National Academies Press: OpenBook
« Previous: 2 Evaluating Research Implementation and Progress
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

3
UPDATING THE RESEARCH PORTFOLIO

The committee intends its portfolio of PM research recommendations to be a dynamic document that will be updated and revised as research results are obtained and changing circumstances warrant. In this chapter, the committee updates and discusses further the ten high-priority research topics presented in its first report (NRC 1998). Most of the recommendations remain substantially unchanged, but research topics 3 and 4 are revised and renamed because of recent developments and further consideration of the current and planned emissions characterization, air-quality model development, and ambient monitoring activities of EPA and other agencies and organizations.

RESEARCH TOPIC 1 OUTDOOR MEASURES VERSUS ACTUAL HUMAN EXPOSURES

What are the quantitative relationships between concentrations of particulate matter and gaseous copollutants measured at stationary outdoor air-monitoring sites, and the contributions of these concentrations to actual personal exposures, especially for potentially susceptible subpopulations and individuals?

Background

As discussed in the committee's first report, currently available information is not sufficient to characterize the relationships of ambient

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

air concentrations of PM and gases to actual human exposures that include indoor environments. Most people spend the majority of their time indoors exposed to a mixture of particles that penetrate from outdoors or are generated indoors. Personal exposures to certain air pollutants have consistently been found to differ from estimates based on corresponding outdoor concentrations. The differences are largely due to the variable contributions of outdoor air to indoor environments, the indoor fate of outdoor contaminants, and the substantial contribution of indoor sources and sinks to total personal PM exposures (Lioy et al. 1990). Studies have found that a significant fraction (50–90%) of small indoor particles have outdoor origins (Koutrakis et al. 1992; Clayton et al. 1993; Thomas et al. 1993). Once indoors, particles may deposit on surfaces, or they can be altered through volatilization, as with ammonium nitrate, or through reactions with other pollutants present indoors, as with neutralization of sulfuric acid by ammonia. Particles are further generated by myriad indoor particle sources, including cooking, resuspension, cleaning, tobacco smoking, pets, insects, and molds. The emission rates of most indoor-particle sources, however, have not been adequately quantified. Furthermore, factors that affect the contribution of outdoor particles to indoor concentrations have not been well characterized.

In its first report, the committee concluded that information is needed on relationships between particulate matter in outdoor air and personal exposure to particulate matter, especially for subpopulations that may be susceptible to the effects of PM exposures, such as the elderly, individuals with respiratory or cardiovascular disease, and children. Hypothesis-driven exposure studies must be designed to provide fundamental information on actual human breathing-zone exposures to PM and gaseous pollutants (NRC 1991). The recommended studies should be used to determine the exposure metrics that are most suitable for establishing exposure-response relationships. To attain these goals, the following specific research activities were recommended in the committee's first report:

  • Field studies that quantify the contributions to personal exposures to PM and gaseous pollutants attributed to outdoor ambient air and to the penetration of ambient air indoors.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
  • Longitudinal panel studies, in which groups of individuals are studied at successive points in time, to examine interpersonal and intrapersonal variability, as well as seasonal and temporal variability in PM exposure.

  • Analyses of information collected from such field and longitudinal studies to determine the contributions of outdoor versus indoor sources for each pollutant, and to examine the degree to which the use of more accurate exposure information would, or would not, alter the findings of epidemiological time-series studies concerning particulate matter and adverse health effects.

The sampling of particulate matter should include measurements of PM2.5 and PM10. as well as other relevant descriptors of particulate matter that might be of value in understanding the impact of particulate matter on human health. The design and execution of a typical panel exposure-assessment study will take approximately 3 years for subject recruitment, field measurements, collection of time-activity data, and data analysis. This research should include potentially susceptible populations in various geographical locations.

Update

At the committee's June 1998 meeting, Dr. Judith Graham of EPA's Office of Research and Development (ORD) presented a particulate-exposure research plan initiated by EPA in response to the committee's first report. That plan includes substantial changes in EPA's allocation of research resources that the committee finds highly commendable. The program will bring about new in-house and extramural research projects and related personnel changes that are highly consistent with the committee's recommendations. Much of the plan has been implemented and has begun to yield results. Overall, these recent efforts by EPA to support human exposure-assessment research for particulate matter are substantive and promising.

In budget terms, Congress increased the resources devoted to research in this area from $3.6 million in the President's proposed budget

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

for Fiscal Year 1999 to $8.2 million in 1999 appropriations, and EPA has proposed a budget of $7.9 million for Fiscal Year 2000 (see Table 1.4).

Studies conducted by EPA scientists in EPA laboratories will characterize microenvironmental particulate exposures to provide information for the development of exposure models. They will characterize and assess human exposures to fine particles to enhance understanding of sources of these particles and their spatial and temporal profiles. Using an experimental model home, EPA scientists will also investigate processes governing the penetration of outdoor particles into indoor environments and their deposition onto indoor surfaces to determine the contribution of outdoor sources to indoor and personal exposures.

EPA is establishing cooperative agreements with universities to characterize the exposures of sensitive subpopulations to particulate matter and related gaseous pollutants. Under these cooperative agreements, studies will be conducted in several urban environments that are characterized by different particle composition and meteorological conditions, including New York, Boston, Atlanta, Los Angeles, and Seattle. The main objectives of these studies are (1) to characterize the personal particulate and gaseous exposures of sensitive as well as healthy individuals; (2) to identify factors affecting such exposures and their corresponding personal exposure versus outdoor concentration relationships; (3) to develop models to predict individual exposures and population exposures to fine-particle mass; and (4) to determine the contribution of outdoor and indoor sources to personal particulate exposures. Under one of the cooperative agreements, studies will also determine the correlations between personal particulate and gaseous exposures.

In each of the cooperative agreements, a large number of personal, indoor, and outdoor measurements will be made in winter and summer for several susceptible subpopulations, including children, senior citizens, asthmatics, and individuals with chronic obstructive pulmonary disease and myocardial infractions. Together, these studies will provide a powerful data base that can be used to characterize particulate exposures for susceptible populations, to determine inter-and intrapersonal variability in particulate exposures, and to quantify and statistically characterize the measurement error that results from exposures

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

estimated from single outdoor monitoring sites. These findings will be useful for the interpretation of results from epidemiological studies and for the accurate determination of exposure-response relationships.

In addition to the mass-based PM2.5 monitoring program being implemented for regulatory compliance assessment, EPA's air regulatory program office is planning to develop two additional particle-monitoring programs: a chemical-speciation monitoring program and a supersites program. The Primary objective of the speciation-monitoring program is to measure particle composition to aid states and EPA to develop and evaluate particle control strategies. The main objective of the supersites program is to develop a better scientific understanding of source-receptor relationships through intensive monitoring of several representative airsheds using state-of-the-art sampling and analytical techniques.

In response to the committee's first report and other considerations, EPA convened expert panels to provide design guidance for both of the additional monitoring programs. Both panels included exposure scientists who contributed to the final monitoring design. It is anticipated that these monitoring programs will produce data that may be used by future particle-exposure studies, because the networks will monitor the spatial and temporal variability of particle mass and its components in several locations throughout the United States. The committee also urged the integration of exposure and health-effects studies into the supersites program. The committee believes that stronger interactions between the atmospheric-modeling and health-science communities are needed to ensure that the programs will be of significant value.

EPA's National Exposure Research Laboratory is hiring additional exposure-assessment experts who will conduct and oversee related research activities. These experts will be assisted by scientists within EPA's exposure and engineering laboratories who have been assigned to work on particle-exposure projects. Further support will be provided by several postdoctoral fellows who have recently joined EPA to conduct particle-related research.

In addition, EPA has begun to improve coordination of its exposure research activities with those conducted by other organizations such as the Health Effects Institute (HEI), Electric Power Research Institute

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

(EPRI), and American Petroleum Institute (API). This coordination will help to ensure that cost-effective research is being conducted to address all particulate exposure research needs.

The committee believes that the EPA efforts described above will make it possible to address most of the exposure research needs included in Research Topic 1 of the committee's first report.

The exposure-assessment research recommendations in the committee's first report placed initial emphasis on needs for short-term measurements of personal exposure to be compared with outdoor exposures to particulate matter in a cross section of locations, using sensitive subgroups and healthy members of the general population. The next set of exposure measurements needed will be concurrent long-term studies of population exposure to particulate matter and copollutants. The design and resources required will be dependent upon the results of the near term research described in the first report. Of particular interest will be the results obtained to define personal exposure to particulate matter and its constituents and to identify biologically active agents and mechanisms of action.

RESEARCH TOPIC 2: EXPOSURES OF SUSCEPTIBLE SUBPOPULATIONS TO TOXIC PARTICULATE-MATTER COMPONENTS

What are the exposures to biologically important constituents and specific characteristics of particulate matter that cause responses in potentially susceptible subpopulations and the general population ?

Background

In its first report, the committee recommended a group of studies to begin about the year 2001, as information improves on PM constituents and as specific chemical constituents or particle-size fractions are indicated as plausible causal agents. These studies should quantify exposures to those constituents for the general public and susceptible subpopulations. The process of obtaining information on such exposures will be iterative, with information developed from earlier studies

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

guiding the planning of later studies. Population-based field studies will provide information on the distribution and intensity of exposure of the general population to experimentally defined particle components and size fractions. The studies should be conducted for statistically representative groups of the general population and for potentially susceptible subgroups. The studies could be coupled to health-outcome investigations, but they should be designed to determine the extent to which members of the population contact these biologically important constituents and size fractions of concern in outdoor air, outdoor air that has penetrated indoors, and air pollutants generated indoors.

In its first report, the committee recommended that the following specific research tasks be addressed in Research Topic 2, after obtaining and interpreting results of studies and information from Research Topic 1:

  • Measure population exposures to the most biologically important constituents and size fractions of particulate matter. These exposure studies should include members of the general population and potentially susceptible subgroups, using personal-monitoring studies and ambient stationary sites to examine the contributions of outdoor pollutants to total personal exposure.

  • Refine sampling and analysis tools to permit their routine application for the determination of biologically important chemical constituents and size ranges of particulate matter.

Some of the recommended population-exposure studies could be initiated soon, but a more targeted set of studies under this research topic should await a better understanding of the physical, chemical, and biological properties of airborne particles associated with the reported mortality and morbidity outcomes. The exposure research should then be conducted expeditiously to inform decisions on source-reduction strategies. Focusing on the specific toxicity-determining attributes of particulate matter will be essential to make population-exposure studies cost-effective.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

Update

Research Topic 2 of the committee's first report called for a more comprehensive approach to particle-exposure assessment, emphasizing the need for characterization of particulate exposures of large populations. Most of the research activities included in this topic are not expected to commence until about 2001, when information from toxicological studies becomes available. However, the committee recommends that it would be beneficial to start small-scale studies immediately to develop new tools and information to design the new generation of exposure research projects. Examples of such studies include the following:

  • Comprehensive intercomparison study of personal samplers—Intercomparison studies of personal samplers are necessary to evaluate the performance of personal sampling devices and to ensure that data sets from different exposure studies are comparable.

