United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park NC 2771 1
Research and Development
EPA/600/S3-89/029 Sept. 1989
&ERA Project Summary
Annular Denuder Sampler for
Phase-Distributed Semivolatile
Organic Chemicals
R. W. Coutant, P. J. Callahan, and J. C. Chuang
The objectives of this study were
(1) to design and construct a high-ef-
ficiency, high-volume denuder sam-
pler to separately collect and main-
tain the integrities of the vapor and
particle-associated fractions of or-
ganic chemicals that may be phase
distributed in the atmosphere; and (2)
to use this apparatus in a series of
field measurements to determine the
phase distribution of selected poly-
nuclear aromatic hydrocarbons.
The design approach involved con-
sideration of diffusive mass transport
and the physical limitations of the
standard General Metal Works PS-1
high-volume sampler. The goal was
to achieve a compact denuder, with a
removal efficiency for volatile PAH of
at least 90 percent at flow rates of up
to 200 L/min, which could readily be
coupled to the PS-1 sampler. The
result is a 20.3 cm x 8.25 cm com-
pound annular denuder consisting of
a solid aluminum core plus 12 con-
centric cylindrical aluminum shells,
with annuli thicknesses of 1.6 mm.
The shells are coated with approx-
imately 30|im-thick layers of silicone
grease that serves as the vapor
phase collector. Laboratory tests of
this denuder show no detectable
(<10 percent) removal of ambient
particulate matter larger than 0.1 iim
mean diameter at flow rates of 100-
200 L/min. The vapor collection effi-
ciency, as measured with naph-
thalene, is better than 95 percent, and
it has the capacity for removal of
approximately 180 pg of naphthalene
with better than 90 percent efficiency.
The field experiments consisted of
three series: (1) outdoors during the
winter; (2) indoors within a labora-
tory; and (3) outdoors during the
summer. In these experiments, a de-
nuder difference approach was fol-
lowed to monitor the phase distribu-
tions of 18 PAH: naphthalene, quino
line, acenaphthylene, anthracene,
phenanthrene, pyrene, fluoranthene,
cyclopenta(c,d,)pyrene, benz(a)an
thracene, chrysene, retene, benzo-
(a)pyrene, benzo(e)pyrene, benzo
fluoranthene, perylene, benzo(g,h,i)
perylene, indeno(1,2,3-c,d)pyrene,
and coronene. The 2-, 3-, and 4-ring
PAH all showed considerable poten-
tial for volatilization, but no evidence
(<0.02 ng/m3) was seen for the
heavier PAH in the vapor phase. The
results in general are consistent with
previous work and extend the overall
body of information on the phase
distributions of PAH and their tenden-
cies for artifact formation as a result
of volatilization during sampling.
This report is being submitted in
fulfillment of Contract No. 68-02-4127
(WA-41 and WA-46) by Battelle
Columbus Division under the spon-
sorship of the U.S. Environmental
Protection Agency. It covers a period
of March 1, 1987, to September 30,
1988, and work was completed as of
September 30, 1988.
This Project Summary was devel-
oped by EPA's Atmospheric Research
and Exposure Assessment Laboratory,
Research Triangle Park. NC, to an-
nounce key findings of the research
project that is fully documented in a
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separate report of the same title (see
Project Report ordering information at
back).
Introduction
Many polynuclear aromatic hydro-
carbons (PAH) are known or suspected
carcinogens. The determination of
concentrations of PAH in ambient air is,
therefore, of considerable importance to
the characterization of air quality. The
task of sampling PAH is complicated by
the fact that many PAH have equilibrium
vapor concentrations that are consid-
erably higher than their normal ambient
air concentrations. This implies a
temperature and concentration depen-
dent distribution of such PAH between
paniculate and vapor phases, and also
suggests the possibility for artifact
occurrence due to volatilization during the
sampling process.
From the viewpoints of atmospheric
fate and transport and, more importantly,
human health risk assessment, it may be
necessary to distinguish between the
vapor and particle-bound PAH. Tradition-
al sampling methods have used only fil-
tration to collect ambient aerosol. More
recently, the use of backup traps
containing polyurethane foam (PUF) or
other vapor sorbents such as XAD-2 to
collect vapor passing through or stripped
from the filter has become more wide-
spread. While this approach may permit
total collection of PAH, it does not take
into account the possibility of artifact for-
mation as a result of either condensation
or vaporization during the sampling
process. Furthermore, there is the pos-
sibility that the integrity of collected sam-
ple may be altered by reaction of PAH
with reactive species such as ozone
during sampling. Other researchers have
used vapor denuder systems to examine
the questions of carbonaceous particle
integrity and sampling of chlorinated
organic compounds.
