United States
Environmental Protection
•Agency
researcr
evelopment
Iki
' Since !'
EXECUTIVE SUMMARY
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The air in every American community will be safe and
healthy to breathe. In particular, children, the elderly,
and people with respiratory ailments will be
protected from health risks of
breathing polluted air.
—EPA Strategic Plan 2000
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EPA 600/S-04/057
July 2004
The EPA Participate Matter Research Program
What Have We Learned About PM Since 1997?
US Environmental Protection Agency
Office of Research and Development
Washington, DC 20460
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The U. S. Environmental Protection Agency (EPA, or the Agency) Clean Air Goal aims for every
American community to have safe and healthy air. However, research has shown that exposure
to particulate matter (PM) air pollution continues to be linked to increases in respiratory
health problems, hospitalization for heart or lung disease, and even premature death. The set
of National Ambient Air Quality Standards (NAAQS) for PM, promulgated by EPA in 1997, was designed
to respond to this research and move the nation closer to achieving the Clean Air Goal. Currently, EPA
estimates that its regulations to reduce air pollution will prevent tens of thousands of premature deaths and
reduce hospitalizations for cardiovascular and respiratory illness by tens of thousands more people each year.
The monetary benefits of reducing mortality alone are estimated to be up to approximately $100 billion
per year; the benefits of reducing illness and minimizing the number of lost workdays and consequences of
restricted activity are estimated to provide savings of billions more dollars each year.
EPA views the reduction of PM emissions through its NAAQS as key to accomplishing its Clean Air Goal.
By expanding its PM Research Program over the last five years, EPA's Office of Research and Development
(ORD)1 is successfully strengthening the science base for the NAAQS and facilitating its implementation.
The PM Research Program
In 1997, EPA revised the NAAQS for PM, with the most
significant change being a new standard for PM smaller
than 2.5 |im in aerodynamic diameter (PM2S or fine PM).
Developed largely on the basis of epidemiological studies
that found consistent associations between ambient PM
concentrations and various adverse health effects, the revised
standards were shadowed by concerns regarding the true
public health significance and credibility of the adverse
effects of ambient PM. In 1998, these concerns led Congress
to increase the President's recommended EPA budget for
the PM Research Program of $27.8 million by $22.4 million
per year—an increase that was largely sustained for the
ensuing five years. EPA's specific charge was to accelerate its
investigation of the role of PM in health effects associated
with air pollution and to strengthen the science to support
implementation of scientifically defensible regulatory actions.
Smoke plumes from wildfires. EPA's PM
Research Program is working to develop more
accurate estimates ofPM emissions from wildfire
events and other sources to help state and local
agencies develop effective plans to achieve air
quality standards for PM.
1 EPA research programs include both intramural components (ORD laboratories) and extramural components [Science To Achieve Results
(STAR) Program grants, cooperative agreements, and other mechanisms]. References to ORD work in this document apply to both its
intramural and extramural work.
What Have We Learned About PM Since 1997?
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As a result of this intensified research program:
Credibility has replaced skepticism concerning the nature and extent of ambient PM's effects on
cardiopulmonary disease and mortality.
> Scientists are uncovering the many of the complex interactions involving PM attributes and human
characteristics, among other factors, that contribute to unwanted health outcomes.
Clear advances have been made in characterizing air pollution sources and atmospheric processes. This
information is needed to plan and implement effective emission reductions to reduce PM.
The emergence of this new information was the result of a comprehensive, national research endeavor
involving the coordinated planning efforts of EPA's intramural scientists, extramural investigators funded by
EPA, and EPA partners such as the Health Effects Institute (HEI). Other federal organizations (including
the National Institutes of Health and the Department of Energy) and others participating in the Air
Quality Research Subcommittee of the Federal Committee
on Environment and Natural Resources (CENR) joined in
a coordinated effort to enhance the research addressing PM.
This research has been performed within a scientific framework
developed by the National Research Council (NRC) of the
National Academy of Sciences, an independent committee of
experts assembled at the request of EPA. The NRC Committee
on Research Priorities for Airborne Particulate Matter (NRC
Committee) issued a series of reports that outlined a research
agenda to address the key scientific questions about PM and
provided periodic assessments of progress.
n three reports, the NRC
.Committee identified important
research topic areas and
recommended to EPA a multi-
year research portfolio and plan
of the highest priority research
topics designed to strengthen and
expand the scientific understanding
of the links between ambient PM
and adverse health effects. ORD
has relied upon these priorities in
setting its PM research agenda.
The NRC Committee's first report (Research Priorities for
Airborne Particulate Matter: I. Immediate Priorities and a Long-
Range Research Portfolio, March 1998) set the stage for the
evolution of EPA's PM Research Program. EPA quickly focused
the expertise of both intramural and extramural scientists to address the NRC priorities. Intramurally, the
program adjusted its priorities in keeping with the NRC recommendations and established goals, time-
lines, and associated internal funding support. The STAR Program, an extramural grant program managed
by the EPA's National Center for Environmental Research (NCER), developed Requests for Applications
(RFAs) for PM research in numerous environmental science, exposure, engineering, and health areas. This
included the establishment of five PM Research Centers that, together with the EPA intramural program,
could broadly address the PM issue. A major goal of the program has been to communicate and coordinate
new findings and research priorities with partners and other Federal agencies. For example, the basic PM
EPA's Particulate Matter Research Program
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Research Program analyses and other analyses conducted independently by the HEI have yielded significant
contributions that have advanced and refined our knowledge of PM. The integration of EPA's PM Research
Program with the programs of partners and other Federal agencies and the communication among them have
been key elements in achieving significant scientific and regulatory advances.
This report highlights and summarizes the salient scientific
advances in PM-related health, exposure, and implementation
research conducted by ORD and EPA-funded researchers since
1997. The following discussions are organized by the priority
research needs stated in the three NRC Committee reports
(Research Priorities for Airborne Particulate Matter I-III) and in
the context of the program and regulatory needs of EPA's Office of Air and Radiation (OAR).
PA's PM research is conducted
through intramural and
extramural research partnerships.
Studies
inhalation studies; cell biology & real
tine latemetry measurements in radarta
Clinical Studies
Human inhalation etudes;
casting; in vitro exposure facilities
Epidemiologi&all Studies
Acute/chronic & panel epidemwlogi-c studies;
bioms-kBr deretopnuent imputation at exposures
Overview of major research areas being addressed by EPA's PM Research Program.
What Have We Learned About PM Since 1997?
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Air monitoring equipment used In
EPA's PM Super sites Program.
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Outdoor Measures
Versus
Actual Human Exposures
"¥ TT That are the quantitative
V V relationships between
concentrations of participate
matter and gaseous co-
pollutants measured at stationary
outdoor air-monitoring sites
and the contributions of
these concentrations to actual
personal exposures, especially for
subpopulations and individuals?
What Have We Learned About PM Since 1997?
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nderstanding the relationship between ambient PM2 s concentrations and personal PM exposure is
fundamental to assessing the health effects of air pollution. In 1997, it was difficult to quantitatively
link outside measurements of PM at ambient monitoring sites to what individuals were actually
exposed, especially because people spend about 90% of their time indoors.
Initially, EPA designed studies that focused on understanding the relationship between PM mass measured at
ambient monitors and local outdoor, indoor, and personal exposure concentrations. Likewise, the effects that
human activities, housing characteristics, and other factors had on these relationships were also investigated.
