Rapid economic growth in East Asia causes consumption of vast amount of fossil fuel for energy source. Emission of acid forming gases such as NOx and SO2 as well as particulate matter affects the environment of the source country, surrounding countries, and moreover, whole northern hemisphere by long-range trans-boundary air pollution. Among these atmospheric pollutants, aerosols attract special attention these days, because there are many unclear points; for example, aerosol spatial distribution, formation mechanisms in the atmosphere, quantitative evaluation of environmental impacts, and so on. Therefore, scientifically supported data of trans-boundary air pollutants observed by well-arranged ground-based observations in this region as well as reliable and detailed model studies are very important. In order to analyze trans-boundary air pollution within and from East Asia observations on isolated islands and/or on the summit of mountains utilizing a network among East Asian and Southeast Asian countries are urgently needed. Emission source analysis with such as statistical analyses and estimation of the contribution of long-range transported aerosols and locally emitted aerosols are also very important.