Abstract In this paper we propose a model for ozone detection in atmospheric conditions. The sensitive layer material used in this study is tungsten oxide. The interaction between the semiconductor surface and the gases is approached by means of the adsorption theory described by Wolkenstein in order to determine the equilibrium state of the grains. The layer conductivity is then determined by computing the current flowing between the grains (in the spherical assumption) across the depletion layer induced by the adsorbed molecules and the semiconductor interaction. This calculation is performed using the “drift diffusion” equation set. We have first analyzed the oxygen adsorption effect, then the ozone adsorption one and finally, the combined action of the two mixed gases on the sensor layer. This model takes into account the fundamental mechanisms implied in the gas detection and the results obtained are in good agreement with the experimental results.