Longitudinal exposure studies were conducted in eight locations around the country representing diverse
conditions in weather, housing, and pollution sources. Researchers studied potentially susceptible subjects with
asthma, chronic obstructive lung disease, or cardiovascular disease.
The exposure studies revealed a number of important relationships between personal PM exposure estimates
and data from community monitors. Associations between the ambient monitor and personal exposure are
strongest for fine particle sulfate — which forms a substantial
fraction of PM2S in the eastern part of the nation — followed
...results from the longitudinal , „,, , . „,, mi.. ,, . 1A
a by PM2 s mass, and then PM1Q (PM smaller than 10 |im in
exposure studies have verified that , . ,. ,. .-p, , c ,
aerodynamic diameter) mass. 1 he strength or the association
for fine PM mass and sulfate, the , ^ , . ^ _ . , . ^ f ,
between ambient concentrations and estimates or personal
ambient monitoring site should , , . , ,. , .c , ,
exposure demonstrated in these studies has verified that,
serve as an adequate surrogate f c ™/i j if *. *. *. *. 1
tor fine PM mass and sulrate, measurements at central
for personal exposure... , <, , c
! monitoring sites should serve as an adequate surrogate tor
personal exposure to ambient PM2 s mass in community-based
epidemiological studies.
Although pooled analysis of the results shows a strong relationship between exposure and central site
concentrations, results for individuals show high variability. Much of this variability is due to the varying
effect of outdoor particles on indoor environments. Building type and ventilation strongly influence the
penetration of ambient PM indoors. Although until recently particles were assumed to readily penetrate into
buildings, studies have shown that this is often not the case, and that penetration efficiencies vary by city and
season. Not surprisingly, the greater the air turnover in a dwelling (via open windows, air leaks, or mechanical
systems), the better the indoor PM2S reflects the PM2S measured by the outdoor monitor. PM1Q and ultrafme
(< 0.1 |im) PM (most often associated with recently generated or "fresh" combustion emissions) penetrate less
well under similar circumstances and penetrate especially poorly into relatively well-sealed dwellings. High
levels of ultrafmes in many homes appear to be associated with human activity and specific indoor sources
(e.g., cooking, space heaters, cigarette smoking), which can also contribute to co-pollutant exposure.
EPA's Particulate Matter Research Program
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Because individuals typically spend most of their time indoors, they are exposed to lower levels of ambient
PM than would be predicted by central site monitors; thus, the strength of the associations between
ambient PM concentration and adverse health effects may be underestimated. Even with this variability
in the relationships between ambient PM and personal exposure, recent studies have not shown significant
differences in personal exposure to ambient PM as a result of health condition.
Gases such as NO2, O3, CO, and SO2 are found along with PM in pollutant mixtures and may complicate the
assessment of health outcomes associated with PM. Strong correlations were found to exist between ambient
PM2 s concentrations and ambient gaseous co-pollutant concentrations (i.e., O3, NO ). However, only weak
correlations existed between personal PM2 s exposure and personal exposures to gaseous co-pollutants. These
data suggest that ambient gas concentrations do not significantly interfere with risk estimates for the effect of
ambient PM exposure on health outcomes.
To assimilate these findings into a tool of use to state and regional regulators, EPA has developed the
Stochastic Human Exposure and Dose Simulation (SHEDS) Model from laboratory and field data collected
in the exposure studies. It is now being improved to incorporate the effect of emission sources on personal
exposures and dose. This model will provide a relevant and sophisticated regulatory tool that will relate
community monitoring or associated atmospheric modeling data to personal PM exposure.
The research activities associated with this topic have, by design, provided critical data to address fundamental
questions regarding PM exposure. These data have now conceptually linked regulatory monitoring data with
the health-outcome findings that were the basis of the initial PM studies. This research has also provided
a platform from which to develop the predictive models needed to implement the NAAQS. As such, the
original objectives of this topic area, as identified in the NRC Committee reports, are nearly complete.
However, to provide more focused exposure estimates for health assessments, to guide model development,
and to enable assessment of the regional variability associated with exposure to putative toxic components,
data for particular PM constituents continue to be gathered in specific geographic areas.
Data from personal exposure
monitors are highly correlated
with measurements ofPM2S
mass concentrations taken
at ambient monitoring sites.
This implies that changes in
community-level ambient PM2
mass concentrations are very
similar to the changes in PM2S
concentration to which people are
exposed, even when they spend
most of their time indoors.
What Have We Learned About PM Since 1997?
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Exposures of Susceptible
Subpopulations to Toxic
Particulate Matter Components
w;;
iat are the exposures to
biologically important
constituents and specific
characteristics of particulate matter
that cause responses in potentially
susceptible subpopulations and the
general population?
What Have We Learned About PM Since 1997?
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. his topic extends the Research Topic 1 research from exposure to PM mass to exposure to
potentially toxic components of PM. Research in this area supports the hypothesis that health
outcomes related to PM are determined by its specific physicochemical attributes. However,
because current evidence suggests that health effects are likely to be associated with a significant number
of the originally hypothesized toxic agents, the focus has shifted from evaluating individual components to
evaluating the association between PM from specific sources and adverse health effects.
First, exposure research on individual PM species has been initiated without waiting for their toxic
components to be definitively identified. Studies are being performed to investigate exposure relationships
for as many of the hypothesized toxic components as are feasible with current technology. Results of these
exposure studies can then be used to inform health studies. Second, source apportionment techniques are
being incorporated into exposure research in order to evaluate the ambient-
personal exposure relationship for PM from various sources as well as for
individual PM constituents.
"personal exposures to
... ambient PM are not
substantially different for
healthy and susceptible
adult populations.
Initial work in this area has focused on developing methods for monitoring
personal exposure to determining PM components and characteristics;
identifying specific sources of PM; and developing lightweight, multi-
pollutant samplers for susceptible individuals to use. EPA's support of
improvements in analytical methods will improve the capability to identify sources of PM found in personal,
residential, and ambient PM samples. Methods used to better define contributions to exposure from wood
smoke and diesel and gasoline combustion are also being improved. Such methods have produced preliminary
results showing that the high amounts of ultrafine particles near highways fall dramatically in relation to
distance from the highway centerline and that ultrafine particles do not readily penetrate into buildings.
Many of the samples that were collected as part of the longitudinal PM exposure studies of Research Topic
1 will be analyzed for the major PM constituents and size fractions and, in some cases, speciated organics.
Preliminary results have shown that penetration efficiencies for ultrafine particles are very low and that, even
in the absence of indoor sources, indoor-outdoor correlations are poor. Other studies have shown that outdoor
concentrations of elemental carbon and several organic species are not homogenous across airsheds and are
influenced by both mobile and stationary sources. For those species that show weak associations between
central site concentrations and exposures or that are not well distributed across airsheds, data and models
will be needed to develop better exposure surrogates for epidemiological studies and to conduct high quality
exposure and risk assessments. Several models that refined the source attribution of PM fractions and their
statistical applications are being expanded to be associated with health outcomes and the possible influence of
the seasons. Research also includes development of new modeling techniques with which to evaluate exposure
to PM constituents and sources.
