In a laboratory-scale circulating fluidized bed combustor (CFBC), which mainly consists of quartz-glass, the relative importance of the radicals, generated by the combustion process, on the N2O and NO formation and destruction paths are studied. The CFBC unit is electrically heated and operating conditions can be nearly independently changed over a wide ranger e.g., the bed temperature was varied between 700 and 900 degrees C. The radicals＇ importance on the destruction reactions of N2O has been investigated under CFBC conditions by a recently developed iodine-addition technique to suppress the radical concentrations. Additionally, CO, CH4, and H2O have been added to study their influence and to change the pool of radicals. Time-resolved concentration changes at the top of the riser have been measured by using a high performance FT-IR spectrometer in combination with a low-volume, long-path gas cell. The FT-IR analysis is focused on the carbon containing species, viz., CO2, CO, CH4, and other hydrocarbons, as well as on the nitrogen-containing species, viz., NO, NO2, N2O, and HCN. In the continuous combustion rests, petroleum coke has been burned in the CFBC. Concentration profiles and concentration changes at the top of the riser have been measured, Iodine has been added and the bed temperature and the initial fuel particle size ape varied. With the knowledge of the N2O destruction reactions, the relative importance of the radicals on N2O and NO formation reactions has been identified and is discussed.