Continued success in treatment of asthma and COPD requires development of new formulations, which may alter spray characteristics and atomisation quality of atomiser devices such as pMDI. Fundamental understanding of the underlying physical phenomena and the dynamic nature of pMDI aerosol plumes is essential to maintain pMDI device atomisation quality. In this paper, we describe a simulation of pMDI aerosol generation and plume development using a model of two-phase flow and atomisation of HFA134/ethanol formulation. The model is implemented within a CFD simulation to study the dynamic aerosol development and predict spray velocity and temperature. The CFD result shows plume velocity slows down over a relatively short distance and droplet temperature settles at a steady value of 291 K approximately at a distance of 30 mm from the spray orifice. This means that droplets reach their final size before reaching the exit of the mouthpiece.