EPA's Particulate Matter Research Program
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New field monitoring studies are being initiated to address the many remaining questions about personal
exposures to PM with specific attributes or from specific source types and how these relate to what is
measured at ambient monitoring sites. Based on the information from these studies, monitoring sites such as
the PM Speciation Trends Network2 sites can provide information about exposure to PM constituents across
the country. This information will provide the basis for airshed-specific health studies which aim to explore
specific associations with these measures and/or their predominant sources in order to improve associated risk
assessments. Improvements in models directed at the spatial and temporal distributions of constituents and
their source attribution will permit the development of models designed to predict exposure at community,
residential, and personal scales.
...new studies are being planned and initiated to more fully
understand and model exposures to PM constituents and
PM from various sources.
The penetration of particles Into the Indoor environment is highly size dependent. Larger particles (>1 ftm) are typically
excluded by their inability to penetrate with the exchange of air. The smallest particles (< 0.1 jim) easily adhere to surfaces and
other items of contact and as a result also do not penetrate efficiently. Those particles between these sizes appear to penetrate
most easily and also are highly respirable. While only slight differences in outdoor-indoor penetration exist between day and
night, there are likely to be seasonal and behavioral differences, such as opened windows.
2 The Speciation Trends Network is a national network of approximately 50 ambient monitoring sites that has the capability to measure
ambient levels of different chemical constituents ofPM, including sulfates, nitrates, and elemental and organic carbon.
What Have We Learned About PM Since 1997?
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Characterization of
Emission Sources
"W TT T"hat are the size
V V distribution, chemical
composition, and mass-emission
rates of particulate matter emitted
from the collection of primary-
particle sources in the United States
and what are the emissions of
reactive gases that lead to secondary
particle formation through
atmospheric chemical reactions?
What Have We Learned About PM Since 1997?
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RD, in collaboration with OAR, has made substantial progress in compiling data on conventional
(industrial) and less conventional (agricultural and other) sources of PM and PM-precursor
emissions. Field and laboratory studies have significantly advanced our understanding of the
chemical and physical characteristics of these source emissions resulting in new and revised "source profiles"
that can be used to generate more complete and accurate airshed emissions estimates needed to allow air
quality models to accurately predict ambient PM levels. Researchers are developing the specialized and
complex measurement techniques needed to determine accurate particle ^^^^^^^^_^^^^^^^^^
sizes and compositions from diverse and often widely dispersed sources >f.--». pn'q rpqparrh
such as wildfires and concentrated animal waste facilities which have 1, *havp fnriiqpri nn
generally been underappreciated in terms of their contributions to ambient
and methods for the source
Based on the NRC priorities and guidance from OAR and state and local
regulatory agencies, EPA focused on five primary areas related to emission
developing measurements
types that are the most
difficult to measure and to
address areas for which the
sources. ^^ current|y avaj|ab|e are
highly uncertain.
(1) Establish standard test methods to measure particle size and
chemical composition for combustion sources. Scientists developed new
or modified measurement approaches (hardware and operating procedures) for characterizing PM, including
a dilution sampling system that collects emissions and allows the behavior of an exhaust plume to be modeled.
The sampler also allows more relevant profiling of both organic and inorganic PM constituents than earlier
versions. This work provided much of the technical foundation for EPA's new regulatory measurement
methodology. Researchers also developed new methods to dynamically characterize the diesel exhaust from
heavy-duty trucks during highway operation. This effort has provided especially valuable data concerning how
PM emissions and characteristics change with fluctuations in real-world engine operation as well as on how
PM evolves in an exhaust plume.
(2) Characterize primary particle size and composition of emissions. To develop or improve the
emission profiles needed for modeling, ORD collected data to improve mass emission factors as well as PM
composition and size information for many important emission sources. These sources have, to date, included
residential wood combustion devices (including wood stoves), a heavy-duty diesel truck tested during highway
operation, and various industrial boilers and combustors. The effects of fuel type and composition, as well as
varied operating conditions, were determined for several of the above source types, along with performance
data for pollution-control devices. Selected portions of this work also addressed questions about the toxicity of
specific emission fractions with the future goal of associating toxicity with sources of ambient PM.
EPA's Particulate Matter Research Program
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In cooperation with scientists from EPA Regions, ORD has addressed the effects of open biomass burning,
which is common in the western U.S. The use of unique tracers or chemical fingerprints is being studied
to estimate emission rates and assess how specific burning activities may influence local ambient air quality.
ORD is also characterizing fugitive road dust contributions to the general air mix. Together, these data
on primary emissions and precursors will update EPA's database of source chemical profiles and emission
factors and will improve atmospheric models used to predict ambient concentrations and secondary particle
formation.
(3) Develop new measurement methods and collect data in order to characterize diffuse sources of
gas-phase ammonia and organic vapors. Gas-phase ammonia is a critical co-pollutant in the evolution
of ambient PM2 s, especially in the eastern half of the country. ORD developed a method using a Fourier
transform infrared (FTIR) laser system to measure ammonia emissions from hog barns and lagoons, which
are significant sources of ammonia. Recent studies indicate that this same methodology can be used to
measure other compounds, including methane and low molecular weight organic compounds from diffuse
sources that usually cannot be measured by traditional stack-testing techniques.
(4) Translate new source-test procedures and source-test data into comprehensive, national, emission
inventories. EPA research has substantially contributed to development of comprehensive, national emission
inventories by OAR and individual states. Directly, EPA provided updated emission factors and improved
speciation and size-distribution data for use in national emission inventories. Indirectly, EPA provided expert
consultation and guidance for data collection and analysis. The advances in source-test procedures and data
were used in national emission inventories in 2002 and are being used currently; the results will reduce the
uncertainty associated with both mass emission rates and size distribution for many source types.
(5) Evaluation of PM and PM-precursor control technologies. Although the area of control technologies
was not addressed by the NRC Committee report, ORD has conducted modest efforts to evaluate the
performance of technologies to control PM and PM precursors to support the implementation of regulatory
strategies to achieve the air quality standards. ORD has partnered with several other organizations, including
industry, to leverage resources and expertise toward development of advanced PM control technologies.
Research has been and continues to be conducted to evaluate innovative approaches to improving the
capture of fine PM from coal-fired power plants. By applying an electric field to a conventional baghouse,
an electrostatically enhanced fabric filter system has been developed that can be retrofitted to plants
currently using an electrostatic precipitator (ESP) or fabric filter system providing a cost-effective approach
What Have We Learned About PM Since 1997?
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to incremental PM reductions. Work is also proceeding to address a potential problem associated with the
installation of existing emissions reduction technologies at coal-fired power plants. In a limited number of
cases, installation of SO and NOx controls can result in the formation of visible acid aerosol plumes. A
review of current literature and available data has been conducted, and experiments are being performed to
identify methods to prevent or eliminate the formation of these plumes.
Ambient PM
Derives from
Varied Sources
EPA's Participate Matter Research Program
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What Have We Learned About PM Since 1997?
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contains three types of modeling
description of atmospheric states and motions, emission models
for man-made and natural emissions that are injected into the
atmosphere, and a chemistry-transport modeling system for
simulation of the chemical transformation and fate.
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RESEARCH TOPIC 4
Air-Quality Model
Development and Testing
"¥ TT That are the linkages
V V between emission sources
and ambient concentrations of the
biologically important components
of participate matter?
What Have We Learned About PM Since 1997?
