Through a room-temperature ultrasound-assisted redox process, mesoporous manganese oxides were synthesized in short reaction times of 3-9 h. At room temperature, the resultant materials showed superior performance for the elimination of low-concentration NO (10 ppm). Specifically, under humid conditions (50-90 % relative humidity), 97 % NO removal efficiency was obtained over 110 h without deactivation. Synergetic effects between Mn2+, Mn3+, and Mn4+ ions were proposed to explain the oxidation of NO to NO2 on the surface of the catalyst. Density functional theory (DFT) calculations indicated that water molecules strengthen the chemisorption of NO2 on manganese oxide (001) owing to a much higher adsorption energy. As a result, the probability of the reaction between NO2 and H2O increases, and the formation of volatile nitric acid ensures that the catalytically active sites are always available.