Effects of gas saturation and sparging on sonochemical oxidation activity in open and closed systems, part II: NO2−/NO3− generation and a brief critical review

•Effects of gas saturation/sparging were studied for sonochemical NO2−/NO3− generation.•Twelve gas conditions of Ar, O2, N2, and binary mixtures were tested.•N2:Ar (25:75) resulted in the highest NO2− and NO3− concentrations under all conditions.•H2O2/NO2−/NO3− related OH radical activity was suggested.•Gas sparging enhanced the generation of NO2− and NO3− for O2:N2, N2, and N2:Ar.