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ORD has invested substantial effort in developing modeling approaches to address the links between
ambient PM and emission sources that could contribute to health risks. Source-based models are
predictive, forecasting the effects of emissions on primary (directly from the source) and secondary
(chemically transformed) atmospheric PM. On the other hand, receptor-based models attempt to unravel the
source attribution at the time of ambient measurements. When used together, these source- and receptor-
oriented models provide regulators with the necessary data to develop, test, and evaluate the effectiveness of
PM emission reduction strategies for State Implementation Plans (SIPs).
Source-based air quality models for PM were developed from earlier models designed for acid rain and ozone.
These disparate models were integrated and updated with new information on atmospheric chemistry to
create the initial Community Multiscale Air Quality (CMAQ) Model, which was released in 1998. The most
recent version of the CMAQJModel, released in June 2002, incorporated the current state of the science in
atmospheric processes at that time. The model is to be further evaluated with the PM2 s data now becoming
available from air monitoring networks and large field studies. In addition, the CMAQJModel will also be
improved through the incorporation of newly developed chemical modules that describe the complex PM
chemistry with a specific focus on the formation of secondary organic aerosols. Through model evaluation and
incorporation of improved atmospheric chemistry, significant improvements in the predictive capability of the
CMAQJModel are planned by its next release in 2005. This release will provide a valuable tool for modeling
air quality for states to use in developing their SIPs.
With SIP development beginning in 2004 and 2005, ORD has endeavored to provide user-friendly versions
of available receptor-based models to state and local regulators. Two PC-based models have been developed:
the Chemical Mass Balance (EPA CMB8.2) and Unmix (EPA
Unmix2.3). CMB fully apportions exposure to the spectrum
of sources and is highly dependent on the quality of the
constituent-linked source-profile database. Unmix internally
generates external source profiles from ambient data and will
probably be a useful tool for handling the vast amount of data
being generated by the national Speciation Trends Network. In
addition to developing receptor modeling tools, EPA has also
applied receptor-based models to identify the relative contributions of gasoline vehicles and diesel vehicles to
ambient fine particle levels.
he Unmix model...[provided the
first! quantitative estimation of
the separate contributions of diesel
and gasoline engines to ambient
levels of PM25
EPA's Participate Matter Research Program
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Observations
(CAST NET)
CMAQ
The CMAQ Model is able to predict changes in particulate sulfate levels by simulating how sulfur dioxide, the
major precursor to p articulate sulfate, is transported and transformed in the atmosphere. This comparison of
measured sulfate levels (in black) with CMAQ Model results (in orange) shows the model is able to predict changes
in particulate sulfate concentrations as meteorology and upwind emissions of sulfur dioxide change over the course
of a year. The ability to identify how particle concentrations change as emissions change is crucial to developing
effective air quality management strategies.
What Have We Learned About PM Since 1997?
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Assessment of Hazardous
Particulate Matter Components
w:
iat is the role of
physicochemical
characteristics of participate matter
in eliciting adverse health effects?
What Have We Learned About PM Since 1997?
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s
everal hypotheses regarding the role of specific hazardous PM attributes3 have emerged from ORD
research since 1997. There now seems to be little doubt that there are adverse, PM-associated effects
on human health and that several potential "active" attributes of the PM mixture may be involved.
S'
t
The "causal" attributes of PM can be classified as either physical, chemical, or biological. EPA has conducted
toxicological studies to build on previous epidemiological evidence that PM-related effects on cardiovascular
or respiratory disease mortality and morbidity are strongly associated with exposure to smaller particles
(effects of PM2S > PM10 > total suspended particulate, orTSP). Some evidence also indicates that the smallest
particles, the ultrafines, may have even greater potency. Further,
in some instances, surface area may be a better dose metric
than mass in evoking lung injury although not all ultrafine
particles behave in a similar manner when comparably tested.
Most epidemiological studies have found minimal effects on
mortality risk for larger, coarser particles (PM10 s), which are
often of crustal origin. Yet time-series epidemiological studies
of various morbidity end points, including respiratory symptom
measurements and cause-specific hospitalization reports, have
recently reported associations with both the fine and coarse PM
fractions. It remains to be determined if health end points are differentially responsive to these size modes.
ince 1997, empirical
I toxicological studies have
provided important, albeit still
limited, evidence indicting specific
PM attributes as being primarily
responsible for the cardiopulmonary
effects linked to ambient PM.
The chemical composition of PM has received considerable scrutiny in toxicological studies; inorganic
constituents have generated the most data to date. Sulfate and nitrate anions derived from combustion
Humans n SaNne
• Extract
Utah Valley extract
[12 TSP filters/year]
3 "Hazardous" in this context does not refer to "hazardous air pollutants" as defined in the Clean Air Act, but is intended to convey the hypothesis
that specific attributes ofPM are responsible for the adverse health effects associated with exposure to ambient PM."
EPA's Participate Matter Research Program
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emissions or atmospheric processes usually combine with other constituents in PM, especially the water-soluble
materials. Although the intrinsic, independent toxicities of many sulfates and nitrates appear to be rather low,
it is hypothesized that they may influence the toxicity or bioavailability of other PM components. Little is
actually known about the cardiovascular effects associated with acidic aerosols or the possibility that they might
mediate some of the reported PM effects, and this issue is now being explored in EPA-funded programs.
EPA toxicological studies have found that inhalation of certain metals results in inflammation in the lung and
cardiac arrhythmias. While these studies were conducted with doses or concentrations of PM higher than
typical ambient conditions, they demonstrate the potential for similar effects to occur in humans. Perhaps
the most striking evidence for the importance of metals is from studies of PM-associated metals extracted
from ambient filters in the Utah Valley at the site of a steel mill that was temporarily closed because of a labor
dispute. Laboratory tests and human and animal exposure studies using material from particles collected
when the plant was open and closed demonstrated similar patterns and types of effects. These EPA-supported
studies corroborate the results of a separate study that found a decrease in hospital admissions for similar
causes in the local population while the plant was closed. Extracts of the Utah Valley particles were tested in
humans, animals, and in vitro cell cultures to compare the effects associated with particles collected during
the periods when the plant was open and closed. Despite the
relatively high doses used in these test systems, the experimental
studies showed a pattern of response that was consistent with the
reported epidemiological findings. Moreover, the experimental
studies supported the hypothesis of a primary role for metals.
n a more focused analysis of
.the data from six U.S. cities,
significant associations were found
between mortality and two key
sources of pollution—traffic and
coal combustion—with the largest
specific effect for the traffic factor.
EPA is investigating the toxicity of other chemical attributes of
PM. Organic constituents are of particular concern due in large
part to the contribution of various industrial sources as well as
diesel and other mobile sources to the fine PM fraction. While
not as overtly toxic as the some of the metallic compounds, some organic compounds appear to be able to
generate oxidants that may cause delayed or subtle effects not readily measured by conventional methods.
Finally, EPA has begun to investigate the relationship between health outcomes and source-specific PM.
If health effects can be linked to particular sources of air pollution, this information will prove useful for
targeting control strategies. Field, epidemiological, and toxicological studies are emerging that can associate
responses with sources. These studies are designed to help determine the PM components, characteristics,
and sources most responsible for health effects. This information is required to ensure that control strategies
are designed and focused on the PM sources that most strongly affect public health and to provide a sound
scientific basis for the development of future PM standards.
What Have We Learned About PM Since 1997?
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Dosimetry: Deposition and
Fate of Particles in the
Respiratory Tract
iat are the deposition
patterns and fate of
particles in the respiratory tract of
individuals belonging to presumed
susceptible subpopulations?
