This numerical study investigates the effect of advection on NH3 adsorption kinetics onto a doped Polyaniline (PAni) sensitive surface in channel flow, under diffusion-limited conditions characterized by a high Damköhler number. The effects of various parameters, such as gas inlet velocity, NH3 concentration, and channel height, are tested and discussed. Results show that increasing channel height increases equilibrium time, while higher flow velocity reduces it. Local-scale analysis indicates that adsorption primarily occurs upstream and downstream of the sensitive surface initially, creating a depleted zone in between. An Adsorption Capacity Coefficient (ACC) is introduced to evaluate adsorption efficiency, revealing an inverse relationship between equilibrium time and efficiency. This study enhances the understanding of adsorption mechanisms by emphasizing the balance between diffusion and advection. These findings could be extended to other gases and sensitive materials, optimizing adsorption processes in various applications.