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3 Synthesis of Research Progress on Particulate Matter
Pages 64-117

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From page 64...
... In this chapter, the committee reviews progress on each of the 10 original research topics (see Box 1-1 in Chapter 1) , summarizing the gains in scientific knowledge for each from 1998 until the middle of 2002 with some additional updating over the next year as this report was written and particularly relevant contributions were made.
From page 65...
... Research carried out in regard to this topic addresses the relationship of monitoring data for ambient air with personal exposures to PM and gaseous copollutants. Data on this relationship are needed not only for healthy people but also for those persons who are particularly susceptible to air pollution and at greatest risk for experiencing adverse effects.
From page 66...
... Below we summarize the major findings that have emerged from either the initial or the completed analyses of the collected data. Relationship Between Personal Exposures and Ambient Concentrations Results from the recent panel studies support the hypothesis that ambient PM2.5 concentrations are significant predictors of corresponding personal exposures, over time, for the investigated cohorts (Ebelt et al.
From page 67...
... Collectively, the results from the panel studies, performed on several hundred individuals across various cities and different seasons, showed that there were varying degrees of association between personal exposures and ambient concentrations for the measured individuals, with almost half of the associations being non significant. For those individuals and for PM2.5, the correlation coefficients were in the range of 0.4 to 0.9.
From page 68...
... . Sulfate is associated mostly with outdoor particle sources and has been used to determine the contributions of outdoor and indoor sources to personal exposures (Wilson and Suh 1997; Ebelt et al.
From page 69...
... The monitoring studies provide the important and generally consistent finding that ambient particle concentrations are a key determinant of the longitudinal variation in personal exposure to particles for those groups studied to date. This finding is critical for interpreting the time-series analyses as well as other epidemiological studies of particles and health.
From page 70...
... 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?
From page 71...
... Specifically, studies have examined the relationships between real-time fine particles and adverse cardiac functions. Alimitednumberofstudieshaveconductedmeasurementsofpersonal exposures to various particulate constituents, including sulfate, nitrate, ammonium, elemental and organic carbon, and elements (Ebelt et al.
From page 72...
... These investigations should examine relationships among personal exposures to particle components of biological relevance and corresponding ambient concentrations for susceptible subpopulations and the general public. Some of these studies should characterize exposure distributions for a variety of microenvironments, such as work, school, and transportation environments.
From page 73...
... For example, particulate ratios of organic carbon to elemental carbon may be higher in ambient observations than in emission inventories because either (1) the inventories underestimate important sources of primary organic particles (such as oil-burning vehicles or vegetative combustion)
From page 74...
... focused on representing PM mass emissions, and it recommended the adaptation of realistic source-test methods and their widespread application to measure mass emissions, chemical composition, and size distributions of PM. The committee also emphasized the characterization of the emission rates of reactive precursor gases (SO2, oxides of nitrogen [NOx]
From page 75...
... Semivolatile organic compounds (direct condensation of organic vapors at ambient conditions) and Contemporary and fossil fuel nonvolatile organic compounds combustion, surface coatings and solvents, and industrial processes, Semivolatile and volatile organic forest fires, and biomass burning compounds (forming secondary organic aerosols)
From page 76...
... on ultrafine particles (for example, in the roadside exposures of animals being carried out in Los Angeles)
From page 77...
... A new standard method for PM2.5 emissionstestingmethodisneededthatdilutessamplestoambienttemperature conditions and allows for the addition of multiple filters and particle sizing instruments. This method will supply more realistic estimates of primary-particle emission rates, as well as options for obtaining source size distributions and chemical profiles.
From page 78...
... Static emission inventories, typical of those used for tracking annual trends, are insufficient for estimating the variability in aerosol properties using air quality models. In addition, emissions from other than anthropogenic sources are poorly estimated.
From page 79...
... RESEARCH TOPIC 4. AIR QUALITY MODEL DEVELOPMENT AND TESTING What are the linkages between emission sources and ambient concentrations of the biologically important components of particulate matter?
From page 80...
... There has been some support of the following specific atmospheric processes: · Nucleation · Uptake of water and thermodynamic properties of aerosols, especially organics · Secondary organic aerosol formation · Representation of aqueous chemistry · Dry deposition · Sub-grid scale processes and vertical mixing · Inclusion of the effects of particles on radiation · Methods to determine the effect of large-scale meteorological processes on long-term particle concentration Data Infrastructure EPA established a speciation trends network (STN) of 54 sites to quantify ambient PM2.5 chemical composition in urban areas and encouragedandsupportedlocalandstateagenciestoenhancethesewithadditional sites.
