The traditional flux‐gradient model for lateral diffusion in the atmosphere has the flux of pollutants related to the concentration gradient. The model investigated in this paper has the flux related to an integral of a weighted concentration difference. The classic solution for diffusion from an elevated point source was obtained from this integral diffusion model without the necessity of assuming variable coefficients. The integral diffusion model was used to confirm that the solution for an area source having finite width is accurately approximated by the solution for an area source having infinite width.