamic cut.
Special substrates and substrate
coatings offered good particle retention
at sampling temperatures and provided
low x-ray background.
Calibration studies were conducted
with a prototype unit designed to allow
various slit widths and jet-to-plate
spacings. These studies provided the
design criteria used to dimension the
final impactor.
With this sampling system, readily
collected samples can be analyzed
directly by wavelength-dispersive x-ray
fluorescence analysis for elemental
composition. No sample preparation
will be required beyond mounting the
substrate in a carrier for analysis.
This Project Summary was developed
by EPA's Environmental Sciences
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
information at back),
Introduction
A new cascade impactor was designed
and constructed to obtain size-fractionated
particulate samples in forms suitable for
direct elemental analysis by x-ray fluo-
rescence. The report describes the design
and operating principles of the device and
provides instructions for its use. Poten-
tially, the device can be used to obtain
particle size distributions of chemical
elements in industrial source emissions
and "elemental fingerprints" for source-
receptor studies.
Impactor Design
Paniculate analysis by x-ray fluor-
escence requires the sample to be a thin,
uniform coating on a noninterfering
substrate. Conventional size fraction-
ating samplers are not useful because
samples obtained with them are either in
bulk material from which aliquots must
be removed and redeposited (cyclones)or
in multiple, discrete deposits of varying
thickness (cascade impactors). The new
sampler is a slit-type cascade impactor
similar to the Lundgren impactor. The
design incorporates five collection stages,
an inertial preseparator, and an integral
backup filter holder. Aerodynamically,
the fractionation diameters are 15, 8, 4,
2, 1, and 0.5 fjm respectively, for the pre-
separator and the five collection stages.
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The collection substrates are mounted on
drums that oscillate beneath the jets
many times during sample collection.
This procedure yields samples of highly
uniform surface density over a 31 - x 34-
mm area.
Mylar is used as a base for the
collection substrates. A polymeric coating
such as vynathene, amorphous poly-
propylene, or butyl rubber also is applied
to minimize errors due to particle bounce
and to retain the sample after collection.
The polymeric materials have superior
properties to the greases normally used
in cascade-impactor sampling, especially
relative to elemental background concen-
trations.
The sampler was constructed of 316
stainless steel; a high-torque, digital-
stepping motor mounted on the outboard
end of the sampling probe was used to
drive the drums on which the collection
substrates are mounted. A minimum
sampling port diameter of 4 in. is required
to insert the sampler onto the stack.
Calibration
A one-and-one-half stage, adjustable
slit width prototype of the proposed
design was constructed and tested for
uniformity of particle deposition and
predictability of size-fractionated particle.
The measured fractionation diameters of
the prototype configurations tested were,
within experimental uncertainties, equal
to the values predicted by Marple's im-
pactor theory. Calibrations were not
made on the final sampler.
Field Trials
The sampler was tested in the field with
emissions from four sources at a pulp and
paper plant. There were no significant
operational problems during these trials.
The samples obtained were submitted for
x-ray fluorescence analysis, but results
were not available for inclusion in this
report.
Conclusions and
Recommendations
Satisfactory mechanical performance
of the impactor and associated equipment
(probe, drive system, flow control, etc.)
has been demonstrated. Although wall
losses and predictability of fractionation
diameters should not be troublesome,
some calibration shouJd be carried out
before the device is used for any extensive
or critical field sampling programs. If
more devices are to be constructed, a
simpler (and cheaper) drive system
should be used to provide the drum
motion.
L G. Felix, D. H. Hussey, andJ. D. McCain are with Southern Research Institute,
Birmingham, AL 35255
Kenneth T. Knapp is the EPA Project Officer (see below).
The complete report, entitled "Development, Design, and Operation of a Cascade
Impactor to Collect Aerosol Samples for Wavelength-Dispersive X-Ray
Fluorescence Analysis," (Order No. PB 83-246 157; Cost: $10.00. 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
GOVERNMENT PRINTING OFFICE 1983-659-017/7191
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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