United States
Environmental Protection
Agency
National Exposure
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-97/034 July 1997
&EPA Project Summary
Field and Laboratory
Evaluations of a Real-Time
PAH Analyzer
Mukund Ramamurthi and Jane C. Chuang
This study is a continuation of a pre-
vious evaluation of a real-time analyzer
for polycyclic aromatic hydrocarbons
(PAH) in air. The responses of the in-
strument, Gossen PAS Models 10001
and 10021, were evaluated for vapor
versus particle phase PAH, and for
variations in the environmental condi-
tions of temperature and humidity. The
noise and ozone levels produced dur-
ing operation were measured. In addi-
tion, a cigarette smoke generator was
developed for use in field evaluations
of the analyzer. The particle transmis-
sion efficiency was also measured for
a range of particle sizes below 1 |am.
In general, the PAS responded only
to PAH in the particulate phase. Small
responses to vapor-phase PAH in two
experiments were found to be associ-
ated with adsorption of the test PAH
on particle surfaces. Small and insig-
nificant ozone levels were measured
within a few inches of the instrument.
Its noise output was below the NC-35
criterion, except in the frequency range
1000 to 3000 Hz, where the noise ap-
proached NC-40. Temperature and hu-
midity did not affect the response of
the PAS to aerosols that were equili-
brated at the test temperature.
The particle transmission efficiency
through the PAS was determined for a
range of aerosols 0.034 to 0.32 |am. Large
particle losses below 0.10 um were iden-
tified. A modified sampling configura-
tion was developed, which increased the
particle transmission efficiency to
greater than 90% over the entire size
spectrum, without having deleterious
effects on the performance of the ana-
lyzer.
This Project Summary was developed
by EPA's National Exposure Research
Laboratory, Research Triangle Park, NC,
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
The PAH analyzers evaluated in this
study were a Model PAS 10001 Photo-
electric Aerosol Analyzer, manufactured
by Gossen, GmbH (Erlangen, Germany)
and two of a newer version, Model PAS
10021, purchased from EcoChem Tech-
nologies, Inc. (West Hills, CA). The PAH
analyzers are based on the principle of
photoelectric ionization of PAH adsorbed
on the surface of aerosol particles. Their
operation is discussed in detail in the re-
port on the first phase of this study (Re-
port on Work Assignment 13, Contract
68-DO-0007).
The earlier evaluation showed the PAS
provides a real-time (< 5 s) response that
correlates with indoor fine particulate-
phase PAH (< 2.5 u.m) and does not re-
spond to two-ring PAH vapors. The re-
sults suggested that the PAS had poten-
tial for screening and semiquantitative
measurement of human exposure to air-
borne PAH in ambient and indoor air, and
for indicating activities that may lead to
PAH exposures.
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The following objectives were estab-
lished for this follow-on study to (1) deter-
mine whether the PAS responds to a num-
ber of different two- to four-ring PAH va-
pors, (2) measure the noise and ozone
output of the PAS, (3) develop a cigarette
smoke generator capable of use in field
evaluations of the PAS, (4) determine the
effects of temperature and humidity on
the PAS operation, (5) investigate the
transmission of aerosol particles through
the PAS and modify it, if necessary, to
improve this transmission, (6) investigate
the response of the PAS to aerosols that
do not contain PAH, and (7) compare the
PAS measurements with PAH concentra-
tions obtained by integrated air sampling
followed by GC/MS analysis.
Results and Conclusions
The PAH analyzer did not respond to
two- to four-ring PAH vapors, including
naphthalene, 1-methylnaphthalene, chloro-
naphthalene, phenanthrene, and fluoran-
thene. A small signal, 0.008 pA, was ob-
served for pyrene vapor at 3 ppb, when 50
to 60 particles/cc were also present in the
chamber. This response was most likely
due to condensation of pyrene on the sur-
faces of the particles.
The PAS noise level was generally be-
low the criterion of NC-35, except at fre-
quencies of 1000, 2000, and 4000 Hz,
where the noise level was close to NC-40.
These sound levels are between the noise
levels typically encountered in private
homes and large offices. The operation of
the PAS did not increase indoor ozone
levels significantly.
The cigarette smoke generator that was
designed and fabricated is capable of pro-
viding field verifications of the performance
of the PAH analyzer. Despite the inherent
variability in the cigarette combustion pro-
cess, the smoke generator elicits a rea-
sonably characteristic frequency distribu-
tion of PAS responses during a cigarette
test. Parameters that characterize this fre-
quency distribution can then be compared
with nominal ranges to verify operation in
the field. Additionally, the PAS response
was well correlated with the particle num-
ber concentration of the cigarette smoke.
Elevated or depressed temperature and
humidity operating conditions do not have
a significant impact on the response of
the PAS to a cigarette smoke aerosol
equilibrated at the test temperature.
The response of the PAS, operating at
typical room conditions, does increase
slightly, relative to particle number con-
centration, as the temperature of the
sampled air increases. Although a mecha-
nism for this insignificant increase is not
established, it appears likely that as the
aerosol temperature increases, the effi-
ciency of ionization of the surface PAH is
enhanced, requiring less energy for the
photoionization process.
Aerosol transmission efficiency test
showed that the PAS, in its original de-
sign configuration, had significant particle
losses in the silicone tubing and in the
electrofilter, particularly at particle sizes
< 0.1 urn diameter, where the transmis-
sion efficiency was < 70%. A modified
configuration, consisting of bypassing the
electrofilter and using stainless steel tub-
ing, provided transmission efficiency > 90%
for all test aerosols, ranging in monodis-
perse size from 0.034 to 0.32 |im. Field
trials in various indoor microenvironments
indicated no deleterious effects on overall
analyzer performance as a result of the
modified design configuration. Under typi-
cal indoor conditions in both smoking and
nonsmoking environments, an improve-
ment in the sensitivity of the analyzer was
also observed.
The PAS response to non-PAH test
aerosols, normalized to aerosol number
concentration, was very small and propor-
tional to particle surface area for sodium
chloride, ammonium sulfate, and phthalic
anhydride aerosols generated from drying
nebulized water solutions of the respec-
tive compounds. When the phthalic anhy-
dride and dioctyl phthalate were nebu-
lized from isopropyl alcohol, the PAS re-
sponse was much smaller and only weakly
proportional to particle surface area. The
results suggest that the weak PAS re-
sponse to non-PAH aerosols arises from
impurities in the solvents used to gener-
ate the nebulized droplets.
In eight homes, fine particle PAH con-
centrations in indoor air, measured from
integrated sampling and GC/MS analysis,
ranged from 27 to 120 ng/m3 These mea-
sured PAH concentrations were within one-
fifth to two times the total fine particle
PAH concentrations estimated from the
PAS response, using a conversion factor
of 3000 ng/m3 per pA of electrometer sig-
nal.
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Mukund Ramamurthi and Jane C. Chuang are with Battelle, Columbus OH 43201-
2693.
Nancy K. Wilson is the EPA Project Officer (see below).
The complete report, entitled "Field and Laboratory Evaluations of a Real-Time
PAH Analyzer," (Order No. PB97-176 838; Cost: $28.00, 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:
National Exposure 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
Official Business
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