We present a Boltzmann equation-based model for transport and reaction in micrometer-scale features such as those found in integrated circuit fabrication. We focus on the adsorption and desorption of one species to understand the transient responses to step changes at the reactor scale. The transport model has no adjustable parameters; the assumptions are detailed. Adsorption and desorption reactions and rates are written as simple reversible Langmuir rate expressions. Kinetic parameter values are chosen for demonstration. Results for the transient behavior of number density, flux to the surface, and the surface coverage are related to those that might occur during the adsorption and purge steps in an atomic layer deposition process. We conclude that for reasonable surface kinetics, the time scale for transport is much shorter than the time scale for adsorption and desorption and that an analytical model provides reasonable estimates for processing times.