A primary concern in the interpretation and use of predictions from atmospheric pollution modeling systems relates to uncertainties arising from the coupling between chemistry, radiation, and atmospheric dynamics. The very nature of the existing "offline" chemistry calculation paradigm introduces room for errors and uncertainties in interpolation of meteorological variables in air quality models and precludes the inclusion of any feedback mechanism that can incorporate the effect of atmospheric loading of various pollutants on calculations of radiation and dynamics of the atmosphere. Additional uncertainties in such calculations could also arise from the use of differing physical parameterizations and numerical schemes in the meteorological model and the chemistry transport model (CTM). In several applications, due to practical limitations such as disk space, redundant calculations often need to be performed in the CTM to re-diagnose certain meteorological information, such as turbulence and cloud formation.

In this paper we describe the development and application of a modular, physically and numerically consistent, fully integrated regional-scale atmospheric dynamics and chemistry modeling system. The modeling system is based on further development and refinement of two existing models: the MM5 meteorological model, and the Multiscale Air Quality Simulation Platform (MAQSIP), a comprehensive atmospheric gas-aerosol model. In developing the integrated model we have directly included modules into the MM5 to represent transport, chemistry, and deposition of various chemical species (gas and aerosols), such that the dynamics and chemistry related model calculations are fully synchronized. The integration of the dynamics and chemistry calculations in a consistent modeling framework also enables the investigation of the potential effects and feedback of radiatively important trace species. Model applications and evaluation of model performance over the eastern United States will be presented. Differences in the online and offline mode of chemistry calculations will be described. Evaluation of the effects of radiative feedbacks related to aerosol loading will be discussed.