United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-83-105 Jan. 1984
Project  Summary
Intercomparison  of Periodic
Fine  Particle  Sulfur and
Sulfate  Concentration  Results

David C. Camp, Richard J. Paur, and Robert K. Stevens
  A one-week study was conducted in
August 1979 to evaluate the compar-
ative ability of representative aerosol
sampling systems to monitor fine partic-
ulate sulfur and sulfate concentrations
periodically in situ. Participants in the
study operated their samplers simulta-
neously in the same location for the
duration of the study. Samplers tested
included five modified flame photomet-
ric detection  instruments and two di-
chotomous samplers, including one
sampler designed to yield near-real-time
sulfur concentrations from on-line, wave-
length dispersive x-ray fluorescence
analysis of fine particles collected on
Teflon substrate.  All  but one of the
samplers were operated from a common
duct located within the same laboratory;
the other was operated on the roof of
the building.
  Normalized results of all sulfur con-
centration levels measured for five of
the six samplers were 1.0 ± 0.05. The
sixth set gave a result of 0.60 ±0.14.
After revised results were resubmitted
for the sixth set, normalized results for
the six sets  of hourly sulfur results
agreed to within ± 8% of their composite-
mean values, with standard deviations
varying from 9 to 22%. One participat-
ing group operated three similar sam-
plers, each  calibrated  by a  different
method, that gave normalized results of
1.06 ± 0.12, 0.93 ± 0.22, and 1.54±
0.25; these results point out the need
for a standard calibration procedure.
  This Project Summary was developed
by EPA's Environmental Sciences Re-
search 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
  In August 1979, a one-week study was
conducted at Washington University, St.
Louis, to compare a family of air pollution
monitoring instruments that are capable
of measuring in near-real-time atmos-
pheric concentrations of aerosol sulfur.
The main objective of this study was to
compare different procedures to measure
aerosol sulfur that use flame photometric
detectors (FPD's) and an automated semi-
real-time x-ray fluorescence (XRF) aero-
sol sample-analyzer. The instruments
that use the FPD's have been used in a
variety of air pollution studies, but  be-
cause each instrument uses  a different
method of sample conditioning prior to
the sulfur  measurement, bias  in  the
measurements may exist. This study
compared measurements of different
automated aerosol sulfur monitors on
both simulated and real ambient  air
samples over  a  period of  7 days to
establish the range of  differences  be-
tween instruments and the basis  for
variations in response characteristics.


Procedure
  Analyzers brought to Washington Uni-
versity by the seven participating groups
included five modified FPD instruments
and two  dichotomous samplers. One
dichotomous sampler was designed to
report near-real-time sulfur concentra-
tions from an on-line,  wavelength  dis-
persive, XRF analysis of the fine particles
collected  on a filter substrate. All sam-

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  piers were operated simultaneously, and
  all but one operated from a common duct
  leading to a common laboratory. The inlet
  to the common duct contained an impac-
  tor  plate  particle-sizing device that  re-
  jected all particles greater than 3.0 (jm in
  aerodynamic diameter. The sampler  not
  using the common duct was operated on
  the roof above the laboratory.

  Results
    Concentration of the sulfur measured
  during  the  study by  the  participants
  consisted of eight  sets of hourly fine
  pa rticulate sulfur values. Only six of eight
  sets were intercompared.  One of  the
  participating groups reported three sets
  of sulfur data based on three different
  calibrations methods. Ambient sulfur
  concentrations measured during the study
  ranged  from just below 1  /ug/m3 to 9
  fjg/m3.  Above  6 //g/m3 the five FPD
  instruments  and  the  automated XRF
  sulfur analyzer  intercompared agreed to
  within ± 25% of their combined compos-
  ite-mean  concentrations. Five of the six
  agreed to within ± 5% of the composite-
  mean values. All of the automated FPD
  instruments were able to  resolve and
  measure the relatively sharp sulfur con-
  centration peaks that occurred daily. The
  source and nature of these short, some-
  times multi-peaked, excursions were not
  investigated.
    Three sets of 6-h sulfate concentra-
  tions were reported and intercompared.
  Their concentrations varied from about
  2 fjg/m3 to 20 jug/m3. At relatively high
  sulfate concentrations (> 14 /jg/m3) all
  three samplers agreed to within ± 10% of
  their composite 6-h means. Regression
  analysis of 6-h composite-mean sulfate
  concentrations, derived from ion chromat-
  ographic  analysis  of fine particles col-
  lected with a dichotomous  sampler, vs.
  equivalent 6-h averages for the hourly
       sulfur  composite-mean  values gave a
       sulfate-to-sulfur ratio of 2.2 for the St.
       Louis study vs. 3.0 observed in two earlier
       studies. This ratio remained at 2.2 for
       both clean and stagnant air and during
       the transient  sulfur excursions. Thus,
       either  all  of the sulfur did not occur in
       sulfate form or the sulfate could not be
       extracted completely from the filter-types
       used by all three independent groups.
         Three sampling systems  operated by
       the host institution provided results based
       on three different  calibration methods.
       Their results  based on  an (NH4)2S04
       calibration were closest to the composite
       mean average (1.06 ± 0.12—an average
       of all hourly results normalized to the
       hourly composite-mean values); whereas
       the sulfur monitors  that used S02 for
       calibration differed substantially from the
       composite mean (1.54 ± 0.25). If either of
       the two worst-result sets of the eight sets
       submitted had been the only set of sulfur
concentrations  measured, the report*
hourly sulfur concentrations would somi
times have been as much as a factor of
higher or lower  than the consensi
composite-mean concentrations from tr
six sets intercompared.

Conclusions and
Recommendations
  Measurements obtained from FPDsy;
terns modified to measure aerosol sulfi
and calibrated by appropriate procedure
agreed within ± 8% with the composii
mean. Data from FPD's calibrated usir
(NH4)2SO4 had less scatter and were i
closer agreement to the composite mea
average than data from FPD analyzei
calibrated using SO2. A standard ASTN
type aerosol calibration procedure neec
to be developed  and documented f<
routine calibration of instruments usedl
measure in near-real-time ambient cor
centrations of aerosol sulfur.
          David C. Camp is a Consultant at 258 Paraiso Drive, Danville, CA 94526; the EPA
            authors, Richard J. Paur and Robert K. Stevens (also the EPA Project Officer,
            see below) are with Environmental Sciences Research Laboratory, Research
            Triangle Park, NC 27711.
          The complete  report, entitled "Intercomparison of Periodic Fine Particle Sulfur
            and Sulfate  Concentration Results," (Order No. PB84-119 940; 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
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