Exposure Assessment to Particulate Organic Compounds
Sally Liu: Contribution of Particulate Organic Compounds to Indoor
and Personal Exposures
Rogge: Residential Cooking
Simpson: Contributions from Outdoor PM Sources to Indoor and Personal
of Particulate Organic Compounds to Indoor and Personal Exposures
Sally Liu, Sc.D., Associate Professor
of Environmental & Occupational Health Sciences
University of Washington, Seattle, WA
carbon (OC) is a major constituent of indoor source emissions
(Long et al. 2000) and a major component of PM2.5
mass. It may be responsible for some of the observed health effects
previously associated with PM exposure. OC contributed an average
of 24% of outdoor PM2.5 in U.S. cities,
ranging from 17.8% in Detroit to 34.7% in Sacramento (U.S. EPA
2003). Recent receptor modeling for indoor measurements indicated
that OC contributed 18% of the indoor PM2.5
in an unoccupied apartment in Baltimore (Hopke et al. 2003) and
65% of indoor PM2.5 in 9 occupied homes
in Boston (Long et al. 2000).
OC contribution to indoor and personal PM2.5
has been difficult to quantify. Many particulate organic compounds
(POC) are semi-volatile and exist in equilibrium between the gas
and particulate phases. This characteristic provides a challenge
of accurate measurement of POC in the presence of artifacts that
can occur during sampling. A “positive” sampling artifact
(Cui et al., 1997; Turpin et al., 1994; McDow and Huntzicker,
1990; Kim et al., 2001) results from the adsorption of vapor-phase,
semi-volatile organic compounds (SVOC) onto the filter that collects
particles, or even onto the particles themselves during sampling.
A “negative” sampling artifact may result from desorption
of vapor-phase SVOC during sampling or subsequent handling (Eatough
et al., 1995; John et al., 1988).
indoor air samples, the net positive sampling artifact was found
to be especially significant. Positive artifacts led to overestimation
of indoor particulate OC measured with quartz filters in non-denuded
Harvard Impactors for PM2.5 by 471% as compared
with the average PM2.5 mass concentration
measured with Teflon filters in identical samplers and outdoor
particulate OC by 153% in the Seattle Exposure and Health Effects
Panel Study (Claiborn & Liu, unpublished results). Adsorption
saturation of quartz filters for gas phase OC was observed at
indoor sites. The average quartz filter saturation level was estimated
to be approximately 5.9 mg C/cm2 of quartz filter area. The highest
volatility carbon fraction (OC1) is mostly from the adsorption
of gaseous OC onto quartz filters during sampling, while the lowest
volatility carbon fraction (OC4) fraction is mostly from the particulate
tandem-filter method was proposed to account for positive artifact
(Fitz, 1990; Turpin et al., 1994). In this method, a single quartz
filter is deployed in a sampler that is collocated with a second
sampler that contains one upstream Teflon filter and one downstream
quartz filter. Another method removes gaseous SVOC in an adsorbent-coated
diffusion denuder upstream of the quartz filter. This method makes
use of the fact that gases diffuse orders of magnitude faster
than particles, allowing the particles to continue through the
denuder to be collected on the quartz filter. To solve for the
negative artifact, a sorbent or second quartz filter may be placed
downstream of the filter. Denuder systems for the removal of gas
phase organic compounds are the Brigham Young University Organic
Sampling System (BOSS) (Eatough et al., 1993) and the sorbent-coated
Integrated Organic Gas and Particle Sampler (IOGAPS) (Gundel and
Lane, 1998; 1999). Both samplers are bulky and may not be suitable
for deployment as personal samplers or in occupied residences.
Pang et al. (2002) developed a promising personal particulate
organic and mass sampler (PPOMS) that uses activated carbon-impregnated
foam as a combined 2.5-mm size-selective inlet and denuder for
assessment of PM2.5 and OC free of the positive
Fourier transformation infrared (FTIR) spectroscopy can be used
to chemically characterize functional group information of outdoor,
indoor, and personal PM2.5 samples, especially
for those poorly understood organic fraction of PM2.5
(Turpin et al. 2003 submitted). Turpin et al. showed the influence
of indoor sources for aliphatic hydrocarbon and amide functional
groups by demonstrating enhanced absorbances attributed to these
groups in indoor and personal PM2.5 (Teflon)
samples. Meat cooking was suggested as a possible source for particulate
of indoor and personal PM2.5
a mass-balance model and 16 measured elements, Koutrakis et al.
