United States
Environmental Protection
Agency
National Exposure
Research Laboratory
Research Triangle Park, NC 27rf t
Research and Development
EPA/600/SR-95/098 April 1997
4*EPA Project Summary
The Particle Team (PTEAM)
Study: Analysis of the Data
H. Ozkaynak, J. Xue, R. Weker, D. Butler, P. Koutrakis, and J. Spengler
EPA and the California Air Resources
Board sponsored a study of human ex-
posure to inhalable particles in the Los
Angeles Basin. Results were reported
in Volumes I and II; this is a summary
of the third and final volume, dealing
with statistical analysis and physical
models. Nicotine and air exchange re-
sults are presented and analyzed. A
model was developed to estimate the
penetration factors and decay rates for
inhalable (PM10) and fine (PM25) par-
ticles, for 15 elements associated with
each size fraction, and for polyaromatic
hydrocarbons (PAHs). The model was
also used to estimate source emission
rates for particles and elements pro-
duced by cigarettes and cooking, and
also for PAHs produced by cigarettes.
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
In 1986, Congress mandated that the
US EPA undertake a study of exposure to
particles. EPA's Atmospheric Research
and Exposure Assessment Laboratory
(AREAL), now part of the National Expo-
sure Research Laboratory (NERL), joined
with California's Air Resources Board to
sponsor a study in the Los Angeles Basin.
The study was carried out primarily ,by the
Research Triangle Institute (RTI) and the
Harvard School of Public Health, with ad-
ditional support from Lawrence Berkeley
Laboratory (LBL), Acurex, and AREAL.
Small portable personal monitors were
designed to measure inhalable particles
(aerodynamic diameter less than 10 pm,
or PM10). In addition, stationary microenvi-
ronmental monitors were designed to
sample both PM,0 and PM25 (fine particles
<2.5 fim in diameter). The personal and
indoor samplers were equipped with fil-
ters to collect nicotine. Monitors were also
developed to measure PAHs and phtha-
late esters. Air exchange rates in each
home were measured using perfluorotracer
(PFT) techniques. A total of 178 residents
of Riverside, CA, took part in the study in
the fall of 1990.
The results of the study are presented
in three volumes. Volume I (Pellizzari et
al., 1993) provides a full description of the
procedures and presents summary popu-
lation-weighted statistics for particles and
elements. A Project Summary for Volume
I is also available (Pellizzari et al., 1993).
Volume II (Sheldon et al., 1993) presents
summary population-weighted statistics for
PAHs and phthalate" esters. Volume III
presents summary statistics for air ex-
Printed on Recycled Paper
-------
change rates and nicotine concentrations,
and also provides more detailed statistical
analyses and physical models for all pa-
rameters measured. This document is the
Project Summary for Volume III.
Procedure
Measurement Methods
A personal exposure monitor (PEM) was
designed to collect PM10 using a sharp-cut
Impactor with a circular set of holes 1.9
mm In diameter. Particles are collected at
a constant flow rate of 4 L/m on a 37-mm
Teffon filter mounted below a greased im-
pactor plate. The PEM consists of a soft
canvas bag containing the pump and bat-
tery pack that can be worn on the hip,
stomach, lower back, or over the shoul-
der. Nearly identical monitors were em-
ployed for concurrent indoor and outdoor
sampling of PM)0 and PMM. For the per-
sonal and Indoor samples, a second filter
treated with citric acid to collect nicotine
was placed behind the first filter.
The monitor for the PAHs and phthalate
esters Included a glass cartridge contain-
ing XAD-2 sorbent preceded by a quartz
fiber filter. A box containing four Medo
pumps sampled air at a constant flow rate
of about 18 L/m during the 12-h monitor-
Ing periods. Both the filter and the car-
tridge were sonically extracted with meth-
ylene chloride. Analysis employed gas
chromatography/mass spectrometry (GC-
MS) in the selected ion mode.
