The Center for Clinical and Translational Research, UCSF Fresno, and the Central Valley Health Policy Institute, California State University Fresno, are proposing a San Joaquin Valley - based epidemiological study that builds on prior findings related to the health effects of PM 2.5 in urban areas of the region. The proposed study will look for statistical associations between varying concentrations of PM 2.5 components (e.g. ammonium nitrate, ammonium sulfate, organic carbon, elemental carbon) and health outcomes, including emergency department visits and hospitalizations associated with selected cardiovascular and respiratory conditions. In a prior study, Tyner et al utilized zip code - resolved health care utilization data obtained from the Office of Statewide Health and Planning Department (OSHPD), air quality data from the California Air Resources Board (CARB) and meteorological data from the California Irrigation Management Information System (CIMIS) to assess the impacts of acute PM2.5 exposure on cardiorespiratory health outcomes. The study included assessments of zip code-defined populations in Modesto, Fresno and Bakersfield, CA. The study found associations between 24 hour average PM2.5 concentration and asthma exacerbation in children (ER and hospital visits) in all three communities, but interestingly, associations between air pollution and asthma in adults were significant only in Fresno, CA. In contrast, PM2.5 was found to be associated with pneumonia ER visits in children in Modesto and Bakersfield, but not in Fresno.