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INDOOR AEROSOLS AND EXPOSURE ASSESSMENT
Citation:
Rodes, C. E. AND R W. Wiener. INDOOR AEROSOLS AND EXPOSURE ASSESSMENT. Chapter 29, Aerosol Measurement Principles, Techniques and Applications. John Wiley & Sons Incorporated, New York, NY, , 859-885, (2001).
Impact/Purpose:
The objective of this task is to develop and employ PM measuring tools for EPA researchers and regulators to use to characterize the exposure of humans to PM of outdoor origin in both outdoor and indoor environments. Achieving these objectives will improve the scientific foundation for risk assessments of PM in future reevaluations of the NAAQS and in assessing exposure of humans to PM.
Description:
This chapter provides an overview of both indoor aerosol concentration measurements, and the considerations for assessment of exposure to aerosols in non-occupational settings. The fixed-location measurements of concentration at an outdoor location, while commuting inside an automobile, or indoors in a residential living area represent only single microenvironments. By comparison, personal exposure assessment reflects a time-weighted average, across all microenvironments encountered. The relative emphasis on aerosol exposure in this chapter reflects the increasing importance of exposures assessments, compared with making simple local concentration measurements in selected microenvironments. In reviewing research priorities for airborne particulate matter, the National Research Council (NRC) observed that "actual exposure to humans is determined by ambient air concentrations, contributions from indoor sources, and human time-activity patterns" (NRC, 1999). An issue highlighted by the NRC was an understanding of the potential "misclassification" of exposure, where concentration measurements from a single microenvironment (e.g. outdoors), are assumed to represent the integrated exposure to a specific aerosol, when in fact the majority of the breathing zone exposure was contributed by another microenvironment.
The focus here is primarily limited to assessments in non-occupational settings. Occupational indoor microenvironments impose special requirements on aerosol characterization, which are discussed separately in Chapter 25. Outdoor aerosol sampling is important on its own as a regulated macroenvironment, and is described in Chapter 27. The reader is cautioned to be aware of inadvertent biasing of non-occupational air samples by occupational exposures (e.g., metal dusts re-suspended into the breathing zone from work clothing worn while at home, as reported by Cohen et al. 1984). The ubiquitous contributions of ambient aerosol to indoor spaces and to integrated exposure assessments, however, also merits limited discussion in this chapter. The ability of outdoor aerosols to penetrate into indoor spaces is well documented (e.g. Alzona et al. 1979; Dockery and Spengler 1989; Lioy et al. 1990; Wallace 1996; Pellizzari et al. 1999a). A recent paper by Thornburg et al. (1999) demonstrated that the penetration process is complex and dependent on a number of factors, and is a function of particle size. These latter considerations are especially important when attempting to understand the relationships between concentrations and exposures, or exposures and doses.
The methodologies and equipment needed to measure both fixed-location indoor concentrations and personal exposures to aerosols are described in modest detail. A representative review of the relevant literature is provided, and specific references should be reviewed for additional details. The limited scale and empirical nature of current indoor air and research studies, has not prompted a wide range of commercially-available measurement options for non-occupational exposure assessments. Although occupational Personal Exposure Monitors (PEMs) are readily available and have occasionally been pressed into service, their weight and obtrusiveness are not always suitable for use in non-occupational studies. This is especially true for exposure studies where the selected participants exhibit a wide range of ages and physical sizes, and may be reluctant to carry burdensome samplers for extended periods.
This work has been funded in part by the U.S. Environmental Protection Agency. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.