  • Temporal-variability studies of personal exposures—Studies examining temporal variability in personal exposures will enable better information to be obtained about the duration and frequency of human exposures. The National Ambient Air Quality Standard (NAAQS) for PM2.5 was based on 24-hour time intervals because epidemiological studies examined the exposure-effect association using 24-hour ambient particle concentrations and health measurements. However, future toxicological investigations and future epidemiological studies may provide a better scientific basis for choosing the appropriate time interval of the exposure.

  • Exposure misclassification studies—As mentioned previously, several exposure studies will examine the relationship between personal exposures and outdoor concentrations. Will these data be sufficient to investigate the effect of exposure misclassification? Do we need to perform additional studies to provide complementary data sets? To make this decision, epidemiologists and exposure scientists will need to work together to develop the analytical framework for this research. Care should be taken to define the

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

spatial and temporal variability of outdoor, indoor, and personal exposure concentrations.

  • Pilot studies characterizing the physicochemical characteristics of pollutants to which individuals are exposed—Pilot projects investigating the physicochemical characteristics of pollutants to which individuals are exposed will make it possible to identify factors affecting exposures to different particle components and sizes. This is necessary for the design of the future population-exposure studies. Such pilot studies should include development of sampling and analytical methods for biological-particle components and refinement of questionnaires for selection of representative populations.

  • Individual and population-exposure modeling studies—The development of individual-and population-exposure models will allow personal exposures to be characterized for large study populations without the need for expensive personal monitoring. These models will likely use information on human activity patterns and microenvironmental concentrations or characteristics to predict short-and long-term exposures.

REFOCUSING RESEARCH TOPICS 3 AND 4

Sound strategies to manage PM risks will require an improved understanding of relationships among the sources of particulate matter, the atmospheric processes that transport and transform it, and the concentrations of particulate matter to which populations are exposed. Computer models based on such understanding will provide state and local air-quality agencies with the tools necessary to develop state implementation plans that control emissions in ways that (1) focus on the most biologically active and relevant components of the PM mixture, and (2) identify cost-effective strategies for reducing the exposure of the general population to those emissions.

In preparing this second report, the committee reviewed current and

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

planned emission-source characterization, model development, and ambient monitoring activities of EPA, other federal, state, and local agencies, the research community, and the private sector. The committee received briefings from the CENR Air Quality Subcommittee, NARSTO, and EPA's Office of Air and Radiation (OAR) on plans for speciation monitoring and supersite monitoring. Based on that information, the committee has refocused and renamed topics 3 and 4 of the research portfolio to integrate more closely these implementation-related research activities, including the development and evaluation of emission-source characterization techniques (see revised Research Topic 3), and source-oriented and receptor-oriented air-quality models (see revised Research Topic 4).

The attainment of national PM risk-reduction goals will require active collaboration (see Figure 3.1) among the research community, OAR and ORD of EPA, other federal, state, and local agencies, and the private sector. Research efforts will be needed to develop and evaluate source-measurement techniques and source-oriented and receptor-oriented models, as described below in revised topics 3 and 4. However, the ultimate success of these research efforts will depend in large part on the collection of key data on particle and precursor concentrations and composition, regardless of whether those data are collected by research organizations, federal and state regulatory programs, or others. Specifically, these efforts will require

  • Collection of emissions data for major categories of sources, and development of the speciated and size-resolved emission inventories necessary to operate and evaluate particle models.

  • Collection, through compliance, speciation, and supersite monitoring programs, of the meteorological and air-quality data that will be necessary to evaluate the performance of particle models.

The paradigm presented in Figure 3.1 calls for a synchronization of activities and extensive collaboration among atmospheric, exposure, and health scientists, as well as among federal, state, and private research and control programs. Efforts by health-effects and exposure-

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

Figure 3.1 A paradigm for scientific and technical activities related to particulate matter.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

assessment scientists are needed to refine (or redefine) the list of particle properties for which atmospheric scientists and environmental engineers and modelers must account. Under the present, real-world constraints of limited time and finite resources, it is essential that efforts be targeted at the most biologically active components of airborne particulate matter. Plausible candidates for biologically active components include several metals, organics, acid sulfates, biogenic agents, and ultrafine particles of any composition.

The distinction with broadest implications for air-quality management is that between primary and secondary particulate matter. Most acid sulfate and some organic material is not directly emitted, but instead is produced by chemical reactions after emissions, forming secondary atmospheric particles over time. Secondary particles generally exhibit more uniform concentration fields, because the processes of chemical formation and physical dilution proceed simultaneously to distribute the product species throughout large air volumes. Secondary particles are major contributors to the regional haze monitored by nonurban samplers. Primary particles are found instead in highest concentrations near their sources, where the least dilution and sedimentation have occurred. Primary particles thus tend to be more important in the atmospheres of urban-industrial population centers. A strategy for the management of secondary particulate matter must be regional in scope, while a strategy for primary particles could legitimately emphasize concentration ''hot spots."

A critical issue in the development of source-receptor modeling tools is the relative roles of source-oriented and receptor-oriented approaches. Source-oriented models, which range from simple plume-dispersion formulae to complex grid models, start from emissions rates and predict expected ambient concentration fields. The models incorporate mathematical representations of critical chemical and physical processes to simulate the transport and transportation of particulate matter in the atmosphere. Receptor-oriented models (e.g., chemical mass balance) begin with particle chemical composition measured in ambient air and at various sources, and infer the relative source contributions to each individual ambient sample by calculating the mixture of effluents needed to account for the observed chemical composition. The models rely on empirical observations to sort out source-receptor

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

relationships statistically. For stable primary particles, receptor models yield credible and precise apportionments of ambient particulate matter between certain contributing source categories. For secondary particles, on the other hand, the transformations by which they are formed are difficult to account for outside the framework of a source-oriented model that incorporates the relevant atmospheric processes.

In its first report, the committee commented upon EPA's plans for the implementation of the national PM2.5 monitoring system, including some 1,500 compliance and speciation monitors and 5–7 supersites. Based on that initial review, the committee stated

"The committee is concerned about the scientific value of the data to be collected in these efforts if such monitoring is fully planned and implemented before some of the immediate research priorities are addressed and data gaps are filled. Moreover, as a secondary but critical goal, such a monitoring system should also be designed to support relevant health-effects, exposure, and atmospheric-modeling research efforts, or else the cost of some important research will increase substantially because of the need for additional monitoring." (NRC 1998, p. 9)

The committee also noted

"Greater use of continuous (hourly) monitors would help determine the times of day and the exposures of people who are commuting, working, or exercising outdoors. More chemical characterization of particulate matter would help to enable testing of more specific indicators than PM2.5 mass alone." (NRC 1998, p. 10)

"Data-collection efforts for model development and testing will require substantial additional resources if the data need to be collected independently of EPA's PM2.5 monitoring program. The additional costs could be as high as $2.0 million to $10 million per urban area." (NRC 1998, p. 59)

After its first report was released in March 1998, the committee met three times with staff from EPA and other agencies and organizations

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

to review the state of the monitoring program and to evaluate the degree to which EPA would be addressing the concerns expressed above. In addition, committee members participated in a workshop held by EPA and NARSTO on July 22–23, 1998, and a workshop held by NARSTO on January 27–29, 1999, that brought together federal, state, and local monitoring specialists with members of the health, exposure-assessment, and atmospheric-modeling research communities to provide guidance for the implementation of the supersites program, and for the integration of that program into the broader monitoring system.

Based on these reviews, the committee found that EPA made several noteworthy adjustments in the plans for the atmospheric-monitoring programs that will improve its ability to provide data useful to meet key research needs. Specifically, EPA reported that it has increased the number of "continuous" PM2.5 monitoring sites from 50 to more than 100 nationwide, and it has revised plans for the routine speciation-monitoring program to include 44 trend sites where speciation will occur every third day, and ten sites where PM chemical-speciation measurements will be made every day. These changes will improve the ability of the monitoring system to provide the measurement data necessary to (1) test and characterize the Federal Reference Method for measuring PM2.5, (2) conduct more-detailed health and exposure research aimed at specific components of particulate matter, and (3) provide initial data for operation and testing of source-oriented and receptor-oriented models. Whether the capability to support health studies and model evaluation studies will actually be used for these purposes remains unclear at present. The committee urges EPA to obtain greater input from the atmospheric-modeling and health-science communities in the design of these monitoring programs, especially the supersites program.

In the following pages, the committee refocuses and renames research topics 3 and 4 from its first report to reflect recent developments and additional information about EPA's revised plans for the PM2.5 monitoring network. Research topics 3 and 4 are intended to describe an entire realm of implementation-related research (i.e., research related to implementation of the PM2.5 NAAQS). In this report, certain methodological development needs cited in the previous report

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

have been reallocated to other tasks in the portfolio with which they are closely aligned. Specifically, in the following pages, the committee

  • Makes more explicit its earlier calls for enhanced source-emissions characterization by refocusing Research Topic 3 on the research needed to develop sophisticated techniques to characterize not only source emissions of particle mass, but other characteristics and components of the emissions as well.

  • Refocuses Research Topic 4 on the development and evaluation of source-oriented and receptor-oriented models and increases somewhat the resources recommended for this topic to reflect a better understanding of areas where the planned EPA monitoring will not provide adequate data for model evaluation and where additional research measurements may be necessary (NRC 1998, p. 59).

  • Reallocates the development of exposure-assessment technologies previously contained in research topics 3 and 4 to the year 2000 for topic 2 (where those techniques will be applied), and the development of advanced analytic methods for monitoring biological responses to toxic PM components.

In contrast to the other research topics, which are simply updated in this chapter, the revised topics 3 and 4 are discussed more expansively in the following pages, using the format in which topics were originally presented in the committee's first report.

In addition, as noted above, the committee continues to see the need for a substantial investment from federal and state regulatory programs and other organizations in conducting source characterizations, developing emissions inventories, and providing the detailed, sustained, and quality-assured monitoring data that will ultimately be necessary to operate and evaluate any models developed under Research Topic 4. Absent of these investments, the research program described in topics 3 and 4 would be substantially more expensive, or it will be unable to accomplish the goal of providing reliable models in time to assist the states in developing effective state implementation plans.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

At its September 1998 meeting, the committee received an updated briefing on the status of the ambient-monitoring programs, including the timetable and organizational structure for implementing the supersites in the context of the larger health, exposure, and atmospheric research program now underway. Several scientists commented previously that the program lacked (1) coordination and leadership to bring together the research program staff and air regulatory staff who must implement it, (2) ongoing mechanisms to provide continued interaction and linkage with outside health, exposure, and atmospheric research communities, and (3) a timely, but deliberate, implementation schedule to ensure that such sites will be an integral part of the measurement program. In response, at the committee's November 1998 meeting, EPA presented a revamped structure and timetable for implementation. The committee commends EPA for taking steps to promote better integration of this important measurement effort into the implementation of the overall research program. In addition, the committee wishes to emphasize the importance of regularly incorporating the experience and expertise of the outside health-and exposure-research communities into the planning and implementation of this program (see Chapter 2).

