The effects of NO addition (1000, 2000 ppm) on the low-temperature oxidation of dimethyl ether (DME) and dimethoxymethane (DMM), as particular cases of oxymethylene ethers (OMEn) with n = 0 and 1, have been investigated in a plug-flow reactor at near-atmospheric pressure in a temperature range of 400-1000 K. An in-situ electron ionization molecular-beam mass spectrometer (EI-MBMS) was used to measure the reactants, intermediates, and products, with particular attention on nitrogenous species that were scarcely detected previously. Explorative modeling with published mechanisms was performed, indicating the necessity of further model development. Potential kinetic fuel/NO interactions are discussed based on the experimental observations. The results reveal an overall inhibiting effect of NO addition on DME reactivity in the low-temperature regime, but a pronounced promoting effect at higher temperatures. For DMM, a similar temperature-dependent effect of NO was observed, but only for high NO concentration (2000 ppm). NO addition significantly suppresses the formation of hydrocarbon intermediates for both DME and DMM, but remarkably promotes the formation of methyl formate and methanol for DME. Several nitrogenous species were detected upon NO addition. The interactions of NO + HO2 and NO + OH, together with the regeneration routes of NO, are thought to be influential for both DME and DMM oxidation, while the significance of the NO + RO2 (R, fuel radical) reaction depends on the reactivity of the respective RO2 radical of DME and DMM. These results contribute to the understanding of OMEn/NO interactions and serve as a basis for further model development by providing new and detailed speciation data for DME/NO and DMM/NO oxidation. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.