A simplified version of the turbulent electrode effect is developed for use as a charge source in a convection current model. Asymptotic analysis is applied to the conservation equations for small ions to show that the conductivity profile in the electrode layer becomes independent of the conduction process in the limit of strong turbulent mixing. In this limit, which is found to be applicable to the atmospheric surface layer under many circumstances, the electrode effect can be described simply by a charge conservation equation with an externally determined mean conductivity profile decreasing to zero at the surface.