Hispanic-Americans have received little direct attention in air-pollution studies conducted to date, despite the fact that they are a growing minority and now represent the majority population in many areas of the United States. Self-identified Hispanics are a heterogeneous population with ancestries (and corresponding exposure and health distributions) that vary substantially across individuals. In this project, we will address the following four hypotheses: Hypothesis 1: Hispanic white (HW) children are more highly exposed to air pollution than non-Hispanic white (NHW) children. Hypothesis 2: The effect of air pollution on childhood asthma and lung function development is greater in HW children than in NHW children. Hypothesis 3: Underlying ancestry within Hispanics is associated with differences in childhood exposure to air pollution. Hypothesis 4: Accurate assessment of air pollution risks in a Hispanic population requires accounting for the possible confounding and modifying effects of underlying ancestry. To address these hypotheses, we will capitalize on existing data in the Children's Health Study (CHS), including longitudinal respiratory health data on over 12,000 children, with 40% (4,800) of Hispanic descent. We will utilize extensive air pollution data recorded over 16 years to study exposures and health effects of several criteria pollutants, including PM10, PM2.5, NO2, and O3, and additional pollutants related to traffic exposure (e.g. NO, elemental carbon, metals). We will also utilize existing genotype data to accurately characterize the ancestral heterogeneity within our Hispanic population. We will examine how that heterogeneity relates to pollution exposure and in turn how it affects population-level estimates of risk. We will use sophisticated statistical models and will carefully consider a wide range of additional cofactors (e.g. socio- economic status, second-hand tobacco smoke) in our analyses. Successful completion of this project will significantly advance our understanding of air pollution exposures and corresponding health effects in Hispanics, a large and growing population in the United States.