Exposure assessment is the core part of the European Union air pollution study. One of its main research topics is whether the information collected by central monitoring stations can represent true population exposures to air pollutants. To better answer this question under current situations in Taiwan, this project will build up a PM2.5 microenvironmental monitoring network, based on our previous project of "Developing criteria for conducting exposure assessments of air pollutants ", as well as the standard operating procedures in the European Union air pollution study. Both long- and short-term outdoor PM2.5 micronenvironmetal samples will be collected in different seasons. Land-use regression models (LUR) and Geographic Information System (GIS) methodology also will be employed for data analyses. Furthermore, the air quality standard for fine particles is currently being developed in Taiwan. In order to set up a reasonable standard for PM2.5, it is important to first identify the related sources and their contributions. During the second and third years of this project, the analytical methods for measuring metals, inorganic salts, and carbon components of PM2.5 will be tested. Receptor models will be applied to analyze the source contributions of PM in one urban area in Taiwan.