Air exchange rates were measured us-
ing perfluorotracer (PFT) methods. Three
continuously emitting sources of PFT in
small boxes heated to 40°C were placed
in each home 24 h before sampling be-
gan. Volumes of the homes were mea-
sured at this time. At each of the subse-
quent visits (the beginning of each of the
two 12-h measurement periods), collector
tubes containing activated charcoal were
placed in the home at three sites. Two
tubes were in the main living area, one in
the bedroom, and one near the center of
the home.
Study Design
The main goal of the study was to esti-
mate the frequency distribution of expo-
sures to PM,. particles for all nonsmoking
Riverside residents aged ten and above.
A second major objective was to estimate
the frequency distribution of concentra-
tions of PM 0 and PM2J!, PAHs, and phtha-
late esters in residences and nearby out-
door air, e.g., back yards. Other objec-
tives Included Identifying important indoor
sources and estimating their emission
rates, determining the effect of outdoor air
on indoor concentrations, and estimating
the contribution of personal activities to
exposure.
A three-stage probability sampling pro-
cedure was adopted. In the first stage, 36
areas within Riverside were selected for
study with a probability proportional to
population size in each area. Areas were
characterized and stratified by income to
ensure a wide socioeconomic representa-
tion. In the second stage, an attempt was
made to contact every household within
these areas and administer a short ques-
tionnaire to determine eligibility for partici-
pation and the frequency of certain strati-
fication variables such as employment and
passive smoking. In the final stage, re-
spondents were selected for monitoring.
Respondents represented 139,000 ±
16,000 (S.E.) nonsmoking Riverside resi-
dents aged ten and above.
Each participant wore the PEM for two
consecutive 12-h periods. (Actual times
monitored depended on participant activi-
ties and ranged from 8-14 h.) Concurrent
PM,0 and PM25 samples were collected
by the stationary indoor monitor (SIM) and
stationary outdoor (ambient) monitor (SAM)
at each home. This resulted in 10 particle
samples per household (day and night
samples from the PEM10, SIM10, SIM25,
SAM,0, and SAM2S). Air exchange rates
were also calculated for each 12-h period.
At a subset of 125 homes (and 65 out-
door areas near the residences), monitors
to measure indoor and outdoor PAHs and
phthalate esters were operated for each
12-h period.
Participants were asked to note activi-
ties that might involve increased particle
levels (nearby smoking, cooking, garden-
ing, etc.). Following each of the two 12-h
monitoring periods, they answered an in-
terviewer-administered recall questionnaire
concerning their activities and locations
during that time.
Up to four participants per day could be
monitored, requiring 48 days in the field.
A central outdoor site was maintained over
the entire period (Sept. 22-Nov. 9, 1990).
The site had two high-volume samplers
(Wedding & Assoc.) with 10-um inlets (ac-
tual outpoint about 9.0 urn); two dichoto-
mous PM10 and PM25 samplers (Sierra-
Andersen) (actual outpoints about 9.5 and
2.5 urn); one PEM and one SAM10 (actual
outpoint about 11.0 nm, as measured in
laboratory studies); and one SAM25 (ac-
tual outpoint = 2.5 urn).
All PEM, SIM, SAM, and dichotomous
sampler filters (about 2500) were ana-
lyzed by energy-dispersive x-ray fluores-
cence (EDXRF) for a suite of 42 elements
(Dzubay et a/., 1988). The analysis was
carried out at EPA's AREAL in Research
Triangle Park, NC. Some filters were ana-
lyzed twice under blind conditions. A sub-
set of about 100 filters was analyzed by
the LBL for quality assurance purposes.
An additional set of about 600 citric-acid
treated filters from personal and indoor
samplers was analyzed for nicotine.
All filters were weighed onsite. Repli-
cate weighings were required to be within
±4 ng/filter. Blank filters were weighed,
sent out with field samples, and reweighed
along with the field samples. Duplicate
indoor and outdoor samples were collected
at 10% of the homes. Duplicate SAM and
PEM samples were also collected at the
central site. Duplicate PEM samples were
also collected by EPA, RTI, and Harvard
scientists while onsite.