RESEARCH TOPIC 3 (REVISED): CHARACTERIZATION OF EMISSIONS SOURCES

What are the size-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?

As discussed above, this is a revised and renamed research topic, replacing Research Topic 3 in the committee's first report.

Description

Airborne particles are emitted from a large variety of anthropogenic and natural sources. Natural sources are many, including forest fires

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

and wind erosion. In cities, several hundred different particle source types can be broadly classified into motor-vehicle exhaust sources, stationary fuel-combustion sources, industrial processes, and fugitive area wide sources. Many different activities fall within each of these categories. Motor-vehicle exhaust emissions arise not only from automobiles and light-duty trucks, but also from heavy-duty diesel trucks and buses, railroad locomotive engines, engines in nonroad construction equipment, marine diesel engines, and aircraft engines. Stationary fuel-combustion sources include boilers, refinery process heaters, and gas-turbine engines—each capable of being built to burn a variety of fuels. Industrial processes range from rock crushers that emit large mineral-dust particles to chemical processes that emit finely divided acid mists and metal-melting furnaces that emit fumes containing fine particles of toxic metals. The category containing fugitive area wide sources is particularly difficult to characterize thoroughly. It includes all of the particle emissions that result from personal activities and many commercial activities in the community, such as the particles released from food cooking, fireplaces and wood stoves, paved and unpaved road dust, construction and demolition dust, wildfires, backyard leaf burning, structural fires, and so forth (Hildemann et al. 1991).

Particles that are directly emitted from sources are transported through the atmosphere in the presence of chemically reactive gases including ozone, sulfur dioxide (SO2), oxides of nitrogen (NOx), ammonia, and volatile organic compounds. Over time, the directly emitted particles become coated with the low-vapor-pressure products of atmospheric chemical reactions involving the pollutant gases mentioned above. As a result, the particle-mass concentration in the atmosphere may increase as primary particles incorporate additional sulfates, nitrates, and organic compounds. The source emissions of reactive gases that act as secondary-aerosol precursors must be characterized if their role in the particle formation process is to be understood and controlled.

Traditional source-test methods for particulate matter typically have been used to determine particle-mass emissions aggregated over all particles smaller than a certain size, with little regard for determination of the chemical composition of the particles. Such measurements are clearly inadequate to support management strategies targeted at specific components or characteristics of particulate matter that health

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

scientists may come to identify as biologically important. Measurements that lack detailed information on particle size and chemical composition are also inadequate to the needs of atmospheric scientists seeking to understand details of atmospheric transport and transformation. For example, atmospheric models that are capable of tracking the accumulation of gas-phase atmospheric reaction products onto preexisting particles require that the size distribution of the emitted particles be known over narrow slices of the particle-size distribution (typically in 15 particle-size intervals or, alternatively, as a continuous size-distribution function over the particle-size range from about 0.01 μm to at least 10 μm in diameter). The chemical composition of the particles in each size interval must be specified to calculate the water-uptake and chemical-thermodynamic status of the particles, which greatly influence whether the particles will interact with soluble pollutant gases. The organic chemical composition of the particles needs to be known to estimate the quantities of vapor-phase organic compounds that will be absorbed into the particles during transport through the atmosphere. These needs have not been met by current monitoring methods; further research and methods development are needed.

Measurement of the size distribution and composition of fine-particle emissions from sources is difficult because many of the organic compounds that will come to equilibrium in the particle phase are still present in the gas phase at the high stack-gas temperatures where source samples must be collected. This problem is being addressed through the use of dilution tunnels that simulate the process of plume cooling by dilution in the atmosphere by mixing a great excess of clean dilution air with the source effluent before making the particulate-source measurements. This serves two purposes. First, it reduces the source effluent to near-ambient temperature and pressure, thereby causing semivolatile gases that will form particles by condensation in the plume immediately downwind of the source to migrate into the particle phase before the particle samples are collected. Second, it creates sampling conditions under which the sophisticated instrumentation that has been developed for characterizing the size and composition distributions of atmospheric particles can be applied to the problem of measuring particles as they are emitted from their original source.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

Recommended Research

The research source-testing procedures mentioned above first have to be evaluated, possibly modified, and then specified in the form of a set of standard methods. Many decisions will have to be made about the best protocols and instrumentation to be used for making particle-size distribution and chemical-composition measurements from the diluted source exhaust.

Following the selection of standard methods, the population of several hundred different types of air-pollution sources will have to be characterized—for the first time, in many cases. In addition, new source-test methods will be needed for accurate and simultaneous determination of the emissions rates of the important gas-phase particle precursors; the existing database is particularly weak as it applies to emissions of ammonia and semivolatile organic vapors (generally consisting of vapor-phase organic compounds with greater than 10 to 12 carbon atoms).

Once new emissions data have been collected for a sufficient number of geographically representative examples of the relevant source types, the data must next be compiled into spatially and temporally resolved comprehensive emissions inventories that represent the emissions from all sources in the country in a way that these data can be used by air-quality scientists and by the regulatory agencies that must draft emissions control plans. Over time, adjustments in the national emissions inventory may be needed to account for any substantial changes in regional emission patterns that may have occurred after source testing was performed.

Scientific Value

Knowledge of the size distribution and chemical composition of PM emissions, as well as the emission rates of reactive gases that act as PM precursors, is basic to the understanding of fine particles in the atmosphere. This understanding involves cause-and-effect relationships that can be verified with atmospheric observations only if emissions are accurately specified. Confidence in the air-quality models emerging

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

from decades of research on the individual physical processes that govern atmospheric chemistry, aerosol thermodynamics, and atmospheric transport and removal will rest on the ability of such models to predict observed ambient particle characteristics from these emissions inputs. Concurrently, knowledge of the size and composition of the emitted particles is needed if the particle-exposure systems used by laboratory toxicologists are to be chosen in a way that accurately represents the relevant differences in the particles emitted from the many different source types.

Decisionmaking Value

Decisions about the relative mix of emissions control measures needed to attain compliance with ambient air-quality standards for particulate matter cannot be made with any confidence unless the emissions themselves have been quantified and the sources of such emissions have been identified accurately (also see Research Topic 4).

Feasibility and Timing

A deliberate intercomparison of alternative measurement methods should first be conducted to select standard source-testing protocols that are suited to obtaining high-resolution data on particle size and composition. Thorough evaluation of the alternative measurement methods under actual field-sampling conditions is a difficult research task that could easily take 2 to 3 years to complete.

Following specification of standard source-testing methods, the research must then turn to quantifying through actual tests the particulate-emissions characteristics of the relevant populations of emissions sources. The emissions inventories maintained by the states and by EPA contain at least 350 source categories for which emissions-source profiles must be assigned (EPA 1985, 1995). If some PM components are subsequently found to be biologically more important than others, it might be possible to focus on a subset of these. Somewhere between 25 and 75 source types probably must be characterized in the

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

near future to meet the goal of accurately representing the sources contributing about 80% of the particle mass present in the atmosphere.

At the outset of this source-test program, the newly developed procedures will be in use for the first time, and the first few groups of sources tested should be viewed as part of the research-and-development program leading to the establishment of the new source-testing protocols. Once the application of the procedures has become routine, the source-testing program should be completed as a part of federal and state regulatory programs. If source-testing programs were to be done over 5 years, then from 5 to 15 source-testing campaigns directed at different source types would have to be conducted per year. Conversion of the information on the emissions from representative sources into a spatially and temporally resolved emissions inventory for the United States would then require about 2 to 3 additional years of effort by a team of individuals skilled in the use of modern geographic information systems (GIS) technology. The entire national emissions inventory program thus will require about a decade for completion.

Cost

One reason emissions data bases generally lack complete information on particle emission rates as a function of particle size and composition is that source tests are complex and expensive. Most regional studies aimed at atmospheric-particle characterization and modeling in the past have neglected to undertake a parallel program of research-quality source emissions measurements, mainly because source measurements are so difficult and expensive to conduct. A thorough evaluation and intercomparison of alternative source-testing methods for determination of PM size and composition—followed by execution of enough real source tests to establish the viability of the methods under actual field-operating conditions—will probably require an expenditure of approximately $2.5 million per year over about 4 years. Many side-by-side source tests will need to be conducted to compare the alternative methods on stationary, mobile, and fugitive sources, and for particles and reactive gases.

Beginning immediately, EPA should create an interim national emis-

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

sion inventory for particulate matter and gaseous particle precursors. This interim inventory should provide the best practicable, spatially and temporally resolved account of the size distribution and chemical composition of particle emissions and gaseous particle precursors given current pollutant source test data. The interim inventory is needed by 2002 to support the initial testing of source-oriented models for particle size and composition that in turn may be needed for control-strategy planning. The cost of this interim emissions inventory effort is estimated at $1 million per year for about 4 years. Once the source test program has been turned over to the regulatory arm of EPA, application of the new standard test methods to the characterization of emissions from a representative selection of examples of a single source type (e.g., oil-fired utility boilers and railroad locomotives) will probably cost $300,000 to $500,000 per source class if a thorough job is done using professional research contractors, or possibly as little as $100,000 per source class if the research is performed mostly by teams of university graduate and postdoctoral scholars. At the rate of 5 to 15 source classes per year, this source-testing effort could easily cost $5 million per year for 4 to 5 years (the range of costs is fairly wide, spanning values from as little as about $1 million per year to as much as $7.5 million per year, depending on how the work is commissioned). Compilation of the full national emissions inventory will probably cost about $1 million per year for about 3 additional years.

Thus, the overall cost estimate for research to develop standard source test methods and to apply those methods to establish their viability under field sampling conditions is $2.5 million per year for 4 years. That research must be accompanied by technical support work by federal and state regulatory programs at about $5 million per year for about 5 years for testing of the most important source types plus about $7.0 million from regulatory programs for the compilation of an interim PM emissions inventory and a national emissions inventory based on the new source test data.

The estimate of $2.5 million per year for 4 years for research on source-test methods is shown in the committee's updated portfolio in Table 3.1. The cost of continued application of the source-test methods is not built into the research budget, because that activity is viewed by this committee as an appropriate task for federal and state

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

regulatory programs. Nevertheless, that activity (represented in Table 3.2) must be undertaken, because the revised emissions inventory lies on the critical path toward timely completion of necessary research into the development and evaluation of models that relate source emissions to ambient air quality.

RESEARCH TOPIC 4 (REVISED):

AIR-QUALITY-MODEL DEVELOPMENT AND TESTING

What are the linkages between emission sources and ambient concentrations of the biologically important components of particulate matter?

As discussed above, this is a revised research topic, replacing Research Topic 4 in the committee's first report.

Description

Airborne particulate matter results from direct emissions of primary particles and atmospheric formation of secondary material (Finlayson-Pitts and Pitts, 1986). In the atmosphere, emitted particles and reactive gases undergo transport and dispersion, chemical and physical processes, and deposition to the earth's surface. Transport and dispersion describe the horizontal and vertical motions of gases and particles due to winds and turbulent diffusion. Chemical transformations include reactions between gases, on particles, and in cloud and fog droplets. Such transformations also involve thermodynamic equilibrium between the gas phase and particle phase. Physical processes of gas-to-particle conversion and growth include nucleation of vapors to form particles, condensation of gaseous species onto existing particles, and, under high-humidity conditions, the activation of particles to form cloud and fog droplets. Deposition, wet and dry, removes the particles from the atmosphere. Dry deposition involves turbulent and molecular diffusion for very small particles and gravitational settling for larger particles. Wet deposition is the removal by falling rain and snow of their nuclei and intercepted particles. The relative importance of these chemical

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

and physical processes determines the contributions of distant and local sources to particulate composition and size structure at any given site.

