Air Pollution, the Automobile, and Public Health (1988) / Chapter Skim
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Assessment of Human Exposure to Air Pollution: Methods, Measurements, and Models
Assessment of Human Exposure to Air Pollution: Methods, Measurements, and Models
Pages 207-238
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BARRY RYAN Harvard School of Public Health Human Exposure: Introduction / 208 Definitions / 208 Concentration, Exposure, and Dose / 208 Components of Exposure / 208 Types of Exposure Information / 209 Individual Exposure Versus Population Exposure / 209 Methods / 211 Air Monitoring / 211 Biological Monitoring / 217 Research Recommendations / 218 Measurements / 219 Air Monitoring / 220 Research Recommendation / 223 Biological Monitoring / 225 Research Recommendation / 225 Modeling Human Exposure to Air Pollution / 226 Statistical Modeling / 226 Physical Modeling / 228 Physical-Stochastic Modeling / 229 Source Apportionment / 230 Validation and Generalization / 230 Research Recommendation / 231 Summary and Conclusions / 231 Summary of Research Recommendations / 232 Air Pollution, the Automobile' and Public Health.
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From page 208... ...
In addition, available evidence indicates that personal exposure to many pollutants is not adequately characterized because the time people spend in different locations and their activities vary dramatically with age, gender, occupation, and socioeconomic status (National Research Council 1981; World Health Organization 1982, 1983; Yocum 1982; Spengler and Sexton 1983; Spengler and Soczek 1985~. In this chapter, the state of the art of air pollution exposure assessment is discussed with emphasis on gaps in our knowledge and the implications of those gaps for future research.
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A personal exposure depends on the air pollutant concentrations that are present in the locations the person moves through as well as on the time spent in each location. Individual exposures for a speci
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Figure 1. Examples of NO2 exposure information: A: a 24-hr exposure profile and associated time-activity pattern data for a specific individual; B: a plot of cumulative exposure and the calculated 24-hr integrated exposure; C: calculated exposures averaged over 3 hr.
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Methods Basically, there are two general approaches to air pollution exposure assessment: (1) air monitoring, which depends on either direct measurements (personal monitors)
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~ , ~ . Personal exposure monitoring is, by its very nature, an intrusive event in the life of the study participants.
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Pump-impactor/precipita- Piezoelectric tor Respirable particles (sulfates, Pump/filter Microbalance PIXE nitrates, metals) Sulfur dioxide, nitrogen Pump/impingers/filter Colorimetric gravimetric dioxide, respirable particles Nonpolar volatile organics Pump/Tenax cartridge Thermal desorption/ GC-MS Organochlorine pesticides, Pump/polyurethane foam GC polychlorinated biphenyls Integrated, Carbon monoxide Diffusion Electrochemical Passive Nitrogen dioxide Diffusion tube (TEA)
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The indirect approach estimates integrated exposure by combining measurements of pollutant concentrations at fixed sites (for example, outdoors at a busy intersection, indoors at home) with data logs and diaries about the times people spend in specific environments (Fugas et al.
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Better documentation of time-activity patterns, as well as more information about approximate indoor and outdoor pollutant concentrations would help investigators specify important microenvironments and choose fixed monitoring sites. In most cases, however, there is not enough infor .
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Examples of the relative contributions from specific microenvironments to an individual's timeweighted, integrated exposure to respirable particles (RSP)
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Biological Monitoring Air monitoring traditionally has been the principal means of exposure assessment. A major shortcoming of this approach is its failure to take account of factors such as respiration rate and depth of inspiration that may cause two individuals with the same measured exposure to receive vastly different doses.
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It is especially important to know, for example, whether potentially susceptible groups such as asthmatics, young children, and the elderly have time-activity patterns that differ substantially from those of the general population. It is also important to determine which population subgroups are likely to experience high exposures to certain air pollutants because of their specific time-activity patterns.