Results
Of 632 permanent residences contacted,
443 (70%) completed the screening inter-
view. Of these, 257 were asked to partici-
pate and 178 (69%) agreed. More than
2750 particle samples were collected,
about 96% of those attempted.
Quality of the Data
Blank PEM and SIM/SAM filters (N = 51)
showed consistent small increases in mass
averaging 9.5 ± 8.4 ng; this value was
subtracted from each field sample. Limits
of detection (LODs), based on three times
the standard deviation of the blanks, were
on the order of 7 to 10 ng/m3. All field
samples exceeded the LOD.
Duplicate samples (N = 363) showed
excellent precision for all types of samplers
at all locations, with median relative stan-
dard deviations ranging from 2% to 4%.
The collocated samplers at the central
site showed good agreement, with corre-
lations between the three types of sam-
plers ranging from 0.96 to 0.99. As had
been previously noted, the central-site
PEMs collected about 12% more mass
than the dichotomous samplers, perhaps
due to their higher outpoint (11 \um com-
pared to 9.5 urn) or to a particle "bounce"
effect, measured in the laboratory at less
than 9%.
Background levels of elements on labo-
ratory and field blanks were low. Analyses
of standard reference materials (SRM 1832
and 1833) were within 7% of the correct
values for all 12 elements contained. Me-
dian relative standard deviations (RSD)
for duplicates analyzed blindly by the prin-
cipal laboratory were better than 15% for
all 15 prevalent elements. Median RSDs
for duplicates analyzed by the principal
laboratory and by the quality assurance
laboratory (LBL) were less than 21% for
all elements except manganese (76%) and
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copper (27%). The LBL reported 10% to
20% higher average values for 13 of 14
elements.
For benzo-a-pyrene, the quantifiable limit
was 0.08 ng/m3, with a median precision
of 3%, a mean amount on the field blanks
of 0.0 ng, and a mean recovery of 95 ±
19%. Similar results were obtained for the
other PAHs and phthalate esters.
Concentrations
Concentrations of particles and elements
have been reported (Clayton et al., 1993;
Ozkaynak et al., 1993; Pellizzari et al.,
1993; Wallace ef al., 1993). Population-
weighted daytime personal PMig concen-
trations averaged about 150 ng/m3, com-
pared to concurrent indoor and outdoor
mean concentrations of about 95 ng/m3.
The overnight personal PM10 mean was
much lower (77 |Ag/m3) and more similar
to the indoor (63 (ig/m3) and outdoor (86
ng/m3) means. About 25% of the popula-
tion was estimated to have exceeded the
24-h National Ambient Air Quality Stan-
dard for PM10 of 150 ng/m3- Over 90% of
the population exceeded the California
Ambient Air Quality Standard for PM10 of
50 ng/m3.
Mean values of the fine (PM25) particle
mass were 48 and 49 ng/m3 for daytime
indoor and outdoor samples, and 36 and
50 ng/m3 for the overnight indoor and out-
door samples, respectively. Thus, fine par-
ticles accounted for about 50% of the total
PM10 mass both indoors and outdoors dur-
ing the day and about 60% both indoors
and outdoors at night.
Nicotine
A total of 334 valid measurements were
obtained for the personal samples, and
230 for the indoor samples. About 30%
(176) of the 564 analyzed nicotine samples
exceeded the LOD of 0.15 jig/filter (corre-
sponding to a nominal value of about 0.05
ng/m3). Most of these were from personal
or indoor samples associated with expo-
sure to cigarette smoke. Mean personal
and indoor nicotine concentrations were
on the order of 1 |ig/m3 for those samples
associated with reported exposure to to-
bacco smoke but were below the LOD for
those samples with no reported exposure.
