Relationship between ozone and respiratory health in college students: A 10-year study.

Although the three mortality and air pollution studies in this issue of EHP contribute to the many previous studies that have evaluated day-today changes in mortality associated with air pollution, they do not provide substantial information on the specific pollutant or mix of pollutants responsible for the observed mortality effects or biological plau-sibility. For example, in the Santa Clara analysis, Fairley evaluated a wide range of air pollutants and found the strongest mortality associations with partides, especially fine particles (< 2.5 pm in aerodynamic diameter; PM2 5) induding ammonium nitrate particles. In Philadelphia, Pennsylvania, only total suspended particulates (TSP) were analyzed by Neas et al. Lee and Schwartz analyzed TSP, SO2, and 03 in Seoul, Korea, and mortality was most consistently associated with SO2. The authors suggested that SO2 may be acting as the better indicator of fine particles in Seoul. Recent reviews (4,12-17) of the overall epidemiologic evidence support a probable link between fine combustion-related particulate air pollution and cardiopul-monary disease and mortality. Also, several recent studies have reported that chronic long-term exposure to inhalable or fine particulate pollution is associated with an elevated risk of mortality (22-25). Nevertheless, there is remaining uncertainty about the role of chemistry versus size of the particles and the role of co-pollutants including 03, CO, SO2, NO2, and others. There is also substantial uncertainty with regard to the biologic plausibility of these associations. Biologic plausibility is enhanced by the observation of a coherent cascade of cardiopulmonary health effects and by the fact that noncardiopulmonary health end points are not typically associated with the air pollution. An overall review of the literature (4,12-17) reveals that a remarkable cascade of cardiopulmonary health end points has been observed to be associated with day-today changes in particulate air pollution. In addition to car-diopulmonary mortality, particulate air pollution has been associated with emergency room and physician's office visits for asthma and other respiratory disorders, hospital admissions for cardiopulmonary disease, increased reported respiratory symptoms, and decreased lung function. Recently, there have been studies that have attempted to look at specific physiologic end points, in addition to lung function, such as plasma viscosity (26), hypoxemia and heart rate (27), heart rate variability (28,29), and acute inflammatory responses (30-31). However, more research on the pathophysi-ologic pathway linking cardiopulmonary mortality and particulate air pollution clearly should be conducted. It is not clear that the case-crossover design is necessarily superior or inferior to …