A photochemical-dynamical gravity-wave model is developed in this paper and is applied to the impact of a nonbreaking propagating gravity wave on chemical species distributions in the mesopause region. The model is time-dependent, two-dimensional, nonlinear, and nonhydrostatic; it includes diabatic processes produced by photochemistry and the effects of the gravity wave on atmospheric chemical species. The model simulates the changes to the distributions of oxygen and hydrogen compounds instantaneously in the presence of the wave and also determines the residual effect on composition after the wave packet has passed through the region. The results indicate that a gravity wave propagating through the mesopause region influences the mean distributions of chemical species even if the wave does not break. The relative perturbations are larger during night than during daytime. The chemical density perturbations persist for several hours after the dynamical wave has propagated out of the region.