A regression of indoor nicotine concen-
trations on the number of cigarettes
smoked in the home during the monitor-
ing period indicated that indoor nicotine
values increased by about 0.12 ng/m3 for
each cigarette reported smoked during the
monitoring period. The ff value is 35.4%
(N = 227).
A regression of personal nicotine levels
on minutes exposed to cigarette smoke
suggested that personal nicotine expo-
sures increased by about 0.013 ng/m3 per
minute of reported exposure to cigarette
smoke. The Ff value is 36.6% (A/ = 334).
PAHs
Median indoor and outdoor concentra-
tions ranged between 0.1 and 2 ng/m3 for
all but the two most volatile 3-ringed PAHs:
acenaphthylene (day and night medians
of 3.5 and 3.8 ng/m3 indoors and 1.8 and
6.9 ng/m3 outdoors) and phenanthrene (16
and 15 ng/m3 indoors and 8.8 and 12 ng/
m3 outdoors). Little difference was seen
between indoor and outdoor concentra-
tions.
Phthalate Esters
Median indoor values for four phthalate
esters ranged between 30 and 400 ng/m3;
they were below the detection limit for di-
n-octylphthalate. Median outdoor levels
were often below the detection limit, with
the highest value being 28 ng/m3 for di-2-
ethylhexylphthalate. Indoor levels of four
phthalates were about 2 to 15 times higher
than outdoor levels.
Air Exchange
A total of 1010 12-h average air samples
were collected. There were 273 duplicate
pairs and 464 single observations. Two
observations were outliers, resulting in 735
values after averaging the duplicates.
About 20% of the samples had PFT
amounts below the LOD.
The 24-h average air exchange rates
were calculated for 175 Riverside homes
using the convention of assigning half the
LOD to values below the LOD. The geo-
metric mean of the air exchange rates
was 0.97 tr1, with a geometric standard
deviation (GSD) of 2.18 (Figure 1).
Correlations
The central site appeared to be a mod-
erately good estimator of outdoor particle
concentrations throughout the city.
Spearman correlations of the central-site
concentrations measured by all three meth-
ods with outdoor near-home concentra-
tions as measured by the new samplers
ranged from 0.8 to 0.85 (p<0.00001). Lin-
ear regressions indicated that the central-
site readings could explain about 60% of
the variability observed in the near-home
outdoor concentrations (Figure 2).
Outdoor concentrations could explain
about 25% to 30% of the variability ob-
served in indoor concentrations (Figure 3).
Spearman correlations of near-home out-
door concentrations with indoor concen-
trations ranged from 0.5 to 0.6. Spearman
correlations of the central-site outdoor con-
centrations with indoor concentrations were
reduced somewhat (about 0.45 to 0.55).
Outdoor concentrations were able to
account for only about 16% of the vari-
ability in personal exposures (Figure 4).
This is understandable in view of the im-
portance of indoor activities such as smok-
ing, cooking, dusting, and vacuuming on
exposures to particles. The higher day-
time exposures were even less well rep-
resented by the outdoor concentrations,
whether measured near the home or at
the central site.
Indoor concentrations accounted for
about half of the variability in personal
exposures (Figure 5). However, neither
the indoor concentrations alone, nor the
outdoor concentrations alone, nor time-
weighted averages of indoor and outdoor
concentrations could do more than ex-
plain about two-thirds of the observed vari-
ability in personal exposures. It appears
that the remaining portion of personal ex-
posure arises from personal activities or
unmeasured microenvironments that are
not well represented by fixed indoor or
outdoor monitors.
One of the variables most highly corre-
lated with particle levels in the home was
an'estimated "dirt level." The technicians'
estimate of dirt level was made while visit-
ing each house. Two technicians carried
out all the measurements. They estimated
dirt and dust levels on a 7-point scale,
and "calibrated" themselves by experiment-
ing on several Boston homes before go-
ing to Riverside. The 24-h averages of
personal and indoor particles and also
indoor nicotine were significantly associ-
ated with estimated dirt level.
