We conducted wind-tunnel experiments to study the atmospheric dispersion over a two-dimensional ridge considering the plume rise process of exhaust air from a cooling tower. The stacks were located at the upstream foot or downstream foot of the ridge. Two different model surfaces, aerodynamically smooth and rough surfaces, were used in the experiments. Exhaust air from the downstream foot of the ridge was immediately trapped by the recirculation flow forming behind the ridge. Although the maximum surface concentration appeared in the vicinity of the source for this case, the amplification factor of the maximum surface concentration from the flat case was limited due to the increase in the horizontal dispersion parameters by the wake flow of the ridge. The decrease in wind speed in the wake region of the ridge also mitigated the increase in the maximum surface concentration by enhancing the initial plume rise of the exhaust air.