We use a combination of field studies and administrative data to study the sources, concentrations and health effects of air pollution throughout the world, and to evaluate interventions and policies for reducing air pollution exposure. We have conducted field studies in Kenya, Ghana, The Gambia and China that, through their innovative design and data, have significantly advanced our understanding of air pollution sources, health effects and interventions. We also use large administrative data such as vital statistics to investigate the health effects of air pollution and temperature, and to understand how changes over time, as a result of control policies or climate change, may influence human health. A particular feature of this work is the development and application of new methodology for estimating variations in effects over age, space and time.