The mean indoor concentrations of
PAHs in homes with smoking appeared
generally higher than in homes without
smoking. Student t-tests showed that for
10 out of 12 PAHs (and for di-n-
butylphthalate), the difference between the
geometric mean concentrations in smok-
ing vs. nonsmoking homes was statisti-
cally significant, usually at p < 0.0001.
Mass-Balance Model
A model developed in Koutrakis et al.
(1992) was solved using nonlinear least
squares to estimate penetration factors,
decay rates, and source strengths for par-
ticles and elements from both size frac-
tions. In this model, which assumes per-
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20
16
12
I
I
I
-2.1 -1.1 -0.1 0.9
Log 24-h Average Air Exchange Rate (1/h)
1.9
2.9
Figure 1. Normal fit to the logarithms of the overnight air exchange rates, assigning
values ofLOD/2 to all nondetectedsamples. The geometric mean = 0.97 h''.
feet Instantaneous mixing and steady-state
conditions throughout each 12-h monitor-
Ing period, the indoor concentration of par-
ticles or elements is given by
/Vclg = number of cigarettes smoked
during monitoring period
Sclg = mass of elements or particles
generated per cigarette
smoked (ng/cig or ng/cig)
TOX* = time spent cooking (min) dur-
ing monitoring period
Scools = mass of elements or particles
generated per minute of cook-
ing (ng/min or ng/min)
Bother = mass flux of elements or par-
ticles from all other indoor
sources (ng/h or ng/h)
With these changes, the equation for
the indoor concentration due to these in-
door sources becomes
C. =
-fa
where
P
a
a+k
[1]
i Indoor concentration (ng/m3
for elements, ng/m3 for par-
ticles)
r penetration coefficient
; air exchange rate (h-1)
i outdoor concentration (ng/m3
or ng/m3)
Qfe = mass flux generated by in-
door sources (ng/h or ng/h)
V = volume of room or house (m3)
k = decay rate due to diffusion or
sedimentation (h-1)
From initial multivariate analyses, the
most important indoor sources appeared
to be smoking and cooking. Therefore the
indoor source term Qte was replaced by
the following expression:
where
t
duration of the monitoring pe-
riod (h)
a + k
(a + K)Vt
(a + k)V
[2]
The indoor and outdoor concentrations,
number of cigarettes smoked, monitoring
duration, time spent cooking, house vol-
umes, and air exchange rates were all
measured or recorded. The penetration
factor, decay rates, and source strengths
for smoking, cooking, and all other indoor
sources (Qott] ) were estimated using a
nonlinear model (NLIN in SAS software).
The Gauss-Newton approximation tech-
nique was chosen to regress the residu-
als onto the partial derivatives of the model
with respect to the unknown parameters
until the estimates converge. On the first
run, the penetration coefficients were al-
lowed to "float" (no requirement was made
that they be < 1). Since nearly all coeffi-
cients came out close to one, a second
run was made bounding them from above
by one. The NLIN program provides sta-
tistical uncertainties (upper and lower 95%
confidence intervals) for all parameter es-
timates. However, it should be noted that
these uncertainties assume perfect mea-
surements and are therefore underesti-
mates of the true uncertainties.
Results are presented in Table 1 for the
combined day and night samples. Pen-
etration factors are very close to unity for
nearly all particles and elements. The cal-
culated decay rate for fine particles is
0.39 ± 0.16 h-1, and for PM10 is 0.65 ±
0.28 rr1. Each cigarette emits 22 ± 8 mg
of PM10 on average, about two-thirds of
which (14 + 4 mg) is in the fine fraction.
Cooking emits 4.1 ±1.6 mg/min of
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I
p
1
600
500
400
300
200
700
Backyard = 1.03'Central + 17.6
R2=0.57 n = 323
50
100
150
Central site reference monitor mean (\\.g/m )
Figure 2. Central-site mean of two dichotomous samplers vs. residential outdoor monitors.