(1992) quantified the contribution of infiltrated outdoor PM and
indoor sources including cigarette smoking, wood stoves, and kerosene
heaters to indoor PM2.5 in 394 homes in
two New York State counties. Yakovleva et al. (1999) used 18 elements
analyzed from indoor, outdoor, and personal samples from 178 subjects
in Riverside, CA, in a positive matrix factorization (PMF) analysis.
They identified major indoor and personal PM2.5
sources to be soil, nonferrous metal operations and motor vehicle
exhaust, secondary sulfate, and personal activities. Hopke et
al. (2003) utilized both trace elements and OC measurements from
indoor and outdoor samples in 3-way PMF and identified nitrate-sulfate,
sulfate, OC, and motor vehicle exhaust as major indoor and outdoor
sources. Their multilinear engine results indicated that sulfate
(46%), personal activities (36%), unknown sources (14%), soil
(3%), gypsum (0.7 %), and personal care products (0.4%) are major
sources of personal PM2.5 exposure among
elderly subjects. Using 3-way PMF, Larson et al. identified vegetative
burning (41%), crustal materials (33%), secondary sulfate (19%),
mobile vehicle exhaust (7%) as major personal PM2.5
for future work
and cross-compare personal samplers that take into account the
OC positive and negative artifacts.
Develop methods to minimize the positive artifacts in existing
OC measurements for exposure characterization.
and characterize particulate organic compounds in indoor air
and personal exposure and the utilization of these species in
source apportionment analysis.
F. Rogge, Ph.D., P.E.
Acting Department Chair and Associate Professor
Department of Civil & Environmental Engineering
Florida International University, Miami, FL
urbanized areas, restaurant and residential cooking often contributes
30% and more to the atmospheric fine particulate organic particle
burden. Whenever no smoking occurs in homes, residential cooking
has been suggested to be the major indoor source for respirable
particulate matter. In order to fully understand the impact of
cooking on indoor air quality and eventually on the overall urban
air quality, we first have to have emission factors for all major
that purpose, a specially designed airtight environmental chamber
made of stainless steel was designed and built (3.7 m (L), 3.0
m (W), 2.5 m (H)). During the cooking studies, the chamber was
operated under controlled airflow conditions, cleaning the incoming
air first with an activated carbon filter bed, prefilter, and
more than 140 cooking experiments were conducted and the emission
rates determined for: CO, NO, NO2, PM2.5,
PM10, TSP. In addition, the PM2.5
samplers were followed by canisters loaded with polyurethane foam
(PUF) plugs. The PM2.5 and PUF samples were
furthermore subjected to detailed molecular analysis. Cooking
was conducted using both electric and natural gas powered ranges
and ovens. Many different food items were cooked using pan-frying,
stir-frying, sautéing, deep-frying, boiling, and oven cooking
methods including baking, roasting, and broiling.
emissions were highest for pan-frying, with up to 11000 mg/kg
of food cooked and varied drastically, depending on the food item
pan-fried. Using natural gas, the TSP emissions were on average
about 15% higher than observed for pan-frying with an cooking
range powered by electricity. The next prominent cooking method
was oven-broiling steaks, with TSP emissions up to 4300 mg/kg
of food cooked. For this cooking method, oven broiling with natural
gas as power source caused 10 times higher emissions than what
was observed for oven broiling with electricity. In contrast,
particulate emission factors for deep-frying did change very little
for different food items. Boiling food with water revealed the
lowest particulate emissions.
on the cooking method, about 20% to 100% of the TSP was made of
PM10, and 30% to 70% of the PM10 consisted
of PM2.5. In most cases, an increase in
food fat content increased as well particulate emissions.
most of the cooking experiments conducted, PM2.5
samples and PUF samples were analyzed for individual organic compounds
using GC/MS and HPLC. Close to 150 individual organic compounds
were quantified, including: n-alkanes, n-alkanoic acids, n-alkenoic
acids, n-alkanols, n-alkanals, n-alkan-2-ones, dicarboxylic acids,
furans, furanones, amides, steroids, polycyclic aromatic hydrocarbons
(PAHs), heterocyclic aromatic amines (HAAs), and others. In general,
oven roasting, broiling, and baking resulted in the highest PAH
emission factors, ranging on average from about 10 mg/kg of food
cooked to about 80 mg/kg of food cooked. In contrast, sautéing
and stir-frying generated PAH emissions from about 2 mg/kg to
5 mg/kg. The PM2.5 and PUF samples were
as well analyzed for 14 HAAs, of which 8 HAAs could be routinely
identified and quantified, including: MeIQx, DiMeIQx, PhIP, AaC,
Trp-P-1, Trp-P-2, harman, and norharman. The highest total HAAs
emission factor was observed for pan-frying bacon, with about
back to top
Outdoor PM Sources to Indoor and Personal PM Exposures
D. Simpson, Assistant Professor
Department of Environmental & Occupational
University of Washington, Seattle, WA
US population typically spends a majority of its time indoors,
and a major fraction of our PM exposures are encountered in indoor
environments. (Klepeis,'01; Klepeis,'96) Nevertheless, PM of outdoor
origin (ambient PM) has been shown to infiltrate indoors efficiently
and accounts for a significant fraction of the population’s
PM exposure. Furthermore, epidemiological evidence links ambient
PM exposures with adverse health consequences (Samet,'00; USEPA,'01),
and it is ambient PM that is regulated under the NAAQS. Therefore
it is important from both a health and a regulatory standpoint
to understand the contributions from outdoor PM sources to indoor
and personal PM exposures.
