Abstract <p>The results of experiments conducted to determine the electrical strength of the air gap between a rod electrode and a cylinder electrode at different ozone concentrations in the gap are considered. A mathematical model of the avalanche-streamer transition in a nonhomogeneous electric field is proposed, taking into account the composition of the gas mixture. The calculated and experimental dependences of the electrical strength of air on the ozone concentration are in good agreement with each other and indicate a slight rise in breakdown voltage with rising ozone concentration</p>