While the last two decades have seen substantial controls placed on sources of air pollution emissions, ambient outdoor concentrations have not shown commensurate reductions. In particular, the secondary pollutants produced by photochemical reactions in the atmosphere (including oxidants, e.g. ozone, acid aerosols, e.g. sulfuric acid, and gaseous acids, e.g. nitric acid) have been increasing in the eastern United States. Epidemiologic studies of populations in rural and suburban areas have suggested adverse respiratory health effects associated with these pollutants, including acute and chronic increases in respiratory illness in children and reduced pulmonary function. The effects of these exposures on urban populations, particularly economically disadvantaged individuals, have not been investigated. The Environmental Protection Agency is undertaking a comprehensive monitoring program to characterize urban exposure to acid aerosols and other photo-chemical pollutants in five major eastern cities, one per year, over the next five years. Sampling will begin in Philadelphia in April 1992, with the remaining four cities still to be named. We propose to conduct four separate epidemiologic studies of the health effects of these pollutants in each of the five urban areas: first, a cross-- sectional study of the association of respiratory symptom reporting and pulmonary function of elementary school children with mean air pollution exposures upwind, downwind and in the central city; second, a repeated measures study of the association of changes in peak flow and respiratory symptom reporting in a panel of children with episodes of summer haze air pollution; third, a time-series study of the association of emergency room visits with daily air pollution concentrations; and fourth, a time-series study of the association of daily cause-specific mortality with ambient air pollution concentrations. Individually these studies win provide city-specific estimates of the health effects of these secondary pollutants. Taken together they provide information on the coherence of such associations from increased mortality, to emergency room visits, chronic respiratory illness, and acute, possibly reversible, changes in lung function. Separately, the robustness of these findings will be evaluated across the five urban areas.