In this work a new optical scheme, named AODEM (Aerosol Optical DEpth Module), for a generic Chemical Transport Model (CTM) is presented. It calculates the aerosols optical properties from the aerosol mass concentration predicted by a CTM. AODEM may be considered as a tool to investigate air quality related variables. In particular, this kind of model may be useful to look into the major uncertainties in regional air quality modeling. An extensive usage of chain MM5/CHIMERE/AODEM through two different experiments is reported. The main goal of this work is to demonstrate how AODEM may be used as a useful post- processing tool for evaluating CHIMERE model, in order to better understand the physical and chemical processes related to atmospheric aerosols cycling and formation.