This project seeks to quantify the climate responses and feedbacks to the direct and indirect effects of tropospheric anthropogenic aerosols and natural aerosols converted by anthropogenic pollutants. We will continue to develop a size- and mixing-resolving aerosol model interactively coupled with the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM). In this study we will: (1) include new anthropogenic aerosol types to better describe the chemical and physical transfer of aerosols across the whole size and mixing spectra; (2) include important chemical conversions of "natural aerosols" of dust and sea salt by anthropogenic pollutants; and (3) fully couple the aerosol model with a chemistry module and a cloud microphysics module in the new version of CCSM. We will examine aerosol-caused climate responses and feedbacks, either occurring locally or remotely from regions of high aerosol loading, and reveal the aerosol effects on the hydrologic cycle including cloud, precipitation, surface water and heat budget. The goal is to advance our knowledge of climate feedbacks and responses to aerosol forcing, making contributions to the next generation of models to predict not only the future climate but also the state of the environment and ecosystems. The results of this project will be useful for climate-related policy decisions, as well as global environment and air quality studies. The project is based on a community model framework and the model developed in this study will be provided to the community.