Although its ambient air quality has improved substantially, China is still facing the worst air pollution problem in the world. Outdoor air pollution has become a major concern for public health. The World Bank (2007) estimated that the total health cost associated with outdoor air pollution in urban areas of China in 2003 was between 157 and 520 billion Chinese yuan, accounting for 1.2–3.3% of China’s gross domestic product. Health end points studied in China in association with air pollution include all-cause mortality, mortality and morbidity due to cardiopulmonary disease, and numbers of outpatient and emergency department visits (Chen et al. 2004). Changes in respiratory and other clinical symptoms, lung function, and immune function are also studied.