From page 81...
... Surveys have since appeared that critically review the models' strengths, limitations, and uncertainties as applied to air quality management (Seigneur, 2003; NARSTO, 2003)
From page 82...
... 82 Research Priorities for Airborne Particulate Matter FIGURE3-1CompositionofPM2.5atrepresentativeurbanandrurallocations.The urban sites are Toronto; Washington, DC; Atlanta; Mexico City; Los Angeles; and Fresno. Averaging periods and average PM2.5 mass are indicated.
From page 83...
... In addition, the lack of sufficiently accurate emission inventories (whose improvement is related to Research Topic 3) hampers the implementation and evaluation of any air quality model.
From page 84...
... . The committee recognizes that source-oriented air quality models are primarily used to determine how area-wide emission reductions will affect the ambient concentrations used for compliance purposes.
From page 85...
... It is still not clear that EPA is making the appropriate commitment needed to have the best models available for ready use at the local air quality management levels. Coupled with little progress on emissions characterization for emission rates and source profiles, the committee has substantial concerns about the air quality management community's access to fully operational tools and databases needed for NAAQS implementation.
From page 86...
... For example, a systematic effort to examine whether the results of air quality models are consistent with the emissions and models in a variety of different regions would aid in improving sources and in expending funds for source inventory work in the most critical areas. Examining whethertheextenttowhichmodelsandemissionscaninformepidemiological studies could speed progress on understanding the toxicity determining characteristics of particles.
From page 87...
... assemble and evaluate meteorological measurements for the domain; (5) apply the specified air quality models and data analyses and compare with ambient concentrations; (6)
From page 88...
... Introduction Particulate matter in ambient air is a mixture of different types of particles, having different sizes and chemical composition, and originating from many different sources, both primary and secondary. In urban air, particle numbers and mass concentrations vary across the size spectrum from the tiniest particles sized in nanometers, equivalent to molecular clusters, to very large particles, such as pollen grains and windblown sand.
From page 89...
... Monitoring for PM10 continues, and the network for PM2.5 is now in place and the methods are being developed for monitoring PM10-2.5. The Supersites Program has provided insights into the complexity of PM covered by this initiative, and the Speciation Trends Network should provide a platform for epidemiological studies directed at assessing particle characteristics and public health.
From page 90...
... , adsorbed volatile organic compounds Biogenic Antigens, microorganisms, toxins (endotoxin and other) , plant and animal debris Secondary Sulfates, nitrates inorganic aerosols Dusts Crustal minerals (crystalline state)
From page 91...
... fraction of PM10; these studies indicate that both fractions can be associated with health responses, although the relevant outcome indicators may not be the same for both fractions. Epidemiological studies have considered the ultrafine fraction of PM;theresultsaredecidedlymixed,withpositiveandnegativeassociations with health measures (for example, Peters et al.
From page 92...
... . These components have been associated with various effects, including production of reactive oxygen species, pulmonary inflammation, enhanced sensitization to antigens, and increased susceptibility to respiratory tract infection.
From page 93...
... The goal would be to ensure that no potentially important characteristic is overlooked and that the totality of potential health outcomes is considered for each characteristic. Differences in the spatial homogeneity and measurement error associated with different components of PM need to be addressed in the design and analysis of epidemiological studies to ensure that all components are appropriately considered.
From page 94...
... Investigation of multiple PM characteristics will present a challenge for epidemiological studies. Many of the measures of particle components and characteristics are highly correlated, making it difficult to separately
From page 95...
... 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?
From page 96...
... Although relatively refined models have been developed over the past 40 years, largely for the purpose of radiation protection, limited emphasis has been given to particle dosimetry in the susceptible subpopulations of greatest concern with regard to airborne particles, particularly persons with underlying heart or lung disease. It is important to understand that the site of concern for deposition or translocation varies among the different health effects, such as nasal deposition for allergic rhinitis, airway deposition for asthma, or alveolar deposition for reduced resistance to pneumonia.
From page 97...
... . There has been less work on clearance; indeed, knowledge of PM clearance in subjects with respiratory tract abnormalities has not advanced substantially in recent years.
From page 98...
... How can the effects of long-term exposure to particulate matter and other pollutants be better understood? Introduction This research topic addresses the independence of the effects of PM on health -- that is, whether the effects of PM depend on or are modulated by the presence of other pollutants, particularly the gaseous copollutants widely present in ambient air.
From page 99...
