An IGAC Task, Mega-Cities:Asia will study the concentrations and chemical characteristics of aerosols and organics in a series of Asian mega-city clusters. The main objective of the Task is to investigate the contribution of pollutant emissions from mega-cities to local and regional (including Asian Pacific) air quality and to the radiation budget. These data will be used to improve models' ability to reproduce current distributions of aerosols (inorganic aerosol, organic aerosol, and black carbon) and oxidants in Asian mega-cities and to improve their accuracy in predicting future changes in air quality and regional climate.