Recent studies have highlighted the value of source-specific organic
chemical tracers - “molecular markers” – to
identify and quantify the contributions of specific sources to
ambient PM (Fraser,'03; Khalil,'03; Manchester-Neesvig,'03; Schauer,'00;
Schauer,'96; Zheng,'02). Examples of molecular markers for biomass
smoke include levoglucosan and methoxyphenols (Fine,'01; '02;
Hawthorne,'92). Examples of molecular markers for vehicle exhaust
include polycyclic aromatic hydrocarbons, hopanes and steranes
(Fraser,'03; Schauer,'99; Schauer,'96), and specific nitro-arenes
(e.g. 1-nitropyrene) (Hayakawa,'00). This presentation aims to
review the state of the science regarding the use of organic tracers
to quantify indoor concentrations of and personal exposures to
ambient PM. In particular, I shall focus on PM derived from diesel
exhaust and biomass combustion.
A variety of metrics have been used to assess exposures to biomass
smoke including measurements of PM mass, CO, OC, potassium (Khalil,'03;
Larson,'94; Maykut,'03). Several organic tracers have also been
used, including methyl chloride, PAHs, levoglucosan and methoxylated
phenolic compounds (methoxyphenols) (Khalil,'03; Larsen,'03; Schauer,'00).
Levoglucosan is an anhydro sugar derived from the pyrolysis of
the major wood polymer cellulose. Levoglucosan is one of the the
most abundant particle associated organic compounds in woodsmoke
(Fine,'01; '02). It is stable in the environment and has been
used extensively to estimate woodsmoke levels in ambient PM samples
(Katz,'04; Schauer,'00). Levoglucosan is present in other biomass
smoke samples including smoke from tobacco, grasses and rice straw
(Sakuma,'80; Simoneit,'98; Simpson). However, under conditions
in which woodsmoke dominates the biomass smoke contribution to
ambient aerosol, levoglucosan can be considered a unique tracer
for woodsmoke. In a recent report measurements of levoglucosan
in filter samples were used to validate the assignment of the
woodsmoke feature in a PMF based source apportionment in indoor,
outdoor and personal PM samples.
It has been reported that typical cooking conditions do not generate
the temperatures required to produce appreciable amounts of levoglucosan.
However in our Seattle panel study we observed that for several
residences, the 24hr average levoglucosan concentrations were
higher indoors than outdoors in a number of samples. Therefore,
the possibility remains that indoor sources of levoglucosan exist
that would confound its use as a tracer for ambient woodsmoke
Methoxyphenols are a class of chemicals derived from the pyrolysis
of the wood polymer lignin. This class of chemicals span a range
of volatilities from relatively volatile (e.g. guaiacol) to exclusively
particle associated (e.g. sinapinaldehyde). These chemicals are
relatively abundant in woodsmoke, albeit the most abundant compounds
are predominantly in the vapor phase (Hawthorne,'89; Schauer,'01).
Smoke from hardwood versus softwood burning can be distinguished
by the relative proportions of substituted guaiacols compared
A variety of metrics have been used to measure diesel exhaust
particles (DEP) in ambient samples, including measurements of
ultrafine particles, elemental carbon (EC) PAHs, hopanes and steranes
(Manchester-Neesvig,'03; Schauer,'03; Schauer,'99). Indeed the
NIOSH method for assessing diesel exposures prescribes measurement
of EC. However, these methods are not specific for DEP, and may
be confounded by non-diesel sources. Some PAHs (e.g. BghiP) are
enriched in DEP relative to other combustion sources, and ratios
of BghiP to other PAHs (e.g. BghiP/iP, BghiP/BaA) have been proposed
as marker for DE. Hopanes and steranes are present in engine lubricating
oil, which comprises a significant component of the particle mass
emitted from both gasoline and diesel vehicles. (Manchester-Neesvig,'03;
Schauer,'99) EC is enriched in diesel exhaust relative to gasoline
exhaust, therefore the abundance of hopanes and steranes relative
to EC can be used to differentiate gasoline from diesel emissions.
