United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-81-006 Mar. 1981
Project Summary
Aerosol Analysis for the
Regional Air Pollution Study
Final Report
J.M. Jaklevic, R.C. Gatti, F.S. Goulding, B.W. Loo, and A.C. Thompson
From May 1975 through April 1977
a total of 35,000 individual ambient
aerosol samples were collected at 10
selected sampling sites in the vicinity
of St. Louis, Missouri, as part of the
Regional Air Pollution Study (RAPS).
The samples consisted of aerosol
particles in the coarse and fine
fractions deposited on membrane
filters using automatic dichotomous
air samplers. The samples were
returned to Lawrence Berkeley
Laboratory (LBL) for analysis
following collection at the field sites.
Particulate mass was determined by a
beta-ray attenuation method, and the
concentrations for 27 elements were
determined using energy dispersive X-
ray fluorescence analysis.
This Project Summary was devel-
oped by EPA's Environmental
Sciences Research Laboratory. Re-
search Triangle Park. NC 27711, 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
An automatic dichotomous sampler
was equipped with a two-stage virtual
impactor which separates particles into
two size fractions: above and below 2.4
ftm aerodynamic diameter. The upper
particle size cutoff for the coarse
particle fraction was determined by the
inlet configuration and is estimated to
be 20 /um. The coarse and fine particle
size fractions were collected separately
on 1.2 //m pore size cellulose ester
membrane filters. The normal sampling
schedule consisted of twelve-hour
sample periods at eight of the stations
and six-hour sample periods at two of
the stations.
The procedures followed in the
sampling program were carefully
controlled to ensure valid data.
Individually numbered clean filters
were loaded into separately numbered
36-sample cartridges at LBL. The
sample identification numbers and the
corresponding tare weights were
recorded on magnetic tape at the time of
the initial beta-gauge measurements.
The samples were then shipped to St.
Louis for exposure in the samplers. The
location and times of sampling were
recorded both on the cartridge labels
and in a separate sampling log. This log
also contained checklists for site visits
and notes of any irregularities in the
sample routine. The exposed filters
were returned to LBL, where final
masses were determined, and the data
pertinent to the sampling conditions
were entered into the computer system
for subsequent data processing.
Mass Measurements
The total mass of particlescollected in
each size fraction was measured using
an automated beta-ray attenuation
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method. The method relies on the
exponential dependence of transmitted
beta-ray intensity upon mass, when a
sample is placed between a 147Pm beta-
ray source and a suitable detector.
Although the measurement is
straightforward, the use of beta-ray
attenuation in the present study is
complicated by the high precision
required. A typical measurement
consists of determining the mass
accumulated on a 4 mg/cm2 filter to an
accuracy of ± 10/ug/cm2. This requires
that each mass measurement be
accurate to 0.1%. The elapsed time
between the measurements of the tare
weight and the exposed weight might be
several months. Frequent calibrations
were made using a set of carefully
weighed polycarbonate films as
standards.
X-Ray Fluorescence
Measurements
The elemental composition of the
particulate deposits was measured,
using an energy dispersive X-ray
spectrometer. The particular X-ray
spectrometer employed was an LBL-
constructed pulsed X-ray excitation
system, computer controlled for sample
sequencing and analysis. The X-ray
excitation was provided by a series of
three secondary fluorescent targets,
which were irradiated with the output of
a pulsed X-ray tube. The precision and
accuracy of the method depended upon
many components in the system, each
of which was carefully controlled.
Several thin films containing copper
were used as the primary calibration
standard. Each film consisted of a layer
of copper deposited on a mylar substrate
and were obtained from Micromatter,
Inc. These standards were accurate to
better than 2%.
The relative excitation efficiencies for
other elements were obtained using
thin film standards prepared by
depositing an aerosol generated from a
carefully prepared solution in which the
relative concentrations of elements
were known. Where possible, the ratio
of elements was established by the
stoichiometry of the chemical
compound. In other cases, solutions
contained individual elements mixed in
known ratios. The accuracies of the
ratios obtained by this method are
estimated to be less than 1%.
Because of the importance of sulfur in
this program, exceptional care was
taken in its calibration. Thin film
standards were prepared by collecting
an aerosol deposit of 0.3 [im diameter
particles in order to eliminate
absorption effects. Attenuation
corrections were made for coarse
particles based on the assumptions of
uniform spheres of composition
approximately that of typical aerosol
particles.
The reproducibility of the aerosol
samples was checked by collecting side-
by-side samples at LBL, using three
automatic dichotomous samplers. The
root mean square deviation for the
coarse particle fraction was approxi-
mately 5%, whereas for the fine parti-
cles, it was about 1.5%. The precision of
the XRF analysis was checked by the
repeated analysis of the same filters
over an extended period of time. The
reproducibility of the major elements
indicates a stability of approximately
+ 1% over a three-month period.
The analytical results were written on
magnetic tape that was sent to the
Environmental Sciences Research
Laboratory, Research Triangle Park, NC
27711, from which copies may be
obtained. Arrangements are being
made to have the tapes available
through the National Technical
Information Service, Springfield, VA.
J. M. Jaklevic, R. C. Gatti, S. F. Goulding, B. W. Loo, and A. C. Thompson are with
the Lawrence Berkeley Laboratory, Berkeley, CA 94720.
Thomas G. Dzubay is the EPA Project Officer (see below).
The complete report, entitled "Aerosol Analysis for the Regional Air Pollution
Study," (Order No. PB 81-157 141: Cost: $8.00, 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
& US GOVERNMENT PRINTING OFFICE. 1961-757-012/7029
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
PS 0000329
U S EMVIR PROTECTION
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