Due to the complex, nonlinear processes involved in atmospheric-particle formation, source-oriented models are the only comprehensive tools available to develop air-quality management strategies for reducing ambient levels of secondary particulate matter (NRC 1993). However, the source-oriented modeling approach is very resource-intensive and relies on comprehensive, accurate descriptions of the relevant source emissions, chemical reactions, and physical processes. Receptor models complement source-oriented models by providing independent assessments of the emission sources contributing to measured concentrations of particulate matter and its components (see Subtopic 4b). Both modeling approaches require special measurements of emissions, meteorology, and gas and particle concentrations before they can be applied and tested.

Because it is not possible at this time to determine which of the many components of particulate matter will ultimately be found to contribute significantly to adverse health effects, models are needed that will describe a broad range of species and detailed particle sizes. Therefore, it is necessary to proceed with the development and testing of sophisticated speciation and size-resolved models so that they will be available as biologically important particulate species are identified. Thus, an iterative approach will be needed to focus modeling efforts on biologically relevant species.

Before any model can be used with confidence, its theoretical soundness and computational integrity must be evaluated, and its performance must be compared with full sets of independent data. A comprehensive source-oriented model evaluation program requires (1) urban or regional field experiments to characterize four-dimensional (space and time) ambient gas-concentration and particle-concentration fields, with the particles resolved by size and chemical composition; (2) a spatially and temporally resolved emission inventory for all particle types and precursor gases; and (3) four-dimensional meteorological fields. Subsets of these measurements suffice for most receptor-oriented models.

Source-oriented models are tested for their ability to reproduce

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

observed concentrations of precursors and products from emissions and meteorological inputs. Receptor-oriented models are tested for the consistency of their concentration-derived inferences with observed emissions and meteorology. Comprehensive measurements, focused on individual representations of chemical and physical processes, are needed for diagnostic testing of both model types. Also, source-oriented models must agree with results from receptor-oriented models. In many areas, the comprehensive field-measurement programs needed for application of source-oriented models may not be possible because of resource constraints, and receptor models, which have less-intensive input data requirements that can be satisfied with the PM speciation network, may be the only modeling tool available.

The first generation of source-oriented particle models has undergone evaluation for a limited number of meteorological conditions and geographic areas. Although the model performance results for these complex systems are encouraging, they still fall well short of results for ozone models (Seigneur et al. 1997). The most extensive testing has utilized databases collected in southern and central California, and clearly there is a need for field experiments in other parts of the United States. The CMB (chemical mass balance) model is a receptor-oriented model that is EPA-approved for primary-particle applications. Quantitative receptor-oriented models for secondary particles have yet to be successfully demonstrated.

4a. Source-Oriented Models

After more than 20 years of development, source-oriented models are now routinely used to predict the effectiveness of emission-control strategies for ozone. Although many of the chemical and physical processes affecting particulate matter are already treated by source-oriented models for ozone, major complications arise from the finer spatial resolutions, longer time scales, and attention to phase partitioning required in particle models. As a result, source-oriented models for particulate matter are still in their formative stages. However, a new generation of source-oriented models that include descriptions of all the relevant processes is being developed (Seigneur et al. 1997).

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

Spatial scales for ozone modeling and particle modeling have traditionally been on the order of hundreds to a few thousands of kilometers, with grid elements ranging from 4 km2 to 20 km2. These dimensions appear to work reasonably well for secondary pollutants, but spatial gradients for primary particles can be much steeper. At spatial scales smaller than the size of grid elements, the ability to represent key transport, dispersion, and deposition processes accurately is lost. Thus, the applicability of grid models to the study of primary pollutants is uncertain, as the ability to provide emissions and meteorological data at finer resolution is doubtful. One possible approach to overcome this limitation of grid models is to use speciated rollback of receptor-modeling results for primary particles with unique chemical-and physical-size fingerprints (NRC 1993).

Source-oriented models, with their intensive computational needs and their extensive requirements for emission and aerometric inputs, are best suited for episodes of a few days' duration. However, the annual-average PM2.5 NAAQS appears likely to be more difficult to meet than the 24-hour-average standard for many urban areas. An annual average can be constructed by applying the model to a representative series of episodes or by employing a simplified version of the model for each day of the year. These approaches have only recently been demonstrated for ozone models (Winner and Cass 1999) and present a more difficult problem because of the greater diversity of particle episodes (Dolislager and Motallebi in press).

Water is associated with many of the particles found in the atmosphere (Saxena and Hildemann 1996). Source-oriented models treat processes of particle growth and evaporation due to water and other components with a thermodynamic-equilibrium model. Such thermodynamic models appear to be satisfactory for inorganic components of the urban atmosphere. However, models of the thermodynamics of organic components are still under development. In addition, models that incorporate the thermodynamics and aqueous-phase chemistry of cloud and fog water droplets are still in early phases of development.

Besides their direct impact on human health, particles influence the rate of formation of ozone by scattering and absorbing ultraviolet (UV) radiation. UV-absorbing particles can inhibit photochemical reactions and ozone production and UV-scattering particles can accelerate those

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

processes. In some cases, such inhibition and acceleration can result in decreased photolytic rates at the surface but increased rates a few hundred meters aloft (Dickerson et al. 1997). Because particle-UV radiation interactions are not represented in most air-quality models, model applications for ozone and particulate matter may not be realistic assessments of the effects of emission controls.

Other uncertainties in present model formulations include the following:

  • Nature of the physical processes that lead to fugitive emissions of particulate matter.

  • Rate of mixing and venting of boundary-layer air with the free troposphere and, conversely, the rate at which free-tropospheric air is mixed into the boundary-layer.

  • Rate of oxidation of volatile organic compounds and production of condensable products.

  • Rate and frequency of SO2 conversion to sulfate and NOx to nitric acid and to nitrate in droplets and fogs.

  • Rate of interaction of semivolatile species with particle surfaces.

  • Rates of wet deposition, including the dependence of these processes on the type of meteorological system of precipitation.

  • Dry deposition and chemical interaction of reactive gases with different surfaces (e.g., vegetation and bare soil).

  • Subgrid-scale treatment of large point sources, and the rate at which urban plumes of different origin mix within a given region.

Recommended Research

An improved understanding is needed of the chemical and physical processes that determine the size-resolved chemical abundance of

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

particulate matter. To gain that understanding, a well-balanced program will be needed to identify the critical processes. This will require sets of intensive experiments at a few well-chosen sites. The representation within models of the processes operating at each site should be evaluated by comparison of model predictions with observations. The chosen sites should include sites subject to local emissions and long-range transport (e.g., eastern United States), sites representative of regional background conditions and unperturbed by local emissions (e.g., national parks), and sites dominated by local emissions (e.g., the West Coast). By describing how the rates of the chemical and physical processes are governed in each particular location and by determining how the characteristics of each location relate to other regions, the understanding gained at these unique sites may be extended to the full domain of regions that are not in compliance with the NAAQS.

An additional area for investigation is the effect of large-scale meteorological processes, such as aqueous reactions and precipitation scavenging. Innovative research methods will be needed that go beyond the intensive but short-term measurements made for model evaluation, to clude coverage of the processes that determine the long-term average particulate concentration. Models that couple to and make use of numerical weather-prediction tools may be of particular value in this respect.

The effects of uncertainties in model inputs need to be addressed before source-oriented models can be used with confidence. For example, how do uncertainties in the specification of the following exacerbate the uncertainty in predictions?

  • Emissions of volatile and semivolatile organic compounds, including biogenic hydrocarbons, ammonia, and primary particles.

  • Meteorological processes above the ground.

  • Physical descriptions of clouds and fogs.

  • Boundary conditions.

Formal methods for uncertainty analysis need to be developed specifically for particle models and applied to refine the definition of

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

model needs and to determine the required accuracy of these model inputs.

PM research studies are under way to advance the state of the science on chemical processes (e.g., secondary organic aerosol formation, thermodynamic equilibrium of organic species) and meteorological processes, but projects on emission characterization (see Research Topic 3), physical processes (e.g., descriptions of clouds and fogs, deposition rates, sand subgrid-scale mixing processes), and uncertainty analysis either have not been undertaken or do not fully address the research needs. In addition, there is little research on the effect of large-scale meteorological processes on long-term annual average fine-particle concentrations.

Scientific Value

Source-oriented models have the potential to embody all that is known about the relevant processes that lead to particle formation in the atmosphere, and, once tested, to be useful in exploring relationships between gas-and particle-phase emissions and ambient levels of particles. These models are needed not only to study urban and regional air-pollution control proposals in advance of their adoption, but also the effects of atmospheric particles on ozone, regional haze, and the earth's radiation balance.

Decisionmaking Value

The ability to relate emissions accurately to ambient concentrations is critical to the optimal design of emission-control strategies to attain the ambient air-quality standards for particulate matter. Credible source-oriented models will help guide decisions on the emission control measures in future air-quality management plans.

Feasibility and Timing

Source-oriented modeling analyses for developing state implementation plans will likely need to be completed prior to the 2005–2008

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

deadlines. However, to have suitable models in place by the time they are needed, initial model development should be pursued now.

Air-quality models useful for emission-control strategy planning are needed as early as 2003 to meet projected regulatory schedules. Development and testing of those models must begin immediately to meet that schedule, yet during the period of model development and testing, new health-effects research results may help to focus attention on biologically important components of the airborne-particle complex. In the interim, relatively complete air-quality models will have to be developed to describe the size distribution, chemical composition, trace-metal content, acidity, and other likely candidates for a more focused control program. Given the complexity and hence relatively long development times of the source-oriented models with their high science content, a family of less-complex modeling tools (e.g., receptor models) also should be maintained for use in the early stages of control strategy planning (see Research Topic 4b).

In addition to the need for simultaneous development of models at different levels of complexity, EPA's projected regulatory schedule also implies that model-evaluation efforts through regional field studies will need to be conducted simultaneously in several portions of the country. The need to work simultaneously in several regions will challenge the capacity of personnel with the ability to apply complex air-quality models. Managers will need to assess the expertise of their staff, coordinate across regions to determine the models that are most suitable and feasible, and provide training on model applications as needed. The committee's cost estimates reflect the expected costs to be incurred when pursuing model development and testing simultaneously on several fronts.

