In this paper, the mechanisms of light emissions, including NO-γ , NO-β and N 2-SPS, produced in a N 2 /NH 3 atmospheric-pressure dielectric barrier discharge considering realistic oxygen impurity (30 ppm) are investigated numerically and experimentally. Self-consistent, one-dimensional fluid modeling is used to numerically simulate the discharge process with 48 species and 235 reaction channels. An optical emission spectrometer (OES) is used to measure the relative intensities of the light emission. The simulations of the light emission intensities for the above-mentioned OES lines generally reproduce the trends observed in the experiments caused by changes in the NH 3 concentration. All of the predicted intensities of NO-γ , NO-β and N 2-SPS decrease with increasing amount of NH 3 caused by various reaction mechanisms. The former is due to the loss of N 2 (A) and NO(A) by the reaction of NH 3 with N 2 (A) and NO(A), respectively. The decrease in NO-β is due to the depletion of N and O because of NH 3 , and the decrease in N 2-SPS is due to electron attachment to NH 3 and a weaker metastable-metastable associative ionization of N 2. All of the simulated results demonstrate that the discharges are typically Townsend-like because the ions outnumber the electrons and the electric field across the gap is distorted only slightly by the charged particles during the breakdown. Finally, a reduced chemical kinetics model for a planar atmospheric-pressure N 2 /O 2 /NH 3 dielectric barrier discharge is proposed and validated by benchmarking against the above complete chemical kinetics. This results in a reduced chemical kinetics consisting of 33 species and 87 reactions with a very limited loss of accuracy of discharge properties, while it is 2.1 times faster in computational time as compared with the complete version.