What Have We Learned About PM Since 1997?
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Because the most relevant exposure measure of PM for health-risk assessment is the actual dose of
particles in the lung, EPA developed a new, non-invasive method to measure the deposition of
inhaled particles in different regions of the human lung. Studies using this method have significantly
advanced our understanding of how different size classes of PM are deposited and the influence of age,
gender, and respiratory diseases on the distribution of particle deposition within the lung.
Surprisingly, the smallest and largest
of the potentially respirable PM, the
ultrafine and coarse (PM1Q-PM2S) PM
fractions, are deposited in a healthy
human respiratory tract in the same
areas. It has long been understood that
fine particles, including the ultrafine
fraction, penetrate more deeply into
the respiratory tract than coarse
PM. However, it appears that the
deposition patterns (as opposed to
the penetration patterns) of ultrafine
particles tend to be more similar to
patterns of coarse particle deposition
than to the patterns of fine particles.
Clearly, the absolute dose deposited
is different for different size fractions
and depends largely on the size
distributions of exposure aerosols. For
urban aerosols with a dominant fine particle mode, mass deposition is similar for fine and coarse particles.
While the number of ultrafine particles deposited may be much larger than the number of fine and coarse
particles, the deposited mass of ultrafine particles tends to be negligible in most cases.
This dosimetry information is important for understanding how a complex mixture of ambient PM may cause
adverse health effects and why some people are more susceptible to adverse effects than others. Preliminary
data suggest that some PM may, as a function of size and composition, migrate from the lung to other organs
and tissues. Although these data need further confirmation, their potential implications are significant,
especially in light of the cardiac effects attributed to PM.
Fraction of inhaled small particles deposited in the lungs of human
subjects. Those with various forms of airway and lung disease have a
higher rate of deposition than normal healthy subjects.
EPA's Participate Matter Research Program
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PM deposition in healthy adults of different ages and in men and women was also studied. EPA researchers
found that the respiratory dose in young and older adults is similar. Therefore, dose itself may not be
responsible for differences in susceptibility to the health effects of PM by age. Similarly, overall respiratory
dose is comparable in men and women but; in general, women tend to receive greater doses in their upper
airway regions than men, possibly because their airways are somewhat narrower. This is consistent with some
data that suggest women are more sensitive to irritant gases.
The respiratory dose of inhaled PM is unevenly distributed within the lung, and the actual dose in local
airway regions can be many times greater than the average lung dose. People with impaired lungs may
experience doses to airway "hot spots" that exceed those in a similar location of a healthy lung by a factor of
8 or 10. Therefore, exposure relationships alone may be inadequate to address responsiveness in potentially
susceptible groups without some assessment of the dosimetry.
' "*he respiratory dose of inhaled
PM is distributed unevenly
within the lung, and the actual dose
at local airway regions can be many
times greater than the overall lung
dose.
Generally, PM dosimetry in adult, healthy, human males has
been well described by EPA researchers. Models have been
developed to describe particle deposition for uniform breathing
(both during rest or exercise) over a wide range of PM size. This
idealized dosimetry has long been the standard for estimating
lung doses of PM exposure. There are also analogous models
for the laboratory rodents that are typically used in toxicological
studies. These models are important for understanding
exposure-dose relationships in toxicological studies conducted
to address questions of mechanism, susceptibility, causality, and composition-specific effects on the lung. In
contrast, dosimetry in impaired lungs is not well defined in animal models; consequently, its quantitative use
in extrapolation to humans is limited.
The efforts in basic human dosimetry studies have waned in response to program priorities. ORD is now
assessing the effect of cardiopulmonary diseases on the distribution of PM of various sizes in the various
compartments of the respiratory system and how these distributions are mimicked in the animal models of
these diseases.
What Have We Learned About PM Since 1997?
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Combined Effects of Particulate
Matter and Gaseous Pollutants
How can the effects of
particulate matter be
disentangled from the effects of
other pollutants? How can the
effects of long-term exposure
to particulate matter and other
pollutants be better understood?
What Have We Learned About PM Since 1997?
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Much of what has been learned about the combined effects of PM and other air pollutants has
emerged from the work done by extramural STAR Program grantees, PM Research Centers,
and HEI. To date, these ORD-sponsored epidemiological and panel studies have found either
no influences or only minor influences from co-pollutant exposure on the estimates of health risk from PM.
The effects of PM appear to be independent from those of other criteria air pollutants.
Long-term health effects from PM that cause shortening
of life, accelerated dysfunction, or exacerbated disease
remain a major concern. At the time the PM regulations
were set in 1997, two national-scale studies of long-term
exposure to PM had been published in the peer reviewed
literature. The Harvard Six Cities Adult Cohort Study and
the American Cancer Society Cohort Study both reported
significant associations between risk of premature mortality
and long-term exposure to PM. To verify these results, HEI
sponsored an extensive re-analysis effort which confirmed
the findings of the original studies. Additionally, the ACS
investigators extended the original study, doubling the
follow-up time from 8 to 16 years; the results replicated the
findings of increased cardiopulmonary risk and documented a
significant association with mortality from lung cancer. Early
methodological criticisms of these studies have been largely resolved, supporting the concerns about adverse
effects of long-term exposure to PM.
Other studies in children exposed to a mixed oxidant-PM atmosphere suggest retardation of lung growth that
is not fully reversible. Ongoing work at the U.S.-Mexico border suggests that asthma and economic status are
important factors in the overall response. Work funded by the STAR Program is beginning to use established
cohorts with the extensive medical histories or unique lifestyles that make them appropriate subjects for
understanding the effects of long-term exposure to ambient PM.
This topic area, perhaps more than any other research priority
identified by the NRC, is in its relative infancy due to the
complexity, expense, and duration of longitudinal epidemiological
studies of PM health effects and the lack of historical fine-
particle monitoring data. Efforts are underway to address
the effects of chronic exposure to ambient PM including new
initiatives to study the health effects of long-term exposure
EPA's Particulate Matter Research Program
ope et al. (2002) extended the
original Adult Cohort Study by
8 years and replicated the findings
of increased cardiopulmonary
mortality risk, but in addition,
reported a significant association
with mortality from lung cancer.
-------
initiated under STAR Program grants. Other initiatives to study chronic health effects in controlled animal
studies have begun focusing on issues associated with the potential influence of the seasons and on identifying
relevant biomarkers for long-term human studies. It is anticipated that the National Monitoring Network
will be a key resource for many of the planned epidemiological studies and that laboratory animal studies will
likewise attempt to use this rich database to assess specific causality and susceptibility hypotheses that link to
potential chronic health outcomes.
What Have We Learned About PM Since 1997?
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A researcher checks the performance of a personal exposure
monitor. Exposure research is helping EPA to understand
when and how people are exposed to ambient PM, even
when they spend significant amounts of time Indoors.
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Susceptible
Subpopulations
lat subpopulations are
at an increased risk of
adverse health outcomes from
particulate matter?
What Have We Learned About PM Since 1997?
