NOx reduction of flue gas by plasma-generated ozone was investigated in pilot test experiments on an industrial power plant running on natural gas. Reduction rates higher than 95% have been achieved for a molar ratio O-3:NOx slightly below two. Fourier transform infrared and ultraviolet absorption spectroscopy were used for spatial measurements of stable molecules and radicals along the reduction reactor. Reactions of O3 injected in the flue gas in the reduction reactor were also modeled. Experiments are in good agreement with numerical simulations. The operation costs for NOx reduction were estimated based on field tests measurements. (C) 2009 Elsevier Ltd. All rights reserved.