A gas analyzer via which exhaust gas to be analyzed is conducted untreated through a first measurement chamber and, after treatment in an oxidation device, through a second measurement chamber, wherein ozone is produced from oxygen to thereby convert nitrogen monoxide into nitrogen dioxide, where the gas analyzer has a first light emitting diode and a second light emitting diode, light of both diodes is conducted through the first measurement chamber onto a first detector, light of the first light emitting diode is partly conducted through the second measurement chamber onto a second detector via a beam splitter arrangement, based on the first detector signal, the nitrogen dioxide concentration of the untreated gas is also measured, based on the second detector signal, the nitrogen dioxide concentration of the treated exhaust gas is measured, and the nitrogen oxide concentration of the exhaust gas is additionally determined from measured nitrogen dioxide concentrations.