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Epidemiological studies in the 1990s indicated that risks of adverse effects from PM are higher in the
elderly, children, and people with cardiovascular or respiratory disease. Children, infants, diabetics,
and those with hypertension may also be at increased risk. EPA research, including clinical studies
using human volunteers and novel animal models of disease, has begun to examine the biochemical and
physiological mechanisms of PM-associated risks. For example, a number of studies have investigated the
underlying biology of lung disease to understand why disease induces heightened sensitivity to PM. These
studies used animal models of lung disease to show that animals with existing pulmonary inflammation may
be intrinsically more responsive to PM. Similarly, a growing body of work has demonstrated PM-induced
alterations in cardiac physiology in both humans and animals and has reinforced the hypothesis that PM
exacerbates cardiovascular disease conditions. Studies in healthy elderly adults have demonstrated that
exposure to concentrated ambient PM causes subtle changes in autonomic control of cardiac function and
clotting factors. Although small, these changes are considered clinically significant based on other studies of
cardiac disease progression.
Susceptible Subpopulations
Effect of PM10 (per 100 pg/ms)
Among People with Each Predisposing Condition
Individual Covariate
Pattern
None of the five conditions
Myocardial Infarction
Diabetes
Congestive Heart Failure
COPD
Conduction Disorder
Increase 95%
in Risk Confidence Interval
23.7%
15.1%
12.9%
5.8%
6.8%
9, 19.1)
(-0.6, 53.8)
(-1.6, 34.1)
(-1.0, 28.8)
(-7.9, 21.5)
(-5.6, 20.8)
The risk of mortality associated with exposure to elevated levels of ambient PM increases, In some cases substantially,
for people with pre-existing health problems. Researchers are studying why certain groups may be more sensitive to the
effects ofPM than others, which can help In the development of public health responses to air pollution events.
EPA's Participate Matter Research Program
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' ':" ':he results supported previous
'>' findings identifying those
with pre-existing cardiopulmonary
conditions at increased risk for
ambient PM effects and implicated
another possible risk factor—
diabetes.
Epidemiological data are emerging on certain types of
medical conditions that potentially predispose individuals to
an increased risk of PM-associated mortality. Recent studies
found that those with pre-existing cardiopulmonary disease or
with diabetes were at increased risk for PM-related effects.
Researchers have begun to investigate the effects of PM
exposures on physiological development in children. The
Southern California PM Research Center is supporting
assessment research on PM and traffic exposure for the
ongoing California Children's Health Study, which has reported an increased risk of impaired lung
development in children living in areas with higher levels of air pollution. Other studies are examining PM
effects in young animals to identify possible effects of prenatal and postnatal exposures.
Thus, studies to date suggest that certain subpopulations are indeed more acutely responsive to PM,
perhaps due to differences in lung deposition or to other biologic aspects of the cardiopulmonary system
or disease. Emphasis on the identification and characterization of susceptible groups will continue, as will
determining whether prolonged PM exposure moves one into a more susceptible state by impairing defenses
or diminishing function. The role of genetic predisposition is largely unknown, but is potentially of great
importance. Another key topic that has not yet been adequately addressed is individual risk and the elements
that define or underlie that risk.
...there is sufficient evidence to conclude that
certain groups are likely to be more sensitive
or responsive to PM than others.
What Have We Learned About PM Since 1997?
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Mechanisms
of Injury
"¥ TT That are the underlying
V V mechanisms (local
pulmonary and systemic) that
can explain the epidemiological
findings of mortality/morbidity
associated with exposure to ambient
particulate matter?
What Have We Learned About PM Since 1997?
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o understand the underlying biological mechanisms that explain how PM might cause adverse
health effects, ORD has investigated several hypotheses. The mechanisms of PM toxicity are
potentially quite complex and may involve interactions and/or interdependencies between several
organ systems or tissues such as the lung, heart, vascular system, and autonomic nervous system. The primary
portal of entry for PM air pollution is clearly the lung, and PM interactions with the lining of the lung may
lead to immunologic and other responses that cause a wide range of pulmonary effects. These effects include
lung injury, inflammation, and changes in resistance to infection or sensitivity to allergens. Exposure to PM or
its reaction products may also alter respiratory rate and tidal volumes. Soluble components of PM may diffuse
into the circulatory system and may be distributed systemically
or may perhaps activate cells within the lung to secrete mediators
that likewise can move throughout the body. Not surprisingly
then, PM appears to exert a number of systemic effects,
particularly on the cardiovascular system.
<*he presence or absence of
an inflammatory response
is an important issue because
inflammation may induce systemic
effects.
The growing number of reports associating PM with cardiac
death, morbidity, or altered cardiac function has spurred
new thinking about how these problems could occur. One route under investigation by EPA is via neural
mechanisms involving the autonomic nervous system. PM may act via direct pulmonary irritant reflexes in the
airways or through reflexes activated during pulmonary inflammation. This effect could affect cardiac function
via nervous system networks that operate to protect the lung or maintain homeostasis. Inflammatory changes
in the heart or stimulation of bone marrow cells could modulate or impair normal function in an already
diseased or stressed heart. Other studies report altered blood viscosity or circulation of cells, both of which
are consistent with an increased risk of cardiac events. Because PM is a complex mixture of many different
components, different components may stimulate different biochemical pathways or interact in other ways to
alter the dose required to evoke a response. Thus, exposure to PM, depending on its chemical and physical
makeup, may result in the activation of one or more pathways.
Chapel Hill (NO CAPs [concentrated ambient particles! cause mild pulmonary
inflammation...
Los Angeles CAPs land! carbonaceous ultrafine particles provide evidence of systemic
markers of inflammation.
PM has also been shown to induce changes in conductance and repolarization of the heart.
Some studies are reporting PM induced increases in several clotting and coagulation
factors and vascular inflammatory cells... that might trigger cardiovascular events.
EPA's Participate Matter Research Program
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Five years ago, a description of PM health effects would typically include a caveat that the underlying
biological mechanisms were unknown. Recent developments that led to multiple novel hypotheses indicate
a rapid growth in our understanding of how PM can cause adverse effects. ORD, through its intramural and
extramural programs, will be focusing specifically on early and primary events to separate the effects of PM
from those of other stressors. Among various susceptible groups, there may be a common thread that explains
what contributes to susceptibility to PM and why health effects occur.
There are numerous pathways by which exposure to ambient PM can lead to cardiac events, including sudden cardiac
death. EPA's research is examining these biological pathways to better understand how PM affects health.
What Have We Learned About PM Since 1997?
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Analysis
and
Measurement
To what extent does the
choice of statistical methods
in the analysis of data from
epidemiological studies influence
estimates of health risks from
exposures to particulate matter?
Can existing methods be improved?
What is the effect of measurement
error and misclassification on
estimates of the association
between air pollution and health?
What Have We Learned About PM Since 1997?
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Since the early 1990s, more than 100 epidemiological studies have reported increases in mortality and
morbidity associated with exposure to ambient PM. Most of these studies relied on novel statistical
models or approaches and involved monitoring data not designed a priori for research use. To address
these concerns and in response to recommendations in the first NRC Committee report, EPA and the
University of Washington held a Workshop on Particulate Methodology in 1998. Since the workshop, many
statistical concerns have been addressed by more detailed temporal and spatial segregation of important
variables, independent re-analysis using alternate models, or a combination of databases for comparative
or more rigorous evaluations. Basic issues such as the adherence to dose-response principles and testing for
potential interactions with co-pollutants have also been addressed. Generally, investigators have concluded
that the health effects of ambient PM are not the result of a statistical or methodological anomaly, but
constitute a real and national problem.
r General
'opulation
Risk
Pool
Death
Is There Harvesting in the Association of Airborne Particles
with Daily Deaths?