The comprehensive field experiments and emission inventories required for the application of source-oriented models typically take 5 to 6 years: 2 years to plan and fund, I year for field measurements, another year for data validation and archiving, and one or two years for development of meteorological and air-quality input files and for model evaluation. Thus, major nonattainment areas would need to be identified soon so that the planning for the field experiments can begin. The Northern Front Range Air Quality Study was recently completed (Watson et al. 1998a), and there is an ongoing study in Atlanta (Edgerton et

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

al. 1998). The only upcoming comprehensive field campaigns approaching adequate funding are in central California and the southeastern United States. The California Regional PM10/PM2.5 Air Quality Study is scheduled to begin data collection in late 1999 and continue to early 2001. The Regional Ozone/Fine Particle Intensive Field Study in the southeastern United States is planned for the summer of 2000. In addition, a large regional study is being planned for the eastern United States.

Cost

Research is needed to develop a better understanding of the individual chemical and physical processes that govern atmospheric particle formation. Although some research on those processes is being supported, the range of sites to study the processes needs expansion. EPA's $15 million supersites program could serve as the nucleus for such a research effort by providing instrumentation and infrastructure support at five to seven sites. The cost of supporting six institutions to conduct research at the supersites is estimated at $1.7 million per year, beginning in 2000 and extending to 2006. However, the research to be conducted in association with monitoring supersites has not yet been well defined, so uncertainty remains about whether or not these needs will be met.

In addition, integrating the results from theoretical, laboratory, and field studies into comprehensive computer models and analysis and evaluation of the models needs to be carried out continuously, including application of the models to the range of sites and physical and meteorological situations envisioned here. This includes studies of physical processes not now being pursued, such as the formation of clouds and fogs and their effects on particles. It also includes exploration of how the representation of subgrid scale processes affects predictions. Finally, the model application studies must also explore the sensitivity of the applications under different meteorological regimes to uncertainties such as the specification of boundary conditions, emissions inventories, and initial conditions. In addition, continuing research to develop better computer representations of physical and

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

chemical processes needs to be supported. These application studies should be pursued following each of the field studies envisioned here and could involve five to six different modeling groups at up to $350,000 per year for a total cost of perhaps $2 million per year.

The committee also sees the need for development of methods to incorporate the effects of large-scale meteorological processes on annual average particle concentrations through the development of simplified versions of present models and through the development of more realistic larger-scale models that can provide boundary conditions for the detailed models. Some of the additional studies could be pursued if the results of prior field studies were better used. One reason for under use of existing data is the difficulty in accessing them. A central national archive of data and model input files from field-measurement programs would facilitate evaluation of particle models. A scaled-down effort on all these tasks—costing about $2 million—was begun in 1998; about $2.8 million per year is needed from 2000 to 2006.

A major obstacle to the advancement of source-oriented models is the lack of detailed data bases to evaluate predictive capabilities. The costs for year-long field campaigns have ranged from $12 million for the 1987 Southern California Air Quality Study (Lawson 1990) to $27.5 million (including model application and evaluation) for the central California study (Watson et al. 1998b). These costs are high because aircraft, lidars, radar wind profilers, and possibly some customized source testing are needed to characterize air quality and meteorology in time and space. Costs for such efforts in the future can only be partially offset by EPA's supersites program and the planned expansion of the nationwide network of speciation and IMPROVE samplers by 400 sites. The supersites can become the focus of a set of intensive measurement programs to carry out the research outlined above, and other network locations, and perhaps specific additions during special campaigns, can serve to provide larger regional understanding of the chemical and physical state of the atmosphere. In addition, a well-balanced aircraft component is essential to campaigns intended to support model evaluations. The scientific infrastructure in the United States can support one or two comprehensive regional field studies per year. Therefore, in addition to the cost of research, about $20 million from

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

public and private sources will be needed each year from 2001 to 2005 for technical work in support of the evaluation and testing of air-quality models for particulate matter. The results of such work will also be applicable to models for tropospheric ozone.

4b. Receptor-Oriented Models

Receptor-oriented models provide an additional tool to develop effective and efficient strategies to improve human health by improving air quality. These models have been used to identify and quantitatively apportion aerosol mass to sources. However, improved methods are needed because there are limitations in the existing, widely used models. One limitation of existing models used with routine data is that they can have difficulty resolving the contributions of chemically similar source categories that require different control measures, such as gasoline evaporation versus automobile-tailpipe emissions, or road dust versus agricultural and construction activities. A second and more fundamental limitation for fine-particle applications is their inability to handle secondary species.

The currently accepted methods, like CMB or principal components analysis, cannot provide definite identification of the sources of secondary particles such as sulfate, nitrate, or secondary organic materials. The usual result of a CMB analysis is to list sulfate as a source or possibly describe it as ''regional sulfate." Similar results are typically obtained through factor analysis.

Three general approaches can be pursued to meet the needs for improved methods. First, additional constituents or properties of the aerosol can be determined and used to identify and apportion sources, enabling much-improved source resolution. In recent years, more intensive analysis of organic compounds in particulate matter has been shown to be an effective way to determine additional sources. Schauer et al. (1996) used a CMB approach to resolve up to nine sources of particulate matter in the Los Angeles area after performing an extensive series of source sampling and ambient sampling coupled with high-resolution gas chromatography and GC/MS techniques. This speciated-hydrocarbon approach produces data on 30–40 compounds that might

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

be present in the source emissions and ambient aerosol. Fujita et al. (1998) applied the speciated-hydrocarbon approach to apportion carbonaceous aerosols in the Northern Front Range area. New analytical methods and identification of additional compounds could provide the ability to identify and apportion additional sources. For example, biological compounds, such as phospholipid fatty acids or DNA, could identify particular crop types being grown on particular soils (Bruns et al. 1998).

Increased resolution can also be provided through examination of individual particles in a sample. Continuous particle-by-particle analysis systems can now qualitatively determine the composition of individual particles and characterize their ambient size distribution, but fully quantitative analysis is still under development. Thus, there is a need for new and improved methods that will provide more detailed characterization of the samples and will thus improve source resolution. However, increased costs are associated with the increased difficulty and sophistication in the analytical methods and related procedures. Therefore, it would be useful if other data-analysis methods were available to use data that can be obtained more easily or are already being obtained routinely for other purposes.

In a second approach, spatial/temporal information can be used to identify potential source locations and emission strengths of the gaseous precursors of secondary particles. This general approach employs a mathematical framework to analyze the values of a single variable measured at a variety of sites at multiple times. Thus, the analysis examines spatial and temporal patterns in the measured variable rather than the interrelationships among different variables. This approach has been used in earlier studies, but generally in a qualitative manner. Recently, efforts have been made to develop factor-analysis methods that yield quantitative apportionment estimates. These methods merit further attention in areas where such widespread sampling has been or will be performed. However, more development, testing, and validation are needed.

Finally, meteorological information in the form of air-parcel-back trajectories can be incorporated into the analysis. Dispersion models describe the transport of the particles from a source to the sampling location. These models can also be used to calculate the trajectories

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

of air sampled at the receptor site backward in time and space to the start of the sampling interval. Various statistical techniques can then be employed to extract patterns of empirical association between the resulting back trajectories and contaminant concentrations in arriving air. Initially, most of these efforts produce qualitative estimates of the importance of various areas on the observed concentrations. Recently, this approach has been extended to yield an apportionment by combining it with the emissions inventory for the area being modeled. Several of these methods can provide quantitative estimates of the contribution of a given area to the concentrations observed at the receptor site. However, these methods have not yet been adequately tested.

Recommended Research

Better mathematical tools are needed to identify patterns in the spatial and temporal variability of PM properties and to relate these to source contributions. These tools must be applicable to data sets containing missing or below-detection-limit values. In addition, the tools must be able to provide solutions that have appropriate constraints. Tested receptor models for secondary particulate matter would be of great value. New models are needed for resolving the components of personal exposure incorporating ambient and indoor sources.

Also needed are new ambient monitoring techniques with the capability of measuring chemical species and particle sizes associated with the inorganic and organic fractions of PM2.5 and PM10. To advance exposure and risk assessment, it is particularly necessary to identify and quantify a much larger fraction of airborne PM mass in terms of specific biologically important compounds. Current methods are only able to identify and quantify about one-tenth of the organic material associated with particles. Significant improvements in analytical methods that lead to readily applicable techniques would be an advance in analytical science and provide for major improvements in exposure and risk assessments.

Finally, as part of the evaluation of receptor and source models, studies should be conducted in which both types of models are run and the results intercompared. The reconciliation of the source apportion-

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

ments produced by the different model types will help to improve both models because they will help to uncover problems and limitations in the models, their input data, or the interpretation of the results.

Scientific Value

The development and use of advanced receptor models would help to improve understanding of source-receptor relationships and provide critical information complementary to the more advanced source-oriented models.

Decisionmaking Value

Accurate identification of the sources of specific types of ambient particles is critical to the development of effective and efficient air-quality-management strategies focused on biologically important PM components. Receptor-modeling methods for the quantitative apportionment of PM mass and/or specific biologically important species will be important tools to provide to state and local regulatory officials to facilitate the development of state implementation plans.

Feasibility and Timing

Numerical tools can now be used to improve the quality of receptor models. Measurement of the critical organic fraction has improved in recent years with improved chromatographic methods, along with better methods to transfer the output of the chromatograph to the mass spectrometer, but those improvements have not been fully developed for atmospheric particulate species. The resolution and sensitivity of mass spectrometers have also improved, so the necessary basic tools are available.

To develop, evaluate, and improve the models, appropriate air-quality data will be needed. A well-designed monitoring program could

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

help facilitate this effort and could minimize the costs of collecting incremental data for modeling purposes. Because plans for the speciation and supersite monitoring programs are still evolving, it is not yet clear just how EPA's PM-monitoring activities will specifically help the atmospheric-modeling community meet the needs of decisionmakers, and the committee looks forward to further clarification and development of EPA's PM-monitoring programs. The committee urges EPA to increase its efforts to work with the scientific community in finalizing the design of these programs.

Cost

About $1 million per year is needed from 2000 through 2002 for the development of advanced receptor models and related analytical methods development.

RESEARCH TOPIC 5: ASSESSMENT OF HAZARDOUS PARTICULATE-MATTER COMPONENTS

What is the role of physicochemical characteristics of particulate matter in eliciting adverse health effects?

Background

This topic encompasses a broad area of research on the physicochemical and biological characteristics of particulate matter that influence adverse health effects following exposure. This category includes evaluation of particulate characteristics such as chemical composition (including any adsorbed materials) and particle size, development of PM surrogates, and assessment of relevant dose metrics. Research in this area is needed to provide information on whether biological effects are nonspecific or whether they depend upon specific physicochemical parameters of particulates. This evaluation also requires studies of the

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

toxic effects of inhaled particles of various sizes that are chemically, biologically, and immunologically inert to determine if there are generic effects of particles.

The committee's first report recommended that the physicochemical characteristics of particles be considered in the following four specific, but overlapping, categories of research:

  • Development and use of PM surrogates for controlled exposures that can mimic daily, seasonal, and regional particle characteristics.

  • Assessment of different dose metrics, such as mass, number, surface area, chemical constituents (oxidant activity, organics, and metal content) that relate to health outcomes.

  • Evaluation of the role of particle size (e.g., ultrafine versus fine versus coarse-fraction particles) in assessing the results of in vitro, whole animal, and controlled human-exposure studies.

