Abstract: Method and apparatus for improved detection of sulfur dioxide by fluorescence are disclosed wherein the effects of interferent hydrocarbons in the test sample are eliminated. In apparatus detecting sulfur dioxide by detecting the fluorescence of sulfur dioxide from narrow band ultraviolet radiation by photomultiplier means, the test sample being fed to the fluorescence chamber is first passed through a reactor to oxidize the hydrocarbons from the sample. The effect of this oxidization is to convert interfering hydrocarbon components in the sample gas into non-interfering materials. In one embodiment employing ozone, moisture removal apparatus is added prior to the oxidization reaction to prevent the error producing formation of H.sub.2 SO.sub.4.