Ft1 = 57%
200
250
-c
C\l
600
500
400
300
200
700
Indoor = 0.54 *Outdoor + 32
z= 27% (n=309)
100
200 300 400
Average 12-h outdoor concentration (}ig/m3)
Figure 3. Indoor vs. outdoor PMW concentrations.
Ft2 =27%
500
600
-------
500
400
300
200
roo
PERS = 0.54 "OUT'+ 62
100
200 300
Backyard concentrations (iig/m3)
400
500
600
FJgun 4. Personal exposures vs. residential (backyard) outdoor PM,0 concentrations.
R*- 16%
500
400
300
200
roo
PEPS = 0.91* Indoor + 39
49% (n=321)
700 200 300 400
Average 12-h indoor concentration (\ig/m3)
FJguraS. Personal exposures vs. residential indoor PM,aconcentrations.
500
600
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Inhalable particles, of which about 40%
(1.7 ± 0.6 mg/min) is in the fine fraction.
All elements emitted by cooking were lim-
ited almost completely to the coarse frac-
tion. Sources other than cooking and
smoking emit about 5.6 ± 3.1 mg/h of
PM , of which only about 1.1 mg/h ± 1.0
(20%) is In the fine fraction.
Decay rates for elements associated
with the fine fraction were generally lower
than for elements associated with the
coarse fraction, as would be expected.
For example, sulfur, which has the lowest
mass median diameter of all the elements,
had calculated decay rates of 0.16 + 0.04
and 0.21 ± 0.04 h-' for the PM,^ and PM10
fractions, respectively. The crustal elements
(Ca, Al, Mn, Fe), on the other hand, had
decay rates ranging from 0.6 to 0.8 fr1.
A similar model was developed for the
PAHs and phthalate esters. However, the
model differs in not including a cooking
source term because initial regression
analyses did not identify cooking as an
important source of PAHs. Also, because
of a much lower sample size for the PAH
and phthalate measurements (only 60
homes with outdoor measurements, com-
pared to 160 for the particles), the param-
eter estimates show much larger uncer-
tainties.
Results showed that penetration factors
for most PAHs were very close to one
(Table 2). Because of the very large un-
certainties involved in trying to estimate
four unknown parameters (penetration co-
efficients, decay rates, smoking source
strengths, and flux from other indoor
sources), the penetration coefficients were
all set equal to one and the remaining
three parameters in Table 2 were calcu-
lated using the nonlinear algorithm.
The estimated average decay rates for
PAHs ranged from 0.4 to 1.6 h-1 with size-
able variation. No apparent dependence
on volatility was noted. Estimated decay
rates for the phthalates had very large
uncertainties.
Estimated indoor source strengths for
smoking forbenzo(a)anthracene, chrysene,
benzo(e)pyrene,benzo(a)pyrene,
benzo(ghi)perylene, and coronene were
122, 192, 86, 264, 244, and 245 ng/ciga-
rette, respectively. Smoking contributed 20%
to 40% of the total concentrations of eight
PAHs in homes reporting smoking. Consid-
ering all homes, outdoor air contributed
more than half the total concentrations of
six PAHs, mostly the less volatile ones,
and tother" (unidentified) indoor sources
contributed more than half of three volatile
PAHs.
These other Indoor sources were re-
sponsible for 97% to 99% of the total
concentrations measured for diethyl ph-
thalate and di-n-butyl phthalate. Smoking
was not indicated as an indoor source for
phthalates.
Other (unidentified) indoor sources were
found to be very important for both of the
phthalates and for the volatile PAHs, but
the estimates of source strengths were
highly uncertain.
The physical models had reasonably
good fit to particulate PAHs, and the cor-
relation between predicted and observed
concentrations averaged about 0.7.
Outdoor air was the major source of
indoor particles, providing about three-
fourths of fine particles and two-thirds of
inhalable particles in the average home. It
was also the major source for most ele-
ments, providing 70% to 100% of the ob-
served indoor concentrations for 12 of the
15 elements. Only copper and chlorine
were predominantly due to indoor sources
in both the fine particle and inhalable par-
ticle fractions.
