The emission of both nitrogen oxides and soot from combustion processes is still a matter of concern. When a flue gas recirculation (FGR) technique is applied, the presence of a given nitrogen oxide in the recirculated mixture can affect the emissions of other pollutants, such as soot, and be used for its control in a combustion process. In this context, the present work is focused on the identification of the effect of the main nitrogen oxides (NO, NO2 and N2O) present in combustion systems on soot and main product gases formation from the pyrolysis of ethylene, at atmospheric pressure and in the 975-1475 K temperature range. The experimental results are examined to assess the effectiveness of each nitrogen oxide in suppressing or boosting soot formation, to achieve the possible nitrogen oxides reduction, and to identify the elementary steps involved in the nitrogen oxides and ethylene conversion as function of the different nitrogen oxides. This analysis is supported on model calculations. The main results indicate that the presence of nitrogen oxides influences the formation of soot, yielding different results depending on the nitrogen oxide added, its initial concentration and the reaction temperature. Among the different nitrogen oxides studied (NO, NO2 and N2O), the lowest sooting tendency has been achieved in the presence of NO2, followed by NO and finally N2O. Different mechanisms appear to be responsible for soot and nitrogen oxides reduction, including both oxidation and reburn type reactions. Furthermore, representative soot samples formed from the different C2H4-nitrogen oxide mixtures have been characterized through elemental analysis, BET surface area analysis and TEM in order to explore the influence, if any, of the nitrogen oxide present. (C) 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved.