This scheme shows the general lines in the oxidation of a VOC. Extremely reactive alkyl radicals reacts almost instantly with O2 to produce peroxy radicals. Many reactions are possible for these peroxy radicals, yielding various stable compounds (hydroperoxides, nitrates, etc.) and/or very reactive alkoxy radicals. The product distribution therefore depends on the abundance of the different sorts of radicals (NO, HO2, other RO2 radicals) which can react with the RO2. The fate of alkoxy radicals is often difficult to predict from our current knowledge, due to the scarcity of direct measurements and the complexity of theoretical methods. Note that the "stable "compounds themselves (indicated by ellipses on this Figure) are oxidized by OH or by photolysis. It is easy to imagine the enormous number of different compounds that will be generated in the oxidation of complex hydrocarbons (e.g. monoterpenes).