In two previous work assignments
conducted under this contract, a research
level denuder sampler was used to
evaluate the phase distributions of se-
lected PAH during ambient air sampling.
Results of that work were published
recently. The denuder used in that study
was an open tubular design that
necessitated limitation of the sampling
rate to only 15 L/min, a rate well below
the 200 L/min normally used for ambient
air sampling with the PS-1 sampler. Many
PAH and other semivolatile organic
compounds (SVOC) are present in ambi-
ent air at levels that are so low as to
require the use of the larger sampling
rate to provide enough sample for
analytical and bioassay purposes. A
practical denuder sampler for PAH and
other SVOC therefore requires the use of
a more efficient denuder system that will
permit sampling at rates of the order of
100-200 L/min.
A paper describing the design, con-
struction and preliminary laboratory
evaluation of a high volume annular de-
nuder sampler that satisfies these needs
has been prepared for publication in the
open literature, and is attached for easy
reference as Appendix A of this report.
Objective
The objectives of WA-41 were to
design and construct a high-efficiency,
high-volume denuder sampler that would
separately collect and maintain the
integrities of the vapor and particle-
associated fractions of organic chemicals
that are phase distributed in the
atmosphere. The specific goal was to
construct compact denuder that could be
readily integrated within the normal PS-1
sampler structure, while achieving at
least 90 percent removal efficiency for
SVOC vapors at a sampling rates up to
200 L/min. Additionally, this device
should not interfere with normal filtration
sampling of ambient particulate matter.
The objective of WA-46 was to utilize
this high efficiency denuder sampler in a
series of denuder difference type
experiments to determine the phase dis-
tribution of selected polynuclear aromatic
hydrocarbons in the ambient air. These
field experiments were to include mea-
surements made during both winter and
summer months to attempt to encompass
the normal range of ambient PAH
sampling conditions.
Procedure
The denuder difference method was
used m a series of ambient PAH
sampling experiments conducted during
both winter and summer months in
Columbus, Ohio. The denuder was a high
volume compound annular denuder
(HVCAD) that was designed for easy
interface with a standard PS-1 sampler
for sampling at flow rates of 100 to 200
L/min. A finite-element model based on
laminar flow with finite wall reaction
kinetics was developed and used for
design of the annular denuder. Analyses
of PUF and filter samples for 18 PAH
were performed by GC/MS.
Results and Discussion
Results of the experiments were
analyzed in terms of (1) the artifact re-
sulting from volatilization of PAH durin
the sampling process, and (2) th
vapor/condensed phase distribution <
volatile PAH. Data analysis included prc
viously reported data from sampling rur
made during 1985-1986 and the currei
set of data. A summary of the vapor an
artifact levels is shown in Table 1. I
general, the tendency for artifac
formation correlates well with th
equilibrium vapor pressures of the pur
compounds, and appreciable artifa<
formation was seen with the 2-, 3-, and <
ring PAH, but not with the heavier PA
such as BaP.
The vapor/adsorbed phase distribution
of the volatile PAH were analyzed
terms of the Dubinin-Radushkevich is<
therm. Use of this isotherm allowed gei
eralization of the observed vapor concei
{rations with specific correlation with tl"
vapor pressures and polanzabihties of tr
PAH. The data were used to derive
general set of Dubinm-Radushkevic
parameters which are recommended f<
consideration of other PAH and.c
sampling conditions.
Conclusions and
Recommendations
A denuder sampler capable <
operating at a minimum of 95 perce
vapor removal efficiency at flow rates L
to 200 L/min was designed and coi
structed. This denuder is compact ar
couples readily to the PS-1 sampler. I
holder serves as an interface to the PS
sampler and as a transport containe
Laboratory tests of this denuder show r
detectable (<10 percent) removal i
ambient particulate matter larger than 0
urn at flow rates of 100-200 L/min. Tf
vapor collection efficiency, as measure
with naphthalene, is better than £
percent, and it has the capacity for r<
moval of approximately 180 ug
naphthalene with better than 90 perce
efficiency.
