Gas analyser for measuring nitrogen oxides in an exhaust gas with - an oxidation device comprising an ozone generator for the generation of ozone from oxygen and embodied to treat the exhaust gas with the ozone in order to convert nitrogen monoxide contained in the exhaust gas into nitrogen dioxide, - a first light-emitting diode that emits with a central wavelength of between 350 nm and 500 nm, - a second light-emitting diode that emits with a central wavelength of between 250 nm and 265 nm, - a measuring chamber through which the treated exhaust gas flows and the light from the first light-emitting diode and the light from the second light-emitting diode pass, - a detector that detects the light from the first light-emitting diode and the light from the second light-emitting diode after it has passed through the measuring chamber and which generates a detector signal with a first signal component resulting from the light from the first light-emitting diode and a second signal component resulting from the light from the second light-emitting diode, - an evaluation device, which ascertains the nitrogen dioxide concentration in the treated exhaust gas in the measuring chamber from the first signal component and outputs this as the nitrogen oxide concentration in the exhaust gas and ascertains the ozone concentration in the exhaust gas in the measuring chamber from the second signal component, characterised in that - the ozone generator can be regulated, and - a regulating device that controls the ozone generator is provided, which obtains the ascertained ozone concentration as an actual value in order to regulate this to a prespecified setpoint value. - an oxidation device comprising an ozone generator for the generation of ozone from oxygen and embodied to treat the exhaust gas with the ozone in order to convert nitrogen monoxide contained in the exhaust gas into nitrogen dioxide, - a first light-emitting diode that emits with a central wavelength of between 350 nm and 500 nm, - a second light-emitting diode that emits with a central wavelength of between 250 nm and 265 nm, - a measuring chamber through which the treated exhaust gas flows and the light from the first light-emitting diode and the light from the second light-emitting diode pass, - a detector that detects the light from the first light-emitting diode and the light from the second light-emitting diode after it has passed through the measuring chamber and which generates a detector signal with a first signal component resulting from the light from the first light-emitting diode and a second signal component resulting from the light from the second light-emitting diode, - an evaluation device, which ascertains the nitrogen dioxide concentration in the treated exhaust gas in the measuring chamber from the first signal component and outputs this as the nitrogen oxide concentration in the exhaust gas and ascertains the ozone concentration in the exhaust gas in the measuring chamber from the second signal component, - the ozone generator can be regulated, and - a regulating device that controls the ozone generator is provided, which obtains the ascertained ozone concentration as an actual value in order to regulate this to a prespecified setpoint value.