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Outdoor measurements are weakly correlated, or not correlated at all, with individual exposure to most air pollutants, especially those with indoor sources. Furthermore, for airborne contaminants such as formaldehyde and many other volatile organic compounds, NO2, CO, and respirable particles, individual exposures are significantly higher than measured outdoor concentrations alone would imply (World Health Organization 1982; Spengler and Sexton 1983; Ott 1985; Spengler and Soczek 1985~.
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17 12 355 Outdoor measurements did not correlate well with personal exposures. Personal exposure and in-home concentrations tended to be higher than outdoor concentrations for many volatile organic compounds.
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Daily variations in mean outdoor, indoor at home, and personal exposure to respirable particles (RSP) for 46 nonsmoking volunteers from 23 residences in Waterbury, Vt.
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project indicate that 11 compounds~hloroform, benzene, carbon tetrachloride, ethylbenzene, among others are commonly present in indoor and outdoor air. Personal exposure to these chemicals was consistently higher than recorded outdoor concentrations, sometimes by an order of magnitude.
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. Among the other pollutants for which indoor sources are the principal cause of personal exposure are environmental tobacco smoke, asbestos, radon, and various microorganisms (National Re search Council 1981; Spengler and Sexton 1983~.
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Direct pollutant concentrations in a representative measurements of personal exposure are sample, and determine to what extent the straightforward but costly, time-con- indirect approach complements direct ex suming, and labor-intensive. Indirect ap- posure measurements.
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Recent advances suggest that available biological measurement techniques can be applied to a wider range of environmental contaminants, including community and indoor air pollution. Studies are needed first to determine the associations among the air monitoring data, the biological markers of exposure, and the ultimate health outcome; and second to establish, prior to the general use of a particular biological measurement technique, its sources of error, the validity of sample collection methodology, the appropriateness of internal and/or external standards, and the adequacy of methods for quality control.
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Modeling Human Exposure to Air Pollution Models are useful tools to quantify the relationship between air pollutant exposure and important explanatory variables (for example, time-activity patterns) , as well as to estimate exposures in situations where measurements are unavailable.
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, to investigate the relationship between air pollutant exposure (dependent variable) and the factors contributing to the measured exposure (independent variables)
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where E is exposure, a is the slope of the line relating exposure to the ambient concentration, Camb is the measured ambient concentration, and b is the exposure when the ambient concentration is zero. Several groups have combined this model with data about personal exposures and ambient
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By the introduction of a stochastic component into a physical model, the physicalstochastic approach attempts to account for the probabilistic nature of the physical processes that determine exposure. In this way, the inherent uncertainty associated with a mathematical abstraction of air pollution exposure is taken into account.
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. specific microenvironments Source Apportionment Before it is feasible to evaluate the adequacy and cost-effectiveness of air pollution control strategies, it is necessary to obtain more and better information about the relative contributions of indoor and outdoor emission sources to measured personal exposures.
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for source apportionment of personal exposures and of indoor air pollution needs to be evaluated and new models need to be developed if existing models are shown to be deficient. Summary anc!
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the creation of extensive data bases on personal exposures, pollutant concentrations in important mi
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The rele vance of existing models (outdoor air) for source apportionment of personal exposures and of indoor air pollution needs to be evalu ated and new models need to be developed if existing models are shown to be deficient.
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1977. Personal exposure to respirable particulates and sulfates ver Human Exposure to Air Pollution sus ambient measurements, Proceedings of the 70th Annual Meeting of the Air Pollution Control Association.
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1984. Estimated distributions of personal exposure to respirable particles, Environ.
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1986. Estimating personal exposures to nitrogen dioxide, Environ.
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1985. Personal exposures to respirable particulates and implications for air pollution epidemiology, Environ.
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1985a. Personal exposures, indoor-outdoor relationships, and breath levels of toxic air pollutants measured for 355 persons in New Jersey, Atmos.
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