Aerosols affect regional and global climate through absorption and scattering (i.e., direct and semi-direct effects) and indirect radiative forcing that modifies microphysics of clouds by acting as cloud condensation nuclei (CCN) (i.e., the first indirect effect) and that influences cloud lifetime, liquid water content, and precipitation (i.e., the second indirect effect). In this work, the NOAA Weather Research and Forecast Model with Chemistry (WRF/Chem) is applied to study the effect of aerosols on regional climate. The model simulations with WRF/Chem at a horizontal resolution of 36 km will be conducted over the continental U.S. for January and July 2001. The model performance in terms of meteorological, chemical, and optical predictions (e.g., precipitation, concentration, aerosol optical depth) will be evaluated using available surface and satellite observations. The aerosol effects on radiation, boundary layer meteorology, precipitation, and wet deposition as well as their seasonal variations will be examined.