Many cities in East Asian countries suffer severe haze pollution due to rapid urbanization, industrializing, and increasing population. Recent research works show that PM2.5 composition in Ulaanbaatar (UB) and Beijing is highly affected by coal combustion sources, which contribute to atmospheric pollution from local to regional levels. Besides, there are many unidentified sources, which become an obstacle to haze pollution mitigation. This study aims to assess the source contributions of PM2.5 based on approaches of sulfur (e.g. 33S and 34S) and carbon isotopes (13C) and other components in PM2.5 collected at UB and Beijing. In the 1st year, intensive PM2.5 sampling will be implemented and sample pretreatment method for S isotope analyses will be adapted. Then, the analytical conditions of the S isotopes will be optimized. In the 2nd year, daily PM2.5 sampling will be conducted for two weeks in each season, and the chemical components of PM2.5 (ions, carbonaceous compounds, trace elements) and S and C isotopes will be analyzed. Regional and seasonal characteristics of the chemical components of PM2.5 will be clarified. Major sources will be distinguished coupling chemical components, C isotopes and simulations. Finally, sulfur isotopes (33S and 34S) of sulfate in PM2.5 aerosols are discussed to better understand the sources and formation of sulfate, which can be crucial for improving the air quality in East Asia.