The evolution of source noises in space-time is analysed in this paper. It characterises the global effect of uncertainties in electrodeposition process control, where the source noises have an effect on the concentration field of relevant species in the diffusion layer and the field is controlled by the Neumann boundary using relatively simple boundary controls. The control errors evolve in the diffusion layer and are dependent upon the source noises and applied controls as a random field process. The covariance structure of the field is found analytically and confirmed numerically. The local source noises are incited by the uncertainties from a realistic control system; they are devised by the process physics and a control system structure. This paper demonstrates that even in a relatively simple system, the local uncertainties have a strong tendency to expand in space-time. Some source noises have a dispersed effect on the overall system uncertainty (control error), others are more local and do not expand in the same way. The noise of the mass flux, which is injected through the Neumann boundary, dies out quickly in the diffusion layer. (C) 2013 Elsevier Ltd. All rights reserved.