Research results under the topics of outdoor measures versus actual human exposures (topic 1), dosimetry (topic 6), combined effects of PM and gaseous pollutants (topic 7), susceptible subpopulations (topic 8), and mechanisms of injury (topic 9) indicate a broadening scope of health concerns since the committee’s 1998 report. At that time, emphasis was largely placed on total morbidity and mortality from respiratory causes, such as exacerbation of chronic respiratory diseases, including chronic obstructive pulmonary disease (COPD) and asthma, and the respiratory health of children. Subsequently, the list of particle-related health outcomes was broadened and now includes several adverse cardiac outcomes, such as changes in heart rate variability, cardiac arrhythmias, ischemic events, and congestive heart failure, as well as reproductive outcomes. Although findings on several of these outcomes remain preliminary and inconsistent, the interest in investigating these outcomes and exploring new ones has grown.

Individuals with chronic lung disease have long been considered to be at increased risk for adverse effects of air pollution, based on compromised physiological reserve capacity. Dosimetry studies show that such persons have enhanced deposition of particles in the central lung, possibly contributing to increased risk. The expanded scope of health studies now includes investigation of other potentially susceptible subpopulations, such as individuals with coronary heart disease or diabetes.

New studies were conducted in many U.S. cities to better understand the relationship between outdoor measures of PM and actual human exposures. Panels of susceptible subpopulations were investigated, including people with COPD or coronary heart disease, older adults, children, and people with asthma. These studies found that there were varying degrees of association between personal exposures and ambient concentrations for the measured individuals, with almost half of the associations being nonsignificant (see Chapter 3). More important, studies conducted in the eastern United States showed little difference in PM2.5 exposures among the different investigated cohorts, despite their differing time-activity patterns. Future research studies should be conducted to investigate populations at high risk residing near source-dominated environments. Progress in air quality model development and testing (topic 4) and characterization of emission sources (topic 3) will facilitate greater accuracy in the identification of populations exposed to high PM concentrations.

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