... The more recent epidemiological and toxicological studies of PM and health provide clear evidence for an independent effect of PM in increasing risk for several adverse health outcomes. The evidence is less certain as to whether the effect of PM on these health outcomes depends on other pollutants.
From page 100...
... Another approach to addressing the combined effects of PM and other pollutants is to relate health risks to indicators of source contributions to ambient air pollution, rather than using specific pollutant concentrations. The purpose of such studies is to identify sources, which might be of interest from a control strategy, but without specific consideration of the concentrations of specific components.
From page 101...
... In its general review, the committee noted that assessments of effect modification in the epidemiological studies have provided little evidence that the effect of PM varies strongly with other major pollutants in ambient air. Interpretation of such analyses is complicated by the secondary nature of some PM, because both nitrogen oxides and sulfur oxides contribute to PM mass.
From page 102...
... RESEARCH TOPIC 8. SUSCEPTIBLE SUBPOPULATIONS What subpopulations are at increased risk of adverse health outcomes from particulate matter?
From page 103...
... Other epidemiological studies focused on people with asthma, COPD, or cardiovascular disorders. Controlled clinical and experimental animal studies examined responses to PM in people with airway diseases and animal models with compromised pulmonary and cardiovascular systems.
From page 104...
... . Another major finding is the greater deposition of fine and ultrafine particles in the respiratory tracts of persons with asthma similar to what was earlier found in COPD patients (Anderson et al.
From page 105...
... To create the knowledge needed to understand the adverse effects of PMonsusceptiblesubpopulations,researchshouldmoreeffectivelyaddress different scales of exposure (from short-term, peak to chronic exposures) , characteristics of exposure (for example, deposition and disposition of fine and ultrafine particles in the respiratory tract)
From page 106...
... that can explain the epidemiological findings of mortality and morbidity associated with exposure to ambient particulate matter? Introduction This topic refers broadly to research on mechanisms that underlie the associations of PM with health outcomes.
From page 107...
... It is increasingly recognized that the respiratory tract may serve as the portal of entry of particles that are related to health effects manifest in organs and tissue remote from the respiratory tract. Using existing epidemiological and experimentaldata,aninterdisciplinaryworkshopsuggestedthatmechanistic considerationsshouldfocusonalterationsintheautonomicnervoussystem; ischemic responses in the myocardium; chemical effects on ion channel function in myocardial cells; and inflammatory responses triggering endothelial dysfunction, atherosclerosis, and thrombosis (Utell et al.
From page 108...
... Studies using CAPs, laboratory-generated carbonaceous ultrafine particles, and diesel particles have all provided evidence for effects on pulmonary or systemic inflammatory markers. For example, levels of cytokines, chemokines, and adhesion molecules following particle exposures in healthy humans have been altered in blood (Salvi et al.
From page 109...
... These findings suggest that PM, especially the soluble iron component, affects the host immune response during pulmonary infection and helps to explain some epidemiological observations. Cardiovascular Effects There is growing clinical and epidemiological evidence that ambient air pollution can precipitate acute cardiac events, such as angina pectoris, cardiac arrhythmias, and myocardial infarction, with the majority of excess PM-related deaths attributable to cardiovascular disease.
From page 110...
... That possibility could become particularly relevant as understanding of the role of PM in endothelial dysfunction expands and could further explain the mechanisms underlying cardiovascular events. What Remains To Be Done?
From page 111...
... 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?
From page 112...
... To some extent, the statistical literature addressed these issues generically, but they had not yet been applied to the type of data collected in health and air pollution epidemiological studies. Since 1997, several new statistical methods have been introduced to analyze the temporal association between air quality measures and health.
From page 113...
... Until the implications of the alternative analytical approaches are fully understood and until there is some scientific consensus about the appropriate method to use, researchers must explore the sensitivity of results to alternative modeling approaches (Sarnat et al.
From page 114...
... Several studies considered the issue of mortality displacement or harvesting, using various analytical strategies. The majority of these studies found that a significant number of deaths cannot be attributed to harvesting alone (Zeger et al.
From page 115...
... They include data on the statistical distributions of the differences between personal exposures to a variety of pollutants and ambient measures for the same pollutants (Sarnat et al.
From page 116...
... SUMMARY To date, the greatest measurable gains have been made on the topics with a narrower scope, such as exposure assessment and dosimetry. Substantial new evidence on exposure to particles has been reported, and there is now an enhanced understanding of the determinants of personal exposures to particles in ambient air (topic 1)
From page 117...
... . Substantial methodological research has yielded new analytical strategies and an enhanced understanding of several issues, including measurement error and possibly mortality displacement.


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