  • Determination of the role of PM chemistry in toxicological responses.

Update

In response to the committee's recommendation for increased research in this area in its first report (NRC 1998), Congress increased the resources devoted to research on this topic from $4.5 million in the President's proposed budget for Fiscal Year 1999 to $8.2 million in 1999 appropriations, and EPA has proposed $7.9 million for Fiscal Year 2000. There has been an increase in the number of studies that make use of concentrated ambient air particles (CAPs) for real-time exposures of normal and compromised (susceptible) animal models. The particle concentrators are designed to be used in permanent as well as mobile facilities, and they include devices capable of producing size-range-specific concentrated ambient particles. In addition, EPA and other

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

organizations are conducting or planning similar studies in normal and mildly asthmatic human subjects. Several efforts are directed toward developing the capability of providing well-characterized resuspensions of filter samples of particulates for use in toxicological studies involving exposures via inhalation and intratracheal instillation.

EPA and other agencies are sponsoring studies directed toward understanding the potential impact of mass, size, number, and surface area of particles on their toxicity. In the past, many studies at EPA were conducted with resuspended materials instilled directly into the lungs of rodents, but more research at EPA and other organizations is now examining potential dose metrics following inhalation exposure.

New toxicological studies are also being sponsored by organizations other than EPA, such as HEI, the National Institute of Environmental Health Sciences (NIEHS), and the California Air Resources Board to examine differences in toxicological responses to particles of different sizes. A new controlled clinical exposure study in the United Kingdom will use subjects exposed to concentrated air particles and ultrafine diesel particles to assess several biological responses. Several new epidemiological studies will examine the role of particle size on toxicity of particles through the new EPA PM research centers. A major epidemiological study sponsored by EPRI, the Department of Energy (DOE), and several other groups is under way in Atlanta. That study is collecting detailed daily air-quality data for several PM size categories along with PM chemical characterization data and several types of health data.

EPA and other organizations are sponsoring new toxicological and controlled clinical studies to study the effects of various aspects of particulate chemistry on toxicological responses. Those studies will also investigate the potential role of organics in producing adverse health effects.

This research topic area remains a critical area of investigation. The committee recommends that additional inhalation-chamber studies of animals and humans using well-characterized and reproducible particle sizes along with specific gases found in ambient air should be conducted to study the role of physicochemical characteristics in particle toxicity. Studies using concentrated ambient air particles must also

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

take into consideration exposure to gaseous copollutants in evaluation of toxic responses. Regional and seasonal differences in pollutant mixes must also be considered in designing laboratory-generated atmospheres.

Efforts should be undertaken to conduct epidemiological studies of the effects of long-term exposures to particle constituents, including ultrafine particles. Unfortunately, it will be difficult to reconstruct past exposures so that cohorts of exposed subjects can be identified. Further work will be necessary to develop biomarkers that reflect chronic exposure to particulates.

Identifying cohorts in which chemical-species-specific exposures can be explored must be considered a high priority. With the potential for detailed chemical-species identification of particle exposures being developed, interactions of specific particles in well-characterized populations, especially those considered as potentially susceptible, should be explored.

Cohorts that can be followed need to be identified for future epidemiological studies. Populations of adults (healthy and susceptible sub-populations), as well as infants and children, will be needed. Linkage to chemical-speciation sites will need to be considered, along with collections of relevant covariate data. These studies are likely to be multicenter efforts that will need central organization and data collection.

RESEARCH TOPIC 6:

DOSIMETRY: DEPOSITION AND FATE OF PARTICLES IN THE RESPIRATORY TRACT

What are the deposition patterns and fate of particles in the respiratory tract of individuals belonging to presumed susceptible subpopulations?

Background

Knowledge of the tissue-specific and cell-specific dose of particulate matter and of PM constituents is a critical link between individual expo-

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

sures and health responses. The concept of dose includes the magnitude and rate of deposition on respiratory tract surfaces; the clearance, dissolution, and translocation of particulate matter from various sites; and the bioavailability of PM-borne toxic compounds. This information not only is critical to understanding exposure-dose-response relationships for health risks, but also to extrapolating the relationships between different types of human subjects and between experimental animals and humans.

The delivery of particle dose to the respiratory tract is not uniform; some regions and localized areas receive much greater doses than others. Work to date in this area has shown that local doses can be increased even further by the presence of respiratory disease.

Mathematical models have been developed for predicting the regional deposition of particles in the respiratory tract. Although the models are available for making useful predictions of the deposition of particles of various sizes in normal adult human airways, there is a basic need for experimental measurements to refine the models and to validate them through studies of deposition in living subjects.

The committee recommended that the following specific research tasks be undertaken with respect to deposition patterns and fate of particles in the respiratory tract:

  • Develop a quantitative description of representative lung morphometry and breathing patterns of potentially susceptible sub-populations (especially subjects with lung diseases, elderly subjects, and children).

  • Obtain a better understanding of particle deposition patterns within the respiratory tracts of susceptible subpopulations as a function of particle size, hygroscopicity, and breathing rate over the entire range of particle sizes.

  • Develop and refine mathematical models for predicting regional and local deposition in the respiratory tracts of subjects with lung disease, elderly subjects, and children for particle sizes of interest. To the extent possible, models should be tested using experimentally collected deposition data.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

Improve understanding of clearance and other defense mechanisms in healthy and susceptible populations, including understanding of phagocyte function, translocation to tissue and extrapulmonary compartments, and the bioavailability of particle-borne constituents.

Update

In addition to the research needs described in the committee's first report, more information is needed on particle dosimetry in different species of laboratory animals to provide a stronger foundation for extrapolation modeling. In particular, improved understanding of the regional deposition and retention of different particle types and sizes in normal and respiratory-disease-compromised animals would aid in the development of extrapolation models aimed at predicting dosimetry in humans with respiratory diseases.

Some of the previously mentioned research needs are being addressed by ongoing or planned research sponsored by EPA and other organizations, but it is not apparent that all of the research needs are being met. A portion of continuing and new research efforts sponsored by EPA, the HEI, DOE, and other organizations is focused on dosimetric issues. Although all of the previously described research needs are important, it is important to obtain a better understanding of the dosimetry of particulates in lungs of susceptible subpopulations. Consequently, the first two of the above four research areas should be given highest priority.

In its first report, the committee noted that dosimetry research needs could be met by approximately 4 years of adequate funding. It was also noted that this work did not depend on the products of other research areas or the establishment of monitoring programs and thus, could begin as soon as funding could be allocated. The committee recommends that EPA increase funding for dosimetric research during the early years of the program, so that these information gaps can be filled and the information can serve as a foundation for research under other topics.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

RESEARCH TOPIC 7: 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?

Background

The Clean Air Act requires the administrator of EPA to set standards for particulate matter and other criteria pollutants to protect the public health with ''an adequate margin of safety." The act implicitly assumes that regulation of individual pollutant concentrations will protect the public from adverse effects. Air pollution in virtually all locations, however, is a complex mixture; the potential for additivity, synergism, and other interactions among the components of the mixture may produce effects that would not be anticipated from predictions based on understanding of the effects of the individual criteria pollutants. Thus, research must also be sustained on other components of the complex pollutant mixtures.

In its first report, the committee observed that to characterize the health risks associated with exposure to particulate matter it is important to consider the effects of combined exposures to particulates and other copollutants. In addition to particulates, ambient air includes gaseous pollutants, including sulfur oxides, nitrogen oxide, carbon monoxide, and ozone, as well as organic compounds. These copollutants, which are often highly correlated with particulate matter, can also present health risks, or can modify the effects of particulate matter as a consequence of combined exposures. Although it is important to attempt to understand the health effects of particulates and to differentiate them from the effects of copollutants, it is critical to understand the modifying effects of copollutants on the health impacts of particulate matter. This is particularly necessary in regard to long-term exposure to particulate matter in the presence of other pollutants.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

The committee noted in its first report that toxicological and epidemiological studies can be used to obtain answers to questions relating to such complex toxicological interactions. Toxicological studies provide opportunities to understand interactions between particulates and copollutants through controlled experiments. Most epidemiological studies involving analysis of multiple pollutants have focused on the effects of short-term exposures. However, in some studies of long-term exposure to particulate matter, excess mortality has been reported. The committee recommended that further epidemiological investigations of the effects of long-term exposure to particulate matter are needed and that such studies be designed to evaluate also the influence of long-term exposures to gaseous copollutants. Such toxicological and epidemiological investigations would clarify the effects of exposure to particulate matter in the presence of concomitant exposures to other gaseous copollutants.

While supporting further epidemiological investigations of the effects of long-term exposures to ambient particulate matter, the committee recommended that exposure-monitoring programs are needed to adequately characterize population exposures to particulates, and that these programs should be in place before or contemporaneously with the initiation of new epidemiological studies. Thus, in strengthening the existing air-pollution monitoring programs in the United States, consideration needs to be given to the need for developing adequate exposure data for future long-term epidemiological investigations of particulates and copollutants.

Research Topic 7 addresses the estimation of the effects of particulate matter in the context of the effects of other pollutants. Statistical analyses can be carried out using observational data for this purpose. Experiments can also be designed that provide information concerning the independent contributions of individual pollutants to toxicity. However, the statistical analyses of observational data and the evidence from experiments may not accurately reflect the biological processes that lead to injury when complex mixtures are inhaled. The committee offers this cautionary reminder and also recommends that efforts be continued to better understand how mixtures exert their adverse effects. Research Topic 10 includes research to investigate measurement

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

errors, which can be particularly important in statistical analyses that include several pollutants with different measurement errors.

Update

In response to the committee's first report, which recommended greatly expanded work in this area, EPA and Congress increased the resources devoted to this research from $0.8 million in the President's proposed budget for Fiscal Year 1999 to $7.4 million in 1999 appropriations, and EPA has proposed $8.5 million in Fiscal Year 2000 (see Table 1.4). The committee supports and welcomes these decisions.

Current studies are investigating toxicological interactions of particles and pollutant gases as part of EPA's extramural Science to Achieve Results (STAR) research grants program. In addition, the National Environmental Respiratory Center has been created at the Lovelace Respiratory Research Institute as part of a long-term program to better understand the respiratory health effects of mixtures of air contaminants and the relative roles of individual constituents in producing health effects from exposure to pollutant mixtures. The work of this center will include evaluation of the relative roles of particulates and copollutant gases and vapors. The center is jointly funded by EPA and other sponsors. In addition, several studies, including the recently funded reanalysis of the Six City and American Cancer Society studies by HEI will also provide an opportunity to explore possible modifying effects of copollutants on the effects seen from particulate exposures.

The success of future studies on the effects of long-term exposures to particulates will depend heavily on the adequacy of exposure data for particulates and other copollutants. In developing its plans to expand the existing PM air-quality-monitoring programs, EPA will need to take into consideration exposure data needs for epidemiological studies as well as for ascertaining compliance with the NAAQS. The current lack of an adequate, coordinated effort by federal research programs to develop and track new cohorts or to enhance existing cohorts threatens to undermine the planning and implementation of new long-term studies in conjunction with the enhanced monitoring.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

RESEARCH TOPIC 8: SUSCEPTIBLE SUBPOPULATIONS

What subpopulations are at increased risk of adverse health outcomes from particulate matter?

