Traditionally, atmospheric chemistry-transport and meteorology models have been applied in an off-line paradigm, in which archived output on the dynamical state of the atmosphere simulated using the meteorology model is used to drive transport and chemistry calculations of atmospheric chemistry transport model (CTM). A modeling framework that facilitates coupled on-line calculations is desirable since it (1) provides consistent treatment of dynamical processes and reduces redundant calculations, (2) provides ability to couple dynamical and chemical calculations at finer time-steps and thus facilitates consistent use of data, (3) reduces the disk-storage requirements typically associated with off-line applications, and (4) provides opportunities to represent and assess the potentially important radiative effects of pollutant loading on simulated dynamical features. A coupled on-line atmospheric modeling system is developed based on the Weather Research and Forecasting (WRF) meteorological model and the Community Multiscale Air Quality (CMAQ) air quality modeling system. The flexible design of the system which facilitates configurations for the both on-line and off-line modeling paradigms will be described. Initial testing of the system and the impacts of varying frequency of coupling between dynamical and chemical calculations will be presented. The impacts of including direct radiative forcing of simulated aerosol distributions on modeled dynamical and chemical features will be discussed. Initial evaluation of the model against measurements from routine networks and specialized campaigns will be presented.