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?


Compliance with the National Ambient Air Quality Standards (NAAQS) for PM is ascertained by measuring ambient concentrations of PM at monitoring sites. With regard to the health effects of air pollution, the risks depend on personal exposure—that is, the exposures received by people in the various specific places, conceptualized as microenvironments, where they spend time. Total personal exposure represents the time-weighted average of particle concentrations in the microenvironments where people spend their time. Exposures to particles generated by outdoor sources take place not only outside but also in indoor environments where the particles penetrate. Indoor particle sources, such as cigarette smoking, insects, molds, and cooking, may thus contribute substantially to total personal exposure to particles. 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. Such persons are referred to collectively as a “susceptible subpopulation” and are further addressed under topic 8 later in this chapter.

What Has Been Learned?

Research findings on topic 1 are relevant to interpreting the findings of the epidemiological studies of PM and to furthering the understanding of the relevance of monitored ambient concentrations for public health protection. Before 1997, the majority of time-series studies of morbidity and mortality associated with PM had relied on ambient air measurements taken for regulatory and tracking purposes. In using these measurement data in

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