Background

As discussed in the committee's first report, epidemiological data suggests that some human subpopulations are especially susceptible to inhaled particulate matter. These subpopulations include persons with cardiopulmonary disease or asthma, as well as the elderly, infants, and children. Other susceptible subpopulations, as well as personal and environmental factors that affect susceptibility, are largely unknown. The likelihood of adverse responses to particles depends upon the degree of exposure and individual characteristics that determine the susceptibility of exposed persons. Susceptibility can relate to a number of factors that vary among individuals, including particle dosimetry (deposition, clearance, and retention); individual characteristics, such as age, sex, prior disease history, and genetic characteristics (e.g., allergic responses); personal habits, such as smoking; and environmental factors, such as exposures to biological or chemical agents.

The behavior and activity patterns of susceptible subpopulations may bring them into contact with pollutant mixtures including particulates, that are different from the exposures of the general population. In addition, individual variations in deposition, retention, and clearance rates may alter a subpopulation's biologically available and effective doses and responses. The lack of information on these important factors impedes the development and validation of effective models for exposure assessment.

The committee recommended studies to determine the importance of short-term, peak, cumulative, and long-term PM exposures on mortality, premature mortality, and acute and chronic adverse health effects. These studies were recommended to include

  • The development of appropriate animal models.

  • Controlled human-exposure studies.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
  • Epidemiological studies in appropriately selected susceptible subpopulations.

Update

EPA and several other organizations are sponsoring studies to examine susceptibility factors, particularly pre-existing cardiopulmonary disease. Several studies are developing or using animal models of disease (e.g., asthma, chronic obstructive pulmonary disease, or cardiovascular disease). Controlled human-exposure studies that use concentrated ambient particulates as well as surrogate particles are also under way or planned; these studies will involve healthy volunteers as well as susceptible individuals with asthma and chronic lung disease. However, ethical considerations preclude studies involving extremely high exposures or individuals with severe diseases. Although in vitro studies with cell lines from normal and susceptible subpopulations are being conducted, the extrapolation of findings from in vitro studies to humans is difficult. However, such in vitro studies may aid in understanding the mechanisms, if dosimetric concerns can be addressed.

Recent studies (Liao et al. 1999; Tolbert et al. in press) have contributed to knowledge about susceptible subpopulations (e.g., the elderly), but much more knowledge is needed to support decisionmaking for PM standards. Additional studies are planned or under way for various parts of the United States that will assess cardiovascular outcomes in individuals believed to be at excess risk.

There is no centralized research inventory of studies of susceptible subpopulations, and the committee is not aware of any coordinated plan by which current and expected studies can be assessed in the context of the research recommendations in the committee's first report. Consequently, it is difficult to determine what research is still needed. For example, it is not clear from available study descriptions how pregnant women, minority, ethnic, or economically disadvantaged subpopulations will be studied. Similarly, available descriptions of the studies do not indicate whether peak levels of particles or ambient biological agents will be investigated.

The committee is concerned that current research efforts in this area may be too limited to be effective in guiding and monitoring research

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

on the effects of particulate matter in susceptible subpopulations. The committee recommends that EPA explore greater collaboration with other federal agencies and private research organizations to leverage resources and maximize ongoing research opportunities. EPA's work must take into account opportunities offered by such major studies as the Women's Health Initiative, the EPRI Veterans' Study, Harvard studies of medical personnel, inner-city asthma studies in various areas, and studies by large health-management organizations (including health maintenance organizations). A strategy containing short-and long-term components of the PM research program is needed to ensure the effective identification of health effects among susceptible subpopulations as well as general population cohorts, and to identify the most appropriate and cost-effective means to address the effects. The com mittee recommends that the strategy include

  • Updating the inventory of large-cohort, health-research studies with relevant co-variables.

  • Identifying what health outcomes need to be addressed.

  • Identifying and prioritizing what susceptible subpopulations still need to be studied.

  • Identifying what research needs, as discussed above and in the committee's first report, will not be addressed by ongoing studies.

  • Identifying potential collaborators with access to cohorts in selected cities (e.g., Los Angeles and Atlanta).

RESEARCH TOPIC 9: MECHANISMS OF INJURY

What are the underlying mechanisms (local pulmonary and systemic) that can explain the epidemiological findings of mortality/morbidity associated with exposure to ambient particulate matter?

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

Background

As discussed in the committee's first report, this is another critical area of research. The value of epidemiological studies will be greatly enhanced if results obtained in controlled exposure studies can provide plausible explanations of underlying biological mechanisms for health effects. This research is needed to provide an understanding of local pulmonary and systemic responses. Although research in several other areas will also contribute to elucidation of pathophysiological mechanisms of particle-induced injuries (see research topics 58), this section focuses on the use of clinical, animal, and in vitro models to evaluate such mechanisms.

Clinical studies are controlled experimental exposures of humans to a substance. When possible, such studies with laboratory-generated surrogate particles or concentrated ambient air particles are an approach of choice. The use of human subjects avoids the need to extrapolate from other species. Human-exposure studies use laboratory atmospheric conditions that can be relevant for ambient pollutant concentrations, and they document physiological responses resulting from exposure that can often be linked to health effects. In these studies, highly controlled environments or well-characterized CAPS can be used to identify health responses to individual pollutants and to characterize exposure-response relationships. In addition, a controlled environment provides the opportunity to examine toxicological interactions among pollutants or with other variables, such as exercise.

In laboratory-animal studies, animal models are used as surrogates for humans. The necessity and urgency of developing and validating appropriate animal models of susceptible human subpopulations remains a critical area of research. The use of such animal models is essential for characterizing potential adverse effects of inhaled particles, as well as for determining specific mechanisms that seem to be operating only in the susceptible organism. Among the different animal models that mimic human diseases, the usefulness of transgenic animals should be evaluated to investigate specific mechanistic hypotheses.

In vitro studies can be used to evaluate some specific mechanistic

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

hypotheses related to health effects from exposure to particles. As reviewed in the committee's first report, the use of relevant target cells, as well as the use of particle doses comparable to exposure scenarios encountered in vivo, is crucial. Although initially higher dose levels may have to be tested, mechanisms that operate at high-particulate doses may be irrelevant for low doses. For example, it is known that high exposure concentrations to low-toxicity particles lead to particle overload, impaired clearance, and specific lesions, such as fibrosis and tumors not seen at lower concentrations. Thus, extrapolation from in vitro data and mechanisms elucidated from the use of high doses may be flawed unless it can be shown that health responses observed following exposure to low doses do indeed follow the same mechanistic pathways. It is also critical that all cell and tissue models be validated; the issue of whether responses observed in these in vitro models reflect those that would occur in vivo is also critical.

Update

In response to the committee's first report, which recommended increased work in this research area, EPA and Congress increased the resources devoted to this research from $4.3 million in the President's budget for Fiscal Year 1999 to $8.3 million in 1999 appropriations, and EPA has proposed $6.8 million in Fiscal Year 2000 (see Table 1.4).

To evaluate particle-induced effects, clinical studies are being conducted or planned in healthy volunteers and individuals with underlying cardiopulmonary diseases, such as asthma, chronic obstructive pulmonary disease, and angina. A variety of techniques to assess airway inflammation will be used, including bronchoalveolar lavage, sputum induction, and measurement of nitric oxide in exhaled air, as well as assessment of systemic effects by measurement of bloodborne biomarkers of effects and exposure. Assessment of cardiac rhythm and the coagulation cascade will also be studied. These studies will provide important information on early physiological responses from exposures to particles and will potentially provide important information on mechanisms of injury related to acute and chronic health effects.

Emphasis has increased on using animal models of diseases that are

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

thought likely to increase human susceptibility to inhaled particulate matter. There is now a broad recognition that research based solely on the use of young, healthy animals is not likely to lead to an adequate understanding of health risks to susceptible human subpopulations. Several genetic and experimentally induced laboratory models of emphysema, asthma, inflammation, infection, aging, and cardiovascular disease are now being used in PM research. Animals are also being used to explore the influence of age on susceptibility. Because all existing animal models have limitations in their ability to fully mimic human conditions, continued effort is needed to make adequate progress in developing and evaluating animal models of the full range of human conditions of interest.

The development of advanced molecular biology techniques makes it possible to employ methods such as in vitro transfection models for evaluating specific mechanisms of particle-cell interactions. Also useful for evaluating specific mechanisms are ex vivo studies in which specific cells of the respiratory tract are isolated after in vivo exposures of animals, and then subsequent in vitro studies are performed.

Careful consideration must be given to the extent to which the animal models represent the human conditions being modeled. For example, interspecies differences in dose to critical tissues, organ-level physiology, and genetics must be considered when judging the degree to which the animal models mimic human doses and responses. Few, if any, animal models accurately represent all features of a human disease, so consideration must be given to determine which features of the disease are modeled by the animal-test systems.

Understanding mechanisms of toxicity remains a high-priority research area, because the primary goal is to provide biological plausibility for the epidemiological findings related to ambient particulate matter. Although the overall funding planned by EPA in this area approaches the recommendations of the committee's first report, it is not clear to the committee how the funds will be allocated among clinical, animal, and in vitro studies.

As discussed under Research Topic 3 in the committee's first report, research is needed to develop advanced analytical methods to monitor responses to toxic components of particulate matter. Such research will involve the use of animal models and human subjects. In its first

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

report, the committee estimated the cost of this research at $1.5 million per year for 3 years beginning in 2001. However, the committee has decided to move that research from Research Topic 3 to Subtopic 9c to consolidate similar activities together.

RESEARCH TOPIC 10: 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?

Background

In its first report, the committee noted that a persistent source of the uncertainty associated with epidemiological studies on the health effects of particulate matter can be tied to questions about the statistical methods used to analyze the data and to the inherent errors associated with variables in the analyses. Several alternative methods have been used in these analyses, and the influence of those methods on the results and conclusions have not been fully understood. In addition, the observational data used in the studies are subject to measurement error.

The influence of any methodological approach on the results of an analysis must be understood. There is also value in determining whether results and conclusions are robust compared with alternative methods. In addition, measurement error can have extensive influence on the results of an analysis. It can bias the estimates of association and dose-response between pollution and health end points; the extent of such bias needs to be assessed and methods need to be found to correct for it.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

Update

The above issues will be amplified in new studies that consider exposures to many pollutants. The inclusion of many pollutants, some of which are correlated with each other, are creating a situation in which it will be difficult to determine the specific pollutants most highly associated with a health outcome. Differences in measurement error compound the difficulties introduced by this situation.

As we achieve greater understanding of the biological basis of health effects of particulates, it will be important to factor this understanding into models and statistical analyses. The current generation of models includes very flexible and powerful tools that can incorporate complex relationships between variables. The challenge is to articulate these relationships and then incorporate them in data analyses.