Results of model analysis suggest that air pollution has a sustained impact on health. It increases the flow of people
(Tl) into the Risk Pool and reduces "recovery" (T2) further increasing the size of the Risk Pool as well as increasing
the those who succumb and move into T3. (Schwartz 2001)
EPA's Participate Matter Research Program
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The developments in statistical methods have allowed researchers to evaluate specific questions concerning
the nature of the mortality risks observed. For example, the question of whether deaths from air pollution
observed in times-series studies occur only in very ill people who are days away from death, even if not
exposed, has been addressed. These analyses indicate that individuals for whom death is imminent comprise
only a small portion of the deaths associated with PM exposure and reported in the time-series studies.
In 2002, statisticians raised the concern that risk estimates for acute PM health outcomes had been
overestimated because researchers had relied on a pre-programmed default assumption in a commonly
used statistical model. To address this issue, ORD convened a workshop in November 2002 to consider the
technical issues and to discuss how to overcome them. The studies deemed most relevant to the reassessment
of the PM NAAQS process were subsequently re-analyzed using alternative statistical techniques. HEI
conducted a peer review of the re-analyses and issued a report on its findings in May 2003. The re-analyses
indicate that the relationship between PM exposures and adverse health outcomes remains statistically
significant. The revised effects estimates were lower in most cases, although in some revised studies no
decrease was noted in the effects estimates. The HEI peer-review panel concluded that the fundamental
understanding of the association of adverse health effects with PM mass was not altered by the re-analyses.
In keeping with its basic health and implementation research efforts, ORD is attempting to associate
outcomes with emission sources and with principal components of PM. Improvements in monitoring
methods, exposure estimates, and data models/analyses will help refine risk assessments and will guide
regulatory activities appropriately.
[The ORD workshop]... led to a substantial clarification of the f
ji,
potential effects of problems in the use of general additive |
models... |
...it appears that the existence of a statistical link between I
t
exposure to ambient PM and health outcomes remains valid... if
What Have We Learned About PM Since 1997?
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Instrument for measuring PM concentrations.
-------
Technical
Support
A
Itmospheric Measurements
and Methods4
4 Projects and methods that support issues are addressed under Research Topics 3 and 4.
What Have We Learned About PM Since 1997?
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/'" ;; ince 1997, EPA has made significant advances in the development and field application of methods to
' 4i, /. measure PM. These efforts are broad-based, range from state-of-the-art methods development and
:':*..:,.-/ validation to monitoring network design and PM characterization, and have relied upon coordinated
activities across the Agency and with the broader scientific community to achieve the program's advances.
With the establishment of the PM2S NAAQS, the refinement and standardization of a Federal Reference
Method for monitoring PM2 s became paramount. The PM2 s methodology has now been validated in the
field and used in the National Monitoring Network to collect the three years of data necessary for use in
compliance determinations. With the anticipated need to specifically sample coarse PM, prototype samplers
are entering their final testing phases. Ultimately, the goal for all these monitoring devices—which, at present,
use filters and usually provide 24-hour measurements—is to achieve continuous, real-time measurement that
can reveal rapid cycles and peaks not previously apparent.
In an effort to define new methods to advance monitoring technology and atmospheric science, EPA
established the PM Supersites Program. These seven sites distributed throughout the nation were
competitively selected to intensively characterize PM and associated co-pollutants and to provide
opportunities to test the latest technologies in aerometric analyses. Early on, EPA made great efforts to
coordinate with members of the private sector (the Electric Power Research Institute, or EPRI) and other
Federal agencies, either directly or through CENR and NARSTO.5 The five eastern sites were organized into
the cooperative Eastern Supersites Program that designed intensive, seasonal studies over a 13-month period
from 2001 to 2002. These data comprise the most extensive database on PM collected to date. Additionally,
many new technologies were tested and validated, including approaches to making continuous measurements,
single particle analyses, and others. The data from these studies are available on the web for public, scientific,
and programmatic use.
PM measurement techniques have advanced, but much remains to be done to bring these techniques into
wider application. Continuous and semi-continuous methods for PM mass (fine, coarse, and PM10) and
its major components are being developed. Likewise, with the emphasis on speciation of PM constituents,
methods for measuring the chemical composition and physical properties of single particles are also emerging
to complement more standard methods. In cooperation with the National Institute of Standards and
Technology (NIST), EPA has been collecting samples to be used as Standard Reference Materials.
5 Formerly an acronym for the North American Strategy for Tropospheric Ozone, the term NARSTO is now commonly used to signify this tri-
national, public-private partnership for dealing with multiple features of tropospheric pollution, including ozone and susp endedp articulate matter.
EPA's Participate Matter Research Program
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Conclusions
What Have We Learned About PM Since 1997?
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Five Years of Progress
As the preceding pages have illustrated, the first five years of EPA's expanded research program have led to a
wealth of new information and significant advances in PM science. EPA established a sound strategy, involved
many partners, and successfully conducted high-priority research. Highlights of key accomplishments include
the following:
Verification of PM-associated health effects: Studies showing that exposure to ambient PM can adversely
affect human health have been replicated many times in a number of locations throughout the U.S. and the
world. Generally, exposure to PM is associated with morbidity and mortality independent of the effects of
other gaseous pollutants in the atmosphere. Recent studies have also underscored that the elderly with pre-
existing cardiopulmonary disease appear to be most at risk. In addition, other groups such as the very young,
asthmatics, and diabetics may also be susceptible to the effects of PM. Even more striking are the findings
that suggest that extended exposure to PM can lead to chronic disease and/or shortened life span.
Confirmation of exposure measures: In 1997, the relationship between outside PM measurements and the
concentrations to which people were actually exposed was not known. Results from exposure studies have
verified that, for fine PM mass and sulfate, the central-site monitor should serve as an adequate surrogate
for exposure in community-based epidemiological studies. While the strength of the correlation may vary by
location, housing characteristics, and season, these data support the assumption used in health studies that
measurements of outdoor PM2 5 concentrations at central monitoring sites provide a valid representation of
personal exposure to ambient PM2 s. Exposure studies have also found that gaseous co-pollutants such as
ozone and nitrogen dioxide measured outdoors can serve as appropriate surrogates for personal PM2 s and are
not likely to interfere significantly with estimates of PM health risks.
Advances in dosimetry: Prior to the advent of the expanded PM Research Program, little was known about
the deposition of fine particles in the impaired lung. Since then, laboratory studies have shown that inhaled
PM is distributed unevenly in the respiratory tract and that actual dose at local airway regions can be many
times greater than the average lung dose. These studies determined that as many as 10 times more particles
are deposited in certain regions of the lungs of people with pulmonary disease. This may indicate that their
increased susceptibility is due to exposure to a higher dose.
Plausible biological mechanisms: While scientists could not explain the observed effects in epidemiological
studies from a biological basis five years ago, there are now multiple hypotheses describing the mechanisms by
which very small concentrations of inhaled PM may produce the cardiovascular and pulmonary changes that
contribute to increased illness and death. Similarly, laboratory studies and animal models that mimic human
EPA's Particulate Matter Research Program
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disease have stimulated several theories about how the physicochemical properties of PM produce toxicity.
