The surface mechanisms involved in the Atomic Layer Deposition of Al2O3 from TMA and H2O are investigated by means of combined experimental and computational analyses. Reactant adsorption, desorption and surface reaction are taken into account by a surface chemistry model, coupled to a CFD model for an industrial reactor treating 200 mm substrates. Once the model validated by comparison with experimental deposition rates, the relative contribution of each surface phenomenon is quantitatively determined between 100 and 300 degrees C through original reaction probability calculations. It is revealed that the competition between surface reactions and desorption of H2O plays a crucial role in the ALD growth of alumina. The H2O desorption is the limiting factor for the growth at low process temperature whereas it is the OH group surface concentration at higher temperature. This integrated (surface chemistry/kinetics and CFD) model shows a direct link between transport phenomena, such as gas flow recirculation and low temperature zones in the reactor, and film uniformity. (C) 2018 Elsevier Ltd. All rights reserved.