Several nitroarenes are enriched in DEP, and some nitroarene isomers
appear to be highly specific markers for DEP. (Hayakawa,'00) 1-nitropyrene
(1-NP) is one of the most abundant particle-phase PAHs in DEP,
at a concentration of ~10-40 ppm . (Bezabeh,'03) Photochemical
nitration of pyrene in the atmosphere forms specifically 2 and
4-nitropyrene, and other combustion sources produce minimal amounts
of 1-nitropyrene. Therefore, 1-nitropyrene has been proposed as
a unique marker for DEP in ambient PM. Although levels of this
compound are relatively low in ambient air (examples) (Bamford,'03;
Hayakawa,'00) analytical methods based on HPLC with fluorescence
of chemiluminescence detection (Hayakawa,'00; Tang,'03), or GC-NICI-MS
(Bamford,'03; Bezabeh,'03) have adequate sensitivity to detect
1-NP in low volume ambient samples.
with the use of organic sources tracers in indoor and personal
Given the success in using organic source tracers to apportion
PM in outdoor (ambient samples), it is reasonable to apply the
molecular marker approach to source apportionment of indoor and
personal PM exposures also. However, the applicability of individual
markers as suitable tracer compounds indoors should be carefully
considered. Some potential concerns that should be addressed when
using organic tracers to quantify indoor concentrations of and
personal exposures to ambient PM are discussed below.
Compounds that are unique tracers for outdoor sources
may be confounded by contributions from additional indoor sources
(e.g. incense burning may confound woodsmoke tracers).
For tracers that are semi-volatile, the particle –vapor
equilibrium will shift away from the particle phase as one moves
indoors, due to elevated temperatures and the presence indoors
of surfaces to adsorb vapor-phase chemicals.
The physical characteristics of the individual particles may be
important also. Infiltration efficiencies are highest for the
size fraction 0.1-0.4 mm, and decline substantially for particles
both smaller and larger than this range. Thus, where outdoor sources
produce PM with different size distributions, we may expect to
observe differential penetration efficiencies for the different
sources of PM. We should also be aware that the concentrations
of molecular markers which adsorb to particle surfaces will maximize
in a different size fraction than PM mass (Fine,'04).
Sensitivity: Typically indoor and personal samples are collected
at low volumetric flowrates (2-10 L/minute). Thus, sampled volume
and mass collected will be much lower for indoor/personal samples
compared to ambient samples, and the analytical detection limits
(expresses as ng/m3) will consequently be higher. These considerations
may dictate the use of more sensitive analytical methods or more
extensive sample extraction/pre-concentration procedures to optimize
sensitivity (Simpson,'04b). We may also have to accept a higher
proportion of data close to the detection limits and missing data,
and a concomitant increase in error in the analytical method.
With measurements of PM mass it has recently been demonstrated
that continuous data has great advantages for calculating ambient
PM infiltration to indoor and personal samples. (Allen,'03) It
is also recognized that indoor and personal PM exposures show
greater short-term temporal variability that is characteristics
of ambient PM. Instrumentation is available that provides continuous
data for chemical classes of particle bounds organics (e.g. PAHs).
Homeland security concerns are driving rapid technological development
of continuous monitoring technology for bioaerosols. As a result,
we can look forward to new generation analytical technologies
capable of providing continuous data for specific particle bound
organic tracers in the near future.
Obtaining accurate measures of personal exposure and, more importantly,
absorbed dose, for particulate air pollution is inherently difficult.
This is due to the substantial spatial and temporal variation
in pollutant levels, coupled with the fact that people constantly
move between different microenvironments. Thus, traditional fixed
site monitors fail to capture the full variability in exposures
experiences by individuals. While active personal monitors are
effective in accurately monitoring personal exposures, it is impractical
and cost prohibitive to implement active personal monitoring on
a large scale. Furthermore, external personal monitors fail to
account for substantial differences in ventilation volume, and
hence inhaled dose, due to physical exertion. An alternative approach
to exposure assessment, which addresses many of the limitations
noted above is biomonitoring. Biomonitoring of exposure to particulate
air pollution involves measurement of PM-derived chemicals in
biological media such as human urine, blood, or hair, and the
chemical so monitored is called a biomarker.
