The investigators propose to test the following two hypotheses using existing daily data on asthma severity, time-activity profiles, and hourly TEOM PM10 data from 4 asthma panel studies conducted in Alpine, California, 1994-96, as well as prospective PM data they propose to collect in Alpine using personal PM10 and microenvironmental PM10 and PM2.5 monitoring: 1) Peak hourly exposures to particulate matter of outdoor origin will be more closely associated with acute asthmatic responses to particles than 24-hour average exposures in susceptible individuals. This difference in association is in reference to epidemiologic findings for adverse effects of 24-hour average PM10 at levels below 150 ug/m3 [U.S. National Ambient Air Quality Standard (NAAQS)]. 2) Estimates of personal hourly exposure to PM from microenvironmental models, and estimated particle dose to target zones in the respiratory tract, will be more closely associated with daily asthma severity than unadjusted outdoor particle concentrations. They will test the consistency of associations with longitudinal analyses in each of 4 retrospective panels and 2 prospective panels with personal PM, and in the aggregate of 6 panels (18 adult and 73 pediatric asthmatics; 7, 884 person-days). The focus will be on children. Results based on adjustments for time-place patterns, and estimates of dose, could clarify hypotheses by showing stronger effects of unadjusted peak PM10 than the unadjusted 24-hour average exposure because peaks are better surrogates for personal outdoor exposures during the daytime, exposures that occur at times of high physical activity leading to greater particle doses. Since averaging time has not been subjected to scientific evaluation, the proposed research could have important implications for evaluating the US NAAQS currently based on 24-hour averages. This research is expected to have an impact on decisions regarding the protection of health in populations frequently exposed to higher particle excursions.