Use of the sampler in a series
outdoor and indoor denuder differenc
sampling experiments yielded pha;
distribution data that are consistent wi
previous work. The results show that <
3-, and 4-ring PAH are sufficiently volati
that measurable quantities of these cor
pounds are found in the vapor phas
Also, these same compounds she
considerable tendencies for volatilizatii
as a consequence of changes in ambie
conditions during the sampling proces
This sampling artifact is shown to I
correlated with the vapor pressures of tl
PAH. The dependence of PAH distrib
tion between vapor and adsorbed stat
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Table 1. Summary of PAH Vapor and Artifact Levels Determined with both OTD and HVCAD
Samplers(a)
Vapor
Compound
Naphthalene(b,c)
Quinoline(c)
Acenaphthylene(c)
Anthracene
Phenanthrene
Pyrene
Fluoranthene
Cyclopentafc, d)pyrene
Benz(a)anthracene
Chrysene
Retene(c)
Benzo(a)pyrene
Benzo(e)pyrene
Benzofluoranthene
Perylene
Benzo(g,h,i)
perylene
lndeno(i,2,3-c,d)
pyrene
Coronene
Range
9.1-47.3
45.4-81
22.3-99 5
74.0-92.3
25.0-865
27.0-97 7
26.6-90
(compound
7.5-67.2
15 0-64 8
30.7-92.3
ND(d)
ND
ND
ND
ND
ND
ND
Median
22.4
623
66.8
56.6
50.6
60.9
60.4
not consistently
32.5
40.3
78.1
ND
ND
ND
ND
ND
ND
ND
ND
Artifact
Range
47.1-89.8
7.7-43.8
169-80.3
12 7-92.2
72.7-80.3
0.7-99.5
4.5-67.7
detected)
8 3-53.0
5 7-50.2
33-27 7
ND
ND
ND
ND
ND
ND
ND
ND
Median
75.5
9.5
57.9
31.9
44.7
16.3
16.5
30.5
17 5
7.4
ND
ND
ND
ND
ND
ND
ND
ND
(a) Expressed as percentage of total amount of each compound
(b) Some PUF data for naphthalene suspect because of possible breakthrough
(c) Compounds determined only in current series of experiments
(d) Not detected consistently in PUF samples
is shown to be well-represented by the
Dubinm-Radushkevich isotherm. As a
rule-of-thumb, ambient PAH vapor conc-
entrations are approximately 1/10,000th
of the equilibrium vapor concentrations of
the pure compounds. Limited data on
quinoline obtained in this study suggest
lower vapor concentrations for this polar
PAH. While the normalized concentra-
tions (using phenanthrene as a reference)
of volatile PAH in ambient air appear to
vary some with the seasons, the normal-
ized concentrations of the same com-
pounds in the adsorbed phase appear to
be relatively constant. Seasonal variations
in the relative amounts of some of the
volatile PAH such as acenaphthylene and
pyrene may be due to the reactivity of
these compounds.
The denuder design and performance
model developed on this program
provides a sophisticated, but easy to use,
mechanism for extending the current
annular denuder design to other sampling
needs and applications. For example, the
design of a compact compound annular
denuder for use with low-volume indoor
samplers would be quite straight-forward.
It is recommended that consideration
be given to the phase distributions of
other types of SVOC than the PAH
included in this study. Such compounds
as the polar PAH and pesticides would
be expected to be more strongly
adsorbed than the compounds studied
here. While, in principle, the Dubmin-
Radushkevich isotherm should apply to
such compounds, with appropriate cor-
rections for their polanzability, other
generalizations derived from the current
work, such as the relationship between
artifact and vapor pressure, may not
apply.
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R W. Coutant, P. J. Callahan and J. C. Chuang are with Battelle Columbus,
Columbus, OH 43201.
Robert G. Lewis is the EPA Project Officer (see below).
The complete report, entitled "Annular Denuder Sampler for Phase-Distributed
Semivolatile Organic Chemicals,' (Order No. PB 89-169 858/AS; Cost: $21.95,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
it
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United States
Environmental Protection
Agency
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EPA600/S3-89/029
CHICAGO
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