Unidentified indoor sources accounted
for most of the remaining particle and
elemental mass collected on the indoor
monitors. The nature of these sources is
not yet understood. They do not include
smoking, other combustion sources, cook-
ing, dusting, vacuuming, spraying, or
cleaning, since all these sources together
account for less than the unidentified
sources. For example, the unidentified
sources accounted for 26% of the aver-
age indoor PM particles, whereas smok-
ing accounted for 4% and cooking for 5%.
Of the identified indoor sources, the two
most important were smoking and cook-
ing (Figures 6 and 7). Smoking was esti-
mated to increase 12-h average indoor
concentrations of PM10 and PM26 by 2
and 1.5 pg/m3 per cigarette, respectively.
Homes with smokers averaged about 30
p.g/m3 higher levels of PM10 than homes
without smokers. Most of this increase
was in the fine fraction. Cooking increased
indoor concentrations of PM10 by about 20
pg/m3, with most of the increase in the
coarse particles.
Emission profiles for elements were ob-
tained for smoking and for cooking. Major
elements emitted by cigarettes were po-
tassium, chlorine, and calcium. Elements
associated with cooking included alumi-
num, iron, calcium, and chlorine.
Other household activities such as vacu-
uming and dusting appeared to make
smaller contributions to indoor particle lev-
els. An interesting finding was that com-
muting and working outside the home re-
sulted in tower particle exposures than for
persons staying at home.
As with the particle mass, daytime per-
sonal exposures to 14 of 15 elements
were consistently higher than either in-
door or outdoor concentrations. At night,
levels of the elements were similar in all
three types of samples.
Discussion
Source of Excess Personal
Exposure
The more than 50% increase in day-
time personal exposures compared to con-
current indoor or outdoor concentrations
suggested that personal activities were
important determinants of exposure. How-
ever, the nature of this "personal cloud" of
particles has not yet been determined.
Scanning electron microscopy was under-
taken on 138 personal filters. Skin flakes
were common on many filters. A prelimi-
nary analysis suggested that the average
number of skin flakes per filter was
120,000 to 150,000. The mass of some
personal filters may have been consider-
ably increased by unusually large num-
bers of skin flakes. However, attempts to
calculate the mass of skin flakes from
estimates of their volume and density sug-
gest an average contribution to the mass
of only about 4 pg/m3, less than 10% of
the mass of the average personal cloud.
Another approach to the composition of
the personal cloud is elemental analysis,
using x-ray fluorescence. Analysis of all
personal and indoor filters showed that 14
of 15 elements were elevated by values
of 50% to 100% in the personal filters
compared to the indoor filters (Figure 8).
This observation suggests that a compo-
nent of the personal cloud is an aerosol of
the same general composition as the in-
door aerosol. This could be particles cre-
ated by activities, e.g., cooking, or
reentrained household dust from motion
(walking across carpets, sitting on uphol-
stered furniture). House dust is a mixture
of airborne outdoor aerosols, tracked-in
soil and road dust, and aerosols produced
by indoor sources. As such, it should con-
tain crustal elements from soil, lead and
bromine from automobiles, and other ele-
ments from combustion sources. This
would be consistent with the observation
that nearly all elements were elevated in
personal samples. The fact that personal
overnight samples showed smaller mass
increases than the personal daytime
samples is also consistent with the fact
that the participants were sleeping for
much of the 12-h overnight monitoring pe-
riod, and were thus not engaging in these
particle-generating or reentraining activi-
ties.
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Cooking 3%
Other Indoor 7%
Other Indoor 8%
Smoking 5%
Cooking 3%
Other Indoor 16%
Other Indoor 16%
Smoking 4%
N - 81 Samples from 31 homes
Figure 6. Sources of fine particles (top) and Inhalable particles
(bottom) In 31 homes with smoking. Relative uncertainties
In the estimates can be determined from the upper and
tower confidence limits for the source strengths provided in
Tabla 1.