A suitable biomarker for specific PM sources should possess the
should be uniquely derived from the exposure of interest.
It should be relatively abundant, such that ambient exposure
levels generate sufficiently high biomarker levels to be measured
parent marker should be chemically stable in the environment,
and the compound (or its metabolites) should be chemically stable
in biological samples.
The excretion kinetics in the media of interest (e.g. urine,
blood etc) should be suited to the exposures and/or health endpoints
for woodsmoke exposures:
Three classess of chemicals have been proposed as biomarkers for
woodsmoke, PAHs, levoglucosan and methoxyphenols have all been
proposed as biomarkers for woodsmoke exposure (Dills,'01; Dorland,'86;
Feunekes et al. measured 1-hydroxypyrene in urine from firefighters.
(Feunekes,'97) They reported a positive association between urinary
1-hydroxypyrene and smoke exposure. In contrast, Rothman et al
reported no association between PAH-DNA adducts in peripheral
blood from wildland firefighters, and smoke exposures. (Rothman,'93)
PAHs are by no means specific to woodsmoke; they are a component
of incomplete combustion and are present in a variety of PM sources
including vehicle exhaust, gas and coal combustion and cooking
fumes (Rogge,'91; '93; Schauer,'99). Furthermore, for non-occupationally
exposed non-smokers, the major portion of PAH dose is taken up
through the diet (Chuang,'99; Vyskocil,'00). Therefore, PAH biomarkers
in urine or blood are only likely to be associated with PM exposures
when woodsmoke exposures are very high, such as occupational exposures.
There is one report describing measurement of levoglucosan in
human urine (Dorland,'86). Dorland et al used an approach combining
TLC and GC/MS, and reported 0 to 0.8 mg levoglucosan per mL of
urine. This finding should be replicated using modern techniques
combining high resolution chromatography and mass spectrometry
as the analytical methods used in the original study have limited
specificity. The upper range of the urinary levoglucosan levels
reported by Dorland et al are higher than would be achieved from
inhalational exposure to woodsmoke at ambient levels, and the
possibility exists of a substantial dietary contribution of levoglucosan
from caramelized sugars.
Our group has described the use of methoxyphenols as potential
biomarkers of woodsmoke exposure (Dills,'01). We have developed
sensitive and specific methods based on GC/MS analysis for determination
of approximately 12 methoxyphenols in human urine. A suite of
isotopically labeled methoxyphenools are used to monitor analyte
recovery in every sample. Multiple methoxyphenols are present
in the urine of individuals with no known elevated exposure to
woodsmoke, and a substantial increase in urinary methoxyphenol
excretion was reported subsequent to inhalation of woodsmoke from
a campfire (Dills,'01). It was also noted that ingestion of food
items containing woodsmoke flavoring (e.g. smoked salmon) caused
a substantial increase in urinary methoxyphenol excretion (Dills,'01).
The utility of methoxyphenols as a biomarker for woodsmoke xposure
at ambient levels was evaluated in a panel study in Seattle WA.
Mutiple methoxyphenols were detected in all urine samples, and
a dynamic range up to 1000-fold between lowest and highest reported
concentrations was observed.
for diesel exposures:
Several biomarkers for diesel exhaust have been proposed, including
PAH metabolites and various nitro-PAH metabolites in urine samples
(short term exposure markers) and as adducts to DNA or blood proteins
(longer term exposure biomarkers. (Kuusimaki,'03; Scheepers,'02;
Seidel,'02; van Bekkum,'97) PAH metabolite levels in urine samples
have shown an association with DE exposure in some occupational
settings, (Kuusimaki,'03) however, as noted above, PAHs are not
source specific tracers. Thus, for exposure to ambient levels
of DE, and where substantial not DE sources of PAHs are present,
urinary PAH metabolites are not likely to be useful biomarkers
for DE exposure. In contrast, several nitro-arenes are unique
to (or at least greatly enriched in) DE, and their urinary metabolites
hold promise as sensitive and specific biomarkers of DE exposure.
Urinary metabolites of 1-nitropyrene and 3-nitrobenzanthrone have
been reported in subjects with known occupational exposure to
DE. (Seidel,'02) Unfortunately in these studies concurrent personal
PM samples were not collected so dose-response information for
the nitro-PAH metabolites in human urine is not yet available.
Future work with these biomarkers should involve establishing
dose-response and timecourse of urinary excretion, adapting analytical
methodology to permit the sensitive and specific determination
of these markers in urine from non-occupationally exposed individuals,
and established baseline urinary levels and variance in individual
exposed to ambient DE.
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