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broad range of many vapor- and particle-phase inorganic and organic chemicals noted in Chapter 2, some of which can undergo pronounced physicochemical changes. Assessing impact on human health and comfort requires the identification of proxy air contaminants for ETS that will permit a determination of exposure in a background of contaminants from other sources (see Chapter 5).

In epidemiologic studies of air contaminants, it is important to specify exposure to specific particulates or gases on a time scale corresponding to the health or comfort effect sought. The impact of exposure to an air contaminant should, ideally, be evaluated in terms of the biologic dose of the contaminant or its metabolites received by the target tissue. In most cases, this is not practical. The uptake, distribution, metabolism, and site and mode of action of the contaminant in humans is neither well understood nor easily measured. Moreover, dose cannot be directly assessed. Factors affecting the uptake of air contaminants include physical characteristics of the contaminant, as well as physiological characteristics and activity levels of the exposed person (see Chapter 7). In the absence of an ability to measure or specify the dose of a contaminant received, exposures to air contaminant(s) are assessed by either using biological markers, measured in the subject population, or by measuring the air-contaminant concentrations in the physical environment (Figure 4–1).

Exposures to airborne contaminants can be assessed by three basic approaches (Figure 4–1):

  • personal air-contaminant monitoring,

  • modeling, based on air sampling, time-activity patterns, and questionnaires, and

  • biological markers.

Personal monitoring employs samplers (worn by subjects) that record the integrated concentration individuals are exposed to in the course of their normal activity for time periods of several hours to several days (see Chapter 5).

The modeling approach employs the use of stationary monitors to measure the air-contaminant concentrations in a number of microenvironments. These measured concentrations are combined with time activity patterns (time budgets) to determine the average exposure of an individual as the sum of the concentrations in each environment weighed by the time spent in that environment.

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