United States National Exposure

Environmental Protection Research Laboratory

Agency Research Triangle Park, NC 27711

Research and Development EPA/600/SR-97/034 July 1997

This study is a continuation of a previous evaluation of a real-time analyzer

for polycyclic aromatic hydrocarbons

(PAH) in air. The responses of the instrument, Gossen PAS Models 1000i

and 1002i, were evaluated for vapor

versus particle phase PAH, and for

variations in the environmental conditions of temperature and humidity. The

noise and ozone levels produced during operation were measured. In addition, a cigarette smoke generator was

developed for use in field evaluations

of the analyzer. The particle transmission efficiency was also measured for

a range of particle sizes below 1 μm.

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 associated with adsorption of the test PAH

on particle surfaces. Small and insignificant 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 approached NC-40. Temperature and humidity did not affect the response of

the PAS to aerosols that were equilibrated at the test temperature.

The particle transmission efficiency

through the PAS was determined for a

range of aerosols 0.034 to 0.32 μm. Large

particle losses below 0.10 μm were identified. A modified sampling configuration was developed, which increased the

particle transmission efficiency to

greater than 90% over the entire size

Project Summary

Field and Laboratory

Evaluations of a Real-Time

PAH Analyzer

Mukund Ramamurthi and Jane C. Chuang

spectrum, without having deleterious

effects on the performance of the analyzer.

This Project Summary was developed

by EPA's National Exposure Research

Laboratory, Research Triangle Park, NC,

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

The PAH analyzers evaluated in this

study were a Model PAS 1000i Photoelectric Aerosol Analyzer, manufactured

by Gossen, GmbH (Erlangen, Germany)

and two of a newer version, Model PAS

1002i, purchased from EcoChem Technologies, 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 report on the first phase of this study (Report on Work Assignment 13, Contract

68-D0-0007).

The earlier evaluation showed the PAS

provides a real-time (< 5 s) response that

correlates with indoor fine particulatephase PAH (< 2.5 μm) and does not respond to two-ring PAH vapors. The results suggested that the PAS had potential for screening and semiquantitative

measurement of human exposure to airborne PAH in ambient and indoor air, and

for indicating activities that may lead to

PAH exposures.
2

The following objectives were established for this follow-on study to (1) determine whether the PAS responds to a number of different two- to four-ring PAH vapors, (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 concentrations 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, chloronaphthalene, phenanthrene, and fluoranthene. A small signal, 0.008 pA, was observed 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 surfaces of the particles.

The PAS noise level was generally below the criterion of NC-35, except at frequencies 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 providing field verifications of the performance

of the PAH analyzer. Despite the inherent

variability in the cigarette combustion process, the smoke generator elicits a reasonably characteristic frequency distribution of PAS responses during a cigarette

test. Parameters that characterize this frequency distribution can then be compared

with nominal ranges to verify operation in

the field. Additionally, the PAS response

was well correlated with the particle number 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 concentration, as the temperature of the

sampled air increases. Although a mechanism for this insignificant increase is not

established, it appears likely that as the

aerosol temperature increases, the efficiency 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 design configuration, had significant particle

losses in the silicone tubing and in the

electrofilter, particularly at particle sizes

< 0.1 μm diameter, where the transmission efficiency was < 70%. A modified

configuration, consisting of bypassing the

electrofilter and using stainless steel tubing, provided transmission efficiency > 90%

for all test aerosols, ranging in monodisperse size from 0.034 to 0.32 μm. Field

trials in various indoor microenvironments

indicated no deleterious effects on overall

analyzer performance as a result of the

modified design configuration. Under typical indoor conditions in both smoking and

nonsmoking environments, an improvement 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 proportional to particle surface area for sodium

chloride, ammonium sulfate, and phthalic

anhydride aerosols generated from drying

nebulized water solutions of the respective compounds. When the phthalic anhydride and dioctyl phthalate were nebulized from isopropyl alcohol, the PAS response was much smaller and only weakly

proportional to particle surface area. The

results suggest that the weak PAS response to non-PAH aerosols arises from

impurities in the solvents used to generate the nebulized droplets.

In eight homes, fine particle PAH concentrations in indoor air, measured from

integrated sampling and GC/MS analysis,

ranged from 27 to 120 ng/m3

. These measured PAH concentrations were within onefifth 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 signal.
3

EPA/600/SR-97/034

United States

Environmental Protection Agency

Center for Environmental Research Information

Cincinnati, OH 45268

Official Business

Penalty for Private Use $300

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

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