In epidemiological studies of the relationship between particles and health, an individual's exposure to particles is estimated most often by measurements taken at an ambient monitor. Rarely are measurements of personal exposure available. The difference between actual exposures and measured ambient-air concentrations can be considered as measurement error. Measurement error for air-pollution exposure has three significant components: instrument error (the accuracy and precision of the monitoring instrument), error resulting from nonrepresentativeness of a monitoring site (reflected by spatial variability of the pollutant measured), and differences between the average personal exposure of a pollutant and the monitored level.

Several efforts are under way to characterize the difference between personal exposures and ambient monitored levels of pollution variables (see Research Topic 1). Those efforts are addressing several populations in several regions. Data are especially needed on human subpopulations thought to be susceptible to air pollution. The distribution of differences between personal exposures and monitored ambient levels must be described. As the number of variables increase, this task will become more difficult. Differences in the underlying attributes of measurement error across population subgroups should be characterized. Differences in error distribution across subgroups could affect causal interpretations.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

For most of the criteria pollutants, data are available to characterize spatial variability—another source of measurement error. However, for many particulate subspecies that we are only beginning to measure, these data are not available. For other species, some efforts to characterize the variability are under way. Errors associated with instrument accuracy and precision also need to be characterized. This could be problematic for some older measurements that are based upon measurement instruments and technologies no longer used.

Research is under way to characterize the consequences of measurement error. Some of these efforts have focused upon measurement errors with very specific properties. The measurement error is assumed to be random (independent of the true measurement), and the errors are assumed to be independent and identically distributed with a symmetric distribution.

Recent research efforts have applied statistical methods to consider multiple pollutants in the same analysis and have examined the sensitivity of model results to assumptions made in times-series models. In addition, two workshops have been held to address these issues. HEI held a workshop on measurement error, and EPA convened a workshop to discuss broad methodological issues.

In addition, methods are being developed and applied to estimate the extent to which the timing of death may be advanced by pollution exposure (''mortality displacement" and "harvesting"). Methods (metaanalysis and hierarchical analysis) are also being studied to combine the results from several similar studies and to determine when such methods are appropriate.

Several methodological issues need to be addressed further. Systematic investigations of alternative methods and models would provide greater insights on the robustness of results. Alternative valid methods should be systematically applied to a few data sets to indicate the potential sensitivity of results to alternative methods. Data must be collected to ensure that we can adequately characterize the nature and distribution of significant errors for independent variables used in statistical models and that data on the errors are used to make adjustments. Studies with detailed environmental data (e.g., the supersites program) present additional methodological challenges. Finally, as

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

biological understanding improves on the relationships between pollution and health, models must incorporate this understanding.

THE UPDATED RESEARCH PORTFOLIO

As discussed earlier, the committee is continuing to evaluate PM research needs and accordingly to update its research investment portfolio (see Table 3.1). Specifically, the research activities and resource estimates for research topics 2, 3, 4, and 9 have been revised since the first report. Over the 11-year span of the updated portfolio, these revisions increase the total estimated cost of the research from $357.1 million to $369.9 million, increasing the average from $32.5 million to $33.6 million per year.

Research Topic 2 has been divided into two subtopics to distinguish between exposure methods development (Subtopic 2a) and exposure studies (Subtopic 2b).

In the first report, Research Topic 3 contained three subtopics that addressed the development of advanced mathematical, modeling, and monitoring tools to represent source-receptor relationships more accurately. Research Topic 4 addressed the research efforts needed to apply these methods and models to link biologically important components of particulate matter to their sources and to efficient air-quality management. In updating and refining its research portfolio, the committee has reconfigured the activities in research topics 3 and 4 and expanded some of the resource estimates to cover the implementation-related research and data collection that are not expected to be conducted by regulatory program efforts.

Research Topic 3 has no subtopics in the revised portfolio and is focused on research and development for methods to characterize emission sources. These activities are estimated to cost $2.5 million per year for 4 years. However, that amount does not include testing of the most important source types because that activity is viewed as part of the ongoing source surveillance program needed for implementation of the regulatory program. Such testing is represented in Table 3.2.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

TABLE 3.1 The Committee's Updated Research Investment Portfolio for Fiscal Year 2000–2010: Timing and Estimated Costs* ($ million/year in 1998 dollars) of Recommended Research on Particulate Matter

 

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

SOURCE/CONCENTRATION/EXPOSURE

1. Outdoor vs. human exposure

3.0

 

 

 

 

 

 

 

 

 

 

2. Exposure to toxic PM components

2a. Methods

1.0

 

 

 

 

 

 

 

 

 

 

2b. Studies

 

4.0

4.0

4.0

4.0

4.0

 

 

 

 

 

3. Emission sources

2.5

2.5

2.5

2.5

 

 

 

 

 

 

 

4. Models

4a. Source oriented**

4.5

4.5

4.5

4.5

4.5

4.5

4.5

 

 

 

 

4b. Receptor oriented

1.0

1.0

1.0

 

 

 

 

 

 

 

 

EXPOSURE/DOSE-RESPONSE

5. Assessment of hazardous PM components

5a. Toxicological and clinical studies

8.0

8.0

8.0

 

 

 

 

 

 

 

 

5b. Epidemiology

1.0

6.0

6.0

6.0

6.0

6.0

6.0

6.0

6.0

6.0

6.0

6. Dosimetry

1.5

1.5

 

 

 

 

 

 

 

 

 

7. Effects of PM and copollutants

7a. Copollutants (toxicology)

4.0

4.0

4.0

4.0

5.0

5.0

5.0

5.0

5.0

5.0

5.0

7b. Copollutants/long term (epidemiology)

6.0

6.0

6.0

6.0

6.0

6.0

6.0

6.0

6.0

3.0

3.0

8. Susceptible subpopulations

3.0

3.0

3.0

3.0

3.0

3.0

 

 

 

 

 

9. Toxicity mechanisms

9a. Animal models

3.0

3.0

3.0

3.0

 

 

 

 

 

 

 

9b. In vitro studies

3.0

3.0

3.0

3.0

 

 

 

 

 

 

 

9c. Human clinical

3.5

3.5

3.5

3.5

 

 

 

 

 

 

 

ANALYSIS AND MEASUREMENT

10a. Statistical analysis

1.0

1.0

1.0

1.0

 

 

 

 

 

 

 

10b. Measurement error

1.5

3.0

2.0

2.0

 

 

 

 

 

 

 

SUBTOTALS ($ MILLION PER YEAR)

47.5

54.0

51.5

42.5

28.5

28.5

21.5

17.0

17.0

14.0

14.0

RESEARCH MANAGEMENT*** (ESTIMATED AT 10%)

4.8

5.4

5.2

4.3

2.9

2.9

2.2

1.7

1.7

1.4

1.4

TOTAL$ ($ MILLION PER YEAR)

52.3

59.4

56.7

46.8

31.4

31.4

23.7

18.7

18.7

15.4

15.4

* The committee's rough but informed collective-judgment cost estimates for the highest-priority research activities recommended in this report. See Chapter 3 of this report and Chapter 4 of NRC, 1998 for explanations. These estimates should not be interpreted as a recommended total particulate-matter research budget for EPA or the nation, for reasons explained in NRC 1998.

** These estimates are in addition to costs for EPA's supersite program and expansion of the nationwide speciation network, as well as likely expenditures by states, local agencies, and industries for source-emissions inventories and field-measurement campaigns in support of model evaluation studies (see Table 3.2).

*** Research management includes research planning, budgeting, oversight, review, and dissemination, cumulatively estimated by the committee at 10% of project costs.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

TABLE 3.2 The Committee's Technical Support Estimates: Timing and Estimated Costsa ($ million/year in 1998 dollars) of additional technical work needed for implementation of emissions control programs for airborne particles

 

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

ACTIVITY

1. Source testing by regulatory programs

 

 

5.0

5.0

5.0

5.0

5.0

 

 

 

 

2. Compilation of interim PM emission inventory

1.0

1.0

1.0

1.0

 

 

 

 

 

 

 

3. Compilation of PM emission inventory based on results of new source information

 

 

 

 

 

 

1.0

1.0

1.0

 

 

4. Field studies in support of air quality model evaluation and testing*

 

20.0

20.0

20.0

20.0

20.0

 

 

 

 

 

TOTALS ($ MILLION PER YEAR)

1.0

21.0

26.0

26.0

25.0

25.0

6.0

1.0

1.0

 

 

* Technical support expenditures by all public and private sponsoring organizations.

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×

In this report, Research Topic 4 has been divided into Subtopic 4a, which addresses the development and evaluation of source-oriented models, and Subtopic 4b, which addresses receptor-oriented models. Because EPA monitoring is not expected to provide adequate data for model evaluation, the committee has increased its resource estimate for source-oriented models from the original estimate in its first report. Subtopic 4b shows the same amount of resources for receptor-oriented model development that was presented in Research Topic 3 of the first report.

Research Topic 9 retains the three subtopics from the first report. However, Subtopic 9c ("Human Clinical") was expanded by reallocating, from Research Topic 3 of the first report, $1.5 million per year for 3 years beginning in 2001 for the development of advanced analytic methods for monitoring biological responses to toxic components of particulate matter.

It is important to recognize that many parts of the research effort will continue to depend heavily upon data developed in technical programs maintained by the government in areas that fall outside the scope of the research activities recommended by the committee. Examples of such activities are testing of emissions sources, compilation of emissions inventories, and much of the collection of ambient data to support testing and evaluation of air-quality models. These technical programs may be carried out by government regulatory or research programs at the federal, state, or local level, or by nongovernmental organizations (see Table 3.2).

Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 39
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 40
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 41
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 42
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 43
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 44
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 45
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 46
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 47
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 48
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 49
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 50
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 51
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 52
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 53
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 54
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 55
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 56
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 57
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 58
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 59
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 60
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 61
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 62
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 63
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 64
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 65
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 66
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 67
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 68
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 69
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 70
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 71
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 72
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 73
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 74
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 75
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 76
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 77
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 78
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 79
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 80
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 81
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 82
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 83
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 84
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 85
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 86
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 87
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 88
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 89
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 90
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 91
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 92
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 93
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 94
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 95
Suggested Citation:"3 Updating the Research Portfolio." National Research Council. 1999. Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio. Washington, DC: The National Academies Press. doi: 10.17226/9646.
×
Page 96
Next: References »
Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio Get This Book
×
Buy Paperback | $44.00 Buy Ebook | $35.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

In the effort to reduce the scientific and technical uncertainties over regulation of airborne particulate matter in the United States, Research Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating the Portfolio, the second book in a four-part series requested by Congress, describes the plans of the committee to monitor the progress of the research on particulate matter conducted by the U.S. Environmental Protection Agency (EPA), other federal and state government agencies, and nongovernmental organizations.

The book also reviews and updates the committee's portfolio of recommended research in its first volume, Research Priorities for Airborne Particulate Matter: I. Immediate Priorities and a Long-Range Research Portfolio (NRC, 1998). The committee substantially revised two of the ten high-priority research areas recommended in Part I. Part II notes that Congress, EPA, and the scientific community have given strong support to the committee's recommendations and have implemented substantial changes in research efforts in response to Part I of the series. One important research area-studies of the effects of long-term exposure to particulate matter and other major air pollutants-however, does not appear to be underway or planned.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!