Variations in constituents such as ozone and aerosols affect air quality, weather and climate. Atmospheric composition is central to Earth system dynamics because the atmosphere integrates spatially varying surface emissions globally on time scales from weeks to years. NASA works to provide monitoring and evaluation tools to assess the effects of climate change on ozone recovery and future atmospheric composition, improved climate forecasts based on the understanding of the forcings of global environmental change, and air quality modeling that take into account the relationship between regional air quality and global climate change. Achievements in these areas via advances in observations, data assimilation, and modeling enable improved predictive capabilities for describing how future changes in atmospheric composition affect air quality, weather, and climate. NASA draws on global observations from space, augmented by suborbital and ground-based measurements to address these issues. Research Questions Atmospheric Composition addresses the following overarching questions: How is atmospheric composition changing? What trends in atmospheric composition and solar radiation influence global climate? How does atmospheric composition respond to and affect global environmental change? What are the effects of global atmospheric composition and climate changes on regional air quality? How will future changes in atmospheric composition affect ozone, climate, and global air quality?