N2O was reported to form in sample containers of flue gases containing NO and SO2. This could have significant implications for the evaluation of N2O buildup in the atmosphere. Existing models are based either on liquid-phase reactions, which cannot account for N2O formation at low humidity, or on termolecular reactions, which are not likely to occur at low concentrations. In this work, we propose mechanisms for N2O formation based on gas-phase reactions, which address the effect of SO2, O2, and moisture. Analytical expressions of the formation rate were derived and compared to reported rates, and rate constants were estimated for limiting cases. The current analyses suggest that N2O2 could be an important precursor for N2O formation from NO, and the mechanism may be important for N2O formation in power-plant plumes.