N = 62 Samples from 33 homes
Figure 7. Sources of fine particles (top) and inhalable particles
(bottom) in homes with cooking. Relative uncertainties in
the estimates can be determined from the upper and lower
confidence limits for the source strengths provided in Table 1.
The measurements at the central site
showed good agreement with the outdoor
measurements at homes throughout the
City of Riverside, indicating that a single
central-site PM10 monitor can characterize
a large urban area adequately. Although
the correlations of indoor air concentra-
tions with outdoor air are lower, there is
evidence that outdoor air PM10 concentra-
tions can affect indoor air concentrations.
The nonlinear least squares method of
solving the mass-balance model improved
on previous formulations in making fewer
arbitrary assumptions and solving for all
unknown parameters simultaneously. An
Interesting result from this effort was the
finding that the penetration factor was very
close to one for nearly all particles, ele-
ments, PAHs and phthalate esters.
Conclusions
The personal and microenvironmental
monitors designed especially for this study
performed well. About 96% of all samples
attempted were collected and median pre-
cision was 2% to 4%.
The major finding of the study was the
50% increase in daytime personal expo-
sures to PM10 compared to indoor and
outdoor concentrations. The increase ap-
pears to be due to personal activities such
as dusting, vacuuming, cooking, and shar-
ing a home with a smoker. This suggests
that reduction of dust levels in the home
could decrease exposure to airborne par-
ticles.
A mass-balance model provided esti-
mates for the source strengths of ciga-
rettes and cooking for particles and ele-
ments in two size fractions. The model
also provided estimates for the source
strengths of cigarettes for a number of
PAHs.
10
-------
Elements in the Personal Cloud
20
80
40 60
Percent increase in personal cloud
Figure 8. Increased concentrations of elements in the personal vs. the indoor samples.
100
120
References
Clayton, C.A., Perritt, R.L., Pellizzari,
E.D., Thomas, K.W., Whitmore, R.W.,
Ozkaynak, H., Spengler, J.D., and
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Dzubay, T., Stevens, R.K., Gordon,
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Ozkaynak, H., Spengler, J.D., Xue, J.,
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Influencing Personal and Indoor Ex-
posures to Particles: Findings from
the Particle TEAM Pilot Study. In: In-
door Air '93: Proceedings of the 6th
International Conference on Indoor Air
Quality and Climate. Vol. 3: pp. 457-
462, 1993.
Pellizzari, E.D., Thomas, K.W., Clayton,
C.A., Whitmore, R.W., Shores, R.C.,
Zelon, H.S., and Perritt, R.L. Particle
Total Exposure Assessment Method-
ology (PTEAM): Riverside, California
Pilot Study. Vol. I. Project Summary.
EPA/600/SR-93/050. Research Tri-
angle Park, NC, 1993. Report EPA/
600/R-93/050 NTIS # PB 93-166957.
NTIS. Springfield VA, 1993.
Sheldon, L, Clayton, A., Keever, J.,
Perritt, R., and Whitaker, D. PTEAM:
Monitoring of Phthalates and PAHs in
Indoor and Outdoor Air Samples in
Riverside, California. Vol. II. Air Re-
sources Board, Research Division.
Sacramento, CA, 1993.
Wallace, L., Ozkaynak, H., Spengler,
J.D., Pellizzari, E.D., and Jenkins, P.
Indoor, Outdoor, and Personal Air Ex-
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11
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H, Ozkaynak, J. Xue, Ft. Weker, D. Butler, P. Koutrakis, and J. Spengler are with
Harvard University School of Public Health, Boston, MA 02115.
Andrew Undstrom is the EPA Project Officer (see below).
The complete report, entitled "The Particle Team (PTEAM) Study: Analysis of the
DataFinal Report, Volume III," (Order No. PB97-102 495; Cost: $85.00, 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
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