Large cities in China, including the capital city of Beijing, and their surrounding areas have some of the highest air pollution levels in the world. With over one half of China's population now living in cities, air pollution and air quality are important local and national policy issues. At the same time, China is undergoing changes in health: Deaths in children have come down impressively, and people live to older ages when diseases of the heart and the lung are more common and important. Air pollution in cities is one of the main causes of health problems and disease in China, with especially large effects on the heart and the lung. We know from research in Europe and North America that air pollution adversely affects human health, but we know little about how and why this happens, and whether air pollution from different sources has more or less effects. Even less is known about what these mechanisms are in China, where air pollution may be from different sources and therefore have different chemistry. This knowledge is important for deciding what the most effective strategies to reduce the health effects of air pollution are. In this research project, leading scientists from China and the United Kingdom will work closely to use modern methods in epidemiology and biological sciences to better understand which components of air pollution affects human health in China, and how these effects occur. This knowledge will be used together with information from our related research projects to identify the most effective ways of protecting human health from air pollution in Chinese cities.