Somewhat surprisingly, there appears to be no single attribute that makes PM toxic, but size and certain
chemical components (e.g., metals) appear to be involved. This is supported by both laboratory and field
evidence.
Development of predictive models and evaluative tools to achieve reduction in PM: EPA is improving
and developing tools to simulate and measure atmospheric processes and concentrations and is working to
identify and characterize sources of PM. It is developing several models to address the links between ambient
PM and emission sources. Such models are needed to estimate how much source-designated PM will reach
populations likely to be affected. EPA's emission-inventory data and accurate air quality models are being
applied to regions all around the country. The PM Research Program is also developing the specialized
measurement techniques needed to determine the detailed particle sizes and compositions of PM from diverse
and often widely dispersed unconventional sources such as wildfires.
Looking Ahead
As recognized by the NRC Committee in its original report, five years of expanded PM research are not
sufficient to answer all of the most pressing questions. The first, very productive portion of this program has
tackled many issues and laid the groundwork for addressing others. In addition, new research topics such
as linking sources of PM to ambient concentrations and to health effects have emerged as promising areas
for further research. Looking ahead, EPA will sustain its commitment to PM research to ensure that future
reviews of the PM NAAQS are on the strongest scientific footing possible and that tools are available to
implement the standards efficiently, effectively, and as inexpensively as possible. Highlights of future efforts
include the following:
Effects of long-term exposure to PM: The role of long-term PM exposure in the development of chronic
disease and how this long-term exposure combines with short-term fluctuations in PM levels to trigger acute
events such as heart attacks is far from understood. In 2003, EPA issued a request for research grant proposals
to conduct a 10-year longitudinal epidemiological study to examine the health consequences of long-term
exposure to PM.
Biological mechanisms explaining susceptibility to PM effects: Now that several plausible mechanistic
hypotheses have emerged, EPA will investigate their significance. These investigations will likely focus on
human subpopulations and animal models with cardiopulmonary and associated systemic diseases that appear
to contribute to PM sensitivity.
What Have We Learned About PM Since 1997?
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PM attributes and source apportionment of health effects: We still do not understand enough about the
physicochemical properties of PM and how they relate to health outcomes. Source attribution of health effects
is a growing area of interest, and ORD plans to expand exposure, toxicological, and epidemiologic research to
pursue source-based linkages of hazardous components and effects. Through these efforts, the contributors to
PM's adverse health effects can be more appropriately targeted for mitigation.
Air Quality Criteria Document (AQCD) for PM: By the end of 2004, EPA will complete its comprehensive
assessment of PM science, the Air Quality Criteria Document for Particulate Matter. This document, which
is required prior to the regulatory review of the NAAQS, will consider the findings of over 2,000 studies
published since the last assessment in 1996. With completion of EPA's Office of Air Quality Planning and
Standards (OAQPS) Staff Paper that evaluates the policy implications of the key scientific information, EPA
will issue a decision concerning possible revision of the PM NAAQS based on the science delineated by the
AQCD.
Human exposure to PM constituents and PM from specific source types: Exposure studies suggest that
ambient concentrations provide an adequate surrogate for personal exposure to ambient fine particle mass
and sulfate in community-based epidemiological studies. However, the same may not hold true for other
components. Research is needed to evaluate exposures and health effects for those components associated
with specific source types. EPA's exposure program will provide information to associate actual human
exposure to ambient levels of PM components and PM from specific sources, which will provide the basis for
more complete understanding of the relationships between source-specific PM and adverse health effects.
Tools for developing PM control strategies: With more than two years of PM2 5 monitoring data now
available from the National Monitoring Network, there is a pressing need for accelerated research related
to the development of the tools and data needed by states and others for the development of approaches
designed to achieve the PM standards. Such data includes the characterization of emissions and improved
regional and local atmospheric modeling of PM2 5. The next generation of analytical tools to help EPA
and the states with NAAQS implementation was released by EPA in 2003. In 2004 and 2005, OAR will
announce which states and regions are not in compliance with the NAAQS based on PM2 s monitoring and
modeling data. This announcement will require the states and regions to develop plans and strategies that will
enable them to meet the NAAQS. Additional EPA research will focus on likely causes of states and regions
being unable to attain the standards beyond failure to implement current and pending regulations to reduce
emissions such as local concentrations of carbonaceous particles.
EPA's Particulate Matter Research Program
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Continuation of research partnerships: EPA's successes in the sciences that have expanded our
understanding of pollutant emissions, transport, and transformation, as these relate to exposure and
associated health effects of ambient PM have resulted from the combined work of EPA scientists, EPA-
funded researchers, and our federal and academic partners. As the scope of studies increases, it becomes
increasingly important to build upon these partnerships, such as with HEI, to achieve the goals of the
program. Epidemiological research to evaluate the effects of PM and co-pollutants across multiple and
diverse locations as a means to better understand how the emissions from specific source types are linked to
health effects is one example of a large-scale effort that can benefit from strategic partnerships, and continue
to provide the science needed to refine future air quality standards.
In addition to the research directions highlighted previously, EPA will rely on the final report of the NRC
Committee to determine whether any additional changes in research direction are warranted. In this way,
EPA's partnership between ORD and OAR remains an essential part of its efforts to achieve the Agency's
Clean Air Goal. EPA will continue to integrate its diverse, yet targeted, health and implementation
research agenda to ensure that air quality standards are scientifically sound and that approaches to achieving
compliance with these standards are based on information and technical tools that are as accurate and effective
as possible.
What Have We Learned About PM Since 1997?
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References
National Research Council (1998). Research Priorities for Airborne Particulate Matter: I. Immediate Priorities and a Long-
Range Research Portfolio. Washington, DC: National Academies Press. ISBN 0-309-06094-X.
National Research Council (1999). Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and
Updating the Portfolio. Washington, DC: National Academies Press. ISBN 0-309-06638-7.
National Research Council (2001). Research Priorities for Airborne Particulate Matter: III. Early Research Progress.
Washington, DC: National Academies Press. ISBN 0-309-07337-5.
Lippmann, M., M. Fampton, J. Schwarz, D. Dockery, R. Schlesinger, P. Koutrakis, J. Froines, A. E. Nel, J. Finkelstein, J.
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Kim, C.S., andT.C. Kang (1997). "Comparative measurement of lung deposition of inhaled fine particles in normal
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Ghio, A. J. and R. B. Devlin (2001). "Inflammatory lung injury after bronchial instillation of air pollution particles." Am
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Dye, J. A., J. R. Lehmann, J. K. McGee, D. W. Winsett, A. D. Ledbetter, J. I. Everitt, A. J. Ghio and D. L. Costa
(2001). "Acute pulmonary toxicity of particulate matter (PM) filter extracts in rats: Coherence with epidemiological
studies in Utah Valley residents." Environ Health Persp 109(Supplement 3):395-403.
Williams, R., J. Creason, R. Zweidinger, R. Watts, L. Sheldon and C. Shy (2000). "Indoor, outdoor, and personal
exposure monitoring of particulate air pollution: The Baltimore elderly epidemiology-exposure pilot study." Atmospheric
Environment 34:4193-4204.
Williams, R., J. Suggs,}. Creason, C. Rodes, P. Lawless, R. Kwok, R. Zweidinger and L. Sheldon (2000). "The 1998
Baltimore particulate matter epidemiology-exposure study: Part 1-Comparison of ambient, residential outdoor, indoor
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EPA's Particulate Matter Research Program
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