Field and Laboratory Evaluations of a Real-Time PAH Analyzer by vivi07


									United States                                National Exposure
Environmental Protection                     Research Laboratory
Agency                                       Research Triangle Park, NC 27711
Research and Development                     EPA/600/SR-97/034 July 1997

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-   spectrum, without having deleterious
vious evaluation of a real-time analyzer     effects on the performance of the ana-
for polycyclic aromatic hydrocarbons         lyzer.
(PAH) in air. The responses of the in-          This Project Summary was developed
strument, Gossen PAS Models 1000i            by EPA's National Exposure Research
and 1002i, were evaluated for vapor          Laboratory, Research Triangle Park, NC,
versus particle phase PAH, and for           to announce key findings of the re-
variations in the environmental condi-       search project that is fully documented
tions of temperature and humidity. The       in a separate report of the same title
noise and ozone levels produced dur-         (see Project Report ordering informa-
ing operation were measured. In addi-        tion at back).
tion, a cigarette smoke generator was
developed for use in field evaluations       Introduction
of the analyzer. The particle transmis-         The PAH analyzers evaluated in this
sion efficiency was also measured for        study were a Model PAS 1000i Photo-
a range of particle sizes below 1 µm.        electric Aerosol Analyzer, manufactured
    In general, the PAS responded only       by Gossen, GmbH (Erlangen, Germany)
to PAH in the particulate phase. Small       and two of a newer version, Model PAS
responses to vapor-phase PAH in two          1002i, purchased from EcoChem Tech-
experiments were found to be associ-         nologies, Inc. (West Hills, CA). The PAH
ated with adsorption of the test PAH         analyzers are based on the principle of
on particle surfaces. Small and insig-       photoelectric ionization of PAH adsorbed
nificant ozone levels were measured          on the surface of aerosol particles. Their
within a few inches of the instrument.       operation is discussed in detail in the re-
Its noise output was below the NC-35         port on the first phase of this study (Re-
criterion, except in the frequency range     port on Work Assignment 13, Contract
1000 to 3000 Hz, where the noise ap-         68-D0-0007).
proached NC-40. Temperature and hu-             The earlier evaluation showed the PAS
midity did not affect the response of        provides a real-time (< 5 s) response that
the PAS to aerosols that were equili-        correlates with indoor fine particulate-
brated at the test temperature.              phase PAH (< 2.5 µm) and does not re-
    The particle transmission efficiency     spond to two-ring PAH vapors. The re-
through the PAS was determined for a         sults suggested that the PAS had poten-
range of aerosols 0.034 to 0.32 µm. Large    tial for screening and semiquantitative
particle losses below 0.10 µm were iden-     measurement of human exposure to air-
tified. A modified sampling configura-       borne PAH in ambient and indoor air, and
tion was developed, which increased the      for indicating activities that may lead to
particle transmission efficiency to          PAH exposures.
greater than 90% over the entire size
   The following objectives were estab-            The cigarette smoke generator that was       electrofilter and using stainless steel tub-
lished for this follow-on study to (1) deter-   designed and fabricated is capable of pro-      ing, provided transmission efficiency > 90%
mine whether the PAS responds to a num-         viding field verifications of the performance   for all test aerosols, ranging in monodis-
ber of different two- to four-ring PAH va-      of the PAH analyzer. Despite the inherent       perse size from 0.034 to 0.32 µm. Field
pors, (2) measure the noise and ozone           variability in the cigarette combustion pro-    trials in various indoor microenvironments
output of the PAS, (3) develop a cigarette      cess, the smoke generator elicits a rea-        indicated no deleterious effects on overall
smoke generator capable of use in field         sonably characteristic frequency distribu-      analyzer performance as a result of the
evaluations of the PAS, (4) determine the       tion of PAS responses during a cigarette        modified design configuration. Under typi-
effects of temperature and humidity on          test. Parameters that characterize this fre-    cal indoor conditions in both smoking and
the PAS operation, (5) investigate the          quency distribution can then be compared        nonsmoking environments, an improve-
transmission of aerosol particles through       with nominal ranges to verify operation in      ment in the sensitivity of the analyzer was
the PAS and modify it, if necessary, to         the field. Additionally, the PAS response       also observed.
improve this transmission, (6) investigate      was well correlated with the particle num-          The PAS response to non-PAH test
the response of the PAS to aerosols that        ber concentration of the cigarette smoke.       aerosols, normalized to aerosol number
do not contain PAH, and (7) compare the            Elevated or depressed temperature and        concentration, was very small and propor-
PAS measurements with PAH concentra-            humidity operating conditions do not have       tional to particle surface area for sodium
tions obtained by integrated air sampling       a significant impact on the response of         chloride, ammonium sulfate, and phthalic
followed by GC/MS analysis.                     the PAS to a cigarette smoke aerosol            anhydride aerosols generated from drying
                                                equilibrated at the test temperature.           nebulized water solutions of the respec-
Results and Conclusions                            The response of the PAS, operating at        tive compounds. When the phthalic anhy-
   The PAH analyzer did not respond to          typical room conditions, does increase          dride and dioctyl phthalate were nebu-
two- to four-ring PAH vapors, including         slightly, relative to particle number con-      lized from isopropyl alcohol, the PAS re-
naphthalene, 1-methylnaphthalene, chloro-       centration, as the temperature of the           sponse was much smaller and only weakly
naphthalene, phenanthrene, and fluoran-         sampled air increases. Although a mecha-        proportional to particle surface area. The
thene. A small signal, 0.008 pA, was ob-        nism for this insignificant increase is not     results suggest that the weak PAS re-
served for pyrene vapor at 3 ppb, when 50       established, it appears likely that as the      sponse to non-PAH aerosols arises from
to 60 particles/cc were also present in the     aerosol temperature increases, the effi-        impurities in the solvents used to gener-
chamber. This response was most likely          ciency of ionization of the surface PAH is      ate the nebulized droplets.
due to condensation of pyrene on the sur-       enhanced, requiring less energy for the             In eight homes, fine particle PAH con-
faces of the particles.                         photoionization process.                        centrations in indoor air, measured from
   The PAS noise level was generally be-           Aerosol transmission efficiency test         integrated sampling and GC/MS analysis,
low the criterion of NC-35, except at fre-      showed that the PAS, in its original de-        ranged from 27 to 120 ng/m3. These mea-
quencies of 1000, 2000, and 4000 Hz,            sign configuration, had significant particle    sured PAH concentrations were within one-
where the noise level was close to NC-40.       losses in the silicone tubing and in the        fifth to two times the total fine particle
These sound levels are between the noise        electrofilter, particularly at particle sizes   PAH concentrations estimated from the
levels typically encountered in private         < 0.1 µm diameter, where the transmis-          PAS response, using a conversion factor
homes and large offices. The operation of       sion efficiency was < 70%. A modified           of 3000 ng/m3 per pA of electrometer sig-
the PAS did not increase indoor ozone           configuration, consisting of bypassing the      nal.
levels significantly.

     Mukund Ramamurthi and Jane C. Chuang are with Battelle , Columbus OH 43201-
     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

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