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A realized novel optical sensor system to measure the concentration of ozone using the emitted light from Light Emitting Diodes in the ultraviolet range is described in this paper. The wavelength selective light interaction of the gas takes place in a fiber coupled and robust reflection cell. The control electronics are separated from the optical sensor head. Therefore it can be used in harsh environment for instance close to discharge plasma in strong electromagnetic fields or at high temperature. The sensor design is potentially low cost, quite small and well suited for a large number of applications. It can be implemented in industrial process control application or in small battery powered hand held devices. This setup is also capable for a parallel and selective measurement of nitrogen dioxide NO2 and sulfur dioxide SO2 - this is already implemented and proved. Further specific LEDs are utilized for this purpose in the setup. For the ozone measurements two different sensor heads where used. A small 4 cm long reflection cell with potential for handheld devices and a 40 cm one thought for high resolution stationary application. The resolution (standard deviation measured at a zero concentration of ozone) of the sensor with the small cell is about 30 ppb at 700 msec measurement time and about 3 ppb at 1,4 sec at the longer cell.