The kinetics and mechanisms of the NH3+NOx (x=1, 2) reactions have been systematically studied by pulsed laser photolysis/mass spectrometry (PLP/MS) and pyrolysis/FTIR spectrometry (P/FTIRS). In the PLP/MS experiment, the total rate constants and product branching ratios of the NH 2+NOx (x=1, 2) reactions have been tested by measuring the time-resolved concentrations of H2O, N2O, and NO 2 in the laser-initiated reaction of NH3 with NO in the presence of varying amounts of NO2 in the temperature range of 300-725K. The measured concentrations can be quantitatively accounted for by the authors' comprehensive mechanism for the H/N/O system recently established for the ammonium dinitramide decomposition reactions, confirming the authors' reported product branching ratio for NH2+NO2→N 3O+→H2O (0.19±0.02) over the temperature range investigated. In the thermally initiated reaction of NH3 with NOx investigated by the P/FTIRS technique in the temperature range of 575-710K, the measured kinetic data for the disappearance of the reactants and the formation of products have been modeled with the same mechanism applied to the PLP/MS study. Agreement between the kinetically modeled concentrations and the experimentally measured values was quite satisfactory for the reactants (NH3 and NOx) and products (NO and N2O). Sensitivity analyses showed that the reaction of NOx with NH 3 is most sensitive to the NH2+NOx reactions, with a slightly lower sensitivity to subsequent reactions involving HONO. The authors' comprehensive mechanism also accounts reasonably for the concentration profiles of NH3, NO2, and N2O reported by Glarborg et al. (1994